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Catalysis Today 189 (2012) 2– 27

Contents lists available at SciVerse ScienceDirect

Catalysis Today

j ourna l ho me p ag e: www.elsev ier .com/ lo cate /ca t tod

he past, present and future of heterogeneous catalysis

oana Fechetea, Ye Wangb, Jacques C. Védrinec,∗

Laboratoire des Matériaux, Surfaces et Procédés pour la Catalyse, CNRS UMR 7515, Université de Strasbourg, 25 rue Becquerel, F-67087 Strasbourg, FranceState Key Laboratory of Physical Chemistry of Solid Surfaces and National Engineering Laboratory for Green Chemical Productions of Alcohols, Ethers and Esters, College of Chemistrynd Chemical Engineering, Xiamen University, Xiamen 361005, PR ChinaLaboratoire de Réactivité de Surface, CNRS UMR 7197, Université Pierre et Marie Curie, 4 Place Jussieu, F- 75252 Paris, France

r t i c l e i n f o

rticle history:eceived 18 January 2012eceived in revised form 4 April 2012ccepted 5 April 2012vailable online 10 May 2012

eywords:eterogeneous catalysisistory

ndustrial realisationsuturehallengesew materialshemicals

a b s t r a c t

This review highlights key catalytic discoveries and the main industrial catalytic processes over the last300 years that involved commodities, fine chemicals, petrochemicals, petroleum transformation for fuelsand energy supply, emission control, and so forth. In the past, discoveries have often followed events suchas wars or embargos, whereas the current driving forces of studies, researches and then discoveries aimat a better understanding of catalytic processes, at reducing the costs of raw materials and processes, atdeveloping new catalytic materials and at addressing environmental issues. This review focuses on thehistory of many catalytic industrial processes, environmental issues, catalytic materials, especially theirexpected catalytic properties, on catalyst characterisation by physical methods and development of in situconditions, i.e., characterisation under actual working conditions with reactants and products analyzedon-line. Emphasis is also placed on high selectivity in catalytic reactions and the major challenges for thefuture, such as environmental issues, energy supply, pollution control for vehicles and industrial plants,air/VOCs/water purification, hydrogen sources and carbon dioxide storage/up grading, transformation of

nergynvironment

biomass as a promising source of raw materials, and catalytic water splitting perspectives.This review is a survey of heterogeneous catalysis and is not comprehensive but leads to the conclusion

that, although many catalysts and catalytic processes have already been discovered and developed overthe past century, many opportunities nevertheless exist for new developments, new processes and newcatalytic materials. It follows that substantial challenges exist for the younger generation of researchersand engineers, as emphasized at the end of the manuscript.

. Introduction

Catalysis is an important field in chemistry, with some 90% ofhemical processes involving catalysts in at least one of their steps1]. At present, because of environmental issues, catalysis appearso be even more important than before and to constitute one ofhe major sources of improvements in our society [2,3]. A surveyf U.S. industries revealed that the annual revenue from chemicalnd fuel production topped all other industrial sectors. The surveylso showed that more than 60% of the 63 major products and 90%f the 34 process innovations from 1930 to 1980 have involvedatalysis, which illustrates the critical role of this field in the fuelnd chemical industries.

This review is intended to present some historical background

f catalysis and the major challenges that this field has faced in theast half century and that it still must face in the future. This reviews focused only on heterogeneous catalysis.

∗ Corresponding author. Tel.: +33 144275514.E-mail address: jacques.vedrine@upmc.fr (J.C. Védrine).

920-5861/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.cattod.2012.04.003

© 2012 Elsevier B.V. All rights reserved.

Our aim in this manuscript is to highlight the major catalysis-related discoveries and processes that have been developed overthe past three centuries. The history of catalysis and its contribu-tion to chemical industries has already been widely described inthe literature, e.g. [4–6]. We intended to review some historicallysignificant steps in the development of catalysis and catalytic pro-cesses. Without discussing ancient beer or wine fermentation, it isinteresting to recall some old processes, as summarized in Table 1[7–13].

Some of these processes have been developed in response todriving forces designated as “pullers” like the expected Chileanembargo on saltpeter as a nitrate source, which motivated Haberand Bosch to develop a process for the fixation of atmosphericnitrogen in ammonia synthesis (1909). Similarly, the need for amore energetic gasoline inspired racing driver and French mechan-ical engineer Eugène Houdry to develop the oil (hydrocarbon) acidcracking process (1930), and catalytic reformation and alkylation

(1940), which have allowed the Allied forces to access a powerfulfuel for air planes during World War II.

More recently, driving forces (pullers) have changed and nowcorrespond more to a market-driven strategy, in which simpler

I. Fechete et al. / Catalysis Today 189 (2012) 2– 27 3

Table 1Historical aspects in heterogeneous catalysis [7–13].

Catalytic process Catalyst Main author Year

Sulfuric acid Lead chamber Roebuck 1746Dehydration of alcohols Acid Priestley 1778Esterification of organic acids Acid Scheele 1782Dehydrogenation of alcohols (ethanol) Metal Van Marum 1796Oxidation of alcohol Pt black Priestley & Döbereiner 1810Decomposition of H2O2 and NH3 Metals Thénard 1813Hydrolysis of starch to glucose Acid Kirchoff 1814Combustion Pt Davy 1817Decomposition NH3 Fe > Cu > Ag > Au > Pt Dulong 1823Oxidation Pt Fusinieri 1824Oxidation SO2 to SO3 (contact process) Pt Phillips 1831Definition of catalysis Berzelius 1836Oxidation of NH3 to nitric acid Pt Kuhlmann 1838HCl + O2 → Cl2 Cu Deacon 1875Esterification of acid Acid Bertholet 1879Hydrolysis of esters Acid Bertholet 1879Sulfuric acid V2O5 1875Friedel-Crafts reactions Lewis acids (AlCl3) Friedel & Crafts 1877Nitric acid synthesis Pt gauzes 1904NH3 synthesis from N2 and H2 under high pressure Fe Haber 1909Hydrogenation Ni Sabatier 1912Active site concept Michaelis 1913Theory of adsorption Langmuir 1915Industrial process of NH3 synthesis under pressure Fe Haber 1918CO + H2 → CH3OH ZnO-chromia BASF 1923CO + H2 → hydrocarbons Fe, Co Fischer & Tropsch 1923Contact catalysis theory Taylor 1925Hydrogenation vegetable oils Ni Raney 1926Catalytic cracking of petroleum Acid Houdry 1930Synthesis gas Bergius & Bosch 1931Alkylation reaction for gasoline fuel Acid Ipatieff & Pines 1940

asewuthmrtftdt1tplErcstcftdmpSo

u

Synthetic zeolitesExhaust gas treatment

nd less-capital-incentive processes and the use of cheaper feedtocks are preferred. Since the end of the twentieth century, soci-tal concerns have also become an important modern motivation,ith intensive research being devoted to convert by-products toseful products and to treat all kinds of wastes for the preserva-ion and protection of the environment. More stringent legislationas been established which has led to research on new catalyticaterials and more efficient processes. More specifically, with

espect to environmental issues, hydrodesulfurization started inhe 1960s as an important method for the removal of sulfur fromuels. Hydrodesulfurization has resulted in a considerable reduc-ion in global emissions of sulfur oxides, while creating increasedemand for the selective methane reaction (SMR) for H2 produc-ion; auto emission control catalysts developed in 1974 (oxidation),978 (three-way), and in the 1990s (Pd three-way); the selec-ive catalytic reduction of NOx by NH3 or N2H4 (SCR) for powerlants in 1980 using V, W, and Ti oxides extruded into mono-

ith forms [14]; ozone emission control catalysts developed byngelhard (now BASF); the replacement of CFCs by HCFCs for theeduction of topospheric ozone concentration (ozone holes), theatalytic destruction of volatile organic compounds from the con-umer products industry; the production of foods and chemicals;he development of diesel oxidation exhaust catalysts in 1990 usingerium salt as additive; a variety of solutions that use metal oxidesor catalytic decomposition of N2O (which resulted in an 81% reduc-ion of all N2O emissions from the world adipic acid plants); theevelopment of Pt–Rh-alkali NOx storage catalysts; the develop-ent of the Toyota Motor in 1994; the development of diesel

articulate elimination catalysts in 2003; the development of urea

CR for NOx emissions control in vehicles in 2004; the developmentf NOx removal in FCC regenerator units in 2007, and so forth.

New studies have also appeared in the past two or three decadesnder driving forces considered as “pushers” for the development

Barrer & Breck 1946General Motors & Ford 1976

of a molecular-level understanding of catalyst function, sur-face sensitive spectroscopies, in situ/operando characterisationtechniques, scientific computing, quantum chemistry, molecularmodelling, thermodynamics and kinetics, reaction and reactormodelling, high-throughput catalyst screening and testing, andso forth. Significant improvements have been made in all of thesedomains, and further developments should continue in the future.

2. The catalysts

Since ancient times, the development and use of materials havebeen one of the basic objectives of our world. Eras, the Stone Age,the Bronze Age, and the Iron Age, have been named after the funda-mental material used by mankind to construct their tools. Materialsscience is the modern activity that provides the raw material for thisendless need, demanded by the progress in all fields of industry andtechnology, for new materials for the development of society.

The International Union of Pure and Applied Chemistry (IUPAC)has defined a catalyst as “a substance that increases the rate ofa reaction without modifying the overall standard Gibbs energychange in the reaction” [15]. The chemical process of increasingthe reaction rate is called catalysis, and the catalyst is both a reac-tant and a product of the reaction, i.e., the catalyst is restored aftereach catalytic act. Furthermore, the catalyst does not influence thethermodynamical equilibrium composition after the cessation ofthe reaction.

More efficient catalytic processes require improvements in thecatalytic activity and selectivity. Both aspects can be improvedby the tailored design of catalytic materials with the desired

structures and the desired dispersion of active sites. Materialssuch as zeolites, AlPO, SAPO, mesoporous materials, PILC, MOFs,etc. offer such possibilities in this regard, with controlled large andaccessible surface areas of the catalysts but without standalone

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ne particles. Moreover, one of the most important applica-ions of these novel porous solid catalysts is the replacementf environmentally hazardous, corrosive, difficult-to-separate-nd-dispose-of homogeneous catalysts (viz. mineral and Lewiscids, organic and inorganic bases and toxic metallic compounds)mployed in the liquid-phase synthesis of bulk and fine chemicalsvide infra) [16]. There are many families of solids catalysts like

etals, oxides, sulfides, carbons, etc. as bulk materials or supportedn a more or less catalytically active support like silica, alumina,irconia, titania, ceria, carbons, etc. These materials may possesspecific chemical properties, such as acid-base or redox or dehy-rogenating or hydrogenating or oxidizing, and physical properties

ike porosity, high surface area, attrition resistance, thermal and/orlectrical conductivity, etc. The largest family corresponds toxides whatever zeolites, clays, mesoporous materials, mixedxides as catalysts or as supports. Among them porous materialsresent some fascinating properties, which are described below.

.1. Zeolites

In the petrochemistry and organic synthesis fields, zeolites havelayed a major role in the twentieth century. Zeolites are inorganicrystalline aluminosilicates which structures consist of a three-imensional arrangement of TO4 tetrahedra (where T is usuallyi4+ and Al3+ tetrahedrally coordinated atoms) assembled togetherhrough the sharing of oxygen atoms to form subunits, which repeato form an infinite lattice [17], consisting of three-dimensional,ourfold interconnected TO4 tetrahedra linked via T–O–T bridges.he T–O–T angles are ideally 140–150◦ and rarely over 180◦. Thexistence of Al in a tetrahedrally coordinated Si structure leaves aegative framework charge, which requires the existence of com-ensating cations, located in the porous system.

Consequently, an interesting feature of zeolites is the versatilityf their structures that arises from a large number of modifica-ion procedures which also tailor their catalytic properties. Theatalytic activity is associated with the presence of active centresn the framework. Such centres may be acid, their strength andumber (Brønsted, Lewis) being adjusted in a controlled mannerither during synthesis by isomorphous replacement of the centrali atom in tetrahedral sites in the zeolite lattice, by for examplerivalent elements like Al, B, Fe, Cr, Sb, As, or Ga, and tetravalentlements like Ge, Ti, Zr, or Hf; and/or post-synthesis including theteam procedure, chemical vapor deposition, ion exchange of inter-titial cations, reduction of exchanged metal ions to a lower valencetate.

A distinction has been made between small-, medium- and

arge-pore zeolites. In the case of small-pore zeolites, such as zeo-ite A, eight SiO4 tetrahedra form a ten member ring (10MR) with

diameter a 0.41 nm and in the case of large-pore zeolites, suchs Y-zeolite (Fig. 1), a cavity with a diameter of 0.74 nm is formed

Fig. 1. Framework of Faujasite (FAU) zeolite (Y or X-Type Si/Al = 2.5 or 1).

day 189 (2012) 2– 27

by twelve SiO4 tetrahedra. The medium-pore zeolites, such as pen-tasil zeolites, contain a ten member ring with an ellipsoidal tubulardiameter of 0.55 × 0.56 nm. The system of channels and cavities inthese molecular sieves produces solids with very high surface areasand pore volumes, which are capable of adsorbing large amountsof hydrocarbons.

Zeolites can be used as sorbents and as catalysts in some cat-alytic processes. The major breakthrough in zeolite catalysts arosefrom the fluid catalytic cracking (FCC) process for oil transforma-tion to fuels and chemicals. The addition of zeolites (FAU and MFI)to acid clays and silica–alumina cracking catalysts in the mid-1960sresulted in a drastic increase in conversion and gasoline yields aswell as in lower quantities of coke and dry gas [18]. The new cata-lysts gave gasolines with lower octane numbers, primarily becauseof their lower olefinicity [19–21]. The first octane-enhancing FCCcatalysts were introduced by catalyst manufacturers in USA in themid-1970s. Octane FCC catalysts consist of two major components,and the zeolites can be used to boost gasoline octane. Chester et al.[22] have reported that, in addition to MFI (ZSM-5), different mem-bers of the MFI family of zeolites (MEL, ZSM-12, ZSM-23, ZSM-35,ZSM-38) have octane-boosting abilities. Zeolites beta (BEA) [23]and offretite (OFF) [24] have been reported to produce higher gaso-line octane numbers than conventional Y (FAU) zeolites and can beused as octane-boosting additives.

Major milestones in this domain are summarized below:

• R. Milton (Union Carbide in 1950s), D. Breck, R. Barrer and E. Flani-gen developed commercially viable routes to various zeolites andMeAPOs.

• J. Rabo, working at Union Carbide, applied the use of zeolites topetroleum refining (isomerization, 1959), whereas C. Plank and E.Rosinski of Mobil Oil applied zeolites to catalytic cracking (1962)of heavy oil fractions.

• P. Weisz and V. Frilette of Mobil Oil developed the concept (1960)of shape-selective catalysts, and W. Haag applied shape selectiv-ity to the production of aromatics.

• G. Kerr of Mobil Oil discovered high silica zeolites in 1967 (ZSM-5,subsequently designated as MFI) and the first large scale commer-cial cracking trial was run in 1983.

• W. R. Grace discovered the steaming of Y zeolite to produce ultra-stable Y (USY) zeolite in 1969.

• Mobil Oil developed the siliceous mesoporous-type materialsdesignated as MCM, HMS, and so forth in the late 1990s.

• M. Taramasso, G. Perego, and B. Notari discovered TS-1 (titaniumsilicalite-1 with the MFI structure), a selective oxidation catalystfor the epoxidation of olefins, at ENI-SNAM Progetti in 1983.

• UOP/HYDRO (1995) developed SAPO-34, a silicoaluminophos-phate molecular sieve applied for methanol to olefins (MTOprocess).

Another fascinating property of zeolites arises from their molec-ular size porous network, which allows certain reactants to enterand products to easily leave the pores or cavities, or to remaintrapped, or to leave the pores with difficulty if they are too bulky.This concept, of shape selectivity, pioneered by Mobil scientists[25], has been developed to explain reactions that do not obeythe classical laws of thermodynamics and that are strongly influ-enced by the size of the pores or cavities relative to the size ofthe reactant or product molecules. Matching the size and config-uration of reacting molecules, intermediates and products withthe geometry and tortuosity of the zeolite channel/cavity systemprovides the basis for controlled shape selectivity. Diffusion and

shape-selectivity catalysis in zeolites have been reviewed in sev-eral publications [26–28]. However, the shape selectivity in zeolitescan manifest itself through: reactant selectivity, product selec-tivity, transition-state selectivity, molecular traffic control, etc.

I. Fechete et al. / Catalysis Today 189 (2012) 2– 27 5

shape

Tldithbftamtstaetalit

Fig. 2. Illustration of a molecule in a pore and

he reactant selectivity, results in the exclusion of molecules tooarge to diffuse into the zeolite pores; a simple example is the dehy-ration of alcohols. Over the narrow-pore zeolite (CaA), n-butanol

s dehydrated, and isobutanol is not. Conversely, as expected, isobu-anol is more readily dehydrated than n-butanol over NaX (whichas wider pores). The former result is readily explained becauseoth forms can enter NaX, but the bulkier isobutanol is excludedrom CaA – product selectivity. In addition to size exclusion, entranceo zeolite crystals may hinder when the unfavorable orientation of

reactant is caused by electrostatic effects. In this case, the align-ent of a zeolitic electrostatic field (perpendicular to the plane of

he window) and a molecule dipole may restrict entry by electro-tatic repulsion, which allows only small molecules formed duringhe reaction to diffuse out of the zeolite pores. For example, in thelkylation of toluene by methanol over H-MFI, yields of p-xylene arenhanced because the diffusivity of p-xylene is much greater thanhat of o- and m-xylenes (vide infra). Even if the primary product of

lkylation is not rich in p-xylene, its more rapid exit from the zeo-ite allows further isomerization of o- and m-xylenes and results inncreased yields of the p-isomer. Restricted transition-state selec-ivity occurs when certain reactions are prevented because the

Fig. 3. Principe of confinement A and anti-co

selectivity in dealuminated mordenite zeolite.

corresponding transition state would require more space than isavailable in the pores. Molecular traffic control [29] occurs in zeo-lites with two types of channel systems. The relationship betweenthe length of the molecules and the size of the zeolite cage as wellas variations in molecular oscillations [30] also affect zeolite shapeselectivity. In addition to geometric factors, shape selectivity canbe due to electrostatic effects [31] which result from the interactionbetween the electric field at the pore mouth and the dipole momentof the reactant molecule. Such an interaction can favour or inhibitthe diffusion of the reactant molecule into the zeolite.

The shape selectivity of zeolites can be modified by ionexchange, dealumination, changes in the framework Si/Al ratio, orby any modification that affects the pore size or geometry [32–45].The shape selectivity of a zeolite is often characterized by its “con-straint index,” which is the ratio of the cracking rate constants forn-hexane and 3-methylpentane [46]. Large-pore zeolites have con-straint indices less than 1; medium-pore zeolites have constraint

indices between 1 and 12; small-pore zeolites have constraintindices higher than 12.

The shape selectivity phenomenon is illustrated inFig. 2 for the synthesis of 4,4′-di-isopropyl-biphenyl and 2,

nfinement C, dimensionality [47–49].

6 I. Fechete et al. / Catalysis Today 189 (2012) 2– 27

Fc[

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ig. 4. Variations of van der Waals energy W and the force between a spheri-al molecule (radius d) and a spherical micropore (radius a) vs. curvature (s = d/a)47–49].

-di-isopropyl-naphthalene compounds that are intermediatesor polyesters or liquid crystals, by alkylation of naphthalene byropylene on dealuminated mordenite. The narrow size of theordenite (10-membered ring) zeolite favours the formation

f the less-bulky para isomer of the di-isopropyl naphthalene,ollowed by the ortho isomer relative to the meta isomer, as isxpected from the thermodynamic equilibrium of approximately5:25:50, respectively.

Another aspect of zeolite properties is the confinement effect, aseveloped by E. Derouane [47–49], which simply considers van deraals forces, i.e., neglecting Pauli repulsive forces, as illustrated in

ig. 3.Derouane et al. have proposed the following equation of the

an der Waals energy (W) of a spherical molecule of van deraals radius (d) confined in a spherical micropore of a radius (a):(s) = −(C/4d3) · (1 − s/2)−3 with C = hω ˛/2, where = e2/mω2 is the

olarizability of an atom seen as a punctual dipolar momentum,uctuating at a frequency ω, and s is the surface curvature. This

atter parameter, s = d/a, can vary between 0 and 1, depending onhe relative sizes of the confined molecule and the micropore. Thean der Waals force is F = (3C/4d4)[(1 − s)/(1 − s/2)4. The extremeases correspond to a flat surface (s = 0) and to a molecule with theame size as the pore (s = 1); this latter case has been referred to byerouane et al. as a “floating molecule” which should diffuse very

apidly because its motion is not hindered by its interaction withhe wall, as compensated by the van der Waals force. It also followsrom the van der Waals equation that Ws=1 = 8Ws=0, which meanshat, according to this model, the adsorption energy due to the vaner Waals confinement factor within the zeolite pore can be up to

times greater than that corresponding to a flat surface. The typef variation of W versus s can be found in Fig. 4.

As a consequence, molecules within the pores may interact morer less strongly with their environment depending on their sizeelative to that of the pores, e.g., 90 kJ mol−1 for p-xylene in SAPO-1. They can also contract themselves to enter the pores, whereashe zeolitic lattice may also slightly contract upon adsorption, as

hown by XRD [50].

At present, more than 300 different types of zeolite frameworksre known, with only a few (BEA, FAU, MFI, MOR, SAPO-34) havingmportant industrial catalytic applications; however, many more

Fig. 5. Adipic acid processes using the old process (left) and the new process (right).

have applications for the manufacture of fine chemicals. Some stud-ies are described below to exemplify some of their properties.

The synthesis of adipic acid is an interesting example. The clas-sical process (annual production of 0.7 Mt, off-gas concentration of25–40%) uses nitric acid as an oxidizing agent with the formation ofN2O, which has to be re-oxidized further to nitric acid and which isan important greenhouse gas. A catalytic process was subsequentlydeveloped for N2O decomposition. However, a process that uses aFe-MFI catalyst, which is able to oxidize benzene directly to phenol[51–58] has been discovered at the Boreskov Institute of Catalysisin Novosibirsk, RU, and a process was developed with MonsantoCo in a spin-off company called Solutia, but does not appear to becommercialised, according to our knowledge. This process is muchmore environmentally friendly because N2O is used instead of oxy-gen to oxidize benzene to phenol. The scheme for this process ispresented in Fig. 5.

Another interesting example is Friedel–Crafts reactions onacidic zeolites. The first mention of acylation related to the laterAl2Cl6 method of Friedel and Crafts appeared in 1873 in a prelim-inary communication by Grucarevic and Merz [59], as reported byOlah in a historical review about Friedel–Crafts chemistry [60,61]on the metal-catalyzed acylation of aromatic compounds. TheFriedel–Crafts acylation reaction consists primarily of the produc-tion of an aromatic ketone by reaction of an aromatic substratewith an acyl component in the presence of a catalyst. Many papersand books have been published and numerous patents have beengranted on this topic, as summarized in a recent review [62]. Inter-ests in electrophilic acylation studies and in the optimization ofpreparative processes were spurred by the considerable practicalvalue of the aromatic ketone products, which constitute importantintermediates in the pharmaceutical, fragrance, flavour, dye andagrochemical industries. The electrophilic acylations are catalyzedby Lewis acids (such as ZnCl2, AlCl3, FeCl3, SnCl4, and TiCl4) or pro-tic acids (such as HF or H2SO4). However, the use of metal halidescauses problems associated with the hydrolysis of the complex,which results in the loss of catalyst and the generation of large vol-umes of corrosive waste streams. Great efforts have thus been madeto achieve the goal of making the Lewis acid using heterogeneoussolid catalysts, in particular acid zeolites. A detailed description ofFriedel–Crafts reactions for arenes (e.g., benzene, toluene, xylenes),aromatic ethers (e.g., anisole) with acetic anhydride or other acy-lating agents on zeolites and on clays, metal oxides, and so forth isgiven in Ref. [60]. The roles of shape selectivity and deactivation bythe products and hydrophobicity versus hydrophilicity for zeolites

have been emphasized. For example, acylation of anisole or toluenewith acetic anhydride was performed on BEA zeolite at 90 ◦C, toreplace the classical AlCl3 catalyst which led to many salts in theeffluents, corrosion problems, low selectivity and a short lifetime

I. Fechete et al. / Catalysis To

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ig. 6. Scheme of the effect of the adsorption rate of reactants on the reactivity,epending on the polarity of the reactants versus that of the zeolite [63,64].

f the catalyst, as already discussed. At variance, the use of H-BEAeolite resulted in 6 times fewer steps, 10 times less solid and 100imes less aqueous discharge, primarily because the hydrophilicityersus the hydrophobicity of the zeolite, for more or less polar reac-ants, which allowed the reactant molecules to enter more or lessasily within the pores while the solvent molecules were preventedrom entering. The relative adsorption rates of reactant moleculesithin the pores regulate the stoichiometry of the reaction inside

he pores, i.e., depending on the relative adsorption rates of theeactants, and one has thus to choose a stoichiometry in the liq-id medium surrounding the zeolite particles that is different fromhat expected from the reaction. For example, a 20:1 stoichiom-try might be chosen for a 1:1 reaction for toluene (non polareactant) acylation by acetic anhydride (polar reactant). This heldsrue particularly for gas phase reactions with solid zeolites, but alsoor liquid phase reactions on solid zeolites, which is an importantspect of fine chemical reactions in zeolites, as schematized in Fig. 6.

Another interesting example relates to the production ofara-xylene (p-xylene). Xylenes, especially the para isomers, areompounds in high demand in the organic chemical industryor the production of polyethyleneterephtalate (PET) fibres, plas-ics, resins, films, and so forth because p-xylene is a chemicalntermediate in these processes. The main source of xylenes ishe C8 cut produced by catalytic reformation and steam cracking65–68]. However, a convenient way to increase p-xylene produc-ion is to transform less-valuable C and C methylaromatics by

7 9atalytic alkylation of toluene with methanol followed by dispro-ortionation and transalkylation with trimethylbenzene. Catalystsor these reactions range from common Brønsted acids (H2SO4,

ig. 7. Historical view of functions of coordination polymers reported from 1990 to 200Zn4O(BDC)3]n (2, right), and the 1-D oxygen array are listed [124].

day 189 (2012) 2– 27 7

H3PO4, HF) to Lewis acids (metal halides) and further to solidacids (Al2O3, SiO2–Al2O3, zeolites). It must be noted, that as a con-sequence of environmental concerns, the zeolite-based catalystscurrently play a significant role in the production of alkyl aromat-ics. Studies reported in the literature describe a wide variety ofzeolitic catalysts that are active in the alkylation of toluene withmethanol [36,38,39,69–78], toluene disproportionation [79–84],transalkylation of toluene–trimethylbenzene [85–89], and xyleneisomerization [90–92]. In general, the catalytic properties (espe-cially the selectivity) and the surface deactivation of zeolitesduring these reactions strongly depend on the nature, numberand strength of the acid centres in the catalyst. For example, thecatalysts with strongly acidic sites have been reported to be lessselective and easily deactivated by coke [93]. Modification of theacidity and structure of zeolites (with large and medium pores)can be considered a way to reduce by-reactions and improvethe selectivity to p-xylene. High activity and predominant shapeselectivity was observed on ZSM-5 [94–97], and the reaction iseffective above 450 ◦C. The high p-selectivity of modified ZSM5has been attributed to the restricted diffusion inside the chan-nels, i.e., the p-xylene, which rapidly diffuses out of the narrowchannels, is preferentially produced. Large-pore zeolites with 12-member channel systems, particularly mordenite [98,99], have alsoemerged as shape-selective catalysts. Although the size of pores isimportant for the para selectivity, this phenomenon was observedon large-pore zeolites when the acidity was modified by isomor-phous substitution or ionic exchange with rare-earth metals. Theformation of p-xylene was also investigated on the zeolite MCM-22 [100–102], discovered by Mobil, which has a unique crystalstructure [103]. It is composed of two channel systems, both ofwhich are accessed through a 10-membered ring (10-MR) window.One system consists of two-dimensional, sinusoidal channels with10-MR opening, whereas the other contains large supercages thatconsist of 10-MR and 12-MR openings with an inner free spaceof 0.71 × 0.71 × 1.82 nm. These channel systems are independentof each other, and molecules cannot pass from one to the otherwithin the same crystallite. The catalytic properties, such as theshape selectivity of MCM-22, have been shown to be intermedi-ate between 10-MR and 12-MR zeolites in various reactions. Theresults for MCM-22 highlight the influence of cages and windowson the shape selectivity. In such cases, the experimentally observedshape selectivity was attributed to variations in the Si/Al ratio andthe nature of the extra framework cations. Toluene disproportion-

the supercages of MCM-22 but not in the 10-MR channels of MCM-22 at the investigated temperatures. The fraction of p-xylene washigher than its equilibrium value and increased further by the

5. Structures of 3-D porous coordination polymers, [Cu(SiF6)(4,4′-bpy)2]n (1, left),

8 I. Fechete et al. / Catalysis Today 189 (2012) 2– 27

F }; bottf

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CSzc

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ig. 8. Self-assembly of polymetallic cluster nodes (left; top: m4-oxo {M4O(-CO2)6

rameworks (center) [125,126].

ealumination. p-Xylene formed within the supercages as a pri-ary product would be isomerized to o- and m-xylene by the acid

ites not only on the external surface but also within the 10-MRhannels. The improvement in the para selectivity by dealumina-ion resulted from the suppression of isomerization activity; theealumination treatment probably eliminated framework Al atomsredominantly on the external surface and inside the 10-MR chan-els compared with those inside the supercages [102].

Many other fine-chemical reactions have been developed byorma, Garcia and their teams [2] at ITQ, Universidad de Valencia,pain. These reactions pertain largely to the field of applications ofeolites in catalysis, which has previously been limited to petro-hemical reactions.

.2. AlPO4-n SAPO4-n, Me-AlPO4-n, Me-APSO4-n

In the early 1980s, the discovery of a new family of molecu-ar sieves was reported by researchers at Union Carbide. Wilsont al. [104,105] described the microporous aluminophosphates pre-

ared hydrothermally from alumina, phosphoric acid and an aminer quaternary ammonium salt as organic templates. The productomposition for these materials is xR·Al2O3·1.0 ± 0.2 P2O5·yH2O,here R is an organic template located in the intracrystalline

ig. 9. MOFs structures: Left: MIL-53, metal terephtalate (with Al, Cr, Fe ou V), which caphose octahedra, constituted by chromates (CrO6), organise in tetrahedra and form cavit

om: {M2(-CO2)4} paddlewheel) and organic linkers (right) yielding metal–organic

pore system. The crystallized materials consist of alternating AlO2and PO2 tetrahedra joined together into electrovalently neutral,three-dimensional frameworks whose structure depends upon thepreparation conditions. These frameworks contain no Al O Alor P O P bonds. The AlPO4-5 structure consists of 4- and 6-membered rings joined together to form the unidimensionalcylindrical channels of 12-membered rings with a free diame-ter of approximately 0.8 nm [106,107,50,108,109]. The porosityof the structures described by Union Carbide researchers variesfrom very small pores (0.3 nm) to relatively large pores (0.8 nm).Because AlPO4 frameworks are neutral, they have no ion-exchangecapacity. They exhibit good thermal and hydrothermal stabilityand have weakly acidic catalytic properties. The absence of strongacidity limits the application of these materials in cracking catal-ysis. By isomorphic substitution of a series of elements into theAlPO4 framework, a new generation of crystalline molecular sieveswas prepared [110]. The elements include framework cationicspecies that range from monovalent to pentavalent, such as Li,Be, B, Mg, Si, Ga, Ge, As, Ti, Mn, Fe, Co, and Zn. The addition of

silicon to the aluminum and phosphorous framework elementsresults in silicoaluminophosphate (SAPO) molecular sieves [111].The SAPO structures are mildly hydrophilic and have low-to-moderate acidity, depending upon the silicon concentration and

tures hydrogen into the framework formed of tunnels. Centre and right: MIL-100,ies of diameter 2–3 nm as observed by electron microscopy from [127].

ysis Today 189 (2012) 2– 27 9

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2

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2

lpwtcmdwaotoM

2

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(2) encapsulation of active species and (3) post synthesis modifica-tion/functionalisation. Fig. 12 shows the relative sizes of differentzeolites and MOFs compared to organic molecules. It is clear that big

I. Fechete et al. / Catal

he structure type. According to Martens [112], even the highlyiliceous SAPOs have a lower catalytic activity as compared witheolites, such USY. SAPO-37 is very active cracking catalyst [113].everal patents describe the use of SAPO-5, SAPO-11, SAPO-37 andAPO-40 in octane FCC catalysts [114]. The isomorphic substitutionf metal ions into AlPO4 frameworks results in metal aluminophos-hates (MeAPO), whereas the isomorphic substitution of metal

ons into SAPOs results in metal silicoaluminophosphate frame-orks (MeAPSOs). Their properties are similar to those of thearent molecular sieves. The thermal and hydrothermal stabilityf MeAPSO is somewhat lower than that of AlPO4 and SAPO molec-lar sieves. MeAPSOs exhibit weak to strong acidity, depending onhe metal type and the framework structure.

.3. Pillared interlayer clays (PILCs)

Pillared interlayered clays (PILCs) have been studied sincehe late 1970s as microporous materials with larger pore size0.4–2.0 nm, but less uniform) and more tunable compositionshan those of zeolites [115–117]. PILCs were identified as goodandidates for heterogeneous catalysis because their pore sizeistribution is quite broad and is still largely in the micro-orous range [2]. The parent clay materials are composed ofharge-balancing cations sandwiched between negatively chargedluminosilicate sheets. PILCs are prepared by swelling the clayheets, ion exchanging the cations with [AlO4Al12(OH)24(H2O)]7+

luminum polyoxocations, and calcining the material to create alu-inum oxide pillars within the clay sheets. The result is a highly

orous structure with a large intracrystalline surface area suit-ble for molecular sieving, adsorption and catalysis [118]. PILC-likeaterials, termed PCHs (porous clay heterostructures) have been

repared using surfactant templating within the clay sheets [119].

he PCHs have controllable, uniform pore sizes of 1.4–2.2 nm andetain the sheet-like characteristics of the original clay material.

.4. Layered double hydroxides (LDHs)

Layered double hydroxides (LDHs), also known as hydrotalcite-ike compounds, are ionic lamellar compounds that consist ofositively charged hydroxide sheets with their interlayers filledith anions and water molecules. Their structure is linked to

hat of the natural mineral brucite, Mg(OH)2 [120,121]. The mostommon group of LDHs can be represented by the general for-ula [M2+

1−xM3+x(OH)2] − [An−

x/n·mH2O], where M2+ and M3+ arei- and tri-valent metal cations that occupy octahedral positionsithin the host layers of hydroxide sheets, and An− is an interlayer

nion that compensates for the charge on the layers. Positive chargen the host layers arises from isomorphous replacement of a frac-ion of the divalent cations with trivalent cations. The combinationf Mg and Al has been studied most frequently, with a variety ofg:Al ratios and interlayer anions.

.5. Metal organic frameworks (MOFs)

The metal–organic frameworks, designated MOFs, are newaterials that were discovered approximately 40 years ago by poly-er scientists. The rapid proliferation of papers in the literature

tarted only approximately 20 years ago [122,123]. Their synthesisorresponds to the reaction of organic and inorganic groups, suchs arsenates, silicates, sulfates, phosphates, phosphonates, etc. Thiseaction builds up three-dimensional frameworks formed of inor-

anic and organic moieties linked by strong bonds. The organicart is variable in nature, length and amount of space occupiedecause it includes more- or less-branched carboxylic acids, aminoomplexes, etc. The history of MOFs is schematized in Figs. 7 and 8.

Fig. 10. MOF: MIL-101 metal terphthalate with cages of 3.2 nm [128].

Descriptions of the structures and porosities of several MOFs areillustrated in Figs. 9–11 for better comprehensiveness of their spe-cific properties. According to Fig. 11, some MOFs may expand uponadsorption (breathing motion) or be distorted, which may resultin different catalytic and adsorptive properties [130–135]. Desorp-tion may be slow without pumping; this property was suggestedby Ferey et al. to be used for the slow delivery of a drug into theblood stream when inoculated to a sick person, e.g., for diabetes[127].

For a catalytic point of view one can distinguish three aspects ofMOFs properties related to: (1) framework atoms or ions activity,

Fig. 11. Schematic behavior observed upon adsorption, desorption of guestmolecules (a) induced pores (b) breathing pore; (c) pores exchanging guest withdeformation, (d) annealing pores [129].

10 I. Fechete et al. / Catalysis Today 189 (2012) 2– 27

Table 2Comparison of MOFs with zeolites for some properties relevant to catalysis [131].

Properties Zeolites MOFs

Lewis acidity High Low to mediumBrønsted acidity Bridging Si(OH)Al hydroxyl groups Introduced by post synthesisSurface area ∼200–500 m2 g−1 Up to 5000 m2 g−1

Pore volume ∼0.1–0.5 cm3 g−1 Over 1 cm3 g−1

Thermal stability >450 ◦C 300 ◦CChemical stabilility High Limited, depends on solventsDiffusion High for small molecules in gas phase, slow in liquid phase High but strongly influenced by linkersBasicity Arises from framework oxygens Introduced post synthesis or through linkersMetal site density Low HighFramework defects Important role in many reactions Expected to play a minor role

mchc

ftlboato

(ablarb

F

Active site environment Mostly hydrophilic, but may also be hydrophobicPoisoning of active sites Reactivation by thermal treatment

Chirality Not possible or difficult

olecules can access the large pores, which should be important foratalytic purposes, if the MOF structure has been functionalised oras active sites and presents accessible framework atoms or metalationic sites (Table 2).

Garcia et al. have described [131] the use of metal–organicrameworks (MOFs) as heterogeneous catalysts for oxidation reac-ion using hydroperoxides or molecular oxygen. The authors haveimited themselves to the oxidation of cycloalkanes, oxidation ofenzylic positions, oxidation of cycloalkenes and aerobic oxidationf alcohols, but many more oxidation reactions may be imaginednd studied. The use of MOFs as catalysts for enantioselective oxida-ions has also been considered with the peculiarity of the requiredxidants and the advantages of having homo chiral MOFs.

Main applications of MOFs concern: adsorption, gas storageH2, CO2, etc.), gas separation, acid (Lewis; Brønsted), basic, redoxnd enantioselective (chirality) catalyses, biomass transformation,iomimetism, enzymes, drug delivery, magnetism, non linear optic,

asers, sensors, luminescence, etc. In catalysis, the thermal stability

nd leaching have been a big problem for many years and restrainedesearches, but now some new systems have been claimed to be sta-le up to 500 ◦C. The MOFs may not replace zeolites in petrorefining

ig. 12. Comparison of sizes of cavities and organic molecules diameters [132].

Considerably hydrophobicThermal treatment not validHomochiral solid from chiral linkers or post synthesis modifications

but well for fine chemistry under more gentle reaction conditions.Already many papers have appeared for some reactions such asoxidation, Lewis-type reaction of cyanosilylation of acetaldehyde[137], etc.

It is clear that catalytic studies with MOFs are in their infancy.It is certainly possible to go into more sophisticated materials withorganic ligands between the metals could be formed by transitionmetal complexes with one or two metals at controlled distance.Such types of materials will allow synthesis of heterogeneous cat-alysts based not only on transition metal complexes but also by thecombination of mono- or multimetallic sites. Such design may leadto materials having a catalytic behaviour similar to that observedwith enzymes.

The possibility to synthesise MOFs with a large variety of transi-tion metals could be largely exploited for Lewis acid-type catalysis,provided that the metal is accessible (free valency available) andable to accept electrons from the reactant. In addition, the organiccomponent of the MOF should support acid, base, or acid-basepairs and should allow one to perform successive reactions. Theremay be interest in the chemical industry in exploiting MOFs asheterogeneous catalysts. Examples include epoxide ring aperturewith alcohols by zinc carboxylates, fine chemical reactions as Friesrearrangements, acylations, alkylaromatic oxidation using cobaltsalts in acetic acid, etc. MOFs offer also some promises as enan-tioselective catalysts, a topic that has not been possible to developusing zeolites. Asymmetric syntheses are routinely practiced in thesynthesis of drugs, and these reactions are almost completely per-formed using expensive homogeneous catalysts. By using chiralligands, a vast number of new MOFs could be available and testedin this field. Considering the simplicity of the synthesis of MOFs andtheir affordability, it will be important to know if MOFs can outper-form in large-scale or asymmetric reactions to replace expensivehomogeneous processes.

Finally, there is a need for theoretical studies in this new field,assisting the design of MOFs and providing insight into the interac-tion of the substrates and MOFs. Clarifying the reaction mechanism,the geometry of the transition states, and the controlling step in thereaction mechanisms may help to develop MOFs in which each ofthe components plays the expected role, as catalytic sites of naturalenzymes.

2.6. Hierarchical zeolites

Hierarchical and mesoporous zeolites and mesoporous oxides(alumina, titania, etc.) have received increasing attention becauseof their improved performance in catalyzed reactions with respect

to conventional (purely microporous) zeolites or common metaloxides [59,138,139]. The principle involves the creation of meso-porosity within the zeolite or within any metal oxide particles.Combined micro- and mesoporous materials have been claimed to

I. Fechete et al. / Catalysis Today 189 (2012) 2– 27 11

in 200

hpdz[srsmpsatfrccoDrmlo

2

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Fig. 13. World energy consumption

ave advantages compared with the exclusively micro- or meso-orous materials. The reactant molecules are thus expected toiffuse more easily [140] within these pores to reach the activeeolite sites. These materials provide better hydrothermal stability141], better multifunctionality to process a large variety of feed-tocks, more controlled leaching rates for a constant and gradualelease of active components, and are more capable of encap-ulating wastes in the micropores [142–144]. Different porousaterials that combine micro- and meso-pores, such as SBA-15,

lugged hexagonal templated silica (PHTS), mesoporous aluminumilicates (MAS), mesoporous titanium silicates (MTS), UL-ZSM-5,nd zeolites, have been developed within the last few years. Ofhese materials, the latter four are mesoporous materials built uprom zeolite precursors. Such porosity in the mesoporous mate-ials with zeolite character can be created after synthesis byhemical treatments, including hydrothermal, acidic, basic, desili-ation/dealumination [2] or recrystallization treatments [145,146],r templating [147–149] or carbon-based [150–153] approaches.esilication in alkaline media has become a widely applied prepa-

ation method to tailor these modified zeolites because of theethod’s optimal combination of efficiency and simplicity. Alka-

ine treatment is also a key step in strategic combinations withther post-synthesis modifications.

.7. Carbon materials

Carbon nanotubes (CNTs) constitute another class of porousaterials. They have been widely studied since their discovery

n 1991 [154]. CNTs have highly unique electronic, mechanical,atalytic, adsorption, and transport properties, which make themnteresting for a variety of applications. Carbon multiwall nano-ubes (MWNTs) and single-wall nanotubes (SWNTs) should beistinguished. They are easily fabricated and may be employedither as catalyst supports, by entrapping active moieties within theores, or to improve photoconversion and electrical energy storagevide infra) [136,155–160]. Other forms of nanographitic carbon

ay also prove to be promising in the development of renewablenergy devices. For example, graphene, which consists of a sin-le sheet of graphite, is considered a promising form of carbon forevice engineering applications and catalysis [161–165]. A signifi-ant volume of literature devoted to graphene and other forms ofarbon, including graphitic nanofibers, has suggested that CNTs areot the only promising nanostructures for either photoconversion

r electrical energy storage applications. The highly unique physicalroperties of carbon nanotubes have been demonstrated for a vari-ty of photovoltaic devices as well as for improved Li-ion batteriesnd electrochemical capacitors.

5 (∼13 TW or 87 Gbarrels oil) [245].

2.8. Mesoporous materials

Many mesoporous silica-type materials have been synthesizedin the years after the pioneering works by Mobil researcherson the M41S family (MCM-41, MCM-48, MCM-50) [166–168].MCM-n mesoporous materials are synthesized using surfactantsas structure-directing agents and can be characterized by well-defined pores of tunable sizes in the range between 2 nm and 10 nmand by specific surface areas between 600 m2 g−1 and 1300 m2 g−1.The most representative M41S materials are MCM-41 and MCM-48. MCM-41 consists of regular pseudo-one-dimensional poresin a honeycomb arrangement, whereas MCM-48 exhibits cubicsymmetry that consists of two interwoven but unconnected three-dimensional pore systems of cylindrical pores. MCM-48 is moredifficult to synthesize and high-quality materials can typically beobtained in the pore-size range between 2 and 5 nm [169]. MCM-50comprises a lamellar phase. Independently, a family of mesoporoussilica materials with properties similar to those of MCM-41 wasdiscovered [170,171]; an important member of this family is FSM-16 [171]. At the microscopic scale, these materials are essentiallyamorphous. Whereas the pore diameter range of MCM-41 mate-rials is restricted to 10 nm, ordered mesoporous silica with porediameters up to approximately 30 nm (SBA-15) can be obtainedusing an amphiphilic block copolymer as a template [172,173].SBA-15 (similar to MCM-41) consists of a hexagonal packing ofcylindrical channels; however, depending on the details of thesynthesis procedure, this material can possess irregular intrawallmicropores that connect adjacent channels [174,175]. Moreover,a great variety of mesoporous materials have been synthesized,such as SBA-1, SBA-2, SBA-12, SBA-16, HMS [176], MSU [177],KSW-2 [178–180], TUD-1 [181], periodic mesoporous organosilicas(PMOs) [182–184], nanoporous carbon with ordered mesostruc-tures [CMK-1, CMK-3) [185,186]. Pure-silica mesoporous materialsare known to exhibit low catalytic activity because of the absence ofactive sites, which typically require heteroatoms. Therefore, one ofthe emerging trends in the area of mesoporous materials synthe-sis is the incorporation of heteroatoms that serve as catalyticallyactive sites. Considerable research interest currently exists in thepreparation and use of heteroatoms that contain mesoporous sil-icas as heterogeneous catalysts. Several elegant procedures havebeen reported for the incorporation of heteroatoms that also per-mit the design of the catalysts with active sites located on highlyaccessible internal surfaces of the pore channels. These proce-

dures include impregnation [187–190], grafting by liquid–solidreaction [191–196], grafting by gas–solid reaction [197], graft-ing by solid–solid reaction [198,199], isomorphous substitution[200–210], molecular designed dispersion approach [211–213] and

1 sis To

tttdalpftthtuihiato

rhctctbaa

2

rhbgcfdstaot[aidwtscchw[eSi8t

roc

2 I. Fechete et al. / Cataly

emplate ion exchange method [214,215]. The objective was to syn-hesize porous materials able to accommodate bulky molecules andhus treat heavier petroleum feedstocks. For example, the intro-uction of Al into such silica frameworks led to medium-strengthcidity compared with the acidity of normal zeolites because ofarger Si O Al bond angles. The applications of such materials inetrochemistry were subsequently limited. At present, research isocused on the introduction of catalytically active functions withinhe mesopores (i.e., functionalization of the walls) or of nanopar-icles of metals or oxides. Interesting results were obtained;owever, to our knowledge, no study has yet produced a break-hrough in catalytic processes. H-Al-MCM41 materials have beensed as catalysts for the conversion of a large variety of substrates

n reactions as diverse as hydrocarbon cracking, hydrocracking andydroisomerization, olefin polymerization, oligomerization and

somerization, Friedel–Crafts aromatic and phenol alkylations andcylations, acetylazations, Beckmann rearrangements, glycosida-ion, aldol condensations, and Prins condensations. Several reviewsn the subject have been published [2,216,217].

Interesting results for the metal-mesoporous materials wereeported with respect to the Fischer–Tropsch reaction [218,219],ydrodesulfurization [220–222], the conversion of methylcy-lopentane [199,201], the acylation of phenol [223], the naph-halene hydrogenation [224], the hydrogenation of arenes [225],yclohexane hydrogenation [226], NO reduction with CO [227],he acylation of aromatic compounds [228], the benzoylation ofenzene [229], the metathesis of oct-1-ene [230], and the photocat-lytic decomposition of NO [231], the oxidation reactions [232,233]nd soforth.

.9. Versatile heterogeneous catalytic systems

Combining confinement and synergy effects has appearedecently as a promising way to synthesise efficient and versatileeterogeneous catalytic systems. For instance, many studies haveeen performed in the past half century to immobilize homo-eneous catalysts on solid supports to synthesize heterogeneousatalysts [234], known to result in easy separation of the catalystrom the reactants and products. Originally, the active centres wereesigned to be away from a support surface in order to minimize theupport destructive influence on the catalytic sites and to maintainhe homogeneous metal complexes environment of ligands with

long spacer and thus catalytic properties [235]. Later on, it wasbserved that a support can even have some beneficial effects onhe anchored homogeneous catalysts [236] such as confinement237] and synergy effects [238–240]. Heterogeneous bifunctionalnd even trifunctional catalysts could then be prepared and stud-ed because a synergy between multifunctional groups could beeveloped within confined spaces. An important further objectiveas to try to synthesise heterogeneous catalysts with enantioselec-

ivity enhanced after chiral catalysts are introduced into confinedpaces. For example, Raja and Thomas [241] have shown that,ompared with the racemic products obtained in homogeneousatalysis, improved enantioselectivity (ee% 53–94%) in asymmetricydrogenation reactions was obtained after chiral RhI complexesere introduced into the channels of mesoporous silica. He et al.

242] have also shown that after a bifuntional catalyst, 9-thioureapi-quinine, was incorporated in the channels of mesoporous silicaBA-15, the heterogeneous catalyst exhibited improved selectiv-ty and enantioselectivity (92.5% selectivity and 99.2% ee versus3.8% selectivity and 93.2% ee) in asymmetric Friedel–Crafts reac-ion between indoles and imines.

Layered compounds, with two-dimensional flexible interlayeregions, are also promising supports for the immobilizationf homogeneous catalysts. For instance, the immobilization ofopper complexes in laponite clay was found [243] to increase the

day 189 (2012) 2– 27

ee from virtually zero to values ca. 40% in the reaction of methylphenyldiazoacetate with tetrahydrofuran.

The idea is to graft, anchor or thether catalytic active entitiesto mesoporous silica. These species may be identical or differentwhich may lead to bifunctional, trifunctional entities within thepores. Their proximity may result in synergistic effect for somereactant within a confined space and opens an important field ofdiscovery of new catalysts, by taking advantage of continuum rangeof distance between anchored functional groups and intrinsic activesites on the support surface. Synergistic effects within anchoredbifunctional catalysts, between two anchored functional groups,and between the anchored groups and hydroxyl groups on solidsurface have been used to synthesise multifunctional catalysts. Let’salso remind that synergistic effects are widely utilized in naturesuch as for enzymes which with limited functional groups can cat-alyze many reactions smoothly with high activity and selectivity atnear room temperature. [244]

3. Energy resources

Currently, petroleum and natural gas represent more than 60%of the primary energy supplied to 7 billions inhabitants on earth.Coal also remains an important source of energy, primarily in Asia.Whether used for energy production, transport, heating or as asource of chemical raw materials, the consumption of oil, natu-ral gas and coal is expected to rise in the near future, while thedevelopment of alternative sources is expected to rise rapidly aftera slow development in the past 20 years. The significant increasein energy demand over the past twenty years has primarily beensatisfied by increasing the production of fossil sources. Because ofthis situation, several governments are approving new laws aimingto reduce CO2 emissions by promoting the utilization of renewableenergy sources and biofuels. The total world consumption in 2005was of 13 TW (∼87 Gbarrels of oil), of which 81% came from fossilresources, as shown in Fig. 13.

Ten percent of the world energy use is derived from biomass,and 7% is derived from nuclear power. Nuclear power is desirableas long as the isotope uranium-235 (235U) is employed. However,a less than twenty-year supply of U235, which may be recoveredat a reasonable cost, is available. When the supply of 235U will beexhausted, it will then be necessary to employ breeder reactors.Unfortunately, the by-product of this reaction is the very hazardouselement, plutonium-239, 239Pu (238U → 239Pu). Moreover since thedisaster following the tsunami in Japan in 2011 and the collapse ofthe nuclear plant in Fukushima, the construction of nuclear plantshave been hardly questioned in many countries, although nuclearpower is non CO2 producer and non fossil resource consumer.

3.1. The case of oil

It is difficult to evaluate the exact oil reserves because it cor-responds to rough estimations called current reserves, which arecontingent resources (conventional and extra-heavy + bitumen)concentrated in a limited number of countries (Saudi Arabia, with20%, Iran, Iraq, and Venezuela; these four countries possess 50%of the world reserves), with 75% in concentrated in 11 countries.The current reserves correspond to approximately 1000 Gbarrelstherefore, approximately 35 years of production at actual consump-tion level, but less than the oil already extracted) and one mayadd 200 Gbarrels for conventional resources and 200–300 Gbarrelsmore for extra-heavy oil and bitumen. Oil is extracted either by

simple pumping (20% of world production), by the injection ofwater (2/3 of oil produced), or by the injection of water + chemicalsor gas (air, CO2 or gas produced (15%)). Efforts to discover newresources are clearly important, and the substitution of oil by

I. Fechete et al. / Catalysis To

Fig. 14. Some perspectives of oil demand in a near future from WEO 2006. Note thatb

rF

3

ERerpcsbcadfvfpwa

i

as high-temperature gasification and pyrolysis and enzymatic fer-

illions tonnes should read giga tonnes.

enewable energies is vital. Some prospects are presented inig. 14.

.2. Perspectives with natural gas (NG)

Natural gas constitutes the largest reserves of fossil resources.leven countries possess 75% of world gas resources, with 45% forussia, 28% for Iran, and 25% for Qatar. The current reserves arestimated to reach 175–200 Tm3 (T = tera = 1012); however, largeesources exist in the form of methane hydrates, which are locatedrimarily in Polar Regions or in deep-water acreage. Natural gasan be used as an energy source (in power plants or as a heatingource, for instance), but it can also be transformed into manyasic materials for chemicals. Nevertheless, currently, only itsonversion to syngas via steam reforming, partial oxidation orutothermal oxidation appears to be industrially viable [246]. Allirect transformations to, for instance, methanol, dimethyl ether,ormaldehyde, aromatics, or olefins are still not economicallyiable. This lack of viability constitutes a real challenge for theuture, although many approaches have been attempted over theast 50 years, starting with the dimerization reaction in the 1970s,ithout commercialization success. The main possible reactions

re summarized below:

Steam reforming −�H0298 (kJ mol−1)

1. CH4 + H2O � CO + H2 −2062. CnHm + nH2O � nCO + (n + m/2) H2 −1175 (for nC7H16)3. CO + H2O � CO2 + H2 (WGS) +41

CO2 (dry) reforming4. CH4 + CO2 � 2CO + 2H2 −247

Autothermal reforming (ATR)5. CH4 + 1½ O2 � CO + 2H2O +5206. CH4 + H2O � CO + 3H2 −2067. CO + H2O � CO2 + H2 +41

Catalytic partial oxidation (CPO)8. CH4 + 1/2O2 � CO + 2H2 +38

Total oxidation9. CH4 + 2O2 → CO2 + 2H2O +802

Boudouard reaction10. 2CO � C + CO2 +172

The main chemical products from natural gas are summarizedn Table 3.

day 189 (2012) 2– 27 13

3.3. Biomass as a source of raw materials and future energy

Biomass, i.e., all products from plants (crops, algaes, wood, agri-cultural wastes, etc.), has emerged as an important future sourceof energy and raw chemicals to replace, at least in part, coal, oiland natural gas. The origin of biomass from CO2 and water undersolar photons and chlorophyll to produce sugar blocks at the ori-gin of cellulose, hemicellulose, lignin, and so forth is well known.Lignin constitutes one of the three major components of ligno-cellulosic biomass; the other two components consist of celluloseand hemicellulose. Lignin is a three-dimensional amorphous poly-mer that consists of methoxylated phenylpropane structures. Inplant cell walls, lignin fills the spaces between cellulose and hemi-cellulose and acts as a glue that holds the lignocellulose matrixtogether. Cross-linking with the carbohydrate polymers then con-fers strength and rigidity to the system [245,247].

In 2005, more than 3% of the total energy consumption in theUnited States was supplied by biomass, and it recently surpassedhydroelectric energy as the largest domestic source of renewableenergy. Similarly, the European Union receives approximately 66%of its renewable energy from biomass, which surpassed the totalcombined contribution from hydropower, wind power, geother-mal energy, and solar power. In addition to energy, the productionof chemicals from biomass is also essential because it is the onlyrenewable source of liquid transportation fuel.

Over the last 30 years, three generations of biomass productshave emerged [248,249], which are distinguished by their nature.Whereas oil was the principal source of energy in the twentieth cen-tury, the 21st century is expected to bring new sources of energy,particularly renewable energies such as bioenergies [248].

Three strategies for biomass valorization can be followed [249].In the first strategy, biomass is gasified to syngas or degraded bypyrolysis to a mixture of small molecules, which can be used toproduce chemicals using technologies developed for petroleumfeedstocks. In the second strategy, extensive removal of the func-tional groups present on the lignin monomers yields simplearomatic compounds, such as phenol, benzene, toluene and xylene.These platform chemicals are then reacted in a second step usingexisting catalytic technology developed for petroleum refineriesto produce bulk and fine chemicals. In the third strategy, biomassis converted directly to valuable chemicals in a one-pot process,which requires highly selective catalysts that eliminate functional-ities and linkages. This strategy is best suited for the production offine chemicals with a high degree of functionality, such as vanillin,that already resemble the lignin structure; however, more com-plicated target molecules may also be produced with additionalimprovements in catalytic technology. Indeed, this approach couldyield a plethora of complex aromatics that are not otherwise read-ily available via conventional petrochemical routes. Because noneof these strategies is expected to yield a single product in highyield, product separation is an important component of each pro-cess. In each case, after the catalytic processing of the lignin stream,the chemicals or fuels produced must be purified, which obviouslymust be taken into account in evaluations of the environmentalimpact of the whole process. Components from the cellulose andhemicelluloses streams are integrated within the lignin framework,but the process arrows are not fully depicted for clarity [245] –Fig. 15.

The transformation of cellulose, which is the main constituentof the most abundant renewable lignocellulosic feedstock and isnon-edible, into chemicals and fuels has attracted significant atten-tion in recent years. Compared with other conversion routes, such

mentation, a low-temperature and selective catalytic route for thetransformation of cellulose in, e.g., a water medium, into a plat-form molecule, which may be facilely transformed into valued

14 I. Fechete et al. / Catalysis Today 189 (2012) 2– 27

Table 3Main chemical products from natural gas.

Products Production (Mtons/y) Energy consumption (GJ/t) CO2 (t/t) Main technology

Ammonia 120 29 1.6 Syngas/synthesisEthylene 100 15 0 .65 Steam cracking of C2H6

Propylene 55 – 0.28 Steam crackingMethanol 30 28 9.0 Syngas/synthesisHydrogen 20 12.6 1 Steam reforming

S

ccaaoto

pbpodeacacptttobhbdmtro

Synfuel 15 67

ource: IFP Energies Nouvelles.

hemicals and fuels in the subsequent step, is more desirable. Glu-ose, polyols, organic acids, and 5-hydroxymethylfurfural (5-HMF)re all promising platform molecules. Some bifunctional catalystsnd catalytic systems that contain both acidity for the hydrolysisf �-1,4-glycosidic bonds in cellulose and metal nanoparticles forhe hydrogenation or oxidation of monosaccharide to polyols orrganic acids have been developed [250–256].

Some analogies can be drawn between the twentieth centuryetroleum refinery and the twenty-first century biorefinery. In theeginning, the petroleum refinery made few products and incor-orated little chemical and energy components. The developmentf the petroleum refinery required considerable effort-spanningecades-to become the highly efficient, integrated system thatxists today. Many of the breakthroughs that allowed this remark-ble transformation involved advances in catalysis. Similarly,urrent biorefineries, which are still in their infancy, produce rel-tively few chemicals (primarily ethanol or bio-oils) with littlehemical and energy integration. Analogous to the history of theetroleum refinery, with the development of catalytic technology,he biorefinery may become an efficient, highly integrated systemo meet the chemical and fuel requirements of the twenty-first cen-ury. To realize this system, in addition to the catalytic conversionsf cellulose and hemicellulose, the lignin fraction of biomass shoulde transformed from a low-quality, low-price waste product into aigh-quality, high-value feedstock for bulk and specialty chemicalsy the development of the appropriate catalytic technology. Theirect transformation of lignin into valued chemicals appears to be

ore difficult than the transformation of cellulose. However, this

ransformation is critical because lignin represents the only viableenewable source for the production of the aromatic compoundsn which society currently depends.

Fig. 15. Lignocellulosic biorefinery scheme with pa

– Syngas/synthesis

It can be concluded that biomass is currently the leading renew-able energy source in the world. Moreover, the introduction ofbiomass into energy systems presents certain advantages, suchas a reduction in greenhouse gas emissions, because its synthe-sis uses CO2 and water. However, its mobilization still presentsmany challenges relative to the competition between uses andthe management of local natural resources (e.g., water, soil, bio-diversity, farmer land and forest private properties). Therefore, thetechnologies involved should be structured so that this resourceis developed to be truly sustainable. Two technologies exist forthe production of diesel replacement fuels: vegetable-oil methylesters (VOME) and hydrotreated vegetable oils (HVO). The latteroils, blended with kerosene, have begun to be used as aviationfuel.

Crop yields depend on the nature of the biosource, as detailedin Table 4. Wood is an important source for lignin. The productionand transformation of wood into biofuel is presented in Table 5.Algae as oil seed appears to be particularly efficient (yield of70 t ha−1 and fuel efficiency of 14 toe ha−1), whereas sugar caneand sugar beets have high yields (ca. 70 t ha−1) but lower fuel effi-ciency (ca. 3 toe ha−1). For comparison, the majority of the otherbiomass resources have yields of 10–20 t ha−1 and efficiencies of2–4 toe ha−1. The cultivation of microalgae to produce oil biomass,cellulose or hydrogen is free of many terrestrial constraints. Suchmicroalgae are cultured in photobioreactors and need only be inproximity to water, light, heat and CO2. Microalgae constitute theprevailing trend in current research.

In the future, solar, geothermal, wind and presumably nuclearpower plants will presumably be used for electricity; biomass,natural gas, coal and oil will be used for syngas and chemi-cals, hydrogen will be used for GTL and hydroprocessing, and

rticular emphasis on the lignin stream [245].

I. Fechete et al. / Catalysis To

Table 4Crops mobilised for energy pruposes versus total production in 2007.

Total harvest (Mt) % for bioenergies

Corn 606 0.3With USA 120 1

Rape sunflower 77 17With USA 23 51

Soybean 221 1With USA 144 2

Palm oil 193 0.2With Asia 165 0.3

Sugar beet 247 4With EU 115 8

Sugar cane 1591 15With South America 641 37

Wheat 606 0.3

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efineries will be used to produce heat, electricity, transports, andulk chemicals (CO2 sequestration).

. Hydrogen as a future energy source

The future supply of energy is dependent on hydrogen as alean energy carrier. Hydrogen can be produced from fossil fuels,ater electrolysis and splitting or biomass. However, the currentebates concerning hydrogen economy are intimately linked to thelean production of hydrogen from fossil fuels (e.g., natural gas,oal propane, methane, gasoline, light diesel), from dry biomassnd biomass-derived liquid fuels (e.g., methanol and biodiesel),nd from water. Because of the low cost and wide availability ofoal, coal gasification to syngas and then to hydrogen through theater–gas shift (WGS) reaction is a promising route to cheap hydro-

en. The success of such a hydrogen production route will only beossible if carbon dioxide is sequestered safely and economically.he key to the cost effective conversion of coal to hydrogen and car-on capture is the development of nanomaterials, such as catalystsor the WGS reaction and inorganic membranes for hydrogen/CO2eparation. In the future, hydrogen will be the dominant fuel andill be converted to electricity in fuel cells, leaving only water as aroduct.

.1. Water–gas shift reaction (WGS)

Since the early 1940s, the WGS reaction has represented anmportant step in the industrial production of hydrogen [257].nterest in the study of WGS catalysts has recently been renewedecause of the importance of such catalysts in PEM fuel cell appli-ations [258,259]. The WGS reaction is an old industrial process inhich water in the form of steam is mixed with carbon monoxide to

btain hydrogen and carbon dioxide. The WGS reaction is reversiblend exothermic. Because of its moderate exothermicity, the WGSeaction is thermodynamically unfavorable at elevated tempera-ures, as illustrated by the continuous decline and eventual sign

able 5ommercial uses of wood (in Mm3) and breakdown of conventional energy uses in 2007.

Wood harvest Sawn wood Wood for pa

World 3,591 1,007 354

Europe 729 330 102

North America 640 386 149

South America 366 82 36

Asia 1,027 150 55

Africa 672 25 6

ource: IFP Energies Nouvelles, D. Lorne, Panorama 2010 Source: FAOSTAT.

day 189 (2012) 2– 27 15

change in the Gibbs free energy as a function of temperature and thecorresponding decreasing equilibrium constant as the temperatureis increased. Low temperatures thermodynamically favour higherCO conversion. For maximum efficiency and economy of operation,many plants operate both a high-temperature stage (350–400 ◦C)and a low-temperature stage (180–240 ◦C). The commercial cata-lyst is composed of copper, zinc oxide, and alumina. The copper andzinc oxide forms are stable under WGS reaction conditions. Copper,the active species, remains active at temperatures as low as 200 ◦C.The zinc oxide provides some protection of the copper from sulfurpoisoning by reacting with adsorbed sulfur compounds while alsoacting as a support for the copper. Because of the relatively lowmelting point of copper, the commercial low-temperature stagecatalyst is more sensitive to deactivation caused by sintering. Dif-ferent catalysts are employed in the WGS reaction, including Fe[260,261], Ni [262,263], Cu [264,265], Ru [266,267], Au [268,269],Pt [270].

The essential role of the industrial WGS reaction is to increasethe production of hydrogen for refinery hydroprocesses, bulk stor-age and redistribution. This role includes the need for gases ofappropriate H2/CO ratios in the production of organic bulk chem-icals such as ammonia, methanol, and alternative hydrocarbonfuels through Fischer–Tropsch synthesis. These gas mixtures, whenapplied in industry, are usually referred to as synthesis gas, orsyngas, and are produced in large-scale facilities by the high-temperature reaction of carbonaceous materials in the presenceof water or oxygen and supported-nickel catalysts.

4.2. Hydrogen production by steam reforming of ethanol

Ethanol is an excellent candidate for the production of hydro-gen. The aim of the procedure for the steam reforming of ethanolis to generate a large amount of hydrogen and carbon diox-ide by breaking the ethanol molecule in the presence of steamover an appropriate catalyst [271–275]. However, numerous reac-tion pathways occur in the ethanol steam-reforming process thatdepends on the nature of the catalysts used. These pathwaysinclude the dehydration of ethanol to ethylene and water followedby ethylene polymerization to form coke [276], the decomposi-tion or cracking to methane followed by steam-reforming [277],dehydrogenation to acetaldehyde [274] followed by decarboxy-lation or steam-reforming of C2H4O, decomposition into acetone,CH3COCH3, followed by steam reforming [278], and steam reform-ing of ethanol to syngas [274]. These processes are accompanied bythe water–gas shift reaction, coking reaction, and other reactions.Tremendous progress is needed to obtain a highly selective catalystto develop a process for hydrogen generation by ethanol steam-ing, which is a sustainable solution for the problem of hydrogenproduction.

4.3. Water splitting as a hydrogen source [279]

Pure hydrogen may be the final destination in the evolutionof fuel usage from coal to petroleum to natural gas, which has

per Wood for board Wood for fuel Fuel wood %

266 1,886 5384 153 2156 54 815 184 53

105 787 773 603 90

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6 I. Fechete et al. / Cataly

ollowed a trail of increasing hydrogen content. A major bottleneckor the hydrogen vehicle is the issue of hydrogen storage. Hydrogenas the highest energy per unit mass, but occupies a large volume.ven in liquid form, the energy density of hydrogen is only 8.4 MJ/L,ompared with 31.6 MJ/L for gasoline. MIL-53 is a potentially usefulaterial for hydrogen storage, as are graphene [280] and bimetallic

d-based alloys.Because of its high energy capacity and environmental friendli-

ess, hydrogen has been identified as a potential energy carrier inany low-greenhouse-gas (GHG) energy scenarios. In a proposed

ydrogen energy system, hydrogen-containing compounds, such asossil fuels (mainly methane), biomass, or even water, are potentialources of hydrogen. When hydrogen is derived from hydrocar-ons such as fossil fuels or biomass, the capture and sequestrationO2 are required in a low-GHG scenario. Although hydrogen pro-uced from water does not present the challenge of unwantedmissions at the point of conversion, it does require that energy beupplied from an external resource. If this energy can be obtainedrom a renewable energy source, such as solar energy, hydrogenan then be considered a green energy alternative, and it is becom-ng increasingly relevant in our world. However, the technologyo produce hydrogen in a cost-effective, low-GHG manner hasot yet been developed. Since the discovery of hydrogen evolu-ion through the photoelectrochemical splitting of water on n-typeiO2 electrodes, the technology of semiconductor-based photocat-lytic water splitting to produce hydrogen using solar energy haseen considered one of the most important approaches to solv-

ng the world energy crisis. Consequently, the development of theecessary semiconductor photocatalysts has been the subject ofonsiderable research. Over the past 40 years, many photocatalystsave reportedly exhibited high photocatalytic activities for split-ing water into a stoichiometric mixture of H2 and O2 (2:1 by molaratio) in the UV-light region. These photocatalysts include La-dopedaTaO3, Sr2M2O7 (M = Nb, Ta), La2Ti2O7, K2La2Ti3O10, NiO/NaTaO3nd �-Ge3N4, among others, photocatalyst, which shows the high-st activity, with a quantum yield of 56% at 270 nm. However, thesexide photocatalysts are only active under UV irradiation. Withespect to the solar spectrum, only a small fraction (ca. 4%) of thencoming solar energy lies in the ultraviolet region, whereas the vis-ble light in the solar spectrum is far more abundant (ca. 46%). It isssential, therefore, as an alternative to UV-active photocatalysts,o develop visible-light-driven photocatalysts that are stable andighly efficient for the practical, large-scale production of hydro-en using solar energy. In recent years, continuous breakthroughsave been made in the development of novel visible-light-riven photocatalysts, which has led to the enhancement ofhotocatalytic activity for water splitting and has inspired greatnthusiasm. A large number of semiconductor materials have beeneveloped as photocatalysts for the splitting of water to hydro-en under visible-light irradiation. Significant process has beenchieved [281] with respect to semiconductor-based photocat-lytic hydrogen generation through water in the hydrogen energyystem.

Photocatalytic systems for water splitting are classified asne of two main kinds: sacrificial-reagent-containing water-plitting systems and overall water-splitting systems. Thus far, theacrificial-reagent-containing water-splitting systems constructedrom the Pt/CdS, Pt-PdS/CdS, and Zn/Cr layered double-hydroxidehotocatalysts have demonstrated the best performance for hydro-en production and oxygen production, with highest quantumields of ca. 60%, 93%, and 60%, respectively, at 420 nm. How-ver, the efficiency of overall water-splitting systems based on

isible-light-driven photocatalysts is still quite low, with a max-mum quantum efficiency of ca. 5.9% over Rh2−yCryO3/GaN–ZnOn the range of 420–440 nm. This result is still far from theuantum efficiency (ca. 30% at 600 nm) designated as the initial

day 189 (2012) 2– 27

starting point for practical applications or the critical conver-sion efficiency of light energy to hydrogen from photocatalyticwater decomposition (15%). Therefore, more efficient visible-light-driven photocatalysts need to be developed to allow theconstruction of the necessary high-efficiency and cost-effectivewater-splitting systems. To develop more efficient visible-light-driven photocatalysts, the band gaps need to be narrowed toharvest visible light in longer-wavelength regions of the spec-trum and to enhance the photogenerated charge separation duringphotocatalysis. Band-gap engineering for the modification of theband structure of semiconductor photocatalysts using ion dop-ing, semiconductor sensitization, or solid solutions all presentsignificant opportunities to render such materials active in thevisible-light region. Computational predictions based on first-principles calculations could provide an efficient way to identifycandidates.

The loading of co-catalysts on the surface of the host photocat-alysts has been shown to be rather effective in inhibiting chargerecombination. Alternative, more economical co-catalysts, such asthe non-noble metals and other derived metal-based compounds,also need to be tested as possible substitutes for the most frequentlyused noble metals, such as Pt, which is very efficient but expen-sive. In addition, new insights are needed into the water-splittingmechanism, particularly regarding the identification of any ther-modynamic and kinetic bottlenecks. Such determinations wouldfacilitate the design of the most effective photocatalytic water-splitting systems.

Presently, the available efficiency for overall water-splittingsystems for the simultaneous production of hydrogen and oxy-gen under visible-light irradiation is still low because of thefast charge recombination and backward reactions. To achieveenhanced and sustainable hydrogen production, the continuousaddition of electron donors is required to make up half of thewater-splitting reaction to reduce H2O to H2. These sacrificialelectron donors can irreversibly consume photogenerated holesand thus prohibit undesirable charge recombination. Taking intoaccount the decreasing cost of solar-to-H2 energy conversion, pol-luting byproducts from industries and the low-cost renewablebiomass from animals or plants are preferential sacrificial electrondonors in water-splitting systems. At little or no cost, they couldbe exploited to simultaneously accomplish the task of hydrogenproduction and that of waste treatment and biomass reforming.Nevertheless, such an admirable goal for the practical applica-tion of water-splitting systems is especially interesting consideringworldwide energy and environmental concerns, but is still in itsinfancy.

The current lack of industrial applications of the semiconductor-based photocatalytic hydrogen generation is largely due to tworeasons: the low photocatalytic efficiency and the lack of exten-sive studies for a successful scale-up of the laboratory setup to anindustrially relevant scale.

In addition to TiO2, heterogeneous photocatalysts such as ZrO3,NaTaO3, BaTa2O6, SrTa2O6, K4Nb6O17, and K3TaSi2O13 can decom-pose water to evolve O2 and H2 without loading any co-catalystsunder UV irradiation [282]. The activities of the majority of thesephotocatalysts are augmented by the loading of a co-catalyst, suchas NiOx, as a proton-reduction site. In this regard, high-donor-doped layered perovskites loaded with NiO have demonstratedphotocatalytic ability for water splitting under UV irradiation.These layered structures with a basic composition AmBmO3m+2,where m 4 or 5, A Ca or Sr, and B Nb or Ti, showed elevatedquantum yields and a stoichiometric evolution of H2 and O2. How-

ever, SrTiO3, KTaO3, Ta2O5, Rb4Nb6O17, K2La2Ti3O10, Rb2La2Ti3O10,Cs2La2Ti3O10, CsLa2Ti2NbO10, Na2Ti6O13, and BaTi4O9 can alsoevolve O2 and H2 with the aid of co-catalysts, such as Pt, Rh, andRuO2 [282].

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. Challenges for refineries

In refineries, we expect the synthesis of clean fuels compo-ents (syngas to liquids, reformulated gasoline with solid acidlkylation to obtain branched C8 alkanes of high octane numberalues), the reduction of S to less than 10 ppm after 2010 by theevelopment of new catalysts and new reactor technologies andy bio-desulfurization, the reduction of aromatics (hydrogenation,asification, cracking), and the reduction of heavy metals fromrude oil by bio-demetalization will predominate. High-octaneon-aromatic blend stock that is sulfur and olefin free will beeeded to meet the new specifications. The future production ofydrogen without the formation of CO2 should come from pho-ocatalytic splitting of water (vide infra) and the conversion of

ethane and light alkanes (C1–C3) to higher/aromatic hydrocar-ons and hydrogen.

.1. Fischer–Tropsch synthesis (FT)

In 1922, Franz Fischer and Hans Tropsch converted a CO/H2ixture to a mixture of hydrocarbons (HCs) and oxygenated com-

ounds using an iron-based catalyst. The cobalt catalysts for thisrocess were discovered a few years later. Although these pro-esses are old technology, they are still relevant. Fischer–TropschFT) synthesis is a heterogeneous catalytic process for the pro-uction of clean hydrocarbon fuels or chemicals from synthesisas, which can be derived from a variety of non-petroleum car-on resources, such as natural gas, coal, biomass, oil sands, oril shales [283]. During World War II, FT technology was used inermany to produce synthetic fuel (16 kbarrels per day) on Co cat-lysts [284] and later, in South Africa (SASOL), in synergy withoal gasification to produce synthetic fuel because of an embargo.ater, SASOL switched to natural gas (NG) for the production ofyngas for FT. The FT synthesis has received renewed interest inecent years because of the global demand for a decreased depen-ence on petroleum for the production of fuels and chemicals.he product distributions with conventional FT catalysts usuallyollow the Anderson–Schulz–Flory (ASF) distribution and are typ-cally unselective with respect to the formation of hydrocarbonsrom methane to waxes. Selectivity control is one of the formidablehallenges in this area.

The most common catalysts used in FT synthesis are still basedn iron or cobalt compounds that work at high pressures (1–6 MPa)nd at temperatures between 200 and 300 ◦C. Under these con-itions, the fuel is of high quality because of the low aromaticitynd the absence of sulfur. The iron-based catalysts produce gaso-ine, hydrocarbons, and linear alpha-olefins, as well as a generallynwanted mixture of oxygenates, such as alcohols, aldehydes, andetones, and excessive amounts of carbon dioxide. With cobaltatalysts, high yields of long-chain linear paraffins, which can befficiently transformed into valuable products (middle distillates)y hydroprocessing, are possible. Moreover, the syngas step shoulde adapted to the type of catalysts to be used to optimize the CO/H2atio in reference to the optimal ratio for the FT catalyst/reactor. Toromote FT over methanation, the FT reactor typically operates at

low temperature (200–240 ◦C), a mild pressure (2–3 MPa), andn the presence of a catalyst (Co- or Fe-based). However, variousatalysts have been tested in the FT reaction [285–287]. To opti-ize the overall liquid production, it is necessary to produce higholecular weight linear waxes for further hydroprocessing steps.

o explain the mechanism of the FT reaction, some authors have

erived the Langmuir–Hinshelwood or Eley–Rideal types of ratexpressions for the reactant consumption, where, in the majority ofases, the rate-determining step was supposed to be the formationf the building block or monomer, methylene.

day 189 (2012) 2– 27 17

Recent developments in core–shell-structured catalysts thatcontain conventional FT catalysts, such as Co/Al2O3 as the coreand zeolite (H-ZSM-5) membrane as the shell, have increased theselectivity to C5–C11 isoparaffins because of the hydrocracking andisomerization ability of zeolite [288]. The use of mesoporous zeo-lite (meso-ZSM-5) as the support for Ru nanoparticles significantenhanced the selectivity to C5–C11 hydrocarbons to greater than80%, which was significantly higher than expected from the selec-tivity based on the ASF distribution (∼45%) [289]. The use of CNTscan also increase the selectivity to a particular fraction of hydro-carbons. For example, Ru/CNT gave a C10–C20 selectivity of ∼60%[290]. The confinement of iron oxide particles inside the CNTs orcarbon spheres could increase the selectivity to C5

+ because of thefacile transformation of iron precursors to iron carbides, which arebelieved to be responsible for C–C coupling [291,292].

5.2. Hydrodesulfurization (HDS) and fluid catalytic cracking(FCC)

Gasoline has the highest concentration of sulfur compounds inthe FCC (fluid catalytic cracking) stage of the refinery process. Envi-ronmental regulations are becoming increasingly stringent withregard to the sulfur content in fuels. At the same time, olefinspresent in the FCC naphtha make a major contribution to the octanenumber in gasoline [293–295]. In this context, desulfurization mustbe performed to hamper olefin saturation in FCC gasoline [293].Hydrodesulfurization (HDS) of petroleum feedstock is one of themost important processes in petroleum refining for the produc-tion of clean, high quality fuels [296–299]. Sulfur compounds inpetroleum fractions include sulfides, disulfides, polysulfides, mer-captans, thiophene, benzothiophene and dibenzothiophene, butthiophene, benzothiophene and dibenzothiophene are used in HDSstudies as model molecules. For example, hydrodesulfurization ofthiophene is one of the most important reactions that occur in thesecond-stage hydrogenation of pyrolysis gasoline in olefin plants[300,301]. A two-stage hydrogenation process is usually usedin industry to eliminate these impurities: (1) hydrogenation forselective hydrogenation of diolefins and (2) thiophene hydrodesul-furization. Therefore, there is a strong incentive to develop catalyticsystems for the FCC/HDS processes. Sulfided Co–Mo or Ni–Mo(W)-based catalysts have been extensively used in industry for HDSreactions [302,303] and have attracted attention as catalyticallyactive sites where Co decorates the edge sites of highly dispersedMoS2 crystallites [304–308]. However, the precise structures of theactive sites and the HDS reaction mechanism still remain ambigu-ous. The active sites of the catalysts are considered to be extensivelypromoted by their selective preparation. The use of a chelatingagent in the preparation of HDS catalysts [309–312] has been foundto be highly effective in increasing the amount of Co(Ni)MoS byincreasing the coverage of Co(Ni) on the edges of MoS2 particles.The preparation of HDS catalysts using citric acid as a chelatingagent significantly improves their catalytic activity [313–316].

The literature contains reports of various attempts to developselective catalysts for this purpose including oxides [317–322],zeolites [323–326] and mesoporous materials [327–329], clays[330–332] and noble metal catalysts [300,324,333–349]. Excellentstudies were conducted on the mild oxidation of thiophenes andthioethers using “green” oxidizing agents [350] on mesoporousmaterials [351,352].

6. CO2 emissions as a prospective source for fuels and

chemicals [353–358]

CO2 is a major contributor to the so-called greenhouse effect,which supposedly leads to warming of the earth and thus to

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hanges in the climate. The energy sector, which is the largestource of CO2 emissions, is responsible for approximately 25% oflobal CO2 emissions. Great efforts have been conducted in the pasto use carbon dioxide as a chemical raw material with a very lowr even negative cost rather than as a waste, e.g. CO2 reductionsnder photoirradiation, or under electrolytic conditions, or produc-ion of synthesis gas by reforming natural gas. However, many ofhese reactions produce rather simple molecules such as carbon

onoxide and formic acid. CO2 has the advantages of being non-oxic, abundant, and economical, attractive as an environmentallyriendly chemical reagent, especially useful as a phosgene sub-titute. The largest obstacle for establishing industrial processesased on CO2 as a raw material is its low energy level. In otherords, a large energy input is required to transform CO2. There

re several methodologies to transform CO2 into useful chemicals,uch as the use of high-energy starting materials such as hydro-en, unsaturated compounds, small-membered ring compounds,nd organometallics; the choice of oxidized low-energy syntheticargets such as organic carbonates or the supply of physical energyuch as light or electricity. Selecting appropriate reactions can leado a negative Gibbs free energy of the reaction [353–358].

Possibilities for the chemical recycling of carbon dioxide to fuelsave been studied largely as a complementary technology to car-on sequestration (CSS) and storage. CSS requires the minimizationf hydrogen consumption to produce fuels [29,258], which can beasily stored and transported, and to use renewable energy sources.rom this perspective, the preferable option is to produce alcoholspreferably ≥C2) by use of solar energy to produce the protonsnd electrons necessary for CO2 reduction. The chemical trans-ormation of CO2 includes a reverse water–gas shift reaction andydrogenation to produce hydrocarbons, alcohols, dimethyl ethernd formic acid, a reaction with hydrocarbons to syngas (suchs dry reforming of methane), and photo- and electro-catalyticnd thermochemical conversions [257,258,359–361]. CO2 can besed as a building block in organic syntheses to obtain valuablehemicals and materials has been discussed in many reports andeview articles. The main applications of CO2 as chemical rawaterials [353] are syntheses of polycarbonates and polyurethanes.rganic carbonates are roughly categorized into cyclic and lineararbonates, which both compounds have three oxygens in eacholecule, and are suitable from a thermodynamic point of view

s synthetic targets starting from CO2. Four industrially importantrganic carbonates are ethylene carbonate (EC), propylene car-onate (PC), dimethyl carbonate (DMC), and diphenyl carbonateDPC). EC, DMC and DPC are useful intermediates for manufac-uring polycarbonates through a non-phosgene process [353]. Inddition, EC, PC and DMC are employed as electrolytes in lithiumon batteries and are widely used as aprotic polar solvents. Fur-hermore, the excellent properties of DMC as a fuel additive havettracted much attention. DMC can be synthesised from methanolnd CO2, over homogeneous catalysts or heterogeneous such asolid acid catalysts of zirconia modified by Ce and acid additivesuch as phosphoric acid, or as a support for heteropolyacids, oria cyclic carbonates (CO2 with epoxides), the cycloaddition of oxi-anes and oxetanes and CO2 over e.g. CeO2–ZrO2 or homogeneousetal complexes catalysts, or coplymerisation of CO2 and oxiranes

n metal complexes, the synthesis of urea (CO2 + NH3) and ure-hane derivatives, e.g. CO2 + secondary or primary amines givingarbamic acid which reacts with organic halides or alcohols givingarbamates (urethanes) or are dehydrated to isocyanate withoutsing phosgene, the synthesis of carboxylic acids, e.g. acrylic acid,he synthesis of esters and lactones by combining CO2 with unsat-

rated compounds such as vinyl ethers, the hydrogenation andydroformylation of alkenes by CO2 and H2, and so forth [353].

Currently, the utilization of CO2 as a chemical feedstock is lim-ted to a few processes, such as the synthesis of urea (for nitrogen

day 189 (2012) 2– 27

fertilizers and plastics), salicylic acid (a pharmaceutical ingredient)and polycarbonates (for plastics). It is worth noting that the actualuse of CO2 corresponds to a small percentage of the potential CO2that is suitable to be converted into chemicals; thus, a chemicaltransformation of CO2 may significantly contribute to a reductionof its emissions, in particular for the fuel pool, the worldwide con-sumption of which is two orders of magnitude greater than thatof chemicals. Note that CO2 transformation requires energy, whichmay produce CO2. Thus, the importance of the transformation ofCO2 into useful chemicals should be closely related to the impor-tance of utilizing a renewable feedstock [353].

Different options exist in heterogeneous catalysis for the con-version of CO2. The hydrogenation of CO2 to form oxygenatesand/or hydrocarbons are the most intensively investigated area ofCO2 conversion. Methanol synthesis from CO2 and H2 has beeninvestigated at the pilot-plant stage with promising results. Analternative possibility is the production of DME, which is a potentialdiesel substitute. Ethanol formation, either directly or via methanolhomologation, and the conversion of CO2 to formic acid are alsopotentially interesting routes. Methanol, ethanol, and formic acidmay also be used as feedstocks in fuel cells, which provide a routeto store energy from CO2 and then produce electricity.

The hydrogenation of carbon dioxide to hydrocarbons consumesmuch more hydrogen (per unit of product) than the formationof oxygenates. Therefore, this route is, in principle, only valuablewhen hydrogen is made primarily from renewable or non-fossilresources; however, other thermodynamic aspects must also beconsidered. The dry reforming of methane with CO2 is a knowntechnology that is available on a nearly industrial scale, althoughthe positive impact on CO2 emissions is questionable [362–364].Specifically, it is important to ensure that CO2 emissions due toenergy consumption are not greater than the amount of CO2 con-sumed in the reaction. An improvement in the positive direction istri-reforming, which operates autothermically and does not requirea pure CO2 feed stream; however, large-scale demonstration unitsare necessary [365,366].

The conversion of CO2 at room temperature and atmosphericpressure using solar light represents a highly challenging approachto close the CO2 cycle and develop approaches that mimic photo-synthesis. An interesting solution could be a photoelectrochemical(PEC) reactor that operates in the gas phase and uses nanoconfinedelectrodes that differ from those used in conventional PEC systems,as described [247].

7. Activation and upgrading of light alkanes

Alkanes are currently two to three times cheaper than the corre-sponding olefins and are thus quite valuable for upgrading. Olefinsare mainly used for polymerization processes. There are severalpossibilities to up-grade to light alkanes (C2–C6). An isomerizationreaction on an acid catalyst can yield branched alkanes of higheroctane number. An acid catalyzed alkylation reaction on isobutanewith butene can yield trimethyl pentanes of high octane numberor other isomers, such as dimethyl hexanes, of much lower octanenumber [367–369]. The main industrial catalysts are HF and H2SO4in solution [370], although significant efforts have been made inthe past 30 years to find a solid substitute without yielding anyreliable/promising process. No industrial processes could emergeas deactivation due to fouling by butene polymerization residueswas too important and selectivity to TMP versus dimethyl hex-anes (DMH) of low octane number was too low (50–60). Another

approach is to proceed by dehydrogenation, e.g., on Pt-Sn/Al2O3,or by oxydehydrogenation of alkanes on V-based mixed oxides.The former reaction is endothermic and highly sensitive to deac-tivation by coke deposits [371–373]. The latter is exothermic with

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ow deactivation by coke fouling, but it may lead to total oxida-ion and CO2 formation and, thus, to a lower selectivity to alkenes.

third way is oxidizing/ammoxidizing the alkanes to the corre-ponding oxygenates or oxynitriles such as aceto or acrylo-nitriles,ldehydes, ketones or acids. Two processes have been developedndustrially, oxidation of butane to maleic anhydride on a vanadylyrophosphate based VPO catalyst or ammoxidation of propane tocrylonitrile on MoVTeNb mixed oxide catalysts. Maleic anhydrides a raw monomer for resin and for THF an industrial solvent pro-uced by Reppe process of maleic ahydride reduction pn Pd catalsyts well as a monomer for segmented polyurethanes (Lycra®) andopolyester elastomers (Hytrel®). Vanadium-based catalysts [374]nd in particular, vanadium phosphates (VPOs) are very well knowns the only catalysts for industrial process of n-butane oxidationo maleic anhydride [375–378], which is a precursor of polyesteresins [379]. In general, VPO catalysts are inexpensive and attrac-ive in selective oxidation processes since they are environmentallyriendly [380]. The reaction follows Mars van Krevelen mechanismhere the adsorbed organic molecule is oxidized by lattice oxygen

rom the catalyst, which is subsequently restored by oxygen reac-ion feed. Acrylonitrile was produced in ammoxidation reaction ofropylene using Fe–Bi–Mo–O and Fe–Sb–O systems as catalystsut this process would be replaced in a near future by ammoxi-ation of propane due to the lower cost and abundance of propane.crylonitrile is the main raw material for production of syntheticbers, plastics, elastomers and polymers as styrene–acrylonitrilend acrylonitrile–butadiene–styrene. By polymerization of acry-onitrile with butadiene synthetic rubber is produced. This processncludes multifunctional molybdates and antimonates as catalysts.owever, propane conversion is about ten times lower than thatf propylene in the same conditions since the activation energyf C H bond is higher. The more performing catalyst developedecently by Japanese industrialists [381,382] is a mixed MoVNbTexide active for the (amm)oxidation of propane to (acrylonitrile)crylic acid [381–384]. A process, designated AlkyClean using aolid acid catalyst (HY-zeolite based) and claimed to be compet-tive with other two processes, was proposed [355] by Akzo Nobel,BB Lummus Global and Fortum with a demonstration unit con-tructed at Fortum facilities in Porvoo, Finland. The reaction isarried out in liquid phase at 50–90 ◦C with isobutane to olefin ratioi/o) of 8 to 10 against 4–10 ◦C and i/o = 8–10 for H2SO4 and 32–38 ◦Cnd i/o = 12–15/1 for HF respectively. Regeneration was realized at50 ◦C under hydrogen. For this research part see special issue ofppl Catal A, Ed. G.S. Patience, J.M. López-Nieto [385].

. Waste air, water and VOCs treatments

Wet air oxidation (WAO) is a liquid-phase reaction betweenrganic material in water and oxygen. The WAO process is usedround the world to treat industrial wastewaters and sludgest moderate temperatures (180–315 ◦C) and at pressures from 2o 15 MPa. Under these conditions, complex organic compoundsre primarily oxidized to carbon dioxide and water, along withimpler forms that are biodegradable. Unlike other thermal pro-esses, WAO produces no NOx, SO2, HCl, dioxins, furans or fly ash.owever, the efficiency of aqueous-phase oxidation can be signif-

cantly improved by the use of catalysts, either heterogeneous oromogeneous. Moreover, key points to be solved are the stabilityf the heterogeneous catalysts and the recycling of the homo-eneous catalysts. Commercial catalytic WAO (CWAO) processestarted as early as the mid-1950s in the USA. Several Japanese

ompanies developed CWAO technologies that relied on hetero-eneous catalysts based on precious metals deposited on titania oritania–zirconia. Compared with conventional WAO, CWAO offersower energy requirements and significantly higher oxidation

day 189 (2012) 2– 27 19

efficiencies. Further developments of this technology shouldinclude highly durable and low-cost catalysts. CWAO provides anenvironmentally attractive option to manage the growing problemsof the treatment of organic sludge and toxic wastewater [386,387].

The treatment of toxic nitrogen-containing compounds, whichare mainly produced in the chemical and pharmaceutical indus-tries, is one of the major applications of the wet air oxidation(WAO) process. Many studies have dealt with the oxidation of ani-line, which is often chosen as a model molecule of a dye-industrypollutant. Particular attention has been paid to selectivity towardorganic by-products (especially azo, nitroso and nitro compounds,phenolic compounds and carboxylic acids) and inorganic forms ofnitrogen (NH4

+, N2, NO2−, NO3

−). Usually, similar catalysts can beused for the CWAO of oxygen-containing (phenol, carboxylic acids)and nitrogen-containing organic compounds. Ammonia is one ofthe most refractory by-products formed during catalytic WAO ofnitrogen-containing organic pollutants and is itself a pollutant.Very high selectivities to dinitrogen have been obtained on certainnoble-metal catalysts. As a rule, catalysts that are active and selec-tive for ammonia oxidation are different (nature of active phase,support, etc.) from the solids proven to be the best catalysts for theCWAO reactions of organic compounds. Multifunctional catalystsare therefore required for the treatment of nitrogenous organiccompounds.

Volatile organic compounds (VOCs) are significant atmosphericpollutants due to their high toxicity and malodorous nature.VOC emissions arise from mobile sources and industrial appli-cations. In this context, the degradation of VOCs has become amajor area of research in environmental protection during recentdecades [388,389]. Common VOCs such as halogenated hydrocar-bons, ketones, alcohols and aromatic compounds have been widelyused in many industries and are often found in the emissions flow[390,391].

Traditional methods of removing VOCs from the polluted airstream include adsorption onto activated carbon or zeolite andthermal combustion. These methods have inherent limitations. Theadsorption process includes recovery treatments that require theregeneration of the adsorbent and also requires durability, whereasthe high temperature of VOC degradation makes thermal degrada-tion not economically feasible.

Many advanced technologies have been developed for the rapidand economical removal of VOCs from indoor air. Among these,catalytic oxidation is the most innovative and promising approach.This oxidation process is promising for air purification becausethe pollutants can be oxidized to H2O and CO2. The catalysts playthe most important role by converting polluting compounds intorelatively harmless compounds at low operating temperatures.A series of catalysts were evaluated for VOC decomposition[388,389,392–402]. The most active catalysts are the noble metalcatalysts dispersed on high surface area supports. The dispersionincreases both the available metal surface area and the thermalstability. Many researchers have suggested that the performance ofnoble metal supported catalysts for the oxidation of VOCs is highlydependent on the oxidation state of the metal. Some authors havesuggested that the oxide species are more active than the metallicspecies for catalytic oxidation, while others argue the opposite.In the case of catalysts with the same oxidation state, the particlesizes may play a more important role in the catalytic activity [403].Several studies have shown a correlation between the catalyticactivity and the oxidation state of the catalyst, the nature of thesupport, the metal-support interaction, and the morphology of thecatalyst particles [389,403–417]. However, the use of noble metals

leads to a high cost purification system and the natural reserve ofnoble metals is limited. Therefore, the substitution of noble metalswith ubiquitous elements is required for environmental andeconomic reasons. Metal oxides have been reported as relatively

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igh activity catalysts for the complete oxidation of VOC [392,393].esearch efforts in this field are oriented towards the developmentf new catalytic materials with low manufacturing costs that showigh activities at moderate temperatures.

. Photocatalysis

In the 1930s, the term photocatalysis was introduced as newranch of catalysis. Photocatalysis is defined as a change in the ratef a chemical reaction under the action of light in the presencef photocatalysts that absorb light quanta and are involved in thehemical transformations of the reaction participants [418,419].he photocatalyst is defined as a solid that functions by pho-oinduced electron transfer at molecule–semiconductor interfaces282,420–423].

Among photocatalytic applications, photocatalytic oxidationnd the reduction of organic compounds in water have becomemportant and have received considerable attention during the lastew years [282,424–427]. These applications involve the oxidationr reduction of an organic compound to an intermediate that con-ains oxygen or to carbon dioxide, water, and a mineral acid if aeteroatom such as nitrogen or chlorine is present. The mecha-ism of the photocatalytic decomposition of organic compounds isupposed to follow these steps: under UV-light illumination, thebsorption of photons creates an electron–hole pair if the photonnergy is greater than that of the band gap; thereafter, the pairsigrate to the surface and are trapped by OH surface groups and

ther surface sites, thereby forming hydroxyl (•OH−), hydrosuper-xide (•H2O) and superoxide (•O2

−) radicals; these free radicalsnally cause the oxidation of the organic compounds [425–428].his process can be used in various areas such as the elimina-ion of odor from drinking water, the degradation of oil spills inurface-water systems, and the degradation of harmful organicontaminants, such as herbicides, pesticides, and refractive dyes.

One of the most widely studied metal oxides is semiconductingiO2 [423]. Three common TiO2 polymorphs exist in nature, which,n the order of abundance, are rutile, anatase, and brookite. Andditional synthetic phase, called TiO2(B), and some high-pressureolymorphs are also known [428]. The rutile and anatase poly-orphs are primarily used in photocatalysis. Both the rutile and

natase crystal structures comprise distorted octahedra. In rutile, slight distortion from orthorhombic geometry occurs, where thenit cell is stretched beyond a cubic shape. In anatase, the distortionf the cubic lattice is more significant, and thus, the resulting sym-etry is less orthorhombic [429]. Titania, in anatase form, exhibits

strong photocatalytic effect, which generates electron–hole pairs.s a result, the material can harvest photons in the near-UV region

<410 nm) to provide its surface strong oxidizing power to decom-ose organic molecules. Photocatalysis is a rapidly growing field oftudy that has attracted intense attention of chemical and materialsesearchers in recent years.

Even though TiO2 exhibits excellent photocatalytic activitiesn the decomposition of VOCs and other organic compounds, thetudy new photocatalysts with different structures that exhibitigher activity is desirable. In this regard, the novel photocata-

ysts made of highly donor-doped (110) layered perovskites, haveecently been developed and were found to be much more effi-ient than bulk-type TiO2. This higher activity results from theighly donor-doped electronic structure, which leads to a nar-ower depletion region and a more facile separation of the chargearriers.

Selective photocatalysis can be achieved using proper molec-lar sieves, such as the titanosilicate ETS-10, which providesn alternative approach. The photocatalytic activity of ETS-10 isue to the presence of photoexcitable Ti–O–Ti chains and the

day 189 (2012) 2– 27

three-dimensional interconnected pore system of large 12-membered ring channels in its structure, which endow the materialwith excellent diffusion properties [430]. This regular channel sys-tem has a direct effect in determining the shape selectivity of thedegradation process [431]. Another approach is the introductionof some transition metals, such as Cr, V, Fe, Cu, Mn, Co, Ni, Mo,or La, into the synthesis mixture of the MCM-41 and MMS [432].The authors then demonstrated that the presence of the transition-metal salts in the gel during the hydrothermal synthesis processhinders the action of the template, which results in MCM-41 poresthat are not well formed. These materials were then loaded withTiO2 via the sol–gel method, and the activity of the TiO2/TM-MCM-41 catalysts toward the degradation of 4-chlorophenol was testedin the presence of UV and/or visible light. The results showed that,although some metals were deleterious, others improved the per-formance of the photocatalysts and even enabled them to utilizevisible light. A wide range of other semiconductors and materialshave been tested for photocatalytic activity. In general, they havebeen found to be less active than titanium dioxide; significant workhas been conducted with V2O5, Fe2O3, ZnO, ZnS, CdS, Pt/CdS, ZnTe,ZrTiO4, MoS2, SnO2, Sb2O4, Sn/SbO2, CeO2, WO3, and Nb2O5.

10. Solar photon conversion [433]

The efficient and cost-effective direct conversion of solar pho-tons into solar electricity and solar fuels is one of the mostimportant scientific and technological challenges of this century. Atleast 20 TW of carbon-free energy (1.5 times the total amount of allforms of energy consumed today globally), in the form of electricityand liquid and gaseous fuels, are estimated to be required by 2050to avoid the most serious consequences of global climate changeand to ensure an adequate global energy supply that will avoideconomic chaos. However, for solar energy to contribute a majorfraction of future carbon-free energy supplies, it must be pricedcompetitively with, or perhaps even be less costly than, energy fromfossil fuels, nuclear power and other renewable energy resources.The challenge of delivering very low-cost solar fuels and electric-ity will require breakthrough advances in both fundamental andapplied sciences. These required advances include new concepts forlow-cost photovoltaic (PV) energy based on chemistry, solar watersplitting, redox catalysis for water oxidation and reduction, pho-toelectrochemical energy conversion, and photoinduced electrontransfer. Note that the total energy capacity at the end of 2009 wasapproximately 7 GW-years (0.2% of global electricity usage). Thus,there is potential for the PV industry to grow substantially in thefuture (by a factor of 100–300) for it to provide a significant frac-tion of the total global electricity needs (currently approximately3.5 TW).

Presently, solar-derived fuels are produced from biomass(labeled as biofuels) and are generated through biological pho-tosynthesis. The global production of liquid biofuels in 2009 wasapproximately 1.6 million barrels/day, equivalent to a yearlyoutput of approximately 2.5 EJ (about 1.3% of global liquid fuel uti-lization). The direct conversion of solar photons to fuels produceshigh-energy chemical products that are labeled as solar fuels; thesefuels can be produced through nonbiological approaches, whichare generally referred to as artificial photosynthesis. The feedstocksfor artificial photosynthesis are H2O and CO2, which react either ascoupled oxidation–reduction reactions, as in biological photosyn-thesis, or by first splitting H2O into H2 and O2 and then reacting H2with CO2 (or CO produced from CO2) in a second step to produce

fuels through the known chemical routes previously described suchas syngas, water–gas shift reaction, or alcohol synthesis. The solargenerated H2 can itself be used as a gaseous fuel, such as in fuelcells. However, currently, no solar-fuels industry exists. Significant

I. Fechete et al. / Catalysis To

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12.4.1. Challenges in automotive catalysis

Fig. 16. Major factors influencing selectivity in catalytic reactions [455].

esearch and developments are required to create a solar-fuelsndustry, which constitutes one of the key challenges for the future.

1. Green chemistry – selectivity in catalysis

A new area of research emerged in the 1990s based on the 12rinciples of green chemistry [434,435] including the atom econ-my, the use of reusable catalysts and the minimization of waste436]. The principle of green chemistry is that rather than usingvery possible chemical process, only those that are environmen-ally benign should be used [437]. Within green chemistry, theres an increasing interest in developing novel materials that can bepplied as heterogeneous catalysts for chemical processes, replac-ng effective but hazardous chemicals, such as H2SO4, HF and AlCl3.rocesses using these novel compounds, such as zeolites, have veryigh E-factors, a quantitative parameter that can be used to assesshe environmental acceptability of a process [438]. It correspondso the ratio of kilograms of waste divided by kilograms of product.or example, the zeolites used in the petrochemical industry haven E-factor of 0.1 (high greenness) and have been widely imple-ented in very large scale industrial processes because they can

asily be separated from the products and reused. Because of theirack of toxicity, they constitute a prime example of green chemistry.

Moreover, a challenge for the XXIst century is the control ofechnological processes in the chemical, petrochemical, and phar-

aceutical industries to develop atom-economical, environmentalriendly processes without by-products [3,439–441]. The chemicalnd petrochemical industries have always attempted to improverocess efficiency and reduce waste using heterogeneous catalysts293,442–447]. High selectivity is the most important aspect of aatalyst. The noble metal catalysts show high activity and selec-ivity, but suffer from several drawbacks, including sensitivity to

etal site poisoning, the limited abundance, and the environmen-al impact of these metals. As a result, the tendency now is toeplace the noble metal catalysts [199,201,447–449]. In light of thebiquitous restrictions imposed by environmental and economical

egislation, use of nanostructured porous molecular sieves, whichan be very selective for the desired products at low temperaturend are recyclable, is one alternative to the use of traditional noble

etal catalysts. We have summarized in Fig. 16 the main factors

hat influence selectivity in catalysis and that must be taken intoccount in all processes.

day 189 (2012) 2– 27 21

12. Major challenges for the future

12.1. Scientific challenges

These challenges cover the design, preparation, evaluation, andoptimization of new catalytic materials, the probing/understandingof catalyst behavior (activity and selectivity) at the molecular level,the enhancement of technology transfer between academia andindustry (bridge the gap), the development of multifunctional reac-tors, combinatorial catalysis, high-throughput catalyst testing, thecharacterisation of catalysts using highly improved physical andchemical techniques, particularly used under working conditionsand simultaneously with several other techniques together [451],heterogeneisation of homogeneous catalysts (vide supra Section2.9), the coupling of chemical and engineering kinetics, and so forth.

12.2. Environmental challenges

These challenges consist of minimizing and/or managingby-products by converting them to useful products, replacing mul-tistep processes by direct schemes to avoid exposure to dangerousintermediates, reducing effluents (gases, solvents, salts), and usingsustainable sources of raw materials and energy supplies. Thedevelopment of biomass for raw chemical materials and energysources should become a key point for the future. The develop-ment of biorefineries is in its infancy; however, with reference tothe past the in petroleum industry, one may imagine that greatimprovements will be developed with continuous research in thisfield.

12.3. Economical challenges

Economical challenges naturally correspond to the use ofcheaper, readily available raw materials, increased productivity,decreased lag-time between discovery to commercialization, thediscovery novel catalytic reactions, the development of processesthat are more selective and intensive, the accelerated discovery ofnew catalysts-based on non noble metals [199,201], and the eval-uation and scale-up of processes.

12.4. Energy challenges

Energy challenges correspond to reduce energy consumption,e.g. by favouring of hydrogen production as a source of energyand as an important chemical material, to develop efficient water-splitting technologies, and to enhance uses [452] of biomass andother renewable sources, such as solar, wind, hydroelectric, andnuclear energies. All these technologies must be developed as alter-native sources to fossil energies. One is still very far from replacingfossil energies, and great effort is required on a short time scale. Thefuture will rely on solar energy and the implementation of efficientmethods for electrical energy storage [450,453]. However, signif-icant scientific advancement is still required for the practical andsafe deployment of both of these technologies. In 2005, 7% of theworld energy use was derived from nuclear power (Fig. 13), 10% wasderived from biomass, 2% was derived from hydroelectric sources,and a mere 1% of the energy consumed was obtained from alternaterenewable resources. Closer examination of the tiny 1% fractionshows that both solar energy in the form of photovoltaics and windpower are drastically underemployed (Fig. 13). These technologies,of course, represent two renewable resources of an infinite supply.

Since the introduction of exhaust gas converters in cars in1976 by Ford, many advances have been realized in reformulatedgasoline or diesel, in particulate emission/trapping control and in

22 I. Fechete et al. / Catalysis Today 189 (2012) 2– 27

Table 6Major problems and challenges in automotive car industry.

Challenge Drivers Problem

Lean burn gasoline engine Efficiency higher by ca. 25% NOx trapping; SOx tolerant trapsDry particulate emissions from diesel engines DOC reduces SOF, HC, and CO; no

current catalyst/system to treat dryCatalyst to lower lightoff T of soot;addition of Cu and Ce-organometallics

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sootDiesel engine lean NOx Direct decomp

NOx in O2-rich

lectronic devices to regulate the air/fuel ratio in the motors. Thenitial three way catalysts for simultaneous CO oxidation, NO reduc-ion, hydrocarbon total oxidation were improved further with these of Pd. Another presentation by R. Farrauto et al. [454] providesetails of the actual performances and of the future prospects. Onlyome major issues are summarized in Table 6. Moreover, the devel-pment of highly active HDS, FCC, Naphtha catalysts is one of theost urgent challenges in the petroleum industry not only to pro-

ect the environment but also to efficiently utilize limited naturalesources.

3. Conclusions

As we have described in this review, our dependence on fos-il fuels (coal, petroleum, and natural gas) is largely due to theirhemical energy being the most convenient and useful form ofransportable energy. However, the extensive use of fossil fuelsas dramatically influenced the environment and peoples’ health,hile world reserves are diminishing inexorably, although newelds are still being discovered and although methane hydratesay provide a substitute for some time. This situation cannot last

or long, and substantial advances are urgently needed.We have also shown that the solution to the challenge of clean

nergy can arise from simple components: sunlight and water455]. Sunlight and water are infinite resources and can provide theequired diversity of energy supplies. To store energy from sunlight,ater can be split to generate hydrogen, a clean and portable energy

arrier that can then be used to supply electricity when needed.igh-performance, light-weight batteries can be used to powerlectric vehicles. However, such technological advances requireystems that are capable of producing electricity, breaking H2Oonds with the separation of H2 and O2, and storing the energyither in batteries or as molecular hydrogen. Currently, such sys-ems pose formidable challenges in terms of the required materials,fficiency, cost, and design of practical devices.

The locus of activity in catalysis continues to move. In theighteenth and nineteenth centuries, major discoveries and devel-pments were performed in Europe. In the twentieth century, bothurope and the USA were the major contributors, although Japannd Korea also provided important efforts and discoveries in theecond half of the century. For the twenty-first century, China,orea, Japan and other Asian countries are expected to lead in theeld of catalysis.

At the end of the last century, major large chemical industrialompanies have more or less abandoned large catalysis researchentres within their laboratories. They now rely on catalysts pro-ucers, institutes and/or academic researchers to discover newatalysts or develop new technologies.

The development of surface, bulk and in situ characterisationechniques [451], molecular modelling, and advanced synthesis

ethods have transformed the preparation of solid catalysts and

he characterisation of their physical and chemical (catalytic) prop-rties from an art into a science. Such a trend should and willontinue in the future with the new generations of scientists, engi-eers and researchers.

to fueln or reduction ofsphere

Larger operating window for PM orBM-catalysts, NH3 or urea SCR.

Acknowledgement

Support from CNRS France is gratefully acknowledged by I.Fechete.

References

[1] American Chemical Society Report, Technology Vision 2020, the Chem-ical Industry, December 1996, http://www/chemicalvision2020.com/pdfs/chem vision.pdf.

[2] A. Corma, Chemical Reviews 97 (1997) 2373.[3] G.A. Somorjai, R.M. Rioux, Catalysis Today 100 (2005) 201.[4] A. Kieboom, J. Moulijn, P. van Leeuwen, R. van Santen, Studies in Surface

Science and Catalysis 123 (2000) 3.[5] B. Lindstrom, L. Petterson, CatTech 7 (2003) 130.[6] J.N. Armor, Catalysis Today 163 (2010) 3.[7] E. Jones, Industrial and Engineering Chemistry 42 (1950) 2208.[8] Ya. Guerasimov, V. Dreving, E. Eriomin, A. Kiseliov, V. Lebedev, G. Pacehnkov,

Ashliguin Curso de Fisica Quimica, Tomo II, Editorial MIR, Moscow, 1971.[9] H. Davy, Philosophical Transactions of the Royal Society 97 (1817) 45.

[10] A. Fusinieri, Giurnali Fisica 7 (1824) 371.[11] J. Berzelius, Annales de chimie et de physique 61 (1836) 146.[12] F. Fischer, H. Tropsch, Brennst.-Chem. 4 (1923) 276.[13] F. Fischer, H. Tropsch, Brennst.-Chem. 7 (1926) 97.[14] J.C. Védrine, Catalysis Today 56 (2000) 455.[15] A.D. McNaught, A. Wilkinson, IUPAC Compendium of Chemical Terminology,

2nd edition, British Royal Society of Chemistry, Cambridge, UK, 1997.[16] J.H. Clark, D.J. Macquarrie, K. Wilson, Studies in Surface Science and Catalysis

129 (2000) 25.[17] W. Holderich, M. Hesse, F. Naumann, Angewandte Chemie International Edi-

tion 27 (1988) 226.[18] C.J. Plank, E.J. Rosinski, Chemical Engineering Progress Symposium Series 73

(1967) 26.[19] J.J. Blazek, Oil and Gas Journal 69 (1971) 66.[20] S.C. Eastwood, R.D. Drew, F.D. Hartzell, Oil and Gas Journal 60 (1962) 152.[21] S.C. Eastwood, C.J. Plank, P.B. Weiss, 8th World Petr. Congr. 4 (1971) 245.[22] A.W. Chester, W.E. Cormier Jr., W.A. Strover, US Patent 4,368,114 (1983).[23] N.Y. Chen, A.B. Ketkar, D.M. Nace, A.Y. Kam, C.R. Kennedy, R.A. Ware, European

Patent Application (1986) 186446.[24] C. Marcilly, J.M. Daves, F. Raatz, European Patent Application 278 (1988) 839,

assigned to IFP.[25] N.Y. Chen, W. Grawood, F. Dwyer, Shape Selective Catalysis in Industrial Appli-

cations, Marcel Dekker, New York, 1995.[26] R.M. Barrer, Advances in Chemistry Series 102 (1971) 1.[27] S.M. Csicsery, ACS Monograph 171 (1976) 680.[28] E.G. Derouane, in: M.S. Whittingham, A. Jacobson (Eds.), Intercalation Chem-

istry, Academic Press, New York, 1982, p. 101.[29] E.G. Derouane, Z. Gabelica, Journal of Catalysis 65 (1980) 486.[30] N.Y. Chen, S.J. Lucki, E.B. Mower, Journal of Catalysis 13 (1969) 329.[31] R.M. Dessau, ACS Symposium Series 135 (1980) 123.[32] P. Tynjala, T.T. Pakkanen, Journal of Molecular Catalysis A – Chemical 122

(1997) 159.[33] S. Inagaki, K. Kamino, E. Kikuchi, M. Matsukata, Applied Catalysis A – General

318 (2007) 22.[34] E. Dumitriu, I. Fechete, P. Caullet, H. Kessler, V. Hulea, C. Chelaru, T. Hulea, X.

Bourdon, Studies in Surface Science and Catalysis 142A (2001) 951.[35] C. Brechtelsbauer, G. Emig, Applied Catalysis A – General 161 (1997) 79.[36] I. Fechete, A. Simon-Masseron, E. Dumitriu, D. Lutic, P. Caullet, H. Kessler,

Revue Roumaine de Chimie 53 (2008) 55.[37] F.J. Llopis, G. Sastre, A. Corma, Journal of Catalysis 227 (2004) 227.[38] I. Fechete, P. Caullet, E. Dumitriu, V. Hulea, H. Kessler, Applied Catalysis A –

General 280 (2005) 245.[39] E. Derouane, J.C. Védrine, Journal of Molecular Catalysis 8 (1980) 479.[40] J.C. Védrine, A. Auroux, P. Dejaifve, V. Ducarme, H. Hoser, S.B. Zhou, Journal of

Catalysis 73 (1982) 147.[41] E.G. Derouane, P. Dejaifve, Z. Gabelica, J.C. Védrine, Faraday Discussions 72

(1982) 331.[42] M.B. Sayed, J.C. Védrine, Journal of Catalysis 101 (1986) 43.[43] G. Coudurier, A. Auroux, J.C. Védrine, R.D. Farlee, L. Abrams, R.D. Shannon,

Journal of Catalysis 108 (1987) 1.[44] M.B. Sayed, A. Auroux, J.C. Védrine, Journal of Catalysis 116 (1989) 1.

ysis To

I. Fechete et al. / Catal

[45] J.C. Védrine, in: R.K. Grasselli, J.F. Bradzil (Eds.), Solid State Chemistry in Catal-ysis, 249, ACS Symp. Ser., 1985, p. 257.

[46] J. Frilette, W.O. Haag, R.M. Lago, Journal of Catalysis 67 (1981) 218.[47] E.G. Derouane, Journal of Catalysis 100 (1986) 541.[48] E.G. Derouane, J.M. André, A.A. Lucas, Chemical Physics Letters 137 (1987)

336;E.G. Derouane, Chemical Physics Letters 142 (1987) 200.

[49] E.G. Derouane, J.M. André, A.A. Lucas, Journal of Catalysis 110 (1988) 58.[50] B.F. Mentzen, J.C. Védrine, R. Khouzami, G. Coudurier, Comptes Rendus de

l’Académie des Sciences – Series II 305 (1987) 263.[51] G.I. Panov, G.A. Sheveleva, A.S. Kharitonov, V.N. Romannikov, L.A. Vostrikova,

Applied Catalysis A – General 82 (1992) 31.[52] G.I. Panov, A.K. Uriarte, M.A. Rodkin, V.I. Sobolev, Catalysis Today 41 (1998)

365.[53] G.I. Panov, CatTech 4 (2000) 18.[54] L.V. Pirutko, S.V. Chernyavsky, A.K. Uriarte, G.I. Panov, Applied Catalysis A –

General 227 (2002) 143.[55] G.K.A. Dubkov, N.S. Ovanesyan, A.A. Shteinman, E.V. Starokon, G.I. Panov,

Journal of Catalysis 207 (2002) 341.[56] T. Ren, L. Yan, X. Zhang, J. Suo, Applied Catalysis A – General 244 (2003) 11.[57] J.B. Taboada, E.J.M. Hensen, I.W.C.E. Arends, G. Mul, A.R. Overweg, Catalysis

Today 110 (2005) 221.[58] D. Meloni, R. Monaci, E. Rombi, C. Guimon, H. Martinez, I. Fechete, E. Dumitriu,

Studies in Surface Science and Catalysis 142 (2002) 167.[59] S. Grucarevic, V. Merz, Chemische Berichte 6 (1873) 60.[60] P.H. Gore, in: G.A. Olah (Ed.), Friedel-Crafts and Related Reactions, vol. III, John

Wiley & Sons Inc, London, 1964, p. 1 (Part 1).[61] G.A. Olah, Friedel-Crafts Chemistry, J. Wiley, New York, 1973.[62] G. Sartori, R. Maggi, Chemical Reviews 106 (2006) 1077.[63] E.G. Derouane, C.J. Dillon, D. Bethell, S.B. Derouane-Abd Hamid, Journal of

Catalysis 187 (1999) 209.[64] E.G. Derouane, G. Crehan, C.J. Dillon, D. Bethell, H. He, S.B. Derouane-Abd

Hamid, Journal of Catalysis 194 (2000) 410.[65] H.G. Franck, J.V. Standelhofer, Industrial Aromatic Chemistry, Springer, Berlin,

1988.[66] J.S. Beck, W.O. Haag, in: G. Ertl, H. Knozinger, J. Weitkamp (Eds.), Handbook

of the Heterogeneous Catalysis, vol. 5, Wiley VCH, Weinheim, 1997, p. 2136.[67] F. Alario, M. Guisnet, in: M. Guisnet, J.P. Gilson (Eds.), Zeolites for Cleaner

Technologies, Imperial College Press, London, 2002, p. 189.[68] F.G. Dwyer, Studies in Surface Science and Catalysis 67 (1991) 179.[69] Z. Zhu, Q. Chen, W. Zhu, D. Kong, C. Li, Catalysis Today 93–95 (2004) 321.[70] P. Ratnasamy, R.N. Bhat, S.K. Pokhriyal, Journal of Catalysis 119 (1989) 65.[71] I. Benito, A. Del Riego, M. Martinea, Applied Catalysis A – General 180 (1999)

175.[72] A.M. Prakash, S.V.V. Chilukuri, R.P. Bagwe, S. Ashtekar, D.K. Chakrabarty,

Microporous Materials 6 (1996) 89.[73] A. Blanco, J.M. Campelo, A. Garcia, D. Luna, J.M. Marinas, A.A. Romero, Journal

of Catalysis 137 (1992) 51.[74] K.J.A. Raj, E.J.P. Malar, V.R. Vijayaraghavan, Journal of Molecular Catalysis A –

Chemical 243 (2006) 99.[75] M. Ghiaci, A. Abbaspur, M. Arshadi, B. Aghabarari, Applied Catalysis A – Gen-

eral 316 (2007) 32.[76] W.S. Wieland, R.J. Davis, J.M. Garcesy, Journal of Catalysis 173 (1998) 490.[77] J.C. Védrine, A. Auroux, G. Coudurier, P. Engelhard, J.P. Gallez, G. Szabo, in:

D. Olson, A. Bisio (Eds.), Proceedings 6th International Zeolite Confererence,Butterworths, Guilford, 1984, p. 497.

[78] T. Nobusawa, J.C. Védrine, Catalysis Science & Technology 1 (1991) 97.[79] V. Ducarme, J.C. Védrine, Applied Catalysis 17 (1985) 175.[80] T.-C. Tsai, Applied Catalysis A – General 301 (2006) 292.[81] S. Amokrane, D. Nibou, Comptes Rendus de l’Académie des Sciences 13 (2010)

538.[82] I. Fechete, E. Gautron, E. Dumitriu, D. Lutic, P. Caullet, H. Kessler, Revue

Roumaine de Chimie 53 (2008) 49.[83] V. Mavrodinova, M. Popova, Catalysis Communications 6 (2005) 247.[84] B. Sulikowski, R. Rachwalik, Applied Catalysis A – General 256 (2003) 173.[85] Roldán, F.J. Romero, C. Jiménez, V. Borau, J.M. Marinas, Applied Catalysis A –

General 266 (2004) 203.[86] E. Dumitriu, C. Guimon, V. Hulea, D. Lutic, I. Fechete, Applied Catalysis A –

General 237 (2002) 211.[87] A. Krejcí, S. Al-Khattaf, M. Ashraf Ali, M. Bejblová, J. Cejka, Applied Catalysis A

– General 377 (2010) 99.[88] V. Mavrodinova, M. Popova, R.M. Mihályi, G. Páł-Borbély, Ch. Minchev,

Applied Catalysis A – General 248 (2003) 197.[89] A.B. Halgeri, T.S.R. Prasada Rao, Studies in Surface Science and Catalysis 24

(1985) 667.[90] N.M. Tukur, S. Al-Khattaf, Chemical Engineering Journal 166 (2011) 348.[91] S. Zheng, A. Jentys, J.A. Lercher, Journal of Catalysis 241 (2006) 304.[92] M. Guisnet, N.S. Gnep, S. Morin, Microporous and Mesoporous Materials

35–36 (2000) 47.[93] K.J. Chao, L.J. Leu, Zeolites 9 (1989) 193.[94] A. Corma, F. Llopis, J.B. Monton, Studies in Surface Science and Catalysis 75

(1993) 1145.[95] D. Fraenkel, M. Levy, Journal of Catalysis 118 (1989) 10.[96] H. Xu, S. Pu, T. Inui, Catalysis Letters 41 (1996) 83.[97] S. Namba, H. Ohta, J.H. Kim, T. Yashima, Studies in Surface Science and Catal-

ysis 75 (1993) 279.

day 189 (2012) 2– 27 23

[98] J. Kim, T. Kunieda, M. Niwa, Journal of Catalysis 173 (1998) 433.[99] A.K. Aboul-Gheit, S.M. Abdel-Hamid, F.M. Abdel-Hay, Applied Catalysis A –

General 93 (1993) 131.[100] B. Adair, C. Chen, K. Wan, M.E. Davis, Microporous Materials 7 (1996) 261.[101] R. Wendelbo, R. Roqul-Malherbe, Microporous Materials 10 (1997) 231.[102] P. Wu, T. Komatsu, T. Yashima, Microporous and Mesoporous Materials 22

(1998) 343.[103] M.K. Rubin, P. Chu, US Patent 4,954,325 (1990).[104] S.T. Wilson, B.M. Lok, C.A. Messina, T.R. Cannan, E.M. Flanigen, Journal of the

American Chemical Society 104 (1982) 1146.[105] S.T. Wilson, B.M. Lok, E.M. Flanigen, US Patent 4,310,440 (1982).[106] W.M. Meier, D.H. Olson, Atlas of Zeolite Structure Types, 2nd edition, Butter-

worths, 1987.[107] B.F. Mentzen, J.C. Védrine, R. Khouzami, Comptes Rendus de l’Académie des

Sciences – Series II 304 (1987) 11.[108] R. Khouzami, G. Coudurier, B.F. Mentzen, J.C. Védrine, in: P.J. Grobet, et al.

(Eds.), Innovation in Zeolite Material Science, vol. 37, Studies in Surface Sci-ence and Catalysis, 1987, p. 355.

[109] J.C. Védrine, G. Coudurier, B.F. Mentzen, in: W.H. Flank, T.E. Whyte (Eds.),Prospective in Molecular Sieve Science, vol. 368, ACS Symposium Series,Washington, 1988, p. 66.

[110] R. Szostak, Molecular Sieves, Van Nostrand Reinhold Catalysis Ser, New York,1989.

[111] B.M. Lok, C.A. Messina, R.L. Patton, R.T. Gajek, T.R. Cannan, E.M. Flanigen,Journal of the American Chemical Society 106 (1984) 6092.

[112] J.A. Martens, M. Martens, P. Grobet, P.A. Jacobs, Studies in Surface Science andCatalysis 37 (1988) 97.

[113] R.J. Pellet, P.K. Coughlin, M.T. Staniulis, G.N. Long, J.A. Rabo, US Patent4,842,714 (1989).

[114] G.C. Edwards, J.P. Gilson, C.V. McDaniel, US Patent 4,681,864 (1987).[115] S. Cheng, Catalysis Today 49 (1999) 303.[116] Y. Ma, W. Tong, H. Zhou, S.L. Suib, Microporous and Mesoporous Materials 37

(2000) 243.[117] F. Marme, G. Coudurier, J.C. Védrine, Studies in Surface Science and Catalysis

121 (1999) 171.[118] A. Dyer, T. Gallardo, C.W. Roberts, Studies in Surface Science and Catalysis 49A

(1998) 389.[119] A. Galarneau, A. Barodawalla, T.J. Pinnavaia, Nature 374 (1995) 529.[120] A. Clearfield, Chemical Reviews 88 (1988) 125.[121] R.P. Bontchev, S. Liu, J.L. Krumhansl, J. Voigt, T.M. Nenoff, Chemistry of Mate-

rials 15 (2003) 3669.[122] B.F. Hoskins, R. Robson, Journal of the American Chemical Society 111 (1989)

5962.[123] M. Eddaoudi, H. Li, O.M. Yagi, Journal of the American Chemical Society 122

(2000) 1391.[124] S. Kitagawa, K. Uemura, Chemical Society Reviews 34 (2005) 109.[125] M. Eddaoudi, J. Kim, M. O Keeffe, O.M. Yaghi, Journal of the American Chemical

Society 124 (2002) 376.[126] M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M.O. Keeffe, O.M. Yaghi,

Science 295 (2002) 469.[127] G. Ferey, Chemical Society Reviews 37 (2008) 191.[128] G. Férey, C. Mellot-Draznieks, C. Serre, F. Millange, Accounts of Chemical

Research 38 (2005) 217.[129] K. Uemuraa, R. Matsudab, S. Kitagawa, Journal of Solid State Chemistry 178

(2005) 2420.[130] L. Josien, A. Simon-Masseron, V. Gramlich, J. Patarin, L. Rouleau, Chemistry-

A European Journal 9 (2003) 856.[131] A. Corma, H. García, F.X. Llabrés i Xamena, Chemical Reviews 110 (2010) 4606.[132] D. Farruseng, S. Aguado, C. Pinel, Angewandte Chemie International Edition

48 (2009) 7502.[133] M. Ranocchiari, J.A. van Bokhoven, Physical Chemistry Chemical Physics 13

(2011) 6388.[134] A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Catalysis Science & Technology 1

(2011) 856.[135] I. Mueller, M. Schubert, F. Teich, H. Puetter, K. Schierle-Arndt, J. Pastré, Journal

of Materials Chemistry 16 (2006) 626.[136] D.S. Su, R. Schlögl, ChemSusChem 3 (2010) 136.[137] T. Ladrak, S. Smulders, O. Roubeau, S.J. Tent, P. Gamez, J. Reedik, European

Journal of Inorganic Chemistry (2010) 3804.[138] M. Hartmann, Angewandte Chemie International Edition 43 (2004) 5880.[139] D. Verboekend, J. Pérez-Ramírez, Catalysis Science & Technology 1 (2011) 879.[140] J. Lee, Y. Park, P. Kim, H. Kim, J. Yi, Journal of Materials Chemistry 14 (2004)

1050.[141] A. Karlsson, M. Stöcker, R. Schmidt, Microporous and Mesoporous Materials

27 (1999) 181.[142] M. Kruk, M. Jarnoniec, S.H. Joo, R. Ryoo, Journal of Physical Chemistry B 107

(2003) 2205.[143] B. Van Der Voort, P.I. Ravikovitch, K.P. De Jong, M. Benjelloun, E. Van Bavel, A.H.

Janssen, M. Benjellouen, E. Van Bavel, P. Cool, B.M. Weckhuysen, E.F. Vansant,Chemical Communications (2002) 1010.

[144] B. van der Voort, P.I. Ravikovitch, K.P. de Jong, M. Benjelloun, E. van Bavel,

A.H. Janssen, A.V. Neimark, B.M. Weckhuysen, E.F. Vansant, Journal of PhysicalChemistry B 106 (2002) 5873.

[145] C. Yu, J. Fan, B. Tain, D. Zhao, G.D. Stucky, Advanced Materials 14 (2002) 1742.[146] J. Pérez-Ramirez, C.H. Christensen, K. Egeblad, C.H. Christensen, J.C. Groen,

Chemical Society Reviews 37 (2008) 2530.

2 sis To

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4 I. Fechete et al. / Cataly

147] W.J.J. Stevens, V. Meynen, E. Bruijn, O.I. Lebedev, G. Van Tendeloo, P. Cool, E.F.Vansant, Microporous and Mesoporous Materials 110 (2008) 77.

148] M. Chiesa, V. Meynen, S. Van Doorslaer, P. Cool, E.F. Vansant, Journal of theAmerican Chemical Society 128 (2006) 8955.

149] J. Wang, W. Yue, W. Zhou, M.O. Coppens, Microporous and Mesoporous Mate-rials 120 (2009) 19.

150] A. Sakthivel, S.J. Huang, W.-H. Chen, Z.-H. Lan, K.-H. Chen, S.-W. Kim, R. Ryoo,A.S.T. Chiang, S.B. Liu, Chemistry of Materials 16 (2004) 3168.

151] Y. Tao, H. Kanoh, K. Kaneko, Journal of the American Chemical Society 125(2003) 6044.

152] A.H. Janssen, I. Schmidt, C.J.H. Jacobsen, A.J. Koster, K.P. de Jong, Microporousand Mesoporous Materials 65 (2003) 59.

153] J. Garcia-Martinez, D. Carloz-Amoros, A. Linares-Solano, Y.S. Lin, Microporousand Mesoporous Materials 42 (2001) 255.

154] S. Iijima, Nature 354 (1991) 56.155] X. Pan, X. Bao, Accounts of Chemical Research 44 (2011) 553.156] T. Charinpanitkul, P. Lorturn, W. Ratismith, N. Viriya-empikul, G. Tumcharern,

J. Wilcox, Materials Research Bulletin 46 (2011) 1604;X.-J. Wu, F. Zhu, C. Mu, Y. Liang, L. Xu, Q. Chen, R. Chen, D. Xu, CoordinationChemistry Reviews 254 (2010) 1135.

157] R. Leary, A. Westwood, Carbon 49 (2011) 741.158] K. Chizari, I. Janowska, M. Houllé, I. Florea, O. Ersen, T. Romero, P. Bern-

hardt, M.-J. Ledoux, C. Pham-Huu, Applied Catalysis A – General 380 (2010)72.

159] J. Amadou, K. Chizari, M. Houllé, I. Janowska, O. Ersen, D. Bégin, C. Pham-Huu,Catalysis Today 138 (2008) 62.

160] M. Becher, M. Haluska, M. Hirscher, A. Quintel, V. Skakalova, U. Dettlaff-Weglikovska, X. Chen, M. Hulman, Y. Choi, S. Roth, V. Meregalli, M. Parrinello,R. Ströbel, L. Jörissen, M.M. Kappes, J. Fink, A. Züttel, I. Stepanek, P. Bernier,Comptes Rendus Physique 4 (2003) 1055.

161] C.-C. Huang, N.-W. Pu, C.-A. Wang, J.-C. Huang, Y. Sung, M.-D. Ger, Separationand Purification Technology 82 (2011) 210.

162] X.-Y. Xue, C.-H. Ma, C.-X. Cui, L.-L. Xing, Solid State Sciences 13 (2011) 1526.163] I. López-Corral, E. Germán, M.A. Volpe, G.P. Brizuela, A. Juan, International

Journal of Hydrogen Energy 35 (2010) 2377;I. Janowska, O. Ersen, T. Jacob, P. Vennegues, D. Begin, M.-J. Ledoux, C. Pham-Huu, Applied Catalysis A – General 371 (2009) 22.

164] Y. Shi, L. Wen, F. Li, H.-M. Cheng, Journal of Power Sources 196 (2011) 8610.165] G.L. Luque, M.I. Rojas, G.A. Rivas, E.P.M. Leiva, Electrochimica Acta 56 (2010)

523.166] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 (1992)

710.167] M. Linden, S. Schacht, F. Schueth, A. Steel, K. Unger, Journal of Porous Materials

5 (1998) 177.168] J.S. Beck, C. Vartuli, W. Roth, M.E. Leonowicz, C.T. Kresge, K.D. Schmitt, T.W.

Chu, D.H. Olson, E.W. Sheppard, S.B. McCullen, J.B. Higgins, J.L. Schlenker,Journal of the American Chemical Society 114 (1992) 10834.

169] M. Froba, K. Kohn, B. Bouffaud, O. Richard, G.V. Tendeloo, Materials ResearchSociety Symposium Proceedings (1999) 547.

170] T. Yanagisawa, T. Schimizu, K. Kuroda, C. Kato, Bulletin of the Chemical Societyof Japan 63 (1990) 988.

171] S. Inagaki, Y. Fukushima, K. Kuroda, Journal of the Chemical Society, ChemicalCommunications 22 (1993) 680.

172] D.Y. Zhao, J.L. Feng, Q.S. Hao, G. Frederickson, B.F. Chemelka, G.D. Stucky,Science 279 (1998) 548.

173] D. Zhao, Q. Huo, J. Feng, B.F. Chmelka, G.D. Stucky, Journal of the AmericanChemical Society 120 (1998) 6024.

174] R. Ryoo, C.H. Ko, M. Kruk, V. Antochuck, M. Jaroniec, Journal of Physical Chem-istry B 104 (2000) 11465.

175] A. Galerneau, H. Cambon, T. Martin, L.C. De Menorval, D. Brunel, F. Di Renzo,F. Fajula, Studies in Surface Science and Catalysis 141 (2002) 395.

176] P.T. Tanev, T.J. Pinnavaia, Science 267 (1995) 865.177] S.A. Bagshaw, E. Prouzetr, T.J. Pinnavaia, Science 269 (1995) 1242.178] T. Kimura, T. Kamata, M. Fuziwara, Y. Takamao, M. Kaneda, Y. Sakamoto, O.

Terasaki, Y. Sugihara, K. Kuroda, Angewandte Chemie International Edition39 (2000) 3855.

179] H.-M. Kao, J.-D. Wu, C.-C. Cheng, A.S.T. Chiang, Microporous and MesoporousMaterials 88 (2006) 319.

180] M.J. Kim, R. Ryoo, Chemistry of Materials 11 (1998) 487.181] J.C. Jansen, Z. Shan, L. Marchese, W. Zhou, N. Puil, T. Maschmeyer, Chemical

Communications (2001) 713.182] S. Inagaki, Y. Guan, Y. Fukushima, T. Oshuna, O. Terasaki, Journal of the Amer-

ican Chemical Society 121 (1999) 9611.183] T. Sefa, G. Ozin, H. Grondey, M. Kruk, M. Jaroniec, Surface Science and Catalysis

141 (2002) 1.184] O. Muth, C. Schellbach, M. Froeba, Chemical Communications (2001) 2032.185] S. Jun, S. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna, O. Terasaki, Journal

of the American Chemical Society 122 (2000) 10712.186] S.H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Journal of Physical Chemistry B 106

(2002) 4640.187] T. Tsoncheva, J. Rosenholm, M. Linden, F. Kleitz, M. Tiemann, L. Ivanova, M.

Dimitrov, D. Paneva, I. Mitov, C. Minchev, Microporous and Mesoporous Mate-rials 112 (2008) 327.

188] L. Lizama, M. Pérez, T. Klimova, Studies in Surface Science and Catalysis 174B(2008) 1251.

day 189 (2012) 2– 27

[189] F. Boubekr, A. Davidson, S. Casale, P. Massiani, Microporous and MesoporousMaterials 141 (2011) 157.

[190] N. El Hassan, A. Davidson, P. Da Costa, G. Djega-Mariadassou, Catalysis Today137 (2008) 191.

[191] S. Jun, R. Ryoo, Journal of Catalysis 195 (2000) 237.[192] X. Hu, M.L. Foo, G.K. Chuah, Journal of Catalysis 195 (2000) 412.[193] C.W. Lee, D.H. Ahn, B. Wang, J.S. Hwang, S.E. Park, Microporous and Meso-

porous Materials 44–45 (2001) 587.[194] W.H. Zhang, J.L. Shi, L.Z. Wang, D.S. Yan, Materials Letters 46 (2000) 35.[195] W.S. Ahn, D.H. Lee, T.J. Kim, J.H. Kim, G. Seo, R. Ryoo, Applied Catalysis A –

General 181 (1999) 39.[196] R. Burch, N. Cruise, D. Gleeson, S.C. Tsang, Chemical Communications (1996)

951.[197] P. van der Voort, M. Mathieu, M. Morey, G.D. Stucky, E.F. Vansant, Studies in

Surface Science and Catalysis 117 (1998) 333.[198] T. Maschmeyer, F. Rey, G. Sankar, J.M. Thomas, Nature 378 (1995) 159.[199] A. Boulaoued, I. Fechete, B. Donnio, M. Bernard, P. Turek, F. Garin, Microporous

and Mesoporous Materials 155 (2012) 131.[200] W. Zhao, L. Kong, Y. Luo, Q. Li, Microporous and Mesoporous Materials 100

(2007) 111.[201] I. Fechete, B. Donnio, O. Ersen, T. Dintzer, A. Djeddi, F. Garin, Applied Surface

Science 257 (2011) 2791.[202] I. Eswaramoorthi, A.K. Dalai, Microporous and Mesoporous Materials 93

(2006) 1.[203] Y. Shao, L. Wang, J. Zhang, M. Anpo, Journal of Photochemistry and Photobi-

ology A: Chemistry 180 (2006) 59.[204] M. Pirouzmand, M.M. Amini, N. Safari, Journal of Colloid and Interface Science

319 (2008) 199.[205] J.F. Bengoa, M.V. Cagnoli, N.G. Gallegos, A.M. Alvarez, L.V. Mogni, M.S.

Moreno, S.G. Marchetti, Microporous and Mesoporous Materials 84 (2005)153.

[206] A. De Stefanis, S. Kaciulis, L. Pandolfi, Microporous and Mesoporous Materials99 (2007) 140.

[207] Q. Zhang, Y. Wang, S. Itsuki, T. Shishido, K. Takehira, Journal of MolecularCatalysis A – Chemical 188 (2002) 189.

[208] Á. Szegedi, Z. Kónya, D. Méhn, E. Solymár, G. Pál-Borbély, Z.E. Horváth, L.P.Biró, I. Kiricsi, Applied Catalysis A – General 272 (2004) 257.

[209] M. Santhosh Kumar, J. Perez-Ramırez, M.N. Debbagh, B. Smarsly, U. Bentrup,A. Bruckner, Applied Catalysis B – Environmental 62 (2006) 244.

[210] Y. Zhang, F. Gao, H. Wan, C. Wu, Y. Kong, X. Wu, B. Zhao, L. Dong, Y. Chen,Microporous and Mesoporous Materials 113 (2008) 393.

[211] P. Van Der Voort, E.F. Vansant, Microporous and Mesoporous Materials 38(2000) 385.

[212] K. Anas, K.K. Mohammed Yusuff, Applied Catalysis A – General 264 (2004)213.

[213] O. Collart, P. Van Der Voort, E.F. Vansant, E. Gustin, A. Bouwen, D. Schoemaker,R. Ramachandra Rao, B.M. Weckhuysen, R.A. Schoonheydt, Physical ChemistryChemical Physics 1 (1999) 4099.

[214] M. Yonemitsu, Y. Tanaka, M. Iwamoto, Chemistry of Materials 9 (1997) 2679.[215] M. Yonemitsu, Y. Tanaka, M. Iwamoto, Journal of Catalysis 178 (1998) 207.[216] A. Sayari, Chemistry of Materials 8 (1996) 1840.[217] T. Linssen, K.L. Cassiers, P. Cool, E.F. Vansant, Microporous and Mesoporous

Materials 103 (2004) 121.[218] J. Panpranot, J. Goodwin Jr., A. Sayari, Catalysis Today 77 (2002) 269.[219] Y. Wang, M. Noguschi, Y. Ohtsuka, Catalysis Today 68 (2001) 3.[220] K. Soni, B.S. Rana, A.K. Sinha, A. Bhaumik, M. Nandi, M. Kumar, G.M. Dhar,

Applied Catalysis B – Environmental 90 (2009) 55.[221] A. Wang, Y. Wang, T. Kabe, Y.Y. Chen, A. Ishihara, W.H. Qian, P.J. Yao, Journal

of Catalysis 210 (2002) 269.[222] T. Klimova, M. Calderon, J. Ramirez, Applied Catalysis A – General 225 (2002)

1.[223] A. Prabhu, L. Kumaresan, M. Palanichamy, V. Murugesan, Applied Catalysis A

– General 360 (2009) 59.[224] K.C. Park, D.J. Yim, S.K. Ihm, Catalysis Today 74 (2002) 281.[225] A.M. Liu, K. Hidajat, S. Kawi, Journal of Molecular Catalysis A – Chemical 168

(2001) 303.[226] S.G. Shyu, S.W. Cheng, D.L. Tzou, Chemical Communications (1999) 2337.[227] R.S. Mulukutla, T. Shido, K. Asakura, T. Kogure, Y. Iwasawa, Applied Catalysis

A – General 228 (2002) 305.[228] V.R. Choudhary, S.K. Jana, N.S. Patil, Tetrahedron Letters 43 (2002) 1105.[229] V.R. Choudhary, S.K. Jana, Journal of Molecular Catalysis A – Chemical 184

(2002) 247.[230] T. Ookoshi, M. Onaka, Chemical Communications (1998) 2399.[231] M. Anpo, M. Takeuchi, K. Ikeue, S. Dohshi, Curr Opin, Solid State & Materials

Science 6 (2002) 381.[232] D.H. Zhang, H.B. Li, G.D. Li, J.S. Chen, Dalton Transactions 47 (2009) 10527.[233] X. Huang, W. Dong, G. Wang, M. Yang, L. Tan, Y. Feng, X. Zhang, Journal of

Colloid and Interface Science 359 (2011) 40.[234] T. Ikariya, I.D. Gridnev, Topics in Catalysis 53 (2010) 894.[235] P.L. Anelli, B. Czech, F. Monatanari, S. Quici, Journal of the American Chemical

Society 106 (1984) 861.

[236] S. Calogero, D. Lanari, M. Orrù, O. Piermatti, F. Pizzo, L. Vaccaro, Journal of

Catalysis 282 (2011) 112.[237] J.M. Thomas, T. Maschmeyer, B.F.G. Johnoson, D.S. Shephard, Journal of Molec-

ular Catalysis A – Chemical 141 (1999) 139.

ysis To

I. Fechete et al. / Catal

[238] E.L. Margelefsky, R.K. Zeidan, M.E. Davis, Chemical Society Reviews 37 (2008)1118.

[239] H.H. Kung, M.C. Kung, Catalysis Today 148 (2009) 2.[240] S. Shylesh, W.R. Thiel, ChemCatChem 3 (2011) 278.[241] R. Raja, J.M. Thomas, M.D. Jones, B.F.G. Johnson, D.E.W. Vaughan, Journal of

the American Chemical Society 125 (2003) 14982.[242] P. Yu, J. He, C. Guo, Chemical Communications 5 (2008) 2355.[243] J.M. Fraile, J.L. Garcia, J.A. Mayoral, M. Roldan, Organic Letters 9 (2007)

731.[244] S. Vijaikumar, A. Dhakshinamoorthy, K. Pitchumani, Applied Catalysis A –

General 340 (2008) 25.[245] J. Zakzeski, P.C.A. Bruijnincx, A.L. Jongerius, B. Weckhuysen, Chemical Reviews

110 (2010) 3552.[246] Q. Zhang, W. Deng, Y. Wang, Chemical Communications 47 (2011) 9275.[247] G.W. Huber, S. Iborra, A. Corma, Chemical Reviews 106 (2006) 4044.[248] J. Zakzeski, B.M. Weckhuysen, ChemSusChem 4 (2011) 369.[249] P. Gallezot, Catalysis Today 124 (2007) 76.[250] S. Van de Vyver, J. Geboers, P.A. Jacobs, B.F. Sels, ChemCatChem 3 (2011) 82.[251] O.L. Dhepe, A. Fukuoka, ChemSusChem 1 (2008) 965.[252] A. Fukuoka, P.L. Dhepe, Angewandte Chemie International Edition 45 (2006)

5161.[253] C. Luo, S. Wang, H. Liu, Angewandte Chemie International Edition 46 (2007)

7636.[254] N. Ji, T. Zhang, M. Zheng, A. Wang, H. Wang, X. Wang, J.G. Chen, Angewandte

Chemie International Edition 47 (2008) 8510.[255] X. Tan, W. Deng, M. Liu, Q. Zhang, Y. Wang, Chemical Communications (2009)

7179.[256] M. Liu, W. Deng, Q. Zhang, Y. Wang, Y. Wang, Chemical Communications 47

(2011) 9717.[257] M.V. Twigg, Catalyst Handbook, 2nd edition, Manson Publishing Ltd, 1996.[258] T. Bunluesin, R.J. Gorte, G.W. Graham, Applied

Catalysis B – Environmental 15 (1998)107.

[259] J.M. Zalc, V. Sokolovskii, D.G. Loffler, Journal of Catalysis 206 (2002) 169.[260] E. Xue, M.O. O’Keeffe, J.R.H. Ross, Catalysis Today 30 (1996) 107.[261] H. Zhao, Y. Hu, J. Li, Journal of Molecular Catalysis A – Chemical 149 (1999)

141.[262] Y. Li, Q. Fu, M. Flytzani-Stephanopoulos, Applied Catalysis B – Environmental

27 (2000) 179.[263] Y. Schuurman, C. Marquez-Alvarez, V.C.H. Kroll, C. Mirodatos, Catalysis Today

46 (1998) 185.[264] N.E. Amadeo, M. Laborde, International Journal of Hydrogen Energy 20 (1995)

949.[265] Y. Tanaka, T. Utaka, R. Kikuchi, K. Sasaki, K. Eguchi, Applied Catalysis A –

General (2002) 6032.[266] A. Basinska, F. Domka, Applied Catalysis A – General 179 (1999) 241.[267] A. Basinska, L. Kepinski, F. Domka, Applied Catalysis A – General 183 (1999)

143.[268] F. Boccuzzi, A. Chiorino, M. Manzoli, D. Andreeva, T. Tabakova, Journal of

Catalysis 188 (1999) 176.[269] D.C. Grenoble, M.M. Estadt, D.F. Ollis, Journal of Catalysis 67 (1981) 90.[270] C. Serre, F. Garin, G. Belot, G. Maire, Journal of Catalysis 141 (1993) 1.[271] A. Le Valant, A. Garron, N. Bion, D. Duprez, F. Epron, International Journal of

Hydrogen Energy 36 (2011) 311.[272] A. Haryanto, S. Fernando, N. Murali, S. Adhikari, Energy and Fuels 19 (2005)

2098.[273] S. Velu, N. Satoh, C.S. Gopinath, K. Suzuki, Catalysis Letters 82 (2002) 145.[274] G.A. Deluga, J.R. Salge, L.D. Schmidt, X.E. Verykios, Science 303 (2004) 993.[275] M.C. Sánchez-Sánchez, R.M. Navarro, J.L.G. Fierro, International Journal of

Hydrogen Energy 32 (2007) 1462.[276] E. Cavallaro, Energy and Fuels 14 (2000) 1195.[277] A.N. Fatsikostas, X.E. Verykios, Journal of Catalysis 225 (2004) 439.[278] J. Llorca, J.P.R. de la Piscina, J. Sales, N. Homs, Chemical Communications

(2001) 641.[279] P. Jena, Journal of Physical Chemistry Letters 2 (2011) 206.[280] P.V. Kamat, Journal of Physical Chemistry Letters 2 (2011) 242.[281] X. Chen, S. Shen, L. Guo, S.S. Mao, Chemical Reviews 110 (2010) 6503.[282] M.A. Pena, J.L.G. Fierro, Chemical Reviews 101 (2001) 1981.[283] G.P. van der Laan, PhD thesis, University of Groningen, The Netherlands, 1999.[284] J.M. Thomas, W.J. Thomas, Principle and Practice of Heterogeneous Catalysis,

VCH Publishers, New York, 1997.[285] K. Thampi, J. Kiwi, M. Graetzel, Nature 327 (1987) 506.[286] M. Vannice et al., US 4,042,614, Exxon (1976).[287] S. Plecha et al., US 6,117,814, Exxon (2000).[288] J. Bao, J. He, Y. Zhang, Y. Yoneyama, N. Tsubaki, Angewandte Chemie Interna-

tional Edition 47 (2008) 353.[289] J. Kang, K. Cheng, L. Zhang, Q. Zhang, J. Ding, W. Hua, Y. Lou, Q. Zhai, Y. Wang,

Angewandte Chemie International Edition 50 (2011) 5200.[290] J. Kang, S. Zhang, Q. Zhang, Y. Wang, Angewandte Chemie International Edi-

tion 48 (2009) 2565.[291] W. Chen, Z. Fan, X. Pan, X. Bao, Journal of the American Chemical Society 130

(2008) 9414.[292] G. Yu, B. Sun, Y. Pei, S. Xie, S. Yan, M. Qiao, K. Fan, X. Zhang, B. Zong, Journal

of the American Chemical Society 132 (2010) 935.[293] S. Brunet, D. Mey, G. Pérot, C. Bouchy, F. Diehl, Applied Catalysis A – General

278 (2005) 143.

day 189 (2012) 2– 27 25

[294] C. Song, Catalysis Today 86 (2003) 211.[295] T.G. Kaufmann, A. Kaldor, G.F. Stuntz, M.C. Kerby, L.L. Ansell, Catalysis Today

62 (2000) 77.[296] F.M. Collins, A.R. Lucy, C. Sharp, Journal of Molecular Catalysis A – Chemical

117 (1997) 397.[297] A. Rabion, F. Fajula, J.R. Bernard, V. Hulea, US Patent 0,102,252 (2003).[298] F. Figueras, J. Palomique, S. Loridant, C. Fèche, N. Essayem, G. Gelbard, Journal

of Catalysis 226 (2004) 25.[299] A.L. Maciuca, C.-E. Ciocan, E. Dumitriu, F. Fajula, V. Hulea, Catalysis Today 138

(2008) 33.[300] Y. Kanda, T. Aizawa, T. Koboyashi, Y. Vemichi, S. Namba, M. Sugioka, Applied

Catalysis B – Environmental 77 (2007) 117.[301] M. Sugioka, L. Andalaluna, S. Morishita, T. Kurosaka, Catalysis Today 39 (1997)

61.[302] H. Topsøe, B.S. Clausen, F.E. Massoth, in: J.R. Anderson, M. Boudard (Eds.),

Catalysis Science and Technology, vol. 11, Springer, Berlin, 1996.[303] K. Kabe, A. Ishihara, W. Qian, Hydrodesulfurization and Hydrodenitrogena-

tion, Kodansha, Tokyo, 1999.[304] B.S. Clausen, S. Mørup, H. Topsøe, R. Candia, J. Phys. Colloq. 37 (1976) C6–C249.[305] H. Topsøe, B.S. Clausen, R. Candia, C. Wivel, S. Mørup, Journal of Catalysis 68

(1981) 433.[306] C. Wivel, R. Candia, B.S. Clausen, M. Mørup, H. Topsøe, Journal of Catalysis 68

(1982) 453.[307] H. Topsøe, B.S. Clausen, R. Candia, C. Wivel, S. Mørup, Bulletin des Societes

Chimiques Belges 90 (1981) 1189.[308] R. Candia, O. Sørensen, J. Villadsen, N. Topsøe, B.S. Clausen, H. Topsøe, Bulletin

des Societes Chimiques Belges 93 (1984) 763.[309] J.A.R. van Veen, E. Gerkema, A.M. van der Kraan, A. Knoester, Journal of the

Chemical Society, Chemical Communications (1987) 1684.[310] Y. Ohta, T. Shimizu, T. Honna, M. Yamada, Studies in Surface Science and

Catalysis 127 (1999) 161.[311] T. Shimizu, K. Hiroshima, T. Honna, T. Mochizuki, M. Yamada, Catalysis Today

45 (1998) 271.[312] L. Medici, R. Prins, Journal of Catalysis 163 (1996) 38.[313] T. Fujikawa, Catalysis Surveys from Asia 10 (2006) 89.[314] T. Fujikawa, M. Kato, H. Kimura, K. Kiriyama, M. Hashimoto, N. Nakajima,

Journal of the Japan Petroleum Institute 48 (2005) 106.[315] T. Fujikawa, M. Kato, T. Ebihara, K. Hagiwara, T. Kubota, Y. Okamoto, Journal

of the Japan Petroleum Institute 48 (2005) 114.[316] J.A. Bergwerff, M. Jansen, B.R.G. Leliveld, T. Visser, K.P. De Jong, B.M. Weck-

huysen, Journal of Catalysis 243 (2006) 292.[317] D. Mey, S. Brunet, C. Canaff, F. Maugé, C. Bouchy, F. Diehl, Journal of Catalysis

227 (2004) 43.[318] S. Hatanaka, T. Miyama, H. Seki, S. Hikita, EP 0736589 A1 (1996).[319] C. Flego, V. Arrigoni, M. Ferrari, R. Riva, L. Zanibelli, Catalysis Today 65 (2001)

265.[320] G. Muralidhar, F.E. Massoth, J. Shabtai, Journal of Catalysis 85 (1984) 44.[321] M. Toba, Y. Miki, T. Matsui, M. Harada, Y. Yoshimura, Applied Catalysis B –

Environmental 70 (2007) 542.[322] V. La Parola, G. Deganello, A.M. Venecia, Applied Catalysis A – General 260

(2004) 237.[323] K.S. Rawat, M.S. Rana, G. Murali Dhar, Studies in Surface Science and Catalysis

135 (1998) 307.[324] R. Navarro, B. Pawelec, J.L.G. Fierro, P.T. Vasudevan, J.F. Cambra, M.B. Guemez,

P.L. Arias, Fuel Processing Technology 61 (1999) 73.[325] P.E. Dai, J.H. Lunsford, Journal of Catalysis 64 (1980) 173.[326] T. Tatsumi, M. Tanigushi, S. Yasuda, Y. Ishii, T. Murata, M. Hidai, Applied

Catalysis A – General 139 (1996) L5.[327] M. Alibouri, S.M. Ghoreishi, H.R. Aghabozang, Journal of Supercritical Fluids

49 (2009) 230.[328] Y. Fan, G. Shi, H. Liu, X. Bao, Fuel 90 (2011) 1717.[329] Y. Huang, Z. Zhou, Y. Qi, X. Li, Z. Cheng, W. Yuan, Chemical Engineering Journal

172 (2011) 444.[330] M.M. Hossain, M.A. Al-Salih, M.A. Shalabi, T. Kimura, T. Inui, Applied Catalysis

A – General 274 (2004) 43.[331] T. Kimura, K. Al-Nawad, S.A. Ali, Y. Suzuki, H. Hamid, T. Inui, Proceedings of

the 220th ACS National Meeting, Washington, August 20–24, 2000.[332] S.A. Ali, M.E. Biswas, T. Yoneda, T. Miura, S.H. Hamid, E. Iwamatsu, H. Al-Suaibi,

Catalysis Science & Technology 127 (1998) 407.[333] J. Lee, A. Ishihara, F. Dumeignil, K. Miyazaki, Y. Oomori, E.W. Qian, T. Kabe,

Journal of Molecular Catalysis A – Chemical 209 (2004) 155.[334] X. Li, A. Wang, Z. Sun, C. Li, J. Ren, B. Zhao, Y. Wang, Y. Chan, Y. Hu, Applied

Catalysis A – General 254 (2003) 319.[335] Y. Yoshimura, H. Yasuda, T. Sato, N. Kijima, T. Kameoka, Applied Catalysis A –

General 207 (2001) 303.[336] M. Sugioka, F. Sado, T. Kurosaka, X. Wang, Catalysis Today 45 (1998) 327.[337] J.P. Greeley, S. Zaczepinski, T.R. Halbert, G.B. Brignac, A.R. Gentry, R.L. Kraus,

Am. Chem. Soc. Prepr. Div. Pet. Chem 45 (2000) 357.[338] B.B. Garland, T.R. Halbert, J.P. Greeley, R.A. Demmin, T.J. Davis, World Refining

10 (2000) 14.[339] G.J. Antos, R.B. Solari, R. Monque, Studies in Surface Science and Catalysis 106

(1997) 27.[340] R.M. Jao, I.J. Leu, J.R. Chang, Applied Catalysis A – General 135 (1996) 301.[341] J. Gislason, Oil and Gas Journal 99 (2002) 74.[342] Q. Debuisschert, J.-L. Nocca, C. Jean-Paul, Proceed. Interf. 2002 Conference,

Budapest, September 19–20, 2002, p. 133.

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6 I. Fechete et al. / Cataly

343] N.H. Sweed, R. Demmin, H. Ryu, Hydrocarbon Engineering 7 (2002) 19.344] J.A. Salazar, L.M. Cabera, E. Palmisano, W.J. Garcia, R.B. Solari, US Patent

5,770,047 to Intevep S.A. (1998).345] J.A. Salazar, N.P. Martinez, J.A. Perez, Meeting RFG specifications, Hydrocarbon

Engineering 3 (1998) 48.346] J. Gentry, T. Khanmamedov, R.W. Wytcherley, Hydrocarbon Engineering 7

(2002) 43.347] J. Gislason, Hydrocarbon Engineering 7 (2002) 39.348] D. French, J. Shah, P. Johnson, Hydrocarbon Engineering 7 (2002) 37.349] K.L. Rock, R.M. Foley, World Refining 9 (1999) 23.350] G. Centi, F. Cavani, F. Trifirro, Selective Oxidation by Heterogeneous Catalysis,

Kluwer Academic/Plenum Publisbers, New York, 2001.351] V. Hulea, F. Fajula, J. Bousquet, Journal of Catalysis 198 (2001) 179.352] V. Hulea, A.-L. Maciuca, A.-M. Cojocariu, C.-E. Ciocan, E. Dumitriu, Comptes

Rendus Chimie 12 (2009) 723.353] T. Sakakura, J.C. Choi, H. Yasuda, Chemical Reviews 107 (2007) 2365.354] M. Prettre, Ch. Eichner, M. Perrin, Transactions of the Faraday Society 42

(1946) 335.355] E.H. van Broekhoven, F.R. Mas Cabré, P. Bogaard, G. Klaver, M. Vonhof, US

Patent 5,986,158 (1999).356] A. Horváth, G. Stefler, O. Geszti, A. Kienneman, A. Pietraszek, L. Guczi, Catalysis

Today 169 (2011) 102.357] N. Bespalko, A.-C. Roger, J. Bussi, Applied Catalysis A – General 407 (2011)

204.358] G. Centi, L. Perathoner, Catalysis Today 148 (2009) 191.359] T. Kakamuto, Energy Conversion and Management 36 (1995) 661.360] Y.X. Pan, C.-J. Liu, Q. Ge, Journal of Catalysis 272 (2010) 227.361] H. Li, H. Yang, H. Li, Journal of Catalysis 251 (2007) 233.362] L. Yin, S. Wang, H. Lu, J. Ding, R. Mostafi, Z. Hao, Chemical Engineering Journal

131 (2007) 123.363] S. Ozkara-Aydinoglu, E. Ozensoy, A.E. Aksoylu, International Journal of Hydro-

gen Energy 34 (2009) 9711.364] J. Cheng, W. Huang, Fuel Processing Technology 91 (2010) 72.365] H. Jiang, H. Li, Y. Zhang, Journal of Chemical Technology and Biotechnology

35 (2007) 72.366] M. Minutillo, A. Perna, Intern, Journ. of Hydrog, Energy 35 (2010) 7012.367] A. Corma, M.I. Juan-Rajadell, J.M. Lopez-Nieto, A. Martinez, C. Martinez,

Applied Catalysis A – General 111 (1994) 175.368] J. Weitkamp, Y. Traa, Catalysis Today 49 (1999) 193.369] F. Cardona, N.G. Gnep, M. Guisnet, G. Szabo, P. Nascimento, Applied Catalysis

A – General 128 (1995) 243.370] P. Wang, D. Wang, C. Xu, J. Liu, J. Gao, Catalysis Today 125 (2007) 263.371] R. Gounder, E. Iglesia, Journal of Catalysis 277 (2011) 36.372] E.A. Mamedov, V. Cortes Corberan, Applied Catalysis A – General 127 (1995)

1.373] J. Scwank, K. Balakrishnan, A. Sachdev, Studies in Surface Science and Catalysis

75 (1993) 905.374] K. Weissrmel, H.J. Arpe, Industrial Organic Chemistry, 4th edition, Wiley-VCH,

2003.375] Y.H. Taufiq-Yap, F. Rezaei, A.A. Rownaghi, Industrial and Engineering Chem-

istry Research 48 (2009) 7517.376] G. Centi, F. Trifiró, J.R. Ebner, V.M. Franchetti, Chemical Reviews 88 (1988)

55.377] Y. Zhang-Lin, M. Forissier, J.C. Volta, Journal of Catalysis 145 (1993) 267.378] M.T. Sananes, G.J. Hutchings, J.C. Volta, Journal of Catalysis 154 (1995) 253.379] G.W. Clouston, S.R. Bare, H. Kung, K. Birkeland, G.K. Bethke, R. Harlow, N.

Herron, P.L. Lee, Science 275 (1997) 191.380] G. Landi, L. Lisi, G. Russo, Journal of Molecular Catalysis A – Chemical 239

(2005) 172.381] T. Ushikubo, K. Oshima, T. Ihara, H. Amatsu, US Patent 5,534,650 (1996),

Assigned to Mitsubishi Chemical Co.382] T. Ushikubo, K. Oshima, A. Kayou, A.M. Hatano, Studies in Surface Science and

Catalysis 112 (1997) 473.383] T. Ushikubo, K. Oshima, A. Kayou, M. Vaarkamp, M. Hatano, Journal of Catalysis

169 (1997) 394.384] J.C. Védrine, E.K. Novakova, in: J.L.G. Fierro (Ed.), Metal Oxides: Chemistry and

Applications, Marcel Dekker, New York, 2005, p. 413.385] G.S. Patience, J.M. López-Nieto, Applied Catalysis A – General 376 (2010) 4

(special issue).386] F. Luck, Catalysis Today 53 (1999) 81.387] L. Oliviero, J. Barbier Jr., D. Duprez, Applied Catalysis B – Environmental 40

(2003) 163.388] Q. Huang, Z. Meng, R. Zhou, Applied Catalysis B – Environmental 115–116

(2012) 179.389] P. Dégé, L. Pinard, P. Magnoux, M. Guisnet, Comptes Rendus de l’Académie

des Sciences – Series II 4 (2001) 41.390] T.T. Shen, C.E. Schmidt, T.R. Card, Assessment and Control of VOC Emission

from Waste Water Treatment and Disposal Facilities, Van Nostrand Reinhold,New York, 1993.

391] S. Wang, H.M. Ang, M.O. Tade, Environment International 33 (2007) 694.392] S. Somokawa, T. Hagiwara, K. Fujii, M. Kojima, T. Shinoda, Applied Catalysis A

– General 409–410 (2011) 209.393] S. Azalim, M. Franco, R. Brahmi, J.-M. Giraudon, J.-F. Lamonier, Journal of

Hazardous Materials 188 (2011) 422.394] R. Bonelli, C. Lucarelli, T. Pasini, L.F. Liotta, S. Zacchini, S. Albonetti, Applied

Catalysis A – General 400 (2011) 54.

day 189 (2012) 2– 27

[395] J.J. Spivey, Industrial and Engineering Chemistry Research 26 (1987) 2165.[396] S. Minicò, S. Scirè, C. Crisafulli, R. Maggiore, S. Galvagno, Applied Catalysis B

– Environmental 28 (2000) 245.[397] S. Minicò, S. Scirè, C. Crisafulli, S. Galvagno, Applied Catalysis 34 (2001) 277.[398] S. Scirè, S. Minicò, C. Crisafulli, S. Galvagno, Catalysis Communications 2

(2001) 229.[399] A. Trovarelli, Catalysis Reviews – Science and Engineering 38 (1996) 439.[400] A. Trovarelli, C. de Leitenburg, M. Boaro, G. Dolcetti, Catalysis Today 50 (1999)

353.[401] Y. Li, Q. Fu, M. Flytzani-Stephanopoulos, Applied Catalysis 27 (2000) 179.[402] T. Bunluesin, R.J. Gorte, Applied Catalysis B – Environmental 15 (1998) 107.[403] S.C. Kim, W.G. Shim, Applied Catalysis B – Environmental 92 (2009) 429.[404] S.K. Ihm, Y.D. Jun, D.C. Kim, K.E. Jeong, Catalysis Today 93–95 (2004) 149.[405] W.G. Shim, J.W. Lee, S.C. Kim, Applied Catalysis B – Environmental 84 (2008)

133.[406] S. Huang, C. Zhang, H. He, Catalysis Today 139 (2008) 15.[407] Y. Yazawa, H. Yoshida, N. Takgi, S. Komai, A. Satsuma, T. Hattori, Applied

Catalysis B – Environmental 19 (1996) 261.[408] R. Burch, P.K. Loader, F.J. Urbano, Catalysis Today 27 (1996) 243.[409] K. Muto, N. Katada, M. Niwa, Applied Catalysis 134 (1996) 203.[410] T.R. Baldwin, R. Burch, Applied Catalysis 66 (1990) 337.[411] Y. Yazawa, H. Yoshida, N. Takagi, S. Komai, A. Satsuma, T. Hattori, Journal of

Catalysis 187 (1999) 15.[412] P. Briot, M. Primet, Applied Catalysis 68 (1991) 301.[413] C.A. Muller, M. Maciejewski, R.A. Koeppel, A. Maiker, Journal of Catalysis 166

(1997) 36.[414] P. Papaefthimiou, T. Ioannides, X.E. Verykios, Applied Catalysis B – Environ-

mental 13 (1997) 175.[415] R.J. Farrauto, M.C. Hobson, T. Kennelly, E.M. Waterman, Applied Catalysis A –

General 81 (1992) 227.[416] M. Lyubovsky, L. Pfefferle, Applied Catalysis 173 (1998) 107.[417] O. Demoulin, G. Rupprechter, I. Seunier, B. Le Clef, M. Navez, P. Ruiz, Journal

of Physical Chemistry B 109 (2005) 20454.[418] S.E. Braslavsky, K.N. Houk, Pure and Applied Chemistry 60 (1988) 1055.[419] J.W. Verhoven, Pure and Applied Chemistry 68 (1996) 2223.[420] H.G. Kim, D.W. Hwang, J. Kim, Y.G. Kim, J.S. Lee, Chemical Communications

(1999) 1077.[421] C.D. Lindstrom, X.-Y. Zhu, Chemical Reviews 106 (2006) 4281.[422] J.-M. Herrmann, Heterogeneous photocatalysis: state of the art and present

applications, Topics in Catalysis 34 (2005) 49; Titania-based true hetero-geneous photocatalysis, in: A. Seidel (Ed.), Photocatalysis, Kirk–OthmerEncyclopedia of Chemical Technology, vol. 19, 5th edition, Wiley & Sons, 2006,p. 73; Photocatalysis fundamentals revisited to avoid several misconceptions,Applied Catalysis B – Environmental 99 (2010) 461.

[423] A. Fujishima, X. Zhang, Titanium dioxide photocatalysis: present situation andfuture approaches, Comptes Rendus Chimie 9 (2006) 750.

[424] H. Aïssa, E. Puzenat, A. Plassais, J.-M. Herrmann, C. Haehnel, C. Guillard,Applied Catalysis B – Environmental 107 (2011) 1–8;C. Sarantopoulos, E. Puzenat, C. Guillard, J.-M. Herrmann, A.N. Gleizes, AppliedCatalysis B – Environmental 91 (2009) 225–233.

[425] A.L. Linsebigler, G. Lu, J.T. Yates Jr., Chemical Reviews 95 (1995) 735.[426] M. Yagi, M. Kaneko, Chemical Reviews 101 (2001) 21.[427] C. Cheng, P. Lei, H. Ji, W. Ma, J. Chao, H. Hidaka, N. Serpone, Environmental

Science and Technology 38 (2004) 329.[428] M. Fernandez-Garcıa, A. Martınez-Arias, J.C. Hanson, J.A. Rodriguez, Chemical

Reviews 104 (2004) 4063.[429] T.L. Thompson, J.T. Yates Jr., Chemical Reviews 106 (2006) 4428.[430] F.X. Llabres, P. Calza, C. Lamberti, C. Prestipino, A. Damin, S. Bordiga, E.

Pelizzetti, A. Zecchina, Journal of the American Chemical Society 125 (2003)2264.

[431] P. Calza, C. Paze, E. Pelizzetti, A. Zecchina, Chemical Communications (2001)2130.

[432] E. Reddy, B. Sun, P. Smirniotis, Journal of Physical Chemistry B 108 (2004)19198.

[433] A.J. Nozik, J.R. Miller, Chemical Reviews 110 (2010) 6443.[434] P. Anastas, N. Eghbali, Chemical Society Reviews 39 (2009) 301.[435] P. Anastas, ChemSusChem 2 (2009) 391.[436] P. Anastas, S.E. Beach, Green Chemistry Letters and Reviews 1 (2007) 9.[437] P. Anastas, Green Chemistry Letters and Reviews 1 (2007) 3.[438] R.A. Sheldon, Comptes Rendus de l’Académie des Sciences – Paris 3 (2000)

541.[439] G.A. Somorjai, H. Frei, J.Y. Park, Journal of the American Chemical Society 131

(2009) 16589.[440] U.K. Singh, M.A. Vannice, Applied Catalysis A – General 213 (2001) 1.[441] I. Fechete, V. Jouikov, Electrochimica Acta 53 (2008) 7107.[442] D. Teschner, L. Pirault-Roy, D. Naud, M. Guerin, Z. Paal, Applied Catalysis 252

(2003) 421.[443] D. Tichit, D. Lutic, B. Coq, R. Durand, R. Teissier, Journal of Catalysis 219 (2003)

167.[444] Y.H. Chin, W.E. Alvarez, D.E. Resasco, Catalysis Today 62 (2000) 159.[445] Y.P. Khitev, Y.G. Kolyagin, I.I. Ivanova, O.A. Ponomareva, F. Thibault-Starzyk,

J.-P. Gilson, C. Fernandez, F. Fajula, Microporous and Mesoporous Materials146 (2011) 201.

[446] A. Djeddi, I. Fechete, F. Garin, Catalysis Communications 17 (2012) 173.[447] A. Djeddi, I. Fechete, F. Garin, Applied Catalysis A – General 413–414 (2012)

340.

ysis To

[453] A.C. Dillon, Chemical Reviews 110 (2010) 6856.

I. Fechete et al. / Catal

[448] R. Ohnishi, M. Katayama, K. Takanabe, J. Kubota, K. Domen, ElectrochimicaActa 55 (2010) 5393.

[449] A. de Lucas-Consuegra, A. Caravaca, J. Gonzalez-Cobos, J.L. Valverde, F. Dorado,

Catalysis Communications 15 (2011) 6.

[450] G.A. Somorjai, Angewandte Chemie International Edition (2008) 9212.[451] M. Che, J.C. Védrine, Characterization of Solid Materials and Heterogeneous

Catalysts: From Structure to Surface Reactivity, J. Wiley-VCH, Weinheim,2012.

day 189 (2012) 2– 27 27

[452] M.G. Walter, E.L. Warren, J.R. McKone, S.W. Boettcher, Q. Mi, E.A. Santori, N.S.Lewis, Chemical Reviews 110 (2010) 6446.

[454] B. Farrauto, Abstract Commun, in: 6th European Conference “Paul Sabatier”on Catalysis“Catalytic Materials for Energy: Past, Present and Future, 26–29thSeptember, Klingenthal, France, 2011.

[455] J. Bisquert, Journal of Physical Chemistry Letters 2 (2011) 270.