Effect of Functional Groups on Autothermal Partial ... · balance. Catalyst Preparation ... GC and used to close material balances on C, H, andO atoms. ... acetaldehyde, and acetic

Published: June 01, 2011

r 2011 American Chemical Society 3157 dx.doi.org/10.1021/ef200455q | Energy Fuels 2011, 25, 3157–3171

ARTICLE

pubs.acs.org/EF

Effect of Functional Groups on Autothermal Partial Oxidation ofBio-oil. Part 1: Role of Catalyst Surface and Molecular OxygenJacob S. Kruger, David C. Rennard, Tyler R. Josephson, and Lanny D. Schmidt*

University of Minnesota, 421 Washington Avenue Southeast, Minneapolis, Minnesota 55455, United States

ABSTRACT:Autothermal partial oxidation is a promising technique to upgrade bio-oil into syngas and commodity chemicals. Thiswork aims to clarify preferred chemical routes in an autothermal system by investigating individually two-carbon moleculescontaining the functional groups found in bio-oil. Acids, alcohols, aldehydes, esters, ethers, and polyols were reacted over Pt� andRh�Al2O3 catalysts. Also, to investigate thermal effects independent of O2-induced reactions, these molecules were passed over thesame catalysts under similar conditions but in the absence of O2. Oxygen and adsorption geometry (the latter deduced from surfacescience literature) appear to play a key role in reaction initiation (manifested via overall conversion) and in the subsequent reactionof intermediate compounds. The catalyst identity also played a significant role in the observed product spectrum, and conversionwas higher over the Rh catalyst. Polyols, ethers, and acids were the least reactive, while esters were the most reactive. The Rh catalystyielded slightly higher selectivity to syngas products, while the Pt catalyst yielded slightly higher selectivity to combustion andintermediate products. Product selectivities and the surface science literature are used to propose reaction pathways.

’ INTRODUCTION

In response to mounting evidence for climate change andfinite supplies of fossil fuels, biomass has emerged as a renewablecarbon source with the potential to alleviate both concerns.Various forms and fractions of biomass have long found use assources of energy, both as a raw feedstock (e.g., combustion ofwood for heat) and in chemically or biologically refined mani-festations (e.g., transesterified vegetable oil as biodiesel). How-ever, traditional uses have suffered from low efficiency because ofthe distributed nature and low energy density of biomass1 and thenecessity of upgrading technologies to use only certain fractionsof the total biomass produced. Consequently, techniques havebeen developed to overcome these limitations. Pyrolysis, or rapidheating in an oxygen-deficient environment, can convert wholebiomass primarily into a relatively energy-dense liquid formthat is more amenable to transportation than raw biomass.2 Thisliquid form or bio-oil can then be shipped to a central refiningfacility for further processing to transportation fuels or commod-ity chemicals.

Bio-oil is a chemically complex mixture, typically consisting ofseveral hundred species of organic molecules, which can beroughly categorized by functional group into acids, alcohols,aldehydes, esters, ethers, and polyols (sugar-like molecules), aswell as a variety of aromatic molecules.3 The relative amounts ofeach functional group depend upon the biomass source andpyrolysis parameters.4 Furthermore, because different functionalgroups can react via different chemical pathways, the productspectrum from bio-oil processing can vary depending upon thecharacteristics of the bio-oil feedstock. Thus, a comprehensiveunderstanding of the reaction pathways of each functional groupin a bio-oil upgrading system is needed to tune reaction para-meters for the desired product spectrum.

In both fossil fuel and biomass upgrading technologies,catalysts are often employed to improve reaction kinetics andselectivity to a certain product. In this work, the noble metalsPt and Rh supported on R-Al2O3 monoliths were employed as

catalysts. Rhodium is known to facilitate conversion of carbona-cious materials to a mixture of CO andH2 known as synthesis gas(syngas), an important intermediate in many production path-ways of synthetic transportation fuels and chemicals.5,6 Platinumhas been found to increase selectivity to non-equilibrium prod-ucts relative to Rh5,6 and was chosen to investigate a potentialdirect bio-oil-to-commodity chemicals route. Additionally, in thepresence of O2, these catalysts show high activity for oxidationreactions, which have the potential to supply the heat necessaryfor vaporization and activation of the feedstock in situ (i.e., tooperate autothermally), making this technology more easilyscalable.

Additionally, short contact time (SCT) reactors performingreactive flash volatilization (RFV)7 are able to couple autother-mal partial oxidation with high heat-transfer rates. Because bio-oil is prone to condensation and polymerization reactions at evenmoderate temperatures, extremely rapid heating is required inbio-oil processing to prevent unwanted reactions, such as cokeformation.8 Preliminary experiments have shown that SCTreactors can process whole bio-oil at flow rates up to 1 mL/minfor 6 h or more,8 but several challenges, including reactionpathway elucidation, must be resolved before the process willbe commercially feasible.

This work investigates the autothermal partial oxidation ofseveral molecules that represent the functional groups present inbio-oil by RFV in a SCT reactor. While the species studied werechosen as two-carbon surrogates of bio-oil constituents, some ofthe species studied (e.g., acetic acid and acetaldehyde) aretypically present in bio-oil in appreciable quantities.9 Thus, theproposed reaction pathways facilitate a direct comparison towhole bio-oil catalytic partial oxidation (CPO) as well as extra-polation to other bio-oil constituents of the same functional

Received: March 24, 2011Revised: May 31, 2011

3158 dx.doi.org/10.1021/ef200455q |Energy Fuels 2011, 25, 3157–3171

Energy & Fuels ARTICLE

group categories. Further, the small size of these molecules limitsthe number of potential products, so that the role of eachfunctional group in surface and homogeneous reactions may bemore easily deduced. We also believe this to be the first report ofacetaldehyde, methyl formate, and dimethyl ether as fuels in anautothermal SCT reactor.

A full systematic study of these compounds in an autothermalsystem requires consideration of reactions on the catalyst surface,in the gas phase, on the support surface, and at the metal�supportinterface, as well as the role of oxygen at each of these locations.While we are certainly observing a convolution of reaction path-ways during autothermal operation, it is possible to gain someinsight by comparing multiple catalysts while holding initialconditions constant. Surface science studies of the reactions ofthese C2molecules on Pt and Rh surfaces also yield an idea of whatproducts to expect from reactions on the catalyst surface. Thispaper considers only reactions on the metal surface with andwithout O2, while part 2 (10.1021/ef200456m) explores homo-geneous and support-mediated reactions in more detail.

’EXPERIMENTAL SECTION

The apparatus used in these experiments was a 19 mm inner diameterquartz tube, clamped to an upstream pyrex end-cap containing one port,as shown in Figure 1. A stainless-steel nebulizer fit vertically into the porton the upstream end-cap; fuel was pumped at approximately 0.8 mL/minthrough the nebulizer (SS 50 from Burgener Research or a lab-builtsimilar model), with high velocity N2. O2 flowed around the nebulizerand was maintained at air stoichiometry with N2. The nebulizer wastypically positioned 3 cm from the catalyst bed, which consisted of three65 pores per linear inch (ppi) R-Al2O3, 17 mm in diameter, 10 mm longfoam monoliths (99% Al2O3, Vesuvius Hi-Tech Ceramics), impreg-nated with 5% Pt or Rh. An uncoated 65 ppiR-Al2O3 foammonolith wasused as a back heat shield and to hold a thermocouple in place. Thethermocouple was positioned near the center of the reactor between theback heat shield and the catalytic monoliths. The reactor contained aside port immediately downstream of the back heat shield, which servedas a sampling port. The reactor was wrapped in aluminosilicate insula-tion to minimize heat loss, although the low flow rates employedprevented the system from approaching adiabaticity.For acetic acid, the nebulizer was positioned 15 cm from the catalyst

bed because the reactor would not operate autothermally at a nebulizer

spacing of 3 cm. In the case of acetaldehyde and methyl formate, anautomotive fuel injector or a vapor saturator replaced the nebulizer tomaintain consistent fuel flow rates. For dimethyl ether, flow was main-tained with a mass flow controller at an approximately equivalent molarflow rate to 0.8mL/min for the liquid fuels. N2 andO2 entered through aside port in the reactor in these cases. Fuels were normallyg99% purity,although methyl formate was 97% purity, with methanol making up thebalance.Catalyst Preparation. Catalysts were prepared by the incipient

wetness technique and contained 5 wt % loading of noble metal on thefoam monoliths. Precursors were aqueous solutions of hexachloropla-tinic acid (H2PtCl6) for Pt catalysts and rhodium nitrate hexahydrate(Rh(NO3)3 3 6H2O) for Rh catalysts. After drying overnight, Pt catalystswere reduced under N2/H2 atmosphere at 300 �C for 6 h; Rh catalystswere calcined in air at 600 �C for 6 h.Reactor Operation. Liquid fuel flow was maintained at a constant

rate, and oxygen flow was varied to obtain different fuel carbon/O2

oxygen (C/O)molar ratios. N2 was maintained in air stoichiometry withO2. Experiments investigated in the range of 1.2eC/Oe 2.0, except forethanol over Pt, in which case autothermal operation could not besustained above C/O = 1.8.

For the experiments without O2 feed, a clamshell furnace providedthe heat necessary to obtain the same backface temperature as observedin the autothermal regime at selected C/O ratios. While the exacttemperature profile within the catalyst bed is difficult to reproducewith an external heat source, the furnace was positioned such that theupstream side of the furnace was approximately 5 cm above the frontface of the catalyst bed to mimic radiative heat transfer upstream fromthe catalyst bed. This setup was designed to provide as close a represen-tation as possible to the autothermal temperature and residence time.N2 was flowed at a rate equal to the sum of the O2 and N2 flow rates forthe autothermal experiments.Product Analysis. Products were analyzed by gas chromatography

(GC). Permanent gases were analyzed by a thermal conductivity detec-tor, while the remainder of the compounds were quantified by a flameionization detector. N2 from the reactor feed was used as an internalstandard.

Molar outflows of carbonaceous species and H2 were measured byGC and used to close material balances on C, H, and O atoms. BecauseH2O is difficult to quantify by GC, all oxygen atoms not represented bythe quantified species were assumed to exit the reactor as H2O. Thehydrogen balance was used to verify this assumption. Balances typicallyclosed to within 10%. Each data point was run in triplicate, and 95%confidence intervals were generally 5�10%.

For high-boiling fuels (ethylene glycol and acetic acid), a condenserwas positioned between the reactor and GC to avoid condensation ofunconverted fuel in GC. The temperature of the condenser was set tocondense only unconverted fuel, and a daily analysis of the condensateconfirmed the presence of only unconverted fuel and water. In thesecases, the carbon balance was closed by assuming all missing carbon tobe unconverted fuel. This assumption was also employed for all fuels inthe experiments with no O2 co-feed, because the very low conversionsmade quantification of the unconverted feed difficult. GC responsefactors were frequently verified; there were no unidentified peaks; andcarbon formation within the reactor was negligible compared to the totalamount of fuel fed. Selectivity was defined as

Si ¼vi, jFjΣjvi, jFj

; j 6¼ fuel ð1Þ

where i is carbon or hydrogen, νi,j is the number of atoms of i in moleculej, and Fj is the molar flow of species j.Experimental Parameters. Four experiments were performed

with each fuel: catalytic partial oxidation of fuels in the autothermaloperating regime for 1.2eC/Oe 2.0 over Pt and Rh catalysts provided

Figure 1. Reactor configurations for the (left) autothermal and (right)O2-free experiments.



data on overall reaction pathways, while experiments over Pt and Rhcatalysts without O2 co-feed, heated to the reactor temperature by aclamshell furnace, probed the role of O2-independent surface reactions.

’RESULTS

Conversion ranged from 30 to 90% in the autothermalexperiments for most of the species investigated, although

conversion of acetic acid was lower over Pt, ranging from 20 to30%. In the absence of O2, conversion was insignificant fortemperatures below 500 �C over Pt and below 450 �C over Rh.Conversion data are shown in Figure 2. In general, the Rh catalystgave higher conversion and produced more syngas species thanPt; Pt in turn produced more combustion species, especiallyH2O. CH4 was a minor product, and CH4 selectivity wasgenerally less than that predicted by equilibrium, especially for

Figure 2. Conversion of C2 molecules. Shaded symbols represent autothermal experiments. The point furthest to the right corresponds to C/O = 1.2,while the point furthest to the left corresponds toC/O= 2.0, except for Pt in panel a, in which case the point furthest to the left corresponds toC/O= 1.8.Solid symbols, no O2; triangles, Rh; and squares, Pt.



C/O > 1.5. However, CH4 selectivity was near equilibrium at allC/O ratios for dimethyl ether over Pt and acetaldehyde overboth catalysts. For each of the compounds investigated, theprimary equilibrium products were CO, CO2, H2, and H2O.Dimethyl ether, methyl formate, acetaldehyde, and acetic acidproduced these compounds almost exclusively, although a non-negligible amount of CH4 was produced from acetaldehyde.The primary non-equilibrium product from ethanol and ethy-lene glycol was acetaldehyde, although in the absence of O2

appreciable amounts of ethylene were also produced fromethanol. Methyl formate also produced a small amount ofmethanol. The product spectrum from each fuel is discussed inmore detail below. For conversion below 0.5%, selectivity dataare not quantitative and not shown.Acetaldehyde. Acetaldehyde conversion ranged from 40 to

90% over Pt and from 60 to 90% over Rh in the autothermalexperiments but was below 15% for both catalysts in the absenceof oxygen (Figure 2b). Selectivity to major products is shown in

Figure 3. Carbon selectivity to major products from acetaldehyde. Shaded symbols represent autothermal experiments. The point furthest to the rightcorresponds to C/O = 1.2, while the point furthest to the left corresponds to C/O = 2.0. Solid symbols, no O2; triangles, Rh; and squares, Pt.



Figure 3 and panels a and b of Figure 4. The major carbonaceousproducts over both catalysts were similar, namely, CO and CO2

in the autothermal experiments and CO and CH4 in the absenceof O2. Theminor products were also similar, namely, CH4, C2H6,C2H4, and methanol.Platinum operated over a much broader temperature range

than Rh, with the backface temperature over Pt ranging from400 �C at C/O = 2.0 to 700 �C at C/O = 1.2. The respectivetemperatures over Rh were 435 and 600 �C. The other notabledifference between the two catalysts is the higher selectivity toCO and H2O over Pt and the higher selectivity to CO2 and H2

over Rh. This difference may be attributable to the steps in thedecomposition of acetaldehyde on the different metal surfaces(Figure 10). On both surfaces, acetaldehyde likely adsorbs via theoxygen atom or the R-C and O atoms and then forms an acylη1(C) intermediate before decarbonylating.10�12 However, thenext step on Rh is believed to be C�C bond scission,10 while onPt, abstraction of β-H to form a ketenyl intermediate may becompetitive with C�C bond scission.11 The simultaneous con-tribution of the acetyl intermediate to surface H as well as surfaceCHx species on Pt may allow for more of the O2 co-feed to beconsumed by oxidizing surface H to produce more H2O andcorrespondingly less CO2.In the absence of O2, acetaldehyde conversion was much

lower, with Pt giving negligible conversion at temperatures below

600 �C (Figure 2b). CO and CH4 accounted for the majority ofproducts formed, comprising >95% of the product spectrum overPt. While competing pathways may govern acetyl dissociationover Pt, in the absence of surface oxygen, surface CHx groupsappear to have a high propensity to combine with surface H anddesorb as CH4 (Figure 10). It is also notable that the selectivityto CH4 is significantly higher than selectivity to CO, perhapsindicating that the reaction is not solely due to homogeneousdecomposition, which would generate equal selectivities to CH4

and CO. A very small amount of H2 is observed, suggesting thepresence of a small amount of surface H, which may bemethanating some CO to CH4.

13 Because CO is in large excess,it is not surprising that H2 is near its detection limit. This reactionmay also account for the non-negligible selectivity to H2O.Rhodium yielded appreciable conversion in the absence of O2

at temperatures as low as 435 �C. The Rh catalyst also displayed ahigh selectivity to CO and CH4 but with the notable productionof H2 and minor amounts of C2H4, C2H6, C3H6, ethanol, andcrotonaldehyde. Thus, it seems likely that surface CHx speciesare more active on the Rh surface than on Pt, producing surfacehydrogen atoms and combining with other adsorbed species toaccount for the observed product spectrum. COmay be relativelyunreactive under these conditions. This hypothesis is supportedby the observation that selectivity to CO in the absence of O2 isalways higher than selectivity to CH4. However, the observation

Figure 4. Hydrogen selectivity from ethanol and acetaldehyde. Shaded symbols represent autothermal experiments. The point furthest to the rightcorresponds to C/O = 1.2, while the point furthest to the left corresponds to C/O = 2.0, except for ethanol�Pt experiments, in which case the pointfurthest to the left corresponds to C/O = 1.8. Solid symbols, no O2; triangles, Rh; and squares, Pt.



of 1�2% selectivity to crotonaldehyde (a condensation productof acetaldehyde) but negligible water suggests that some steamreforming of CH4may also occur. Because CH4 would be in largeexcess, it is not surprising that water was not a final product.Ethanol. Selectivity to major products from ethanol is shown

in panels c and d of Figure 4 and Figure 5. In the autothermalexperiments, Pt selected primarily for CO, CO2, CH4, andacetaldehyde, with all other carbonaceous products representing

less than 5% selectivity. At low temperatures, acetaldehyde wasthe dominant product, approaching 70% selectivity. As tempera-ture increased, a decrease in selectivity to acetaldehyde corre-sponded to an increase in selectivity to CO and CH4 (Pearsoncorrelation coefficient R =�0.99 and�0.96, respectively), likelybecause of the decomposition of acetaldehyde, either on thecatalyst surface or homogeneously. The selectivity to H2 was alsohighly correlated to the CO, CH4, and acetaldehyde selectivities,

Figure 5. Carbon selectivity to major products from ethanol. Shaded symbols represent autothermal experiments. The point furthest to the rightcorresponds to C/O = 1.2, while the point furthest to the left corresponds to C/O = 2.0, except for the Pt experiments, in which case the point furthest tothe left corresponds to C/O = 1.8. Solid symbols, no O2; triangles, Rh; and squares, Pt.



showing a positive correlation with CO and CH4 and a negativecorrelation with acetaldehyde (R = 0.95, 0.97, and �0.97,respectively). This observation can be rationalized by consider-ing the stepwise decomposition of ethanol on the Pt surface(Figure 10). Ethanol likely adsorbs through the hydroxyl oxygenand forms an ethoxy intermediate by abstraction of the hydroxylhydrogen, subsequently forming acetaldehyde by abstraction ofan R-H atom.14 Concerted abstraction of hydroxyl and R-H isalso possible,15 although adsorbed acetaldehyde is likely theintermediate in either case. At this point, desorption of acet-aldehyde may be competitive with further reaction.16 Further-more, as discussed above, decarbonylation of this species to yieldadsorbed CH3 and CO is likely competitive with further dehy-drogenation steps.11 Abstraction of the second R-H would leadto an acyl intermediate, which may undergo β-H abstraction,followed by C�C bond scission.14 The adsorbed H atoms cancombine to form H2. C�C bond scission would yield adsorbedCO and CH2; CO likely desorbs, while CH2 may predominantlydissociate rather than combine with adsorbed H atoms to formCH4, as evidenced by the low selectivity to CH4. At the lowertemperatures observed, desorption of acetaldehyde appears todominate further reaction, yielding fewer adsorbed H atoms andC�C bond scission products, decreasing selectivity to H2, CO,and CH4. Ethanol can also dehydrogenate in the gas phase toyield acetaldehyde, which in turn can decompose in the gas phaseto yield CO and CH4.

17 However, the relatively low selectivity toCH4 suggests that gas phase dissociation of acetaldehyde is aminor pathway. The relative contribution of homogeneouschemistry is discussed in part 2 (10.1021/ef200456m).18 Pro-duction of CO2 is not significantly correlated to any of the otherproducts (R e 0.70) and, thus, may occur via a parallel channel.CO2may be formed homogeneously or on different index planesof the Pt surface at stepped or defect sites.15

In the absence of oxygen, the Pt catalyst is highly selective toacetaldehyde (Figure 5d) but, at the lower range of temperaturesobserved, is also active for dehydration reactions, producingethylene and diethyl ether (Et2O) (panels e and f of Figure 5).This phenomenon could be attributed to homogeneous chem-istry or the acidic nature of the alumina support, but theobservation that these products are not formed over a Rh�Al2O3

catalyst may indicate that Pt is involved. It is also possible that Rhis more effective in converting these intermediates; both effectsmay contribute to the observed difference between Pt and Rh. Itis noteworthy that, over Pt, selectivity is much higher to theseproducts when the conversion and temperature are low and inthe absence of oxygen. Under these conditions, Pt was found tobe active for C�Obond cleavage for methanol, leading to surfacecarbon.19 A similar reaction could lead to ethylene formationfrom ethanol. Analogously, over Pt mesh, methanol did notproduce dimethyl ether;19 the production of diethyl ether inthese experiments thus suggests that the condensation reactionmay occur at the metal�support interface. The same referencesuggested that C�O bonds remain intact over a Rh surface,precluding dehydration and condensation reactions.19

In contrast to Pt, the Rh catalyst selected less for acetaldehydebut more for CO and CH4 in the autothermal experiments(panels a and b of Figure 5). The main differences may resultfrom the mechanism by which ethanol reacts on the metalsurface. On Pt, ethanol likely reacts through an acetaldehydeintermediate, but on Rh in the absence of O2, ethanol may prefera η2 oxametallacycle through the oxygen atom and the β-carbonatom (Figure 10).16 The significance of the oxametallacycle may

be direct subsequent scission of the C�C bond, increasingselectivity to H2, CH4, and CO while reducing the selectivityto acetaldehyde.10,16 On Rh in the presence of O2, ethanol islikely converted to a surface acetate via aη2(C,O) intermediate.20

The correlations of CO, CH4, H2, H2O, and acetaldehyde in theautothermal experiments over Rh are high (RCO�X = �0.81,�0.98, 0.97, and�0.92 for X =CH4, H2, H2O, and acetaldehyde,respectively) but follow a different trend than over Pt. For Rh, asthe temperature increases, selectivity to CO and H2 increases,while selectivity to CH4, H2O, and acetaldehyde decreases(panels c and d of Figure 4 and panels a, b, and d of Figure 5).The trend can be explained by considering conversion of ethanolto η2(C,O) acetaldehyde, followed by decarbonylation of acet-aldehyde, either through an acetate intermediate or acyl decom-position on the Rh surface to yield CO and CH4.

10 ProducedCH4 can then be consumed by steam reforming, because it isknown that Rh/Al2O3 is an active catalyst for the steam reform-ing of CH4 at short contact times,21 and the steam reformingactivity of Rh was implied in the acetaldehyde experimentsas well.Interestingly, over Pt, autothermal operation could not be

obtained at C/O > 1.8, while the Rh catalyst maintained auto-thermal operation to C/O = 2.0. A similar trend was observed bySalge et al.,22 where the autothermal range of Pt was limited. Inthe overlapping range of C/O ratios explored, conversion inthese experiments was similar to those observed by Salge et al.over both catalysts,22 although selectivities were different. Selec-tivities to CH4 and C2H4 were lower in these experiments forboth Pt and Rh, while selectivity to acetaldehyde was significantlyhigher. In the range of overlap, selectivities to H2 and H2O weresimilar for Rh, while for Pt, selectivity to H2 was lower andselectivity to H2O was slightly higher in these experiments. Thedifferences may be due to the higher observed temperatures andshorter catalyst bed in the Salge experiments.Ethylene Glycol. Figure 6 shows the selectivity to major

products from ethylene glycol. The most notable features arehigher selectivity to CO and H2 (panels a and e of Figure 6) forthe Rh catalyst and higher selectivity to acetaldehyde (Figure 6d)for the Pt catalyst, especially in the absence of O2. The highselectivity to syngas from ethylene glycol over Rh has beenpreviously observed in autothermal systems5 and is believed toresult because C�O bonds do not dissociate on Rh.23 In fact, thereaction sequence proposed by Brown and Barteau23 on a Rhcatalyst generally agrees well with the product spectrum obervedhere. Ethylene glycol likely adsorbs to the metal surface via bothoxygen atoms, followed by O�H scission from both hydroxyls(Figure 10). Subsequent C�C scission may yield adsorbedformyl species, which decompose to H2 and CO, or subsequentH atom abstractions may precede C�C bond scission, ultimatelyyielding CO and H2. In the presence of O2, these species may befurther oxidized to H2O and CO2.Over the Pt catalyst, a different mechanism may be active, as

Salciccioli et al.24 found that scission of one O�H bond uponadsorption of ethylene glycol on Pt(111) was favorable but notthe other. In fact, those authors proposed that several subsequenthydrogen abstraction steps likely precede scission of the C�Cand second O�H bonds of ethylene glycol on Pt(111). The finalproducts of decomposition in that study were similar to those onRh,23 and the initial hydrogen abstractions were suspected to berate-limiting, possibly providing a rationale for why potentiallystable intermediate species, such as hydroxyacetaldehyde, werenot observed in significant quantities here.



Acetaldehyde may be formed from ethylene glycol by bothgas phase and surface mechanisms. The most intuitive routeincludes a dehydration step to produce vinyl alcohol, which canrearrange to form acetaldehyde. This pathway may be catalyzedby the acidic alumina support, although if the dehydrationoccurred primarily over the alumina support, the effect wouldbe expected for the Rh catalyst as well. Thus, this reaction mayoccur at the metal�support interface or in the gas phase, becauseacetaldehyde was not observed from ethylene glycol reactionson Pt(111).24,25 The desorption of acetaldehyde is then likely

competitive with further reaction, as seen with ethanol. It is alsopossible that Rh is more efficient in consuming the acetaldehydeintermediate, because Rh showed a somewhat higher conversionthan Pt for acetaldehyde (Figure 2b). The net observation maybe due to both effects; however, the difference in selectivitybetween the Pt and Rh catalysts suggests that the surface mayplay a role in acetaldehyde formation.The increased selectivity to CH4 in the absence of O2 over

Pt is observed mostly at high temperatures and coincides withincreased selectivity to CO (panels a and c of Figure 6). It is thus

Figure 6. Selectivity to major products from ethylene glycol. Shaded symbols represent autothermal experiments. The point furthest to the rightcorresponds to C/O = 1.2, while the point furthest to the left corresponds to C/O = 2.0. Solid symbols, no O2; triangles, Rh; and squares, Pt.



likely due to the decomposition of acetaldehyde, perhaps in thegas phase after desorbing from the Pt surface. The lower CH4

selectivity from the Rh catalyst, which also produced lessacetaldehyde, corroborates this hypothesis. While the Pt surfaceappears to be particularly efficient at dissociating surface methylgroups in the autothermal experiments (as evidenced by theconsistently low selectivity to CH4 in those experiments), thelack of surface oxygen in the O2-free experiments may allowfor CH4 to form on the surface as well. It is therefore difficultto discern the relative contributions of surface and gas phasedecomposition of acetaldehyde in the absence of oxygen,although results from part 2 (10.1021/ef200456m) suggest thathomogeneous chemistry of acetaldehyde in the absence of O2

may be minor.18 Selectivity to CH4 slightly lags selectivity to COas the temperature increases, but it is difficult to interpret thisphenomenon as an effect of surface decomposition of acetalde-hyde followed by further reaction of the methyl group or simplythat, at higher temperatures, there is sufficient energy to sever theC�C bond of ethylene glycol in a Pt-catalyzed complex.It is interesting to note that the production of CO from

ethylene glycol on both surfaces (Pt around 525 �C and Rh at<380 �C; Figure 6a) is consistent with the observation by ZumMallen and Schmidt19 for the formation of CO from methanolover these surfaces, lending support to the formyl intermediateproposed in that work.Acetic Acid. Acetic acid displayed very different activities over

the Pt and Rh catalysts, as shown in Figure 7. Conversion over Ptin the autothermal regime ranged from 20 to 30% (Figure 2d);O2 breakthrough was observed; and the only products observedwere CO2, H2O, and acetone. Because of the low conversion andoxygen breakthrough, the production of only combustion speciesis not unexpected, because adsorbed oxygen necessarily persistedthroughout the catalyst bed, fully oxidizing any adsorbed species.The low reactivity may be due to the configuration of theadsorbed acetate intermediate, which may position β-C awayfrom the surface (Figure 10), requiring an active gas-phasespecies for further reaction (i.e., an Eley�Rideal-type mechan-ism). Interestingly, the low reactivity was not observed for largercarboxylic acids in an autothermal system,26 possibly because ofthe larger number of reactive configurations of the larger mole-cules in the gas phase and on the surface. That is, for C3 and largersurface carboxylates, the third carbon is not necessarily posi-tioned perpendicular to the surface andmay havemore rotationalfreedom with which to find an active surface site, facilitatinghigher conversion. The difference in conversion between aceticacid and higher carboxylic acids suggests that the proximity ofa carbon atom to the surface in the initial adsorbed configurationof the feed molecule may play a role in further reaction of themolecule.Ultimately, however, the cause of the low reactivity of acetic

acid on Pt is not yet well-understood for autothermal systems,although other researchers have noted the stability of surfaceacetates on Pt15,14 and the difficulty of oxidizing acetic acid oversupported Pt catalysts, although at lower temperatures thanthose observed here.27,28 Some researchers have observed carbonformation from decomposition of acetic acid on Pt,29,30 but thepersistence of oxygen throughout the catalyst bed should effec-tively inhibit surface carbon formation.In the absence of O2, conversion was negligible for both

catalysts below 400 �C, which is consistent with steam-reformingexperiments of acetic acid.31 At higher temperatures, acetone,CO2, and H2O were the major species, with CO and H2 also

present. The selectivity of the three major products is consistentwith an oxide-catalyzed bimolecular reaction (eq 2), likely fromthe alumina support.32,33

2CH3COOH f ðCH3Þ2COþ CO2 þH2O ð2Þ

The minor selectivities to CO and H2 are consistent with amechanism proposed by Gao et al.,34 in which acetic acid adsorbsvia both oxygens in a bidentate configuration and decomposesto surface H, C, O, and CO. These surface adsorbates can thenrecombine to give the observed CO, CO2, H2, and H2O.The Rh catalyst gave much higher conversion in the auto-

thermal experiments and operated at a higher temperature. Nooxygen breakthrough was observed, and conversion approached70% as the temperature increased (Figure 2d). The majorproducts were still CO2 and H2O, although selectivity to H2

and CO was also significant. As the temperature increases, selec-tivity to CO and H2 increases, while selectivity to CO2 and H2Odecreases, consistent with an increase in reforming activity athigher temperatures.In the absence of oxygen, the Rh catalyst selected mainly for

acetone, CO2, and H2O (panels c, d, and f of Figure 7) but alsoa non-negligible amount of CO, CH4, and H2. Similar to thePt/Al2O3 system, the former three products were likely producedby the alumina support. Selectivity to CO andH2O is comparablefor the two systems, but selectivity to acetone is lower over Rh,suggesting that some of the observed CO, CH4, and H2 may befrom further reaction of the acetone. However, the selectivities tothese three products are not significantly correlated to theselectivites to acetone, CO2, and H2O, suggesting that a secondpathway may also exist. The Rh surface may be active for thedecomposition of acetic acid to produce CO2 and CHx species,the latter of which could combine with a surface H atom anddesorb as CH4 (Figure 10). If hydrogenation of CHx species isconsidered to occur under these reaction conditions, a mecha-nism proposed by Houtman et al.20 is consistent with theobserved product spectrum. In this scenario, acetic acid wouldadsorb to the surface initially via the acidic oxygen. Subsequentabstraction of the acidic hydrogen would yield an adsorbedacetate; subsequent abstraction of a β-H atom and C�C bondcleavage would yield adsorbed CO2, CHx, and H species. In thepresence of oxygen, abstracted H atoms form surface hydroxylsand can be oxidized to H2O.Methyl Formate.Methyl formate was the most reactive of the

model compounds investigated; conversion was essentially com-plete for C/O e 1.5 for the Pt catalyst and at all C/O ratios forthe Rh catalyst. Selectivity to major products is shown inFigure 8.The major carbonaceous products for both catalysts in the

autothermal experiments were CO and CO2, with small amountsof CH4 andmethanol. Over Pt, selectivities to CO2 andmethanoldecrease as the temperature increases, corresponding to anincrease in CO selectivity. Because these three species accountedfor >99% of the observed products at all C/O ratios, the trendscan likely be explained by the following scheme. Methyl formatemay decompose in the gas phase to produce CO and methanol35

or on the surface (discussed below) to yield adsorbedH, CO, andmethoxy species. As the temperature increases, more of themethanol likely reacts further, producing primarily CO and likelysome CO2 as well. The seemingly counterintuitive trend ofdecreasing selectivity to CO2 as the temperature (and O2 feed)increases can possibly be attributed to reverse water�gas shift



(WGS) activity. The relative amounts of species are not nearthose predicted by WGS equilibrium, but the change in selec-tivity for the respective species is closely mirrored by the changeexpected from the WGS reaction equilibrium.In contrast, the Rh catalyst follows the same trend for

methanol selectivity but with selectivity to CO slightly decreasingand selectivity to CO2 slightly increasing with the temperature(panels a, c, and d of Figure 8). Similar to the Pt catalyst, the Rhcatalyst produces lower selectivity to H2 and correspondingly

higher selectivity to H2O as the temperature increases (panels eand f of Figure 8). One possible explanation can be found in therelative reforming activities of Pt and Rh over the observedtemperature range. In these systems, selectivity to CO2 isexpected to pass through a minimum as O2 feed varies becauseof the interplay of reforming and combustion. This minimumcorresponds to a maximum in reforming activity, as discussed inthe following. Selectivity to CO2 increases as O2 feed increasesbecause of increased combustion; reforming becomes less

Figure 7. Carbon selectivity to major products from acetic acid. Shaded symbols represent autothermal experiments. The point furthest to the rightcorresponds to C/O = 1.2, while the point furthest to the left corresponds to C/O = 2.0. Solid symbols, no O2; triangles, Rh; and squares, Pt.



prominent because of increased oxidation of all intermediateproducts. Selectivity to CO2 also increases as O2 feed decreasesbecause less heat is generated to drive endothermic reformingreactions. It is also well-established that Rh is a more activereforming catalyst than Pt,36,37 which in this system would yield aminimum in CO2 selectivity at a lower temperature over Rh thanPt. Thus, the continual decrease in selectivity to CO2 over Ptas the temperature and O2 feed increase may indicate that, atC/O = 1.2, selectivity to CO2 has not yet reached a minimum or,

conversely, that the reforming activity of Pt has not yet reached amaximum. The O2 feedmay thus preferentially formH2O, whichwould decrease selectivity to H2.Although surface science studies of methyl formate on Pt and

Rh are sparse in the literature, some insight may be gainedby considering the surface reactions of methyl formate onother transition-metal surfaces. Methyl formate adsorbs via thecarbonyl carbon/oxygen on Ni(111), producing adsorbed meth-oxy, CO, and H groups, yielding eventually CO and H2.

38 On

Figure 8. Carbon selectivity to major products from methyl formate. Shaded symbols represent autothermal experiments. The point furthest to theright corresponds to C/O = 1.2, while the point furthest to the left corresponds to C/O = 2.0. Solid symbols, no O2; triangles, Rh; and squares, Pt.



Ag(111), methyl formate adsorbs via carbonyl oxygen andmethyl carbon but does not dissociate.39 On oxygen-dosedAg(110), methyl formate also adsorbs via the carbonyl oxygenbut produces instead adsorbed methoxy and formate species,ultimately yielding CO2 and H2.

40 The high selectivity to CO forboth Pt and Rh suggests that adsorption through the carbonylcarbon/oxygen is preferred for both catalysts (Figure 10).Scission of the formyl H and subsequent C�O cleavage wouldgive adsorbed H, CO, and OCH3 species. The high conversionsuggests that transformation of η1(O) to η2(C,O) and subse-quent C�Oe cleavage may be fast, where Oe is the oxygen boundto both carbon atoms and C is the carbonyl carbon. The surfacemechanism from this point would likely be similar to the partialoxidation of methanol on Pt and Rh, which was described indetail by Zum Mallen and Schmidt.19

In the absence of O2, selectivity to CO2 is nearly negligible,while selectivity to methanol is significantly increased. It isimportant to recall that the feed contained around 3% methanol,which was accounted for in calculating conversion and selectiv-ities from methyl formate. However, because of this additive, aconversion ofe3.5% was considered negligible (a cutoff of 0.5%conversion was used for the other fuels). Over Pt, selectivities toCO and methanol are approximately 1:1 and account for 90% ormore of the product carbon (panels a and d of Figure 8),demonstrating the likely predominance of the C�Oe bondscission pathway. Over Rh, selectivity to CO was higher andselectivity to methanol was lower, indicating the higher activity ofRh for decomposition of methanol ormethoxy groups to CO andH2. The other carbonaceous species observed in the absence ofO2 include CH4 (<1% over Pt and <2% over Rh), CO2 (<2%over Pt and <4% over Rh), and dimethyl ether (not shown; <5%over Pt and <2% over Rh). CH4 and CO2 can likely be explainedby a small amount of bond scission between methyl carbon andbridging oxygen, while dimethyl ether may be formed homo-geneously, over the alumina support or at the metal�supportinterface.In a previous study of esters in an autothermal system, signi-

ficant homogeneous chemistry was observed.26 The relative rolesof surface and homogeneous pathways of methyl formate arediscussed in part 2 (10.1021/ef200456m).18 We note here thatthe reduced homogeneous chemistry may be due in part to therelative size of the methyl formate molecule. Whereas largeresters are able to form stable intramolecular cycles,26 cyclic tran-sition states of the methyl formate molecule would be consider-ably more strained and, thus, may lead to reduced homogeneousconversion, as least after O2 is consumed.Dimethyl Ether. Dimethyl ether exhibited the widest span of

conversion, ranging from 90% at C/O = 1.2 to 30% at C/O = 2.0in the autothermal experiments (Figure 2f). Conversion wasalways under 2% in the absence of oxygen. The major carbon-containing products were CO, CH4, and CO2 in the autothermalexperiments, while in the absence of O2, CH4 became prominent.Propane and isobutene were also detected in appreciable quan-tities in the absence of O2, but these were impurities in the feed. Itcannot be ruled out, however, that they were in fact reactionproducts, because some metal oxides are known to produce arange of hydrocarbons from dimethyl ether.41,42 Oxidation ofdimethyl ether on Al2O3-supported Pt and Rh also producedsmall amounts of these hydrocarbons,43 although after account-ing for the quantity of impurity, selectivities to propane andisobutene were found to be negligible in this system. Selectivityto major products is shown in Figure 9.

Surface science studies of dimethyl ether on Pt are rare, largelybecause of the fact that it desorbs molecularly from Pt(111) atless than 100 K.44 However, a recent study showed that adsorp-tion occurs initially via the oxygen atom with an accompanyinginteraction of one methyl group at an adjacent site, in both thepresence and absence of surface oxygen (Figure 10).45 Abstrac-tion of a hydrogen atom by surface oxygen was found to berate-limiting in that study, and the resulting η2 conformation waspreviously predicted on the basis of the adsorption and reactionof similar molecules.44 In the absence of oxygen, conversion wasnegligible for all temperatures explored below 619 �C, whileCH4, CO, andH2Owere the major products at that temperature.CH4 and CO are predicted pyrolysis products of dimethylether,46 although H2O is not predicted to form from dimethylether in the absence of oxygen either in the gas phase or on the Ptsurface. Thus, H2O may be formed over the support or at themetal�support interface. It is worth noting that the dimethylether decomposition pathway over Pt implied by Rendulic andSexton44 is consistent with the concomitant production of COand H2 as the temperature increases; the apparently high selec-tivity to CH4 may be due to reactions resulting in undetectedformaldehyde, as discussed in part 2 (10.1021/ef200456m).18

On the Rh surface, two distinct decomposition pathways havebeen found, depending upon the availability of surface oxygen.47

In both cases, initial adsorption likely occurs through the oxygenatom. In the presence of surface oxygen, cleavage of one C�Obond may lead only to the formation of adsorbed methoxyspecies, which can then further decompose to CO, CO2, H2,and H2O.

47 The relative amounts of each likely depend uponthe availability of surface oxygen. In the absence of oxygen,dehydrogenation steps are believed to occur after the initialadsorption to produce an adsorbed CHxOCHx species, whichdecomposes to CO, H2, and surface carbon.47 This mechanismgenerally agrees well with the observed product spectrum,although the non-negligible selectivity to CH4 (Figure 9b),especially in the absence of O2, suggests that either some surfaceCHx species may be hydrogenated as well or homogeneouschemistry contributed significantly to the product spectrumunder these conditions. The increase in selectivity to CO andH2 and the decrease in selectivity to CH4, C2H6, and H2O as thetemperature approaches 550 �C suggests that reforming of thehydrocarbon products is also significant over this catalyst.

’DISCUSSION

Trends with Functional Groups. The trends observed acrossfunctional groups appear to be more geometric than thermo-dynamic, at least under fuel-rich conditions. That is, all of thefeedstocks investigated adsorb to the surface via at least oneelectronegative oxygen atom. However, molecules with a pre-ferred η2 adsorption configuration in which at least one carbonatom is near the surface tend to be more reactive than those thatadsorb only in a η1 configuration. From the η1 configuration,desorption of intact or minimally decomposed feed molecules islikely competitive with further reaction. Thus, methyl formate,which may adsorb essentially η2 via carbonyl C and O over bothcatalysts, and ethanol, which likely forms an oxametallacycle overRh, both displayed high conversion, while ethylene glycol andacetic acid, which both adsorb via two oxygen atoms, dimethylether, which initially adsorbs via its lone oxygen atom, andacetaldehyde over Pt, which initially adsorbs only via carbonyloxygen, had relatively low conversion. This trend is apparent at



high C/O ratios (low temperatures), while at low C/O ratios(high temperatures) sufficient thermal energy is likely availablefor feed molecule activation, regardless of adsorption geometry.Homogeneous reactions also likely contribute significantly to themeasured conversion at low C/O ratios.Additionally, the relative activities of Pt and Rh in C�C bond

scission may explain the higher activity of Rh for these fuels.Rhodium appears to form a Rh�C bond early in the reactionsequence (e.g., η2 adsorption of acetaldehyde and formation of

an oxometallacycle from ethanol), which may enhance C�Cbond scission relative to desorption. Rhodium also appears to bemore active for C�C bond scission, as evidenced by preferentialcleavage of that bond over dehydrogenation reactions in thesurface science literature.Proposed Mechanisms. A proposed reaction mechanism for

each feed molecule over Pt and Rh catalysts in the presence andabsence of O2 is shown in Figure 10. The proposed mechanismsare rationalized primarily from surface science studies in the

Figure 9. Carbon selectivity to major products from dimethyl ether. Shaded symbols represent autothermal experiments. The point furthest to the rightcorresponds to C/O = 1.2, while the point furthest to the left corresponds to C/O = 2.0. Solid symbols, no O2; triangles, Rh; and squares, Pt.



Figure 10. Proposed surface mechanisms of C2 molecules in an autothermal reactor. (O)H denotes that, in the presence of surface oxygen, surfacehydroxyl formation is favored, while in the absence of surface oxygen, surface hydrogen is formed. References for these proposed mechanisms are in themain text. For clarity, pathways that are believed to be homogeneous or require the ceramic support (e.g., acetaldehyde from ethylene glycol and ethylenefrom ethanol) are not included.



literature, which are largely consistent with the product spectrumobserved here. Products observed here but not in surface sciencestudies are generally those observed in reactions of thesemolecules in the gas phase. For brevity, those products areomitted here and discussion on their formation is relegated topart 2 (10.1021/ef200456m).18

’CONCLUSION

The Rh catalyst gave higher conversion than the Pt catalyst forall of the investigated C2 feedstocks. The Pt catalyst showedlower activity for oxygenate reforming, but evidence of this trendwas only found for some of the fuels. In general, conversion in theabsence of O2 is negligible below about 500 �C for Pt and below450 �C for Rh.

Acetaldehyde appears to be a common intermediate in thedecomposition of ethanol and ethylene glycol over Pt�Al2O3,while surface acetates are a likely intermediate in the decom-position of acetic acid and acetaldehyde over Rh. Surface formylspecies are implied for ethylene glycol and methyl formate. Thereactivity of the model compounds appears to be a function ofsurface adsorption geometry, which is governed by functionalgroups. The ability to adsorb a carbon atom significantly en-hances conversion. The trend accounts for the higher reactivityof ethanol and methyl formate and the lower reactivity of aceticacid, ethylene glycol, and dimethyl ether. It may also explain whyRh is more active than Pt, because surface mechanisms aredifferent over these two catalysts, often establishing a C�Rhbond early in the reaction process. A reaction scheme for thevarious functional groups over Pt and Rh catalysts in an auto-thermal system is proposed.

’AUTHOR INFORMATION

Corresponding Author*E-mail: [email protected].

’ACKNOWLEDGMENT

Funding for this research was provided by the NationalRenewable Energy Laboratory (NREL) and the United StatesDepartment of Energy (DOE).

’REFERENCES

(1) Wright, L.; Boundy, B.; Perlack, B.; Davis, S.; Saulsbury, B.Biomass Energy Data Book; U.S. Department of Energy Publications:Washington, D.C., 2006.(2) Poothakham, T.; Kumar, A. Bioresour. Technol. 2010, 101,

414–421.(3) Huber, G.; Iborra, S.; Corma, A. Chem. Rev. 2006, 106, 4044–

4098.(4) Oasmaa, A.; Czernik, S. Energy Fuels 1999, 13, 914–921.(5) Dauenhauer, P.; Salge, J.; Schmidt, L. J. Catal. 2006, 244,

238–247.(6) Rennard, D.; Kruger, J.; Schmidt, L.ChemSusChem 2009, 89–98.(7) Salge, J.; Dreyer, B.; Dauenhauer, P.; Schmidt, L. Science 2006,

314, 801–804.(8) Rennard, D.; French, R.; Czernik, S.; Josphson, T.; Schmidt, L.

Int. J. Hydrogen Energy 2010, 35, 4048–4059.(9) Bridgwater, A.; Czernik, S.; Diebold, J.; Meier, D.; Oasmaa, A.;

Peacocke, C.; Piskorz, J.; Radlein, D. Fast Pyrolysis of Biomass: AHandbook; CPL Press: Speen, U.K., 2008.(10) Houtman, C.; Barteau, M. J. Catal. 1991, 528–546.

(11) Vesselli, E.; Coslovich, G.; Comelli, G.; Rosei, R. J. Phys.:Condens. Matter 2005, 6139–6148.

(12) McCabe, R.; DiMaggio, C.; Madix, R. J. Phys. Chem. 1985,854–861.

(13) Chakrabarty, D.; Rao, K. M.; Sundararaman, N.; Chandavar, K.Appl. Catal. 1986, 69–79.

(14) Gursahani, K.; Alcal�a, R.; Cortright, R.; Dumesic, J. Appl. Catal.,A 2001, 222, 369–392.

(15) Wang, H.-F.; Liu, Z.-P. J. Am. Chem. Soc. 2008, 10996–11004.(16) Mavrikakis, M.; Barteau, M. J. Mol. Catal. A: Chem. 1998,

135–147.(17) Laidler, K.; Liu, M. Proc. R. Soc. London, Ser. A 1966, 365–375.(18) Kruger, J.; Rennard, D.; Josephson, T.; Schmidt, L. Energy Fuels

201110.1021/ef200456m.(19) Zum Mallen, M.; Schmidt, L. J. Catal. 1996, 230–246.(20) Houtman, C.; Brown, N.; Barteau, M. J. Catal. 1994, 145,

37–53.(21) Venkataraman, K.; Wanat, E.; Schmidt, L. AIChE J. 2003,

1277–1284.(22) Salge, J.; Deluga, G.; Schmidt, L. J. Catal. 2005, 235, 69–78.(23) Brown, N.; Barteau, M. J. Phys. Chem. 1994, 12737–12745.(24) Salciccioli, M.; Yu, W.; Barteau, M. A.; Chen, J. G.; Vlachos,

D. G. J. Am. Chem. Soc. 2011, 133, 7996–8004.(25) Skoplyak, O.; Menning, C.; Barteau, M.; Chen, J. Top. Catal.

2008, 51, 49–59.(26) Rennard, D.; Dauenhauer, P.; Tupy, S.; Schmidt, L. Energy Fuels

2008, 22, 1315–1327.(27) Masende, Z.; Kuster, B.; Ptasinski, K.; Janssen, F.; Katima, J.;

Schouten, J. Top. Catal. 2005, 87–99.(28) Mikulov�a, J.; Barbier, J., Sr.; Rossignol, S.;Mesnard, D.; Duprez,

D.; Kappenstein, C. J. Catal. 2007, 172–181.(29) Takanabe, K.; Aika, K.-I.; Seshan, K.; Lefferts, L. J. Catal.

2004, 101–108.(30) Vajo, J.; Sun, Y.-K.; Weinberg, W. Appl. Surf. Sci. 1987,

165–178.(31) Wang, D.; Montan�e, D.; Chornet, E. Appl. Catal., A 1996,

245–270.(32) Pestman, R.; Koster, R.; van Duijne, A.; Pieterse, J.; Ponec, V.

J. Catal. 1997, 265–272.(33) Gl�inski, M.; Kijen’ski, J.; Jakubowski, A. Appl. Catal., A 1995,

209–217.(34) Gao, Q.; Hemminger, J. J. Electron Spectrosc. Relat. Phenom.

1990, 54/55, 667–676.(35) Francisco, J. J. Am. Chem. Soc. 2003, 10475–10480.(36) Jones, G.; Jakobsen, J.; Shim, S.; Kleis, J.; Andersson, M.;

Rossmeisl, J.; Abild-Pedersen, F.; Bligaard, T.; Helvig, S.; Hinneman,B.; Rostrup-Nielsen, J.; Chorkendorff, I.; Sehested, J.; Nørskov, J.J. Catal. 2008, 259, 147–160.

(37) J. Barbier, J.; Duprez, D. Appl. Catal., B 1993, 3, 61–83.(38) Zahidi, E.; Castonguay, M.; McBreen, P. J. Am. Chem. Soc.

1994, 5847–5856.(39) Schwaner, A.; Fieberg, J.; White, J. J. Phys. Chem. B 1997, 101,

11112–11118.(40) Barteau, M.; Bowker, M.; Madix, R. Surf. Sci. 1980, 303–322.(41) Hargis, D.; Kehoe, L. Conversion of methanol and dimethyl

ether to C2 to C6 monoolefins using a partially hydrated zirconiumsulfate catalyst. U.S. Patent 4,072,732, 1978; http://www.freepatentson-line.com/4072732.html (accessed on Oct 15, 2010).

(42) Hutchings, G.; Hunter, R.; van Rensburg, L. J. Appl. Catal.1988, 41, 253–259.

(43) Solymosi, F.; Cser�eni, J.; Ov�ari, L. Catal. Lett. 1997, 44, 89–93.(44) Rendulic, K.; Sexton, B. J. Catal. 1982, 78, 126–135.(45) Ishikawa, A.; Neurock, M.; Iglesia, E. J. Am. Chem. Soc. 2007,

129, 13201–13212.(46) Aronowitz, D.; Naegeli, D. Int. J. Chem. Kinet. 1977, 9, 471–479.(47) Bugyi, L.; Solymosi, F. Surf. Sci. 1997, 385, 365–375.

Documents

Effect of Functional Groups on Autothermal Partial ... · balance. Catalyst Preparation ... GC and used to close material balances on C, H, andO atoms. ... acetaldehyde, and acetic