Characterization and catalytic activity of CoMo HDS catalysts supported on alumina-MCM-41

Applied Catalysis A: General 197 (2000) 69–78

Characterization and catalytic activity of CoMo HDScatalysts supported on alumina-MCM-41

Jorge Ramıreza,∗, Roberto Contrerasa, Perla Castilloa, Tatiana Klimovaa,René Zárateb, Rosario Lunab

a UNICAT, Departamento de Ingenierıa Quımica, Facultad de Quımica, UNAM, Cd Universitaria, México D.F. 04510, Mexicob Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas No. 152, México D.F. 07730, Mexico

Abstract

A series of CoMo HDS catalysts supported on alumina with different amounts of aluminum-modified MCM-41 wasprepared, characterized by different techniques (SBET, NH3-TPD, TPR, UV–VIS-DRS, HREM and NO adsorption analyzedby FTIR) and tested in the dibenzothiophene hydrodesulfurization reaction. The results show that the incorporation of MCM-41to the catalyst formulation leads to higher catalytic activity. The TPR results indicate a diminished interaction of the Co and Mophases with the support, compared to those existing in the alumina-supported catalyst. This decrease in the interaction causesthe formation of greater amounts of polymeric Mo species and a decrease in the population of tetrahedral Co as CoAl2O4,as evidenced by the DRS results. The changes in the intensity and position of the NO adsorption IR bands indicate that aninteraction between Co and Mo exists and that not all the Co present in the catalysts is completely sulfided, and therefore,may not contribute to the formation of the catalytically active Co–Mo–S mixed phase. © 2000 Elsevier Science B.V. All rightsreserved.

Keywords:CoMo catalysts; Hydrodesulfurization; MCM-41; Characterization; DBT Catalytic activity

1. Introduction

The need of new hydrotreating catalysts to promotehigh hydrodesulfurization rates in intermediate andheavy petroleum distillates has prompted the researchon new acidic HDS catalytic supports with high sur-face area and wide pore diameters. Among the newmaterials with interesting textural and acid propertiesfor this purpose, the new ordered mesoporous materi-als of the MCM-41 type represent an interesting op-tion. These materials, recently discovered by Mobil

∗ Corresponding author. Tel:.+52-5-622-5366;fax: +52-5-622-5366.E-mail address:[email protected] (J. Ramırez)

researchers [1,2], are basically solids made of SiO4tetrahedra in which Al or other metal [3,4] substitutessome of the Si atoms. These solids can have surfaceareas close to 1000 m2/g and they consist of an or-dered hexagonal array of pores with amorphous walls[5]. The size of the pores in these materials can bevaried, according to the synthesis procedure, between20 and 100 Å. They also have mild surface acidity [6].These materials have been already tested for mild hy-drocracking [7,8], aromatic hydrogenation when im-pregnated with platinum [9] and as components forfine chemistry catalysts [10–17]. Because of their largesurface areas, wide diameter pores and medium sur-face acidity, these materials present an interesting op-tion as catalytic supports for hydrotreating catalysts

0926-860X/00/$ – see front matter © 2000 Elsevier Science B.V. All rights reserved.PII: S0926-860X(99)00534-7

70 J. Ramırez et al. / Applied Catalysis A: General 197 (2000) 69–78

[18–20]. Since pure MCM-41 type materials have poormechanical properties for its application in industrialHDS catalysts, it is necessary to incorporate them intoa matrix, which will provide the desired mechanicalproperties. In this respect, alumina seems like a goodmatrix material for HDS catalysts. However, the in-corporation of MCM-41 into an alumina matrix willalter not only the textural properties but also, in part,the chemical surface properties of the whole support.For its use as HDS catalytic support, it should be in-teresting to test if it is possible to disperse and sul-fide adequately the molybdenum and cobalt phasesand if greater catalytic activities than those of purealumina-supported catalysts are obtained.

The object of the present work is to study in moredetail the characteristics of CoMo HDS catalysts sup-ported on MCM-41, with a Si/Al ratio of 100, incor-porated into an alumina matrix. To this end, a series ofCoMo catalysts supported on alumina-MCM-41withamounts of MCM-41 from 0 to 70 wt.%, wereprepared and characterized by various techniques(SBET, NH3-TPD, TPR, UV–VIS-DRS, HREM andNO adsorption analyzed by FTIR) and tested inthe dibenzothiophene (DBT) hydrodesulfurizationreaction.

2. Experimental

The MCM-41 was prepared with a SiO2/Al2O3 ratioof 100, according to the method reported before [21].The alumina matrix was made from pseudo-boehmite(Catapal B). The mixture MCM-41-boehmite wasprepared using as binder a gel prepared at roomtemperature with bohemite and nitric acid. The re-sulting paste was made into cylindrical extrudates(1.51 mm diameter, 2.62 mm length) and was subse-quently dried in static air (373 K, 2 h) and air-calcined(773 K, 5 h). The Al2O3-MCM-41 supports, calledhereafter Al-MCM(x), wherex is the weight percentof MCM-41 in the support, were then simultaneouslyimpregnated by the pore volume method, with anaqueous solution containing the proper amounts ofammonium heptamolybdate, and cobalt carbonate toobtain catalysts with 10.5 wt.% MoO3 and 2.35 wt.%CoO. The catalysts were then air-dried (393 K, 2 h)and calcined (723 K, 5 h). Hereafter, the catalysts willbe referred as CoMo/Al-MCM(x).

The textural properties of the catalysts were de-termined in a Micromeritics ASAP 2000 automatednitrogen physisorption apparatus. The isoelectricpoint was measured in a Zeta-meter 3.0+apparatususing 50 mg of solid sample and 5 ml of LiCl 0.1 Min 500 ml of de-mineralized water. The pH of thedispersion was adjusted with HCl or LiOH solutions(0.01 M). The UV–VIS-DRS spectra were taken ina Cary |5E| NIR spectrophotometer. The IR experi-ments using NO as probe molecule were performedin a Nicolet 510-model FTIR spectrometer with a res-olution of 4 cm−1 and 500 scans. The sample waferwas placed in a high vacuum glass cell with CaF2windows connected to a gas manipulation manifold.The wafers of the oxidic powders were sulfided inthe glass cell at atmospheric pressure using a streamof H2/H2S 15% (v/v) for 4 h at 673 K. The acti-vated sample was pretreated in a vacuum system(10−6 Torr) at high temperature (723 K) for 2 h. A firstIR spectrum was taken at this time. Then, a 40 TorrNO pulse was allowed to enter the cell and a newspectrum was taken. A third IR analysis was madeto the sample after evacuating the NO gas out of thecell. Temperature-programmed ammonia desorption(TPD) experiments were carried out in an automatedISRI-RIG-100 characterization system equipped witha TC detector. In order to remove water and othercontaminants, the samples (50 mg in all cases) werepretreated successively in air and helium flow (773 K,1 h each time) before ammonia adsorption. The sam-ples were then cooled to room temperature and con-tacted with a He/NH3mixture (90/10 v/v) at a flowrate of 30 ml/min for 1 h. The desorption step wasperformed in helium (20 ml/min), with a heating rateof 5 K/min−1. After reaching 773 K the sample wasmaintained at this temperature until the signal reachedthe base line. The temperature-programmed reduc-tion (TPR) of the samples was performed in an ISRIRIG-100 automated characterization system, equippedwith a thermal conductivity cell. The pretreatment ofthe samples (125 mg in all cases) consisted of in situcalcination at 773 K under air flow (20 ml/min, 2 h).The cooling of the samples took place in an Argonstream. The reduction step was performed with anAr/H2 mixture (30/70 v/v, 25 ml/min), with a heatingrate of 10 K/min. After reaching 1273 K the samplewas maintained at this temperature until the tracereached the base line. The HREM micrographs were

J. Ramırez et al. / Applied Catalysis A: General 197 (2000) 69–78 71

obtained in a Jeol 2010 microscope with 1.9 Å pointto point resolution.

The dibenzothiophene (DBT) catalytic activitytests were performed in an automated high pres-sure ISRI RIG-100-HP micro-reaction equipmentoperating at 573 K, 400 psi, WHSV=9.0 h−1, a ra-tio H2/HC=6.3 mol/mol, and a flow of hydrogen of104 ml/min. Prior to the catalytic test the catalystswere sulfided at 573 K and 400 psi for 4 h, using amixture of 3 mol% CS2 in cyclohexane as liquid feedand a hydrogen flow of 104 ml/h.

3. Results and discussion

3.1. Textural characterization

Table 1 presents the textural characterization resultsof the catalysts and some supports used in this study.The incorporation of the MCM-41 into the aluminamatrix produced a surface area decrease, due to theblockage of some of the MCM-41 pores. For instance,the support sample with 70 wt.% MCM-41, which ac-cording to the surface areas of the pure componentsshould have a surface area of 616 m2/g, presented anexperimental value of 545 m2/g. Therefore, about 12%of the surface area was lost during the preparation ofthe composite Al-MCM(70) support. The incorpora-tion of the metals, Mo and Co, to this support pro-duced a surface area decrease to 385 m2/g, meaningthat about 29% of the composite support surface wasblocked by the impregnation of the metals. However,the surface area of the catalysts increased linearly withthe MCM-41 content in the support.

The observed decrease in surface area indicates that,at the conditions of impregnation, the Mo and Co metalsalts are not adequately dispersed. This lack of disper-

Table 1Textural characterization of CoMo/Al-MCM(x) catalysts and some supports

Sample Surface area (m2/g) Pore volume (cm3/g) Average pore diameter (Å)

MCM-41 789 0.99 35.8Al-MCM(70) 545 0.68 40.2CoMo/Al-MCM(0) 167 0.39 64.6CoMo/Al-MCM(30) 254 0.38 50.0CoMo/Al-MCM(50) 323 0.43 44.5CoMo/Al-MCM(70) 385 0.47 42.9

Fig. 1. Zeta potential of MCM-41 as a function of pH. The dottedline indicates the isoelectric point.

sion, which under calcination causes the partial block-age of the MCM-41 pores may be due to the fact that,as Fig. 1 shows, the isoelectric point of the MCM-41(pH=2.3) is below the pH of the impregnating solu-tion (pH=5.5). Under this condition, the surface ofthe MCM-41 is negatively charged, and therefore, themolybdate anions do not readily adsorb on the surfacecausing some agglomeration of the Mo phases. Thisresult is in line with the behavior of pure silica sup-ports, on which the molybdenum ions cannot be welldispersed.

3.2. Surface acidity

The results from surface acidity measurements byNH3-TPD in the catalysts show that the general shapeof the TPD traces of the Al-MCM(x)-supported cata-lysts are very similar to those supported on pure alu-mina (Fig. 2). They also indicate that the total amountof acid sites (Fig. 3) increases slightly with MCM-41


Fig. 2. Ammonia TPD thermograms of CoMo/Al-MCM(x) cata-lysts. Isothermal period (773 K), after the axis break.

Fig. 3. Total amount and density of acid sites versus MCM-41content in CoMo/Al-MCM(x) catalysts.

content. However, the density of acid sites, also shownin Fig. 3, decreases with MCM-41 loading. Clearly,if the total acidity does not vary very much and thesurface area increases significantly the acid site den-sity must decrease. This means that the MCM-41 hasa low density of acid sites compared to alumina andso, the total number of acid sites increases in theAl-MCM( x)-containing formulations is only due to itslarge specific surface area. In fact the results indicatethat the density of acid sites in MCM-41 is about halfof those in pure alumina.

The quantitative evaluation of weak (373–473 K),medium (473–573 K), and strong (573–773 K) acidsites is presented in Table 2. According to these results,the incorporation of MCM-41 into the alumina matrixleads to an increase in the number of medium and weakacid sites, and a decrease in the strong ones. This resultis well in line with previous results, which indicatethat MCM-41 has medium strength acid sites [6].

3.3. Temperature programmed reduction

In order to envision the type and reducibility of theCo and Mo species present in the catalysts precur-sors, TPR experiments were performed with all thecatalyst samples in their oxide form. Fig. 4 shows theTPR patterns. For the pure alumina-supported cata-lyst, a TPR trace typical of a CoMo/Al2O3 catalystis obtained. It presents two main reduction peaks,assigned to the reduction of octahedral Mo species(peak atTmax=706 K), and tetrahedral Mo speciesin strong interaction with the alumina support (peakat Tmax=1040 K). It is also observed the presence ofshoulders at 773 K, due to the reduction of polymericoctahedral Mo species, and at 1004 K, due to thesecond reduction step of octahedral Mo species. Thereduction of Co species takes place at about 873 K. AsMCM-41 is incorporated into the support, a decreasein the peak assigned to the reduction of tetrahedralMo species in strong interaction with the support isobserved. The maximum of this reduction peak is,therefore, shifted towards 973 K, where the reductionassociated to the second reduction step of octahedralMo(VI) takes place. In line with this, a significantincrease in the size of the two low-temperature peakscorresponding to octahedral Mo species is observed.In fact, the magnitude of the reduction peak at about


Table 2Distribution of acid sites in CoMo/Al-MCM(x) catalysts (mmole NH3 per 50 mg of catalyst)

Sample CoMo/Al-MCM(0) CoMo/Al-MCM(30) CoMo/Al-MCM(50) CoMo/Al-MCM(70)

Weak 122 161 165 192Medium 84 104 100 109Strong 92 65 60 53Total 298 330 325 354

773 K increases so much that a change in the rela-tive size of the two low-temperature peaks is clearlyevident. In line with the above, the total hydrogenconsumption, and therefore, the reducibility of theCo and Mo species, increases with MCM-41 loading.These results indicate a clear shift in the populationof Mo species, from tetrahedral to octahedral ones, asMCM-41 content is increased in the catalyst support.

The TPR traces also show an increase in the hydro-gen consumption in the region around 873 K, wherethe Co species are reduced. This indicates that thepopulation of reducible Co (Co in octahedral coordi-nation) also increases with MCM-41 content. This ob-servation is well in line with the results obtained withCo/SiO2 catalysts, in which the Co species remainin octahedral coordination and are easily reducible.

Fig. 4. TPR patterns of CoMo/Al-MCM(x) catalysts.

In contrast, in the alumina-supported catalysts part ofthe Co forms tetrahedrally coordinated CoAl2O4, thatis hardly reducible. Clearly, the higher total hydro-gen consumption, due to increased reduction of bothCo and Mo, observed in the MCM-41-containing cat-alysts, is due to a shift in the type of Co and Mospecies from tetrahedral to octahedral ones. This resultis clearly related to the milder interaction of the metalphases with the MCM-41 in the support compared tothe alumina-supported catalysts. This milder interac-tion of the Mo and Co species with the support mayinduce interactions between Mo and Co. Because ofthis, the formation of species such as CoMoO4 cannotbe discarded, especially due to the form and position ofthe maximum of the TPR peak observed at 771–785 Kand the shoulder at about 973 K. These features coin-cide with the data reported by Moulijn [22] for the re-duction of CoMoO4, which was reported to reduce intwo steps, leading to two reduction peaks at 790 and980 K. The observed increase in hydrogen consump-tion with MCM-41 content would also be in line withthe presence of increased amounts of reducible Co, inthe form of CoMoO4 or other reducible Co species,at the expense of Co in CoAl2O4, which is hardlyreducible.

3.4. UV–VIS-diffuse reflectance spectroscopy

The changes in the electronic spectra of the sam-ples with support composition will reflect changesin the coordination of Co and Mo. According to theliterature [23–26], Mo tetrahedral species absorb at250–280 nm, while Mo octahedral species presenttransitions at 230–330 nm. A triplet due to the ex-istence of Co in tetrahedral coordination, assignedin alumina-supported catalysts to the presence ofCoAl2O4, appears between 500–700 nm. OctahedralCo species present transitions at 400 and 700 nm. AsFig. 5 shows, the DRS experiments clearly support


Fig. 5. UV–VIS-DRS spectra of CoMo/Al-MCM(x) catalysts.

the diminishing of the Co tetrahedral species withincreasing MCM-41 content. The intensity of the ab-sorption due to the typical triplet assigned to the pres-ence of CoAl2O4 clearly diminishes as the content ofMCM-41 increases. The formation of Co3O4 is notinduced by the incorporation of MCM-41 as indicatedby the decrease in intensity of the absorption regionaround 400 nm. This seems logical since the surfacearea of the catalysts increases with MCM-41 content,and therefore, a better dispersion of the Co speciesmight be expected, decreasing the possibility of itsagglomeration as Co3O4. This high dispersion of theCo species is well in line with the increased reductionof Co species detected in the TPR experiments.

The DRS spectra, however, do not clearly showan increase in Mo octahedral species. The absorptionedge of the charge transfer band due to octahedralMo species in MCM-41-containing catalysts does notshift its position significantly with respect to the cat-alyst supported on alumina. This would be the case ifin the alumina-supported catalyst already exist signif-icant amounts of octahedral Mo species of the sametype as those present in the MCM-41-containing cat-alysts.

3.5. IR of adsorbed NO

To enquire more about the dispersion of the Moand Co phases some experiments were performedanalyzing the adsorption of NO on the sulfided

catalysts by infrared spectroscopy. Nitric oxide is oneof the most frequently used molecules to characterizehydrotreatment catalysts. The analysis of the infraredspectra of the adsorption of NO on the catalysts intheir oxided and sulfided state can render informationabout the dispersion, oxidation state, and the degreeof unsaturation of the active sites. One of the impor-tant features of the adsorption of this molecule is thatit provides independent and simultaneous informationon the adsorption sites associated to Mo and Co inthe oxided and sulfided state. Freshly calcined Mocatalysts, where molybdenum is as Mo(VI), do notadsorb NO [27]. However, if a reducing treatment isperformed, the characteristic doublet of NO adsorbedreadily appears in the IR spectrum. With Mo in oxidedstate the symmetric stretching vibration mode appearsat about 1800–1815 cm−1, and the anti-symmetricstretching vibration mode at about 1700–1715 cm−1

[28–41]. For sulfided Mo catalysts, the bands appearshifted to lower wavenumbers [35–38,41–46]. Theadsorption of nitric oxide on Co species produces sim-ilar type of doublets as those found for the Mo-basedcatalysts. However, the position is markedly different.In this case, the band corresponding to the sym-metric stretching vibration mode appears at about1800–1880 cm−1 [29,38,39,43–45,47], and that corre-sponding to the asymmetric stretching vibration modeat about 1700–1800 cm−1. Also in this case, the sul-fidation treatment causes a shift in the bands to lowerwavenumbers. Additionally, it has been found that forcatalysts in the oxided state there are some differencesin the intensity and shape of the NO bands dependingon the Co species to which NO is adsorbed [29]. Thisinformation is useful to determine in a qualitative waythe direction of some of the changes in the supportedspecies induced by the change in the formulationof the support. For CoMo catalysts it should be,therefore, taken into account that the anti-symmetricvibration mode of NO adsorbed on Co overlaps withthe symmetric vibration mode of NO adsorbed onmolybdenum. Therefore, in this case, only the bandsat about 1850 cm−1 and 1690 cm−1 are useful in theanalysis of the Co and Mo species, respectively.

Fig. 6 shows the IR spectra of NO adsorbed on thesulfided catalysts. All the spectra show the character-istic features of sulfided CoMo catalysts. However,clear differences arise in the intensity and positionof the bands as MCM-41 is incorporated to the cata-


Fig. 6. IR spectra of NO adsorbed on the sulfided CoMo/Al-MCM(x) catalysts.

lyst. Compared with the alumina-supported catalyst,those containing MCM-41 present a large increase inthe intensity of the Co-associated symmetric NO vi-bration. This increase in intensity with the MCM-41content may be due either to a significant increase inthe dispersion of the Co species, or to the formationof new NO adsorbing Co species at the expense ofnon-adsorbing ones. The position of this band ap-pears shifted to higher wavenumbers (1863 cm−1)with respect to that in the alumina supported catalyst(1841 cm−1). However, it must be taken into accountthat changes in the type of support can induce shifts inthe position of the bands ([27] and references therein).The shift in the NO band associated to Co could also

Table 3Product distribution and DBT conversion in the DBT hydrodesulfurization reaction

Feed CoMo/Al-MCM (0) CoMo/Al-MCM (30) CoMo/Al-MCM (50) CoMo/Al-MCM (70)

Dibenzothiophene (%) 2.55 1.00 1.16 0.82 0.60Biphenyl (%) 0.01 1.24 1.11 1.47 1.63Cyclohexylbenzene (%) – 0.30 0.26 0.25 0.30DBT conversion (%) 60.6 54.4 67.8 76.43

be due to the presence of some CoMoO4 or CoAl2O4.In the case of the alumina-supported catalyst the ex-istence of the latter species is quite probable. Indeed,the presence of a shoulder at higher wavenumbers inthe band due to Co in the alumina-supported catalystsuggests that some of the Co in this catalyst is inthe form of CoAl2O4. However, in the catalysts con-taining MCM-41 this could not be the case since theintensity of this band should decrease as the MCM-41content increases. The DRS results also support thedecrease in the population of CoAl2O4 with MCM-41content. The fact that while the NO band associatedto Co increases, the one associated to Mo decreases,suggests an interaction of Co with Mo. This interac-tion can be explained either by the formation of theCo-Mo-S mixed phase, or by the existence of specieslike CoMoO4in the oxide form of the catalysts, thatunder sulfidation lead to partially sulfided Co-Mo-Ospecies. Since in CoMoO4 both Co and Mo are inoctahedral coordination, this possibility would notdisagree with the TPR results that show a decreasein the tetrahedral Mo species, and suggest the for-mation of CoMoO4. In any case, the behavior of thebands associated to Co and Mo seem to indicate thepresence of some kind of interaction between the Coand Mo atoms in the sulfided catalysts. This Co-Mointeraction would be enhanced by the decrease in theinteraction of the Co and Mo surface species with thesupport.

3.6. Catalytic HDS activity

The results from the dibenzothiophene HDS activ-ity tests, given in Table 3, show that at high MCM-41contents, 50% or more, the activity of the catalysts in-creases with MCM-41 content, and is larger than forthe pure alumina-supported catalyst. The quantitativeanalysis of the NO adsorption results do not show aclear correlation between the amount of NO adsorbed


Fig. 7. HREM micrographs of sulfided catalysts, showing the characteristic lamellar structures of MoS2. (a) CoMo/ Al-MCM(0), and (b)CoMo/ Al-MCM(70).

either on Mo or Co, with the HDS activity of the cat-alysts. This suggests that some of the Co and/or Mospecies that adsorb NO are not contributing to theformation of the catalytically active Co–Mo–S mixedphase. This suggestion is additionally supported by:(i) The opposite intensity changes of the NO bands as-sociated to Co and Mo (the intensity of the band asso-ciated to Co increases, while the one associated to Modecreases), and (ii) The shift to higher wavenumbers,of the NO IR bands associated to Co, suggesting thatnot all the Co is completely sulfided. Additional NOadsorption experiments on sulfided, oxide and reducedCo/Al-MCM(70) catalyst samples were performed toassign the position of the NO–Co bands to sulfided oroxide Co species.

The catalytic activity trend with MCM-41 contentwould be the result of opposite effects. In one hand,the incorporation of MCM-41 to the catalyst provideslarger areas and decreases the interaction of the Co andMo phases with the support, allowing a better reduc-tion and possibly a better sulfidation of the metallicphases. On the other hand, the greater population ofCo and Mo species in weak interaction with the sup-port, induce some polymerization of the Mo phases inthe oxide state, that leads to larger and more stackedMoS2 crystallites, as the HREM micrographs show(see Fig. 7). This is well in line with the values of theisoelectric point of the pure supports (8.5 for aluminaand 2.3 for MCM-41), and the pH of the impregnat-ing solution (5.5), that induce a lower Mo adsorption


on MCM-41 than on alumina, leading to the observedagglomeration of the Mo phases.

4. Conclusions

From the above results, we can summarize the con-clusions as follows. The incorporation of MCM-41to the catalyst formulation leads to higher catalyticactivity in the DBT HDS reaction than the catalystsupported on pure alumina. It also leads to a dimin-ished interaction between the Co and Mo phases withthe support, compared to those existing in the aluminasupported catalyst. This decrease in the interactioncauses the formation of greater amounts of poly-meric Mo octahedral species and a decrease in thepopulation of tetrahedral Co as CoAl2O4. These twolatter changes seem to be partly responsibly for theincreased catalytic activity. The opposite variation ofthe intensity of the infrared NO adsorption bands withincreasing MCM-41 content (the band associated toMo decreases as the one associated to Co increases),indicate that Co is associated to Mo, inducing a goodpromotion. This leads to higher catalytic activity inspite of the fact that not all the Co present in thesulfided catalysts is completely sulfided, as evidencedfrom the shifts in the position of the NO IR-bandassociated to Co.

Acknowledgements

This work was performed with the financial sup-port of PEMEX-Refinación and the Mexican Instituteof Petroleum (IMP). The authors would like to ac-knowledge Norma Oropeza for performing the IR-NOadsorption experiments and Ivan Puente-Lee for theHREM micrographs.

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Characterization and catalytic activity of CoMo HDS catalysts supported on alumina-MCM-41