An Investigation of the Reduction Behavior of MoS2/Al2O3 and the Subsequent Detection of Hydrogen on the Surface

McGarvey, G.B.; Kasztelan, S.

doi:10.1006/jcat.1994.1196

Cited by 50 publications

(17 citation statements)

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“…For example, if we reference the BE to the S2pvalue of de Jong et al [8], we obtain the same Mo3d BE. The same exercise on the values of McGarvey et al [20] and Ozkan et al [21] found for MoSa supported on yA1203 leads to similar results. The differences between the Mo3d BE and the S2p BE are equal In most cases, indicating the same structure.…”

Section: Molybdenumsupporting

confidence: 73%

“…The estimated atomic S/Mo of 1.6 agrees well with the ratio obtained by McGarvey et al [20] after the reduction of MoS2 supported on A1203 at 673 K. Resulphlding did not affect the Mo3d BE of 229.3 eV and re-established a slightly higher sulphur/ metal ratio (1.9) than the first sulphldatlon.…”

Section: Molybdenumsupporting

confidence: 40%

“…In general the results for Re and Mo were In agreement with the existing literature with regard to sulphiding behaviour and sulphur loss. Speciflcally, the sulphided state of Mo/Si wafer was In good agreement with the study by de Jong et al [8] and McGarvey et al [20], when differences In the reference level and sensitivity factors are taken into account. Sulphldatlon of the Fe/Si wafer and the ultrapure Fe2Oa yielded in both cases pyrrhotite (Fe(r.x)S) in agreement with Jones et al [24].…”

Section: Discussionmentioning

confidence: 49%

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Cyclic Sulphidation/Reduction of Transition Metal Model Compounds: A Quasi in situ XPS Study

Oen

Hellgardt

Chadwick

1995

Bulletin des Soc Chimique

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INTR OD UCTlONAs the allowable level of sulphur in refinery products is reduced, the H2S concentrations to which catalysts are exposed during the final stages of hydrotreating can be expected to decrease. Although the precise H2S/H2 ratio will be dependent on the reactor configuration, this may lead to loss of sulphur from the catalyst surface with consequent effects on catalyst structure and activity. This problem Is likely to be more acute for catalysts based on precious metals with their potential use for deep desulphurization, slnce thermodynamic calculations suggest, for example, that Pt and Re sulphides are reducible in H2 atmospheres containing less than 1 % H2S [l ,2,3] whereas base metals show greater stability of their sulphldes towards reduction by H2.Studies of the sulphidation of hydrotreating catalysts show that their activlty depends on several factors. Coupled or stepwise sulphidatlon/reduction seems to yield the most active catalysts (41, but other factors also affect the final performance. For example, oxygen incorporation in the sulphided catalyst can give sites of higher activii [5], and reduction after sulphidation can give either higher acti-The present study forms part of a programme of research to probe the surface compositions of the suiphided state of various transition metal model compounds after cyclic treatments simulating low H2S concentration hydrotreating conditlons and resulphldation. For this task a quasi in situ XPS system has been built to allow measurement of surface sulphurlmetal ratios of transition metals after various cyclic treatments of the same sample without air exposure. This work concentrates on the precious metals Pt and Re, as well as Mo and Fe. These materials were investigated as thin films on Si wafers, as SiO2 supported catalysts in the case of Pt and Re, and as bulk materials in some cases. EXPERIMENTALFor this study a gas-cell-type reactor was constructed in the preparation vessel of a Vacuum Generators ESCA 111 XPS Instrument. Cyclic treatments and surface analysis were performed on the same sample without air contactlng the sample between treatment and analysis. A sketch of the reactor set-up is given in Figure 1. The sample is held on the end of a movable probe and the reactor hangs from a bellows system. For sample treatment, the reactor is lowered down onto a support, the sample is moved into the reactor and sealed with a metal gasket. Further details of the reactor construction and performance can be found in another publication [7]. XPS spectra were taken using Mg or A1 radiation and binding energles were referenced to the Cls binding energy of 264.6 eV or cross-referenced to Si2p312 at 103.2 eV in some cases. For the Mo/Si wafer and the MoS2 single crystal, the S2p was set at 162.0 eV, corresponding to the average of a range of values taken from literature [8,9]. This is discussed further below. Constant spectrometer pass energies of 50 or 20 eV were applied.

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Section: Molybdenumsupporting

confidence: 73%

Section: Molybdenumsupporting

confidence: 40%

Section: Discussionmentioning

confidence: 49%

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Cyclic Sulphidation/Reduction of Transition Metal Model Compounds: A Quasi in situ XPS Study

Oen

Hellgardt

Chadwick

1995

Bulletin des Soc Chimique

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“…The observed release of H 2 S above 673 K in the TPR-S proves that hydrogenation of more strongly bonded sulfur atoms proceeds beyond this temperature. Most likely these are stoichiometric sulfur atoms, such as the bridging sulfur atoms that are part of the edge structure of the MoS 2 slabs (27).…”

Section: Evidence For Two Types Of Hds Sitesmentioning

confidence: 44%

Structure and Nature of the Active Sites in CoMo Hydrotreating Catalysts Conversion of Thiophene

Leliveld¹,

Dillen²,

Geus³

et al. 1998

Journal of Catalysis

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The performance of sulfided (Co)Mo/alumina catalysts was studied in the conversion of thiophene between 423 and 773 K at atmospheric pressure. Reaction orders for thiophene, H 2 , and H 2 S were determined at several temperatures. The reaction order in thiophene increases with rising temperature, indicating a LangmuirHinshelwood mechanism. Beyond 550 K the conversion curve deviates from pseudo-first-order kinetics, demonstrating the influence of the surface coverage of thiophene on the reaction rate. Above 673 K the reaction rate rises exponentially with temperature which can be ascribed to the presence of a second type of active site that is only active at high temperatures. These catalytic data can be combined with recent structural studies using EXAFS spectroscopy to derive an activity-structure relation. It is proposed that at low temperature the active sites are terminal sulphur vacancies on the Co-promotor atom. In addition around 673 K a second type of sites becomes active, which is believed to consist of bridging sulphur vacancies in between Co and Mo atoms on the MoS 2 edges.

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“…For hydrogenation and hydrodesulfurization reactions over sulfide catalysts, many kinetic studies have been carried out in the literature so far [11,12,[25][26][27][28][29]. In the same spirit as [10,25,27], we have tested several relevant models and determined the model able to reproduce at best the experimental catalytic results obtained previously.…”

Section: Microkinetic Modelingsupporting

confidence: 38%

Dual Effect of H₂S on Volcano Curves in Hydrotreating Sulfide Catalysis

Guernalec

Geantet

Raybaud³

et al. 2006

Oil & Gas Science and Technology - Rev. IFP

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Résumé -Effet dual d'H 2 S sur les courbes en volcan en catalyse d'hydrotraitement -Les progrès récents des techniques de modélisation moléculaire quantique ont permis l'interprétation rationnelle des tendances périodiques observées en catalyse par les sulfures de métaux de transition. Les courbes en volcan obtenues de façon empirique peuvent être expliquées par des modélisations microcinétiques inté-grant des descripteurs chimiques judicieux calculés ab initio. Cette approche a été appliquée avec succès en catalyse d'hydrotraitement en utilisant l'énergie de liaison metal-soufre comme descripteur ab initio. L'objectif du présent travail était d'étendre cette approche en explorant les effets des conditions réaction-nelles (pression partielle en H 2 S) sur les courbes en volcan. Dans ce but, les images de microscopie électronique à transmission haute résolution (METHR) combinées à la modélisation moléculaire des morphologies et des surfaces présentes ont permis de fournir une évaluation du nombre de sites potentiellement actifs. Cette approche est illustrée dans le cas du sulfure de cobalt supporté et non supporté. Un modèle microcinétique amélioré permet d'interpréter l'effet dual de l'H 2 S observé en hydrogénation du toluène: effet inhibiteur pour les sulfures MoS 2 , Rh 2 S 3 , RuS 2 , NiMoS et effet promoteur pour les sulfures Cr 2 S 3 et Co 9 S 8 . Les résultats expérimentaux combinés à la modélisation cinétique montrent que la position du maximum de la courbe en volcan correspondant au catalyseur optimal le plus performant dépend des conditions du milieu réactionnel. Abstract -Dual Effect of H 2 S on Volcano Curves in Hydrotreating Sulfide Catalysis -Recent progresses achieved by quantum molecular modeling techniques enabled the rational interpretation of catalytic trends of series of transition metal sulfide catalysts. Empirical volcano curves can be explained by microkinetic models including chemical descriptors calculated at an ab initio level. This approach was successfully applied in the field

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An Investigation of the Reduction Behavior of MoS2/Al2O3 and the Subsequent Detection of Hydrogen on the Surface

Cited by 50 publications

References 0 publications

Cyclic Sulphidation/Reduction of Transition Metal Model Compounds: A Quasi in situ XPS Study

Cyclic Sulphidation/Reduction of Transition Metal Model Compounds: A Quasi in situ XPS Study

Structure and Nature of the Active Sites in CoMo Hydrotreating Catalysts Conversion of Thiophene

Dual Effect of H₂S on Volcano Curves in Hydrotreating Sulfide Catalysis

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An Investigation of the Reduction Behavior of MoS2/Al2O3 and the Subsequent Detection of Hydrogen on the Surface

Cited by 50 publications

References 0 publications

Cyclic Sulphidation/Reduction of Transition Metal Model Compounds: A Quasi in situ XPS Study

Cyclic Sulphidation/Reduction of Transition Metal Model Compounds: A Quasi in situ XPS Study

Structure and Nature of the Active Sites in CoMo Hydrotreating Catalysts Conversion of Thiophene

Dual Effect of H2S on Volcano Curves in Hydrotreating Sulfide Catalysis

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Dual Effect of H₂S on Volcano Curves in Hydrotreating Sulfide Catalysis