Bimetallic Catalysts .VI. Surface Composition of Pt-Mo/SiO2 Catalysts: Influence of Reaction Media

Leclercq, G.; Gharbi, A. El; Gengembre, L.; Romero, Trino; Leclercq, Loı̈c; Pietrzyk, S.

doi:10.1006/jcat.1994.1241

Cited by 18 publications

(15 citation statements)

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“…(b) Molybdenum. Contrary to what have been observed for Pt, we have shown (24) that the reduction at 500 °C in pure hydrogen reduces uncompletely molybdenum. Only a fraction of molybdenum had been reduced into Mo 0 , the remaining molybdenum being probably at various oxidation states.…”

Section: Resultscontrasting

confidence: 99%

“…(a) Platinum. After reduction at 500 °C, it had been shown (24) that the binding energies (BE) corresponding to the Pt 4f 7/2 level (71.7 ( 0.1 eV) are the same for all the Pt-Mo catalysts, indicating that no electronic modification of Pt by Mo was evidenced. The values of the BE, although slightly higher than those obtained for bulk Pt (40), but significantly lower than the BE of Pt in oxidized compounds (41,42), led to the conclusion that Pt is completely reduced into metal.…”

Section: Resultsmentioning

confidence: 99%

“…The use of a dry N 2 -purged glovebox attached between the spectrometer and a reactor in which reductions in flowing hydrogen were performed allowed examination of the reduced samples without contact with air. The detailed procedure is described in ref 24.…”

Section: Methodsmentioning

confidence: 99%

“…Molybdenum seems to be one of these potentially interesting additives since it is not expensive, is largely available, and is widely soluble in Pt, at least up to 72 atom % (16). The bimetallic Pt-Mo system can be easily studied by physico-chemical methods (XPS, ESR, ...) because of the rather different properties of the two elements, and it has attracted the attention of several groups of research (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28).…”

Section: Introductionmentioning

confidence: 99%

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Investigation on Active Sites in Pt−Mo on Silica Catalysts for Reactions of Hydrocarbons with Hydrogen

Leclercq¹,

Pietrzyk²,

Romero³

et al. 1997

Ind. Eng. Chem. Res.

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A series of bimetallic catalysts Pt-Mo deposited on silica, with the same (Pt + Mo) metal atom content but various Mo/Mo + Pt ratios, has been synthesized and characterized by XPS, ESR, hydrogen chemisorption, and oxygen uptake during their reoxidation after reduction, in order to determine the oxidation state of Pt and Mo and the catalyst surface compositions. They have been further tested for their activities in the dehydrogenation of cyclohexane, the hydrogenation of benzene, the hydrogenolysis of butane, and the reactions of hexane, on the one hand, and of 3-methylpentane, on the other hand, with hydrogen. Finally the kinetics of butane hydrogenolysis has been extensively studied in order to determine the equilibrium constants of butane adsorption and the rate constants of the steps of C-C bond breaking on all the Pt-Mo/SiO 2 samples. The main results are that, while Pt is completely reduced in a metal state, only a fraction of Mo, which depends only on the reduction temperature, is reduced into metal. Mo at various oxidation states is present in the same proportion for all the bimetallic catalysts. A Mo surface enrichment has been evidenced after reduction in hydrogen, but it has been shown that this enrichment decreases or even disappears in the presence of oxygen and of aromatic hydrocarbons strongly adsorbed on the metal particle surfaces. Two kinds of reactions are distinguished: cyclohexane dehydrogenation, alkanes isomerization, and cyclization, with a ratedetermining step occurring preferably on Pt, and alkanes hydrogenolysis, which is much faster on Pt-Mo because of preferential adsorption on a mixed Pt-Mo site. The nature of Pt and Mo species participating to this mixed site is discussed.

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Section: Resultscontrasting

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigation on Active Sites in Pt−Mo on Silica Catalysts for Reactions of Hydrocarbons with Hydrogen

Leclercq¹,

Pietrzyk²,

Romero³

et al. 1997

Ind. Eng. Chem. Res.

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“…8,12 In order to overcome this problem while employing relatively inexpensive metals, bimetallic Pd-Mo and Pd-W catalysts have been proposed. [13][14][15][16][17][18][19][20][21] Using inorganic salt precursors, catalysts with adequate metal-metal contacts can be prepared and employed, but they require the use of high catalyst loadings, which might lead to tungsten or molybdenum oxide vapors. 17 Previously, we have shown that Pd-M/γ-Al 2 O 3 (M = Mo or W) prepared from the photochemical activation of the organometallic precursor [M(CO) 6 ] displayed Pd-M interactions with low metal loadings and led to an enhanced activity for NO decomposition with M = W. 22 6 ] (M = Mo and W) on alumina, and we investigate the influence of the metal particle size and of the presence of a second metal on the catalysts performance.…”

Section: Introductionmentioning

confidence: 45%

Pd-W and Pd-Mo catalysts for NO decomposition and NO/CO reduction reactions

Dallago¹,

Baibich²

2009

J. Braz. Chem. Soc.

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Pd/γ-Al 2 O 3 catalysts with two different metal particle sizes were prepared from [Pd(acac) 2 ]. Subsequently, the photochemical reaction of [M(CO) 6 ] (M = Mo or W) in the presence of Pd/γ-Al 2 O 3 was used to prepare bimetallic Pd-M/γ-Al 2 O 3 catalysts. DRIFTS FTIR spectra of the catalyst surfaces prior to thermal decomposition showed unstable subcarbonyl [M(CO) n ] species. Chemisorption and CO/NO adsorption results indicated a blockage of the Pd active sites when the second metal was incorporated. The catalytic activity and the selectivity for the NO/CO reaction were higher for Pd with higher particle size, but they were both inhibited when Mo or W were incorporated. On the other hand, when the catalysts were tested for NO decomposition, the presence of Mo or W led to an increase in the catalytic activity, with optimal results observed in the presence of Mo.

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Preparation, Characterization, and Catalytic Activity of Molybdenum Carbide or Nitride Supported on Platinum Clusters Dispersed in EMT Zeolite

Bécue¹,

Manoli²,

Potvin³

et al. 1999

Journal of Catalysis

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Bimetallic Catalysts .VI. Surface Composition of Pt-Mo/SiO2 Catalysts: Influence of Reaction Media

Cited by 18 publications

References 0 publications

Investigation on Active Sites in Pt−Mo on Silica Catalysts for Reactions of Hydrocarbons with Hydrogen

Investigation on Active Sites in Pt−Mo on Silica Catalysts for Reactions of Hydrocarbons with Hydrogen

Pd-W and Pd-Mo catalysts for NO decomposition and NO/CO reduction reactions

Preparation, Characterization, and Catalytic Activity of Molybdenum Carbide or Nitride Supported on Platinum Clusters Dispersed in EMT Zeolite

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