Skeletal isomerization of hydrocarbons on molybdenum catalysts. I. X-ray photoelectron spectroscopy study of alumina-supported catalysts
MoO/sub 3//Al/sub 2/O/sub 3/ catalysts with 6, 12, 18, or 30 wt% MoO/sub 3/ have been studied by X-ray photoelectron spectroscopy (XPS) in their original oxide form and in a reduced state. Comparisons between bulk MoO/sub 3/ or MoO/sub 3/-alumina mechanical mixture and alumina-supported MoO/sub 3/ catalysts have shown in the latter a binding energy increase of about 0.5 eV for the molybdenum 3d level. This increase has been interpreted by a charge transfer from molybdenum to alumina. The supported oxide also shows a decrease in resolution of the Mo 3d doublet due either to the alumina surface heterogeneity from the point of view of its electron-accepting properties or to the coexistence of molybdenum ions in tetrahedral and octahedral sites. The high-temperature reduction of 6% MoO/sub 3//Al/sub 2/O/sub 3/ has been studied at 550, 750, and 950/sup 0/C under 760 Torr hydrogen. After 550/sup 0/C treatment, the catalyst is close to its original oxide form. The 750/sup 0/C treatment leads to an intermediate form where molybdenum atoms close to oxide and close to metal coexist. Even after reduction at 950/sup 0/C, molybdenum is not perfectly reduced; it is very close to the metallic state but there remain some weakly oxidized sites at its surface. This study has shown that there is aggregation of molybdenum in large particles at the surface; after reduction under hydrogen at 950/sup 0/C the amount of molybdenum contributing to the observed Mo XPS signal is divided by a factor close to 2. An oxygen treatment at 550/sup 0/C not only reoxidizes, but also redisperses, all molybdenum. These XPS results are useful in the interpretation of the catalytic properties of these systems.
- Research Organization:
- Universite Louis Pasteur, Strasbourg, France
- OSTI ID:
- 5451522
- Journal Information:
- J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 104:1; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020400* -- Petroleum-- Processing
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
BINDING ENERGY
CATALYST SUPPORTS
CATALYTIC EFFECTS
CATALYTIC REFORMING
CHALCOGENIDES
CHEMICAL REACTIONS
ELECTRON SPECTROSCOPY
ENERGY
HYDROCARBONS
MOLYBDENUM COMPOUNDS
MOLYBDENUM OXIDES
ORGANIC COMPOUNDS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PHOTOELECTRON SPECTROSCOPY
REDUCTION
REFORMER PROCESSES
REFRACTORY METAL COMPOUNDS
SPECTROSCOPY
TRANSITION ELEMENT COMPOUNDS
X-RAY SPECTROSCOPY