Characterization of supported cobalt and cobalt-rhodium catalyst. I. Temperature-programmed reduction and oxidation of Co-Rh/Al/sub 2/O/sub 3/
Temperature-programmed reduction and oxidation (TPR and TPO) have been used to study the state of cobalt and rhodium in a series of Co-Rh/..gamma..-Al/sub 2/O/sub 3/ catalysts. The results show that rhodium enhances the reducibility of part of the cobalt, but that it does not prevent the formation of cobalt aluminate, which is irreducible below 773 K. TPR of the coimpregnated Co-Rh/..gamma..-Al/sub 2/O/sub 3/ catalyst shows a reduction peak at a much lower temperature than that of Co/Al/sub 2/O/sub 3/. This and the slight shift relative to the peak of Rh/Al/sub 2/O/sub 3/ indicates that cobalt and rhodium ions are not far apart after coimpregnation, which explains the easy formation of bimetallic particles during reduction. Passivation (oxidation at room temperature) of the reduced bimetallic catalyst leaves the structure the bimetallic particles largely intact, but cobalt is oxidized to a great extent while rhodium remains metallic. Passivated Co-Rh particles thus consist of a rhodium kernel covered by cobalt oxide. TPR of passivated catalysts also suggests that already in the reduced state the bimetallic particles are surface-enriched in cobalt. A thorough oxidation of the bimetallic catalysts, on the other hand, leads to a restructuring, i.e., the formation of metal oxide particles which are in close proximity.
- Research Organization:
- Eindhoven Univ. of Technology (Netherlands)
- OSTI ID:
- 5286349
- Journal Information:
- J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 97:1; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
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ALCOHOLS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
BIMETALS
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL PROPERTIES
CHEMICAL REACTIONS
COBALT
ELEMENTS
FISCHER-TROPSCH SYNTHESIS
HYDROXY COMPOUNDS
MEASURING METHODS
METALS
METHANOL
ORGANIC COMPOUNDS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
REDUCTION
RHODIUM
SURFACE PROPERTIES
SYNTHESIS
TRANSITION ELEMENTS