Moessbauer emission studies of calcined Co-Mo/Al/sub 2/O/sub 3/ catalysts: catalytic significance of Co precursors
The nature of Co in calcined Co-Mo/Al/sub 2/O/sub 3/ catalysts and the changes that occur upon sulfiding have been investigated by Moessbauer emission spectroscopy (MES). The studies of Co-Mo/Al/sub 2/O/sub 3/ catalysts show that changes in the Co loading, calcination temperature, and impregnation procedure significantly alter the Co phase distribution. In catalysts with low Co loading, two different types of Co species are generally present: one is identified as tetrahedrally coordinated Co (Co/sub tet/) and another is ascribed to cobalt atoms located in octahedral-like coordination (Co/sub oct/). The Co/sub oct/ species, which seem to be located at or close to the surface of the alumina, dominate at low calcination temperatures, whereas calcination at high temperatures favors formation of the Co/sub tet/ species which appear to be predominantly located in the interior of the alumina. The Co/sub tet/ species have MES parameters different from those of CoAl/sub 2/O/sub 4/. Catalysts with high Co loadings also contain Co/sub 3/O/sub 4/. The concentrations of the different Co species in the various calcined Co-Mo/Al/sub 2/O/sub 3/ catalysts have been compared with the corresponding data for the same catalysts after sulfiding. It is found that the fraction of Co which is present in the alumina after sulfiding is related to the amount of Co/sub tet/, the amount of Co/sub 9/S/sub 8/ is related to Co/sub 3/O/sub 4/, and Co in the catalytically active Co-Mo-S phase is related to Co/sub oct/. As a consequence of the latter, the thiophene hydrodesulfurization activity is related to the amount of Co/sub oct/ in the calcined catalysts. 51 references, 14 figures, 4 tables.
- Research Organization:
- Technical Univ. of Denmark, Lyngby
- OSTI ID:
- 6196204
- Journal Information:
- J. Catal.; (United States), Vol. 87:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALUMINIUM OXIDES
IMPREGNATION
SULFIDATION
CATALYSTS
CHEMICAL REACTION KINETICS
STRUCTURAL CHEMICAL ANALYSIS
COBALT
CATALYTIC EFFECTS
MOLYBDENUM
CALCINATION
CATALYSIS
DESULFURIZATION
EMISSION SPECTROSCOPY
EXPERIMENTAL DATA
MOESSBAUER EFFECT
MOESSBAUER SPECTROMETERS
PHASE STUDIES
QUANTITY RATIO
TEMPERATURE DEPENDENCE
THIOPHENE
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
DATA
DECOMPOSITION
ELEMENTS
GAMMA SPECTROMETERS
HETEROCYCLIC COMPOUNDS
INFORMATION
KINETICS
MEASURING INSTRUMENTS
METALS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PYROLYSIS
REACTION KINETICS
SPECTROMETERS
SPECTROSCOPY
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENTS
020400* - Petroleum- Processing
400104 - Spectral Procedures- (-1987)