Broensted acid sites in transition metal oxide catalysts: modeling of structure, acid strengths, and support effects
The trends and origin of Broensted acidity of dispersed, ..gamma..-alumina-supported transition metal oxides are investigated via a new theoretical method. The method is based on first-principles quantum mechanical calculations for the acid site and includes a realistic model of the acid-base interaction. Both free and supported transition metal (TM) oxide clusters of Ti, Nb, and W are considered. For tetrahedrally coordinated unsupported TM oxide clusters, it is found that the Broensted acidity depends strongly on the number of terminal oxygen atoms (terminal O effect). For supported TM oxides, the calculations show that the charge delocalization extends into the support, leading to a strong additional increase in the Broensted acidity. This novel inductive effect of the support together with the terminal O effect is responsible for the high Broensted acidity of the catalysts. The strong support effect suggests that support modifications may significantly alter the catalytic properties of supported transition metal oxides. The calculated trends are in good agreement with the experimental measurements of relative Broensted acidity of the catalysts.
- Research Organization:
- Exxon Research and Engineering Co., Annandale, NJ
- OSTI ID:
- 7043973
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 91:6
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
02 PETROLEUM
NIOBIUM OXIDES
CATALYTIC EFFECTS
MOLECULAR STRUCTURE
PH VALUE
TITANIUM OXIDES
TUNGSTEN OXIDES
ALUMINIUM OXIDES
BROENSTED ACIDS
CATALYST SUPPORTS
CATALYSTS
MATHEMATICAL MODELS
QUANTUM MECHANICS
THEORETICAL DATA
WAVE FUNCTIONS
ALUMINIUM COMPOUNDS
CHALCOGENIDES
DATA
FUNCTIONS
HYDROGEN COMPOUNDS
INFORMATION
INORGANIC ACIDS
MECHANICS
NIOBIUM COMPOUNDS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
REFRACTORY METAL COMPOUNDS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN COMPOUNDS
400201* - Chemical & Physicochemical Properties
020400 - Petroleum- Processing