Relationships between microstructure and surface acidity of Ti-Si mixed oxide catalysts
- Univ. of Virginia, Charlottesville, VA (United States)
The surface acidities and reactivities of titania, silica, and a series of Ti-Si mixed oxides have been investigated with a variety of surface-sensitive techniques, including temperature-programmed desorption/reaction of ammonia and 2-propanol, IR spectroscopy of adsorbed ammonia, and catalytic reaction of 1-butene. Results from TPD, TPR, and IR spectroscopy indicated that total acidity and relative acid strength decreased as silica was incorporated into titania. However, the areal rate of 1-butene isomerization was almost four times greater over a titania-rich mixed oxide than over pure titania. Infrared spectroscopy of adsorbed ammonia revealed that all of the acid sites on pure titania were of the Lewis type, whereas about 80% of the sites on the mixed oxides were of the Broensted type. Therefore, the enhancement of butene isomerization activity over titania-rich mixed oxides was attributed to the Broensted acid sites that were not present on pure titania. The appearance of Broensted acidity in titania-rich mixed oxides was due to the local charge imbalance associated with tetrahedrally coordinated silica chemically mixing with the octahedral titania matrix. In silica-rich mixed oxides, Ti substituted isomorphously for Si in the tetrahedral silica matrix, thus eliminating the local charge imbalance that caused Broensted acidity. The molar ratio of NH{sub 3(ads)}/Ti for a silica-rich mixed oxide was approximately 0.3, which was nearly the same as the fraction of nontetrahedrally coordinated Ti in the sample. 33 refs., 7 figs., 2 tabs.
- OSTI ID:
- 110982
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 149; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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