The role of prehydrolysis in the preparation of zirconia-silica aerogels
- Carnegie Mellon Univ., Pittsburgh, PA (United States)
Prehydrolysis of an unreactive metal alkoxide precursor is a well-known strategy for promoting homogeneous mixing in sol-gel preparations of mixed oxide catalysts. Using a series of 50 mol% zirconia-50 mol% silica aerogels, we show how adjustment o rehydrolysis conditions, especially the molar ratio of water to silicon precursor ({open_quote}prehydrolysis ratio{close_quote}), allows a fine degree of control of the mixed oxide`s acidic and textural properties. As prehydrolysis ratio increases from 0.00 to 3.22 mols H{sub 2}O/mol Si, molecular-scale mixing of the zirconia and silica components improves, resulting in increased acid site density, fractional Bronsted acidity, and 1-butene isomerization activity. Higher prehydrolysis ratios also more effectively stabilize zirconia in an x-ray amorphous form. NMR data enable us to relate the changes in the properties of the calcined mixed oxides to differences among the types of hydrolyzed silicon products that form at different prehydrolysis ratios in the initial step of the preparation.
- OSTI ID:
- 126760
- Report Number(s):
- CONF-950402--
- Country of Publication:
- United States
- Language:
- English
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