CATALYTIC AND ACIDIC PROPERTIES OF SILICA-ALUMINA PREPARED BY CHEMICAL VAPOR-DEPOSITION

Attempts were made to prepare a supported type of silica-alumina by depositing silica on an alumina surface by chemical vapour deposition (CVD). Silica was effectively and uniformly deposited on alumina using tetraethoxysilane at 240°C in the presence of oxygen. The resulting silica-alumina (CVD SiO2/Al2O3) exhibited high catalytic activities for several types of organic reactions such as 2-butanol dehydration, m-xylene isomerization, cumene cracking and n-heptane cracking. The catalytic activities of CVD SiO2/Al2O3 varied with silica loading, attaining maximum conversions for the respective reactions at different silica loadings, and were comparable to those of commercial silica-aluminas. The catalytic activities did not correlate with the total amount of acid measured by ammonia chemisorption, but could be associated with the amount of Brønsted acid. 31P magic angle spinning NMR measurements on trimethylphosphine chemisorption elucidated that the Lewis acid sites on alumina were completely converted into Brønsted acid sites by the deposition of silica. © 1990.