SILICA CATALYSTS WITH CONTROLLED TITANIUM DISTRIBUTIONS

摘要

A method for preparing a titanium on silica catalyst, in the form of formed particles such as macrospheres, achieves a controlled titanium distribution type, namely either uniform, eggshell, or intermediate, by selecting the particular titanium precursor depending on its reactivity with hydroxyl groups and by selecting the molar titanium:hydroxyl ratio. Selecting a titanium precursor with a low reactivity and/or adding sufficient titanium precursor to achieve a high molar titanium:hydroxyl ratio aids in forming a uniform distribution of titanium. On the other hand, selecting a titanium precursor with a high reactivity and/or adding only a little titanium precursor resulting in a low molar titanium:hydroxyl ratio aids in forming an eggshell distribution of titanium. In particular, the method involves first preparing formed particles, such as macrospheres, of silica hydrogel then drying the formed particles. Next, the formed particles are contacted with the titanium precursor, selected based on its reactivity and added in a suitable amount, both depending on the desired distribution type. Then, the titanium-impregnated formed particles are recovered as the catalyst. Preferred titanium precursors for aiding in the formation of an eggshell distribution of titanium include n-propyl titanate and n-butyl titanate, and preferred titanium precursors for aiding in the formation of a uniform distribution of titanium include titanocene and titanium acetylacetonate. Such silica on titanium catalysts can be used to make epoxidation catalysts, oxidation catalysts, hydroxylation catalysts, and the preferred distribution type depends on the particular application.