Titania-silica epoxidation catalysts modified by acetoxypropyl groups

• Published in: Catalysis letters 2000, Vol.64 (1), p.9-14
• Main Authors: MÜLLER, C. A, SCHNEIDER, M, GISLER, A, MALLAT, T, BAIKER, A
• Format: Article
• Language: English
• Subjects: Carbonyl groups; Carbonyls; Catalysis; Catalysts; Catalysts: preparations and properties; Chemistry; Epoxidation; Exact sciences and technology; General and physical chemistry; Reaction time; Selectivity; Silica aerogels; Silicon dioxide; Surface area; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Titanium
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1023/A:1019074617565

Mesoporous titania–silica aerogels with TiO2SiO2 = 1:9 weight ratio and varying amounts of covalently bound 3‐acetoxypropyl groups were prepared from 3‐acetoxypropyltrimethoxysilane, tetramethoxysilane and titanbisacetylacetonatdiisopropoxide. The textural properties of the hybrid aerogels were strongly influenced by the concentration of acetoxypropyl groups. The BET surface area and specific pore volume were significantly lowered upon introduction of the polar organic modification. Despite these less favorable textural properties, all modified aerogels were remarkably more active epoxidation catalysts, and in the epoxidation of cyclohexenol also more selective, than the unmodified titania–silica aerogel. For example, incorporation of only 2 mol% acetoxypropyl groups lowered the BET surface area from 813 to 339 m2 g-1, whereas the selectivity to 2,3‐epoxy‐cyclohexenol increased from 76 to 90%, and the reaction time (required to achieve 70% TBHP conversion) decreased from 46 to 5 min. The higher epoxide selectivity and the small enhancement in cis/trans ratio in the epoxide may indicate an electron pair donor interaction between the ester carbonyl group and the Ti active site.