An Efficient Hybrid, Nanostructured, Epoxidation Catalyst: Titanium Silsesquioxane-Polystyrene Copolymer Supported on SBA-15

• Published in: Chemistry : a European journal Vol. 13; no. 4; pp. 1210 - 1221
• Main Authors: Zhang, Lei, Abbenhuis, Hendrikus C. L., Gerritsen, Gijsbert, Bhriain, Nollaig Ní, Magusin, Pieter C. M. M., Mezari, Brahim, Han, Wei, van Santen, Rutger A., Yang, Qihua, Li, Can
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-01-2007; WILEY‐VCH Verlag
• Subjects: epoxidation; mesoporous materials; organic-inorganic hybrid composites; polystyrene; titanium
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200600752

A novel interfacial hybrid epoxidation catalyst was designed with a new immobilization method for homogeneous catalysts by coating an inorganic support with an organic polymer film containing active sites. The titanium silsesquioxane (TiPOSS) complex, which contains a single‐site titanium active center, was immobilized successfully by in‐situ copolymerization on a mesoporous SBA‐15‐supported polystyrene polymer. The resulting hybrid materials exhibit attractive textural properties (highly ordered mesostructure, large specific surface area (>380 m2 g−1) and pore volume (≧0.46 cm3 g−1)), and high activity in the epoxidation of alkenes. In the epoxidation of cyclooctene with tert‐butyl hydrogen peroxide (TBHP), the hybrid catalysts have rate constants comparable with that of their homogeneous counterpart, and can be recycled at least seven times. They can also catalyze the epoxidation of cyclooctene with aqueous H2O2 as the oxidant. In two‐phase reaction media, the catalysts show much higher activity than their homogeneous counterpart due to the hydrophobic environment around the active centers. They behave as interfacial catalysts due to their multifunctionality, that is, the hydrophobicity of polystyrene and the polyhedral oligomeric silsesquioxanes (POSS), and the hydrophilicity of the silica and the mesoporous structure. Combination of the immobilization of homogeneous catalysts on two conventional supports, inorganic solid and organic polymer, is demonstrated to achieve novel heterogeneous catalytic ensembles with the merits of attractive textural properties, tunable surface properties, and optimized environments around the active sites.
Attractive textural properties and high activities were obtained by using a novel interfacial hybrid epoxidation catalyst in the epoxidation of alkenes, with tert‐butyl hydrogen peroxide (TBHP) or aqueous H2O2 as the oxidant. The catalyst is prepared by a new immobilization method for homogeneous catalysts, by coating an inorganic SBA‐15 support with a polystyrene polymer film containing titanium silsesquioxane. Its structure and its location during the reaction are illustrated.