A shape-selective catalyst for epoxidation of cyclic olefins:: The nanoporous nickel phosphate VSB-5

Nickel in the form of porous nickel phosphate VSB-5 has been used as a shape-selective catalyst for epoxidation of cyclic olefins such as cyclohexene and cyclooctene using hydrogen peroxide. The VSB-5 showed high selectivity to cyclohexene oxide and cyclohexane diol, much higher productivity per catalyst weight in the epoxidation of cyclohexene, and high selectivity to cyclooctene oxide in the epoxidation of cyclooctene. The VSB-5 behaved as a heterogeneous catalyst in the epoxidation and can be used many times without structure degradation, leaching of active nickel species, or significant activity loss. It has been concluded that the epoxidation reaction with VSB-5 proceeds via a free-radical mechanism by taking into consideration a sharp activity loss in the presence of a radical scavenger, hydroquinone. The effect of radical scavengers with different molecular dimension on the catalytic activity also indicates the shape selectivity in the pores of VSB-5. (c) 2006 Elsevier Inc. All rights reserved.