Synthesis and characterization of cobalt-substituted SBA-15 and its high activity in epoxidation of styrene with molecular oxygen

Abstract

Cobalt-substituted SBA-15 (Co-SBA-15x) was successfully synthesized by a simple and effective method designated as “pH-adjusting”. Based on series of characterizations, the material still retained a highly ordered mesostructure of SBA-15 when a certain amount of cobalt was introduced. The cobalt species in Co-SBA-15x mainly existed in the single-site Co(II) state. Most of them were incorporated into the silica framework of SBA-15, locating at tetrahedrally coordinated sites. For epoxidation of styrene with O2, Co-SBA-15x exhibited the highest catalytic activity among the cobalt-based catalysts prepared by different method with the same cobalt content, and the single-site Co(II) in Co-SBA-15x was the most active in the reaction. The influences of reaction conditions such as reaction temperature, catalyst amount, solvent, solvent amount, reaction time, oxidant, and oxidant amount on the performance of Co-SBA-15x were also investigated in detail. Co-SBA-15x possessed excellent stability and recyclability in the reaction.