Enhanced catalytic performances by surface silylation of Cu(II) Schiff base-containing SBA-15 in epoxidation of styrene with H2O2

Schiff base functionalized SBA-15 mesoporous materials were synthesized by post-grafting of salicylaldehyde onto silylated and non-silylated amino-modified SBA-15 and followed by the introduction of Cu(II) ions via a ligand exchange reaction. Both hybrid materials prepared were characterized by XRD, FT-IR, UV-vis spectroscopy, N2 adsorption/desorption, TG/DTA and ICP-AES techniques and comparatively examined as catalysts in epoxidation of styrene with 30 wt.% aqueous hydrogen peroxide as oxidant. It was found that the silylated material was more active and selective to styrene oxide than the non-silylated one in CH3CN. The considerably improved activity (86.1%) and styrene oxide selectivity (95.2%) were achieved after 30 min when adding sodium hydroxide to maintain a pH of 7.5-8.0 in reaction medium. Moreover, the silylated catalyst showed good recoverability and relatively high stability against leaching of active copper species. These superior effects were attributed to the high hydrophobic character of the solid surface produced by the silanol neutralization.