Synthesis and characterization of Co(II) salen functionalized MCM-41-type hybrid mesoporous silicas and their applications in catalysis for styrene oxidation with H2O2

Schiff base functionalized MCM-41-type hybrid mesoporous silica (MCM-41-SalenH) was synthesized by co-condensation of tetraethyl orthosilicate (TEOS) and the precursor of salicylaldehyde modified (3-aminopropyl)triethoxysilane (SalenHSi) in the presence of cetyltrimethylammonium bromide (CTAB) followed by surfactant extraction. Imprinting technique was carried out to recover the salicylaldimine groups disrupted during the acid extraction process. The recovery of the Schiff base was confirmed by Fourier transform infrared (FT-IR) spectroscopy. Solid state CP-MAS NMR spectroscopy of 29Si (29Si CP-MAS NMR) showed a highly condensed siloxane network. The co-condensation and imprinting technique produced MCM-41-SalenH hybrid mesoporous silica with uniform mesoscale channels, high specific surface areas (>1200 m2 g−1) and large pore volumes (>1.25 cm3 g−1). Solid oxidation catalysts can be obtained by introducing Co2+ into the hybrid materials via a ligand exchange reaction. The solid catalysts showed higher activity for the liquid-phase oxidation of styrene with H2O2 under mild condition and stability against leaching of active Co2+ compared with the corresponding homogeneous catalysts.