Sulfonic acid-functionalized phenylene-bridged periodic mesoporous organosilicas as catalyst materials

Abstract

Three solid acids based on bridged periodic mesoporous organosilica structure (PMO) with a benzene ring as the rigid unit incorporated in the framework and functionalized with anchored sulfonic acid groups were synthesized. Samples were prepared by either sol–gel polymerization of 1,4-bis(triethoxysilyl)benzene (BTEB) or co-condensation of BTEB and 3-mercaptopropyltrimethoxysilane (MPTMS) in the presence of octadecyltrimethylammonium bromide surfactant. Physical characterization data (X-ray powder diffraction, nitrogen adsorption and desorption, and NMR spectroscopy) and acid–base titration indicate the formation of ordered structure and successful functionalization. Catalytic properties were studied in both gas-phase and liquid-phase reactions. The catalytic performance of the PMO-based samples in the isopropylation of phenol in the gas-phase, particularly their stability, exceeds markedly those of functionalized mesoporous ordered materials (MCM-41, HMS and SBA-15). Selectivities in the Fries rearrangement of phenyl acetate over the PMO-based catalysts differ significantly from that of the homogeneous reaction. The sample with benzenesulfonic acid surface functions exhibits higher activities and different selectivities in the dimerization of 2-phenylpropene and in the rearrangement–aromatization of ketoisophorone as compared to samples functionalized with propanesulfonic acid groups.