Amine-bridged periodic mesoporous organosilica nanospheres as an active and reusable solid base-catalyst for water-medium and solvent-free organic reactions

An amine-bridged periodic mesoporous organosilica catalyst in uniform nanospheres (∼85 nm) (NH-PMO-NS) was synthesized by surfactant-directed co-condensation between amine-bridged silane and tetraethoxysilane (TEOS). As-prepared NH-PMO-NS contained short and straight mesoporous channels with amine-groups integrally incorporated into silica walls. In water-medium Knoevenagel condensation and solvent-free Henry reactions, this catalyst exhibited much higher activity and selectivity than both the common amine-bridged PMO (NH-PMO-com) with irregular shape synthesized by traditional method and the amine-functionalized MCM-41 in nanospheres (NH-MCM-NS) prepared by grafting amine-groups onto the pore surface. In addition, it displayed comparable catalytic efficiencies with the homogeneous base-catalyst (diethylamine), and could also be easily recovered and used repetitively. Based on the structural characterizations and kinetic studies, the high catalytic activity and selectivity were ascribed to the short and straight mesoporous channels in nanospheres with amine-groups incorporated into silica walls. The accessible basic catalytic sites may facilitate the diffusion and thus, promoted the adsorption of organic reactant molecules, leading to the enhanced activity and selectivity.

Amine organocatalyst incorporated into silica walls of PMO nanospheres was synthesized by surfactant directed co-concentration, which exhibited comparable efficiencies with the diethylamine homogeneous catalyst in water-medium and even solvent-free organic reactions, and could be easily recycled and used repetitively.Figure optionsDownload high-quality image (344 K)Download as PowerPoint slideHighlights
► A PMO-type solid base-catalyst in uniform nanospheres (∼85 nm) was prepared.
► Amine-groups were incorporated into silica walls of mesoporous channels.
► The catalyst showed matchable catalytic efficiency with the homogeneous catalyst.
► The catalyst could be easily recycled and used repetitively.