Imine-bridged periodic mesoporous organosilica as stable high-activity catalytic for Knoevenagel reaction in aqueous medium

An imine-functionalized mesoporous solid base catalyst (BA@BE-PMO) was prepared by template agent-directed self-assembly condensation of bis3-(triethoxysilyl)propyl]amine and 1,2-bis(triethoxysilyl)ethane in acid solution. The imine groups with catalytic activity were integrally embedded into mesopore walls of as-made BA@BE-PMO. In Knoevenagel reactions in aqueous medium, the BA@BE-PMO catalyst exhibited better catalytic activity than imine-functionalized SBA-15 catalyst synthesized using the traditional co-condensation method, which can be attributed to the pore surface with strong hydrophobicity originating from –CH₂CH₂– group fragments incorporated into pore walls. The strong hydrophobicity of the surface facilitates adsorption and diffusion of organic compounds on the catalyst surface in reactions in aqueous medium. Moreover, it exhibited comparable catalytic activity to dipropylamine homogeneous base catalyst because of the uniform dispersion of imine group active sites. The BA@BE-PMO catalyst could also be recovered and reused in up to five runs without significant loss in activity without any negative environmental impact.