The one-pot synthesis, characterisation and catalytic behaviour of mesoporous silica-sulfated zirconia solids

摘要

A series of non-periodic mesoporous silicas impregnated with both framework and nanocrystalline sulfated zirconia was prepared by a sol-gel process using an ionic liquid as a template. The physico-chemical properties of the mesoporous sulfated zirconia materials are described. Analysis of the new silicas indicates isomorphous substitution of silicon with zirconium and reveals the presence of extremely small (<10nm) polydispersed zirconia nanoparticles in the materials with zirconium loadings of 28-41 wt.%. The materials with higher zirconium loadings catalyse the Meerwin-Ponndorf-Verley reductions of aldehydes and ketones for substrates with hydrogen-bond basicities, pK_(HB)>1.10. In order to explain the catalytic activity, analysis of the acid sites of the materials using pyridine as a probe molecule reveals that in all cases the majority are Bronsted acid sites, with only a small number of Lewis acid sites present in those materials with low zirconium loadings.