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

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 (<10 nm) 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, pKHB > 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.

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► One-pot synthesis of sulfated zirconia-impregnated mesoporous silica.
► Materials with Zr loadings of 28–41% possess polydispersed zirconia nanoparticles.
► The materials catalyse the Meerwin–Ponndorf–Verley reduction of ketones/aldehydes.