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The composite silica-zirconia xerogels have been prepared via sol–gel method using zirconium oxychloride, oxynitrate, acetate and sodium silicate as the precursors. The prepared materials have been characterized using FTIR, TG/DTA, EDX and surface area analyses. It has been established that surface area of silica-zirconia xerogels significantly depends on the zirconium source, but phase transitions and structural features of the xerogels seem to be unaffected by the choice of the zirconia precursor. Prepared xerogels increase the activity of chiral inductor in the asymmetric Biginelli reaction. The anion of the zirconium salt adsorbed on the surface of the synthesized material and the presence of Si–O–Zr heterolinkages determines the reaction yield. The highest chemo- and enantioselectivity towards formation of ee isomer have been provided by the catalyst prepared from zirconium oxychloride.

Gels were prepared via sol-gel method by addition of zirconium oxychloride solution into sodium metasilicate (SZ) and sodium metasilicate solution into zirconium oxychloride (ZS) at varying final pH. Si/Zr molar ratio equaled 1/1. Synthesized gels were dried with calcium chloride until they reached a constant mass. SEM and nitrogen adsorption analysis have shown that SZ gels have surface area 175-200 m 2 g -1, consist of 20-30 nm grains. ZS samples have surface area about 1 m 2 g -1, consist of grains smaller than 10 nm. Thermal and X-ray phase analysis have shown that transition of amorphous ZrO 2 to crystalline form shifts from 430 to 850-870 °C for SZ gels. Unlike zirconia gels phase transitions that proceed in order: "amorphous (430 °C) - tetragonal (800 °C) - monoclinic (1,000 °C) phases", themonoclinic phase inZSgels appears immediately after transition from amorphous to crystalline state; the tetragonal phase in SZ samples is stable until 1,000 °C. © Akadémiai Kiadó, Budapest, Hungary 2012.