TiO2(SiO2)x and ZrO2(SiO2)x Cryogels as Catalysts for the Citronellal Cyclization to Isopulegol

Abstract

TiO2(SiO2)x and ZrO2(SiO2)x mixed oxides prepared by a simple sol–gel procedure plus freeze-drying achieve very high surface areas. Such cryogels are shown to catalyze the cyclization of citronellal to isopulegol. The dispersion of the active metal has been optimized, as it is shown that high specific surface areas are the key for the catalytic activity of the cogels. Nevertheless zirconia–silica cryogels depict much higher catalytic activity, with only 5 mol% Zr being required, than the corresponding titania-silica mixed oxides.