Preparation of SiO2–ZrO2–Na2O Porous Glass Supports

A new method for preparing porous supports was investigated by heating a sol-gel-derived SiO2–ZrO2 and SiO2–TiO2 microspherical gel in the presence of NaCl. In the SiO2–ZrO2 system, the surface of the products comprised a sponge-like structure similar to the porous glasses manufactured by the phase-separation method. Their pore volume ranged from 1.48 to 3.18 cm3 g−1 and the surface area ranged from 10 to 48 m2 g−1. They contained a significant amount of Na2O, whereas the Cl content was less than 0.1 wt%. The alkaline durability was excellent, as was expected from the composition of SiO2–ZrO2–Na2O. On the contrary, a heat treatment of the sol-gel-derived SiO2–TiO2 microspherical gel, together with NaCl, caused crystallization of titania and silica, and the formation of glassy mixed oxide was not observed.