Freestanding blocks of mesoporous, titania-silica aerogel catalyst were prepared and tested for gas phase photocatalytic oxidation of trichloroethylene (TCE) in a new photoreactor where the reactant gases flow through the aerogel block. The intimate contact between the reactants and catalyst resulted in a higher conversion. TS01 aerogel was prepared by ethanol supercritical drying, and contained nanometer-sized crystalline domains of anatase TiO2 (i.e., Ti-O-Ti sites) within an amorphous Si-O-Ti and Si-O-Si network. The TSO2 aerogel prepared by CO2 supercritical drying remained amorphous even after high temperature treatment, and analysis indicated that the Ti-O-Si is the predominant site on this catalyst. The reaction results indicated that only the TS01 aerogel containing anatase TiO2 was active, but the formation of dichloroacetaldehyde on the amorphous Si-O-Si sites led to a rapid catalyst deactivation. However, a stable catalyst was obtained after these sites were passivated by ozone pretreatment under ultraviolet (UV) irradiation. The TS01 aerogel catalysts exhibited an average conversion of 30% and a quantum yield of 0.27 at a TCE concentration of 56 ppm, feed flow rate of 40 sccm and UV irradiation of 710 mu W cm(-2). (C) 2007 Elsevier B.V. All rights reserved.