Silica-supported TiO2 powders were synthesized by a wet method under mild conditions. The aim of the work was the preparation of TiO2/SiO2 additives for photocatalytic cements. Three types of commercial SiO2 were used as supports: Cabot, Axim and Fly Ash. Cabot silica was ultra-pure whereas the other two silica contained different percentages of various oxides. The TiO2/SiO2 samples, denoted TiO2/Cabot, TiO2/Axim and TiO2/Fly Ash, were prepared by boiling suspensions obtained by addition of silica to a solution of TiCl4 in water (volume ratio 1:10). The photocatalytic activity was evaluated in a gas-solid system both in batch and in continuous reactors using 2-propanol as probe molecule. SEM-EDX analysis revealed that titanium dioxide was quantitatively deposited on silica. TiO2/Axim and TiO2/Fly Ash were scarcely active whereas a good photoactivity was exhibited by the TiO2/Cabot sample both in the batch and in the continuous system. Consequently only the last sample was tested for both NO, abatement and for 4-nitrophenol photodegradation in a liquid-solid system. (C) 2009 Elsevier B.V. All rights reserved.