TiO2 (40-64 wt%) and ZrO2 (48-62 wt%) were inserted in SBA-15 mesostructured silica by chemical solution decomposition or hydrolysis of the corresponding alkoxides inside the host pores. It yielded composites with 85-94% TiO2 crystallinity (anatase) and > 95% crystallinity of ZrO2 (tetragonal phase). The 4.5 nm (ZrO2) or 5.0 and 8.5 turn (TiO2) nanocrystals did not block the SBA-15 pores, and their surface was fully accessible for adsorbed nitrogen or ethyl acetate molecules. After deposition of 0.3 wt% Pt the activity of Ti(Zr)O-2/SBA-15 materials in ethyl acetate combustion was proportional to the surface area of the corresponding transition metal oxide nanoparticles, being a function of their loading and crystal size. The platinized composite materials displayed 1.7-3 times higher activity compared with platinum on bulk Ti(Zr)O-2 oxides prepared by the same methods and two orders of magnitude higher activity relative to Pt/SBA-15 and Pt/gamma-Al2O3 catalysts. (C) 2003 Elsevier Inc. All rights reserved.