TiO2 and Pt nanoparticles were deposited in the channels of siliceous MCM-48 via a sequential incipient wetness-impregnation method employing (NH4)2PtCl4 as platinum source. The resulting composite Pt/TiO2-MCM-48 (1 wt% Pt, ca. 3 wt% Ti) was characterized using XRD, TEM, nitrogen physisorption, hydrogen chemisorption, UV-vis spectroscopy, and XPS; its catalytic activity for CO oxidation was also explored. These data were compared with those of Pt/MCM-48 prepared via an analogous route. The results reveal that the platinum was deposited inside the intact pore system in both cases. It remains inside upon mild reduction but tends to segregate out of the pore system at higher reduction temperatures or during CO oxidation. Both composites were found to be highly active in CO oxidation, with 50% conversion at 460-475 K after activation of the unreduced catalysts in the (net oxidizing) feed. Striking differences in this activation process between Pt/MCM-48 and Pt/TiO2-MCM-48 suggest that the precursor reduction is influenced by an interaction with the TiO2 component in the latter. © 2009 Springer Science+Business Media, LLC.