Preferential oxidation (PROX) of carbon monoxide in excess hydrogen has been studied on low Pt loading (0.5-1 wt%) catalysts supported on a series of FSM-type mesoporous silica materials. A support effect has been observed, in which the catalytic activities are closely related with the pore diameter of the support, despite their similar specific surface areas. Pt nanoparticles supported on mesoporous silica with 4.0 nm pore diameter possess the highest CO conversion over a wide range of reaction temperature, i.e. ca. 100% CO conversion in 298-423 K. As a comparison, the Pt particles in small pore supports (1.8 nm) exhibit poor performance under the same reaction conditions, which is barely comparable to the Pt catalysts on amorphous silica. The discrepancy in the mesoporous silica is proposed to be related with the different activities of surface silanols in various supports. (C) 2009 Elsevier B.V. All rights reserved.