Selective oxidation of CO in a H-2-rich gas stream was investigated over a series of Pt-Ce and Pt-Sn catalysts supported on activated carbon (AC). In order to study the effect of AC surface chemistry on the catalytic performance of AC supported catalysts, three types of activated carbon, namely (i) grinded and HCl washed activated carbon (ACl), (ii) air-oxidized form of AC I (AC2), and (iii) HNO3 oxidized form of AC I (AC3), were prepared and used as catalyst supports. The results have shown that the activities of AC supported catalysts increased with the increase in reduction temperature. Higher conversion levels were observed for 1% CeOx-1 % Pt/AC and 0.25% SnOx-1% Pt/AC catalysts supported on oxidized AC supports compared to those prepared on non-oxidized support. Between these catalysts, the highest activity, ca. 80% CO conversion, is obtained on 0.25% SnOx-1% Pt/AC2. (C) 2003 Elsevier Science B.V. All rights reserved.