The effect of metal additives on the catalytic performance of Rh/SiO2 for the selective reduction of NO with H-2 in the presence Of O-2 and SO2 was investigated. The addition of Zn was effective to enhance the catalytic activity of Rh/SiO2 for NO reduction at low temperatures and high O-2 concentrations. The structural characterizations of Zn/Rh/SiO2 samples and in situ FT-IR measurements revealed that Zn additive plays two important roles in enhancing the catalytic activity of Rh/SiO2: (i) prevention of catalyst deactivation as an oxidation-retardant for the active Rh metal species supported on SiO2 and (ii) promotion of a reaction step, which generates NHx species as a key reaction intermediate for NO reduction by H-2 in the presence Of O-2 and SO2. (c) 2005 Elsevier B.V. All rights reserved.