Cerium containing mordenites catalysts were prepared by impregnation (CeMimp), solid-state ion exchange (CeMss) and in situ incorporation during synthesis (CeMin). The structure of the samples has been investigated by X-ray diffraction. FT-IR, N-2 adsorption, thermal analyses (TG and DTA) and pyridine-FT-IR. Water-gas shift reaction (WGSR) was carried out over various catalysts and the catalytic reaction was monitored using in situ FT-IR. The results obtained showed the presence of cerium silicate phase, in case of CeMin sample as evidenced by XRD and FT-IR spectroscopy. In case of CeMimp and CeMss, a separate CeO2, phase was observed in a highly dispersed state in the former than in the latter, which measured the highest specific surface area. FT-IR results of pyridine adsorption indicate the presence of acid-base site pairs on the surface of CeMimp and CeMss samples where only Lewis acidity was found on CeMin, reflecting the presence of Ce3+ with Si4+ cations at tetrahedral lattice sites in mordenite. CeMimp showed the highest catalytic activity followed by CeMss. It has been shown that reduction by H-2 carried out at 500degreesC was responsible for activating different carbonyls attached to Ce3+; such as Ce3+-CO and Ce3+-(CO)2 which decomposed into CO2 (ads). The role of basicity, Ce dispersion and surface texture of reduced Ce-mordenites on their catalytic activity in CO oxidation by H2O was evaluated and discussed. (C) 2004 Elsevier B.V. All rights reserved.