The influence of molybdenum on ceria activity, CO2 selectivity and resistance to sulphur poisoning was investigated. Different molybdenum-cerium catalysts, with various atomic ratios (Mo/Ce = 0.001, 0.01, 0.1, 0.2 and 0.3), have been prepared and tested with respect to carbon black (CB) combustion and the oxidation of propene before and after treatment under SO2. Based on their catalytic behaviour and according to molybdenum loadings, the catalysts have been classified into two groups: (i) ceria and low molybdenum loading catalysts (1Mo1000Ce, 1Mo100Ce) which present a good activity, an excellent CO2 selectivity and a bad resistance to sulphur poisoning; (ii) catalysts containing higher molybdenum loadings (1Mo10Ce, 2Mo10Ce, 3Mo10Ce) show lower activity and CO2 selectivity but a better resistance to sulphur poisoning. The role of molybdenum against ceria sulphur poisoning has been evidenced. (C) 2003 Elsevier B.V. All rights reserved.