The effects of the sulfur level in diesel exhaust gas and the type of support material (MOx) of the Pt catalyst on the performance of the catalyst with regard to soot oxidation were investigated. The experiments were carried out both under simulated exhaust conditions using granular-formed samples and under practical conditions using a catalyst-loaded diesel particulate filter (DPF) placed in a diesel engine exhaust. Under the simulated conditions, the catalytic activity increased as the SO2 concentration of the reactant gas increased. A promotive effect due to the sulfate produced by the oxidation of SO2 on the Pt surface appeared for soot oxidation when SO2 = 15 ppm, but was markedly lower for SO2 = 1.5 ppm. In the engine tests, the catalytic activity also increased as the sulfur content of the fuel increased. Among the support materials investigated, TiO2 derived from either Ti(SO4)(2) or a TiO2 colloidal sol showed relatively higher activity. (C) 2002 Elsevier Science B.V. All rights reserved.