Since the emission of diesel soot damages both the environment and human health, a method for the catalytic combustion of soot at low temperatures is needed. In this study, CeO2-based oxides were investigated with respect to their catalytic activities in soot combustion to clarify the roles of ceria and an additive. The oxidation behavior of a carbon black layer over CeO2 and Al2O3 substrates in air was examined by in situ microscopy. While the carbon layer over Al2O3 gradually became thinner with an increase in temperature, it disappeared from the circumference over the CeO2 substrate. The produced gas species was also analyzed during carbon oxidation over CeO2-based catalysts containing a transition metal or rare earth oxide. Complete oxidation to CO2 was facilitated by the addition of transition metal elements to the catalysts, which could be explained by the activities of the catalysts for CO oxidation. Moreover, the effect of the support material on the carbon oxidation activity was studied for supported CuO catalysts. The reducing property of CuO over the support was related to its catalytic activity. (C) 2014 Elsevier B.V. All rights reserved.