The catalytic activity of Cu-Cr oxides for the simultaneous removal of NO_x and diesel soot particulate has been investigated with special attention being placed on effects of the composition of oxide catalysts. The temperature programmed reaction technique in which the mixture of a catalyst and soot was heated at a constant rate in an NO+O_2 gas stream was used to evaluate the catalytic performance. Spinel-type CuCr_2O_4 was superior to CuO, Cr_2O_3 and their mechanical mixture in terms of the selectivity to NO_x reduction. The catalytic performance of Cu-Cr oxides depended significantly but complicatedly on the Cr/Cu molar ratio as well as the partial substitution of transition metal and alkali metal cations. The effect of preparation method of CuCr_2O_4 was also studied. As compared with the conventional acetate process, the citric acid-aided process gave the monophasic CuCr_2O_4 spinel at lower temperatures, and the oxides prepared by the citric acid-aided process were more active than those prepared by the acetate process
