Investigation of performances of commercial diesel oxidation catalysts for CO, CH, and NO oxidation.

Four commercial monolithic diesel oxidation catalysts (DOCs) with two different platinum group metal (PGM) loadings and Pt:Pd ratios of 1:0, 2:1, 3:1 (w/w) were investigated systematically for CO, CH, and NO oxidation, CO-CH co-oxidation, and CO-CH-NO oxidation reactions via transient activity measurements in a simulated diesel engine exhaust environment. As PGM loading increased, light-off curves shifted to lower temperatures for individual and co-oxidation reactions of CO and CH. CO and CH were observed to inhibit theoxidation of themselves and each other. Addition of Pd to Pt was found to enhance CO and CH oxidation performance of the catalysts while the presence and amount of Pd was found to increase the extent of self-inhibition of NO oxidation. NO inhibited CO and CH oxidation reactions while NO oxidation performance was enhanced in the presence of CO and CH probably due to the occurrence of reduced Pt and Pd sites during CO and CH oxidations. The optimum Pt:Pd ratio for individual and co-oxidations of CO, CH, and NO was found to be Pt:Pd = 3:1 (w/w) in the range of experimental conditions investigated in this study.