Investigation of performances of commercial diesel oxidation catalysts for $CO,C_3H_6$, andNO oxidation

Abstract

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 $CO,C_3H_6$ , and NO oxidation, C$CO,C_3H_6$ co-oxidation, and $CO,C_3H_6$ -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 $CO,C_3H_6$ . CO and$CO,C_3H_6$ were observed to inhibit the oxidation of themselves and each other. Addition of Pd to Pt was found to enhance CO and $CO,C_3H_6$ 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 $CO,C_3H_6$oxidation reactions while NO oxidation performance was enhanced in the presence of CO and C3 H6 probably due to the occurrence of reduced Pt and Pd sites during CO and $CO,C_3H_6$ oxidations. The optimum Pt:Pd ratio for individual and cooxidations of $CO,C_3H_6$ , and NO was found to be Pt:Pd = 3:1 (w/w) in the range of experimental conditions investigated in this study.