Investigation of performances of commercial diesel oxidation catalysts for CO, C3H6, and NO oxidation.

Hande Güneş,Deniz Şanli Yildiz,Gökhan Hi̇sar,Selmi Erim Bozbağ,Hüseyin Barkın Özener,Can Erkey

doi:10.3906/kim-2012-18

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, C3H6, and NO oxidation, CO-C3H6 co-oxidation, and CO-C3H6-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 C3H6. CO and C3H6 were observed to inhibit theoxidation of themselves and each other. Addition of Pd to Pt was found to enhance CO and C3H6 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 C3H6 oxidation reactions while NO oxidation performance was enhanced in the presence of CO and C3H6 probably due to the occurrence of reduced Pt and Pd sites during CO and C3H6 oxidations. The optimum Pt:Pd ratio for individual and co-oxidations of CO, C3H6, and NO was found to be Pt:Pd = 3:1 (w/w) in the range of experimental conditions investigated in this study.

Highlights

Aftertreatment systems (ATSs) are used to abate exhaust emissions of diesel vehicles
The heat generated by highly exothermic oxidation of injected diesel in diesel oxidation catalysts (DOCs) is utilized for active regeneration of the diesel particulate filter (DPF) which is generally placed after the DOC
The ratio of NO2 to NOx influences the rate of NOx reduction in selective catalytic reduction (SCR) unit, which is usually placed after the DPF [1]

Summary

Introduction

Aftertreatment systems (ATSs) are used to abate exhaust emissions of diesel vehicles. Kim et al reported similar results for the catalytic activity of NO oxidation [9] In their experiments, catalysts with 50 g/ft PGM loading were used. They found that the overall optimum Pt:Pd ratio was 1.8:1 (w/w) for maximizing hydrocarbon and CO oxidation [11,12,13] Another important factor which affects DOC performance for a particular component is promotion and inhibition effect associated with the composition of the exhaust mixture [14]. Shakya et al observed that the NO2/NOx ratio at the outlet decreased in the presence of various hydrocarbons due to HC-SCR reactions over bimetallic DOCs with total PGM loading of 11 g/ft and Pt:Pd ratios of 1:3, 1:1, 3:1, and 10:1 [8]. Self-inhibition of the feed gases on oxidation reactions as well as their inhibition/promotion effects on the oxidation of one another in the presence of Pt and Pd were investigated

Materials and methods

Results and discussion

Conclusions