Evaluation of amines for the selective catalytic reduction (SCR) of NOx from diesel engine exhaust

Abstract With a view to developing onboard generation of selective reductants for NO x removal from diesel engine exhaust we compared the performance of a primary, secondary and tertiary amine to NH 3 using a typical mini core NH 3 -SCR catalyst. Primary amines with short hydrocarbon chains, e.g. CH 3 NH 2 (maximum NO x conversion, 50%) approached the NO x conversion obtained using NH 3 (maximum NO x conversion, 70%). Increasing the amine to NO x ratio greater than 1 results in NO x conversions closer to those of NH 3 (maximum NO x conversion increased to 60%). Secondary and tertiary amines had smaller NO x conversions as a function of temperature and the drop in NO and NO x conversion decreased with increasing amine hydrogen substitution. Also, the maximum NO x conversion for each reductant tends to move to a lower temperature as the degree of substitution increases. Unlike NH 3 , the amines can react in the gas phase at temperatures within the range of diesel engine exhaust. Due to this gas phase reactivity the NO x conversions measured using the mini core SCR catalyst also contain a gas phase conversion component. Gas phase conversions were investigated by replacing the mini core SCR catalyst with an equivalent length of quartz beads. Subtraction of the two results highlighted the differences between the mini core catalytic and gas phase conversions measured in this manner over the temperature range investigated. These differential NO x conversions for the three amines had maxima at about 375 °C.