Experimental study on the performance and diagnosis of hydrothermally aged selective catalytic reduction over a copper-based catalyst

Abstract

The conversion of nitrogen oxides (NOx) by hydrothermally aged copper (Cu)–based selective catalytic reduction (SCR) is an irreversible phenomenon. Tail exhaust NOx emission control and on-board diagnostics (OBD) monitoring are difficult with hydrothermally aged Cu–based SCR because the on-board NOx sensor has cross sensitivity to NH3 in the exhaust. In this study, the performance and diagnosis of hydrothermally aged SCR under real engine exhaust were studied. The influence of hydrothermally aged SCR on NH3 storage, tail exhaust NOx, urea injection, and OBD diagnosis were quantitatively analyzed under the World Harmonized Transient Cycle (WHTC). The results show that hydrothermally aged SCR had a great influence on the NH3 storage capacity. In terms of SCR conversion efficiency and OBD detection, compared with fresh SCR, hydrothermally aged SCR was more sensitive to space velocity than to temperature. Under different OBD monitored release conditions, the NOx conversion efficiency was greatly different; hence, the occurrence of a false diagnosis can be avoided through the selection of appropriate release conditions. These research results provide a reference for SCR size design, NOx control, and diagnostic strategies.