Estimating the In-use Degradation Mechanism of a Pre-oxidation Catalyst for Heavy-duty Urea-SCR Vehicles Complying with the New Long-term Target-based Regulation in Japan

Abstract

Urea-SCR systems have been installed in heavy-duty vehicles for complying with the new long-term target-based regulation in Japan, contributing to reduce NO_x emissions. However, in fiscal 2011, a survey of Ministry of the Environment, Japan reported in-use degradation of the systems in heavy-duty urea-SCR vehicles. In fiscal 2012, in-use degradation mechanisms of a SCR catalyst and ammonia slip catalyst were reported to be hydro carbon poisoning. On the other hand, the degradation mechanism of a pre-oxidation catalyst has been a remained issue in the urea-SCR systems. We studied the in-use degradation mechanism of a pre-oxidation catalyst in urea-SCR systems and revealed temperature and sulfur conditions impacting on the degradation.