A Study on the Improvement of NO_x Reduction Efficiency for a Urea SCR System

摘要

Urea SCR (Selective Catalytic Reduction) exhaust after-treatment systems are one of the most promising measures to reduce NO_x emissions from diesel engines. Both Cu-zeolite (Cu-SCR) and Fe-zeolite (Fe-SCR) urea SCR systems have been studied extensively but not many detailed studies have been conducted on the combination of both systems. Thus, we carried out studies on such Combined-SCR systems and their capability to reduce NO_x under various engine operating conditions. We also conducted transient engine tests using different catalyst systems to compare their performance. The results show that combined-SCR systems can reduce NO_x more effectively than Fe-SCR or Cu-SCR alone. The best NO_x reduction performance was achieved at a Cu ratio of 0.667 (i.e. Fe: Cu =1: 2). Combined-SCR thus apparently benefits from the characteristics of both Cu-SCR and Fe-SCR, allowing it to reduce NO_x over a wide range of operating conditions.