Knowledge and know-how in improving the sulfur tolerance of deNOx catalysts

Catalytic removal of NOx under lean-burn conditions is challenging to attain the future stringent NOx emission standards. Selective catalytic reduction (SCR) of NOx with different reducing agents and NOx storage-reduction (NSR) are viewed as the two most promising technologies for NOx removal. Although a variety of catalytic systems have been developed for these processes, their practical applications remain difficult due to catalyst deactivation caused by SO2 in the exhaust gases. Therefore, improving catalyst tolerance against SO2 is one of the most important targets in the deNOx catalyst development. This review focuses on the knowledge and know-how that have been developed in improving the sulfur tolerance of deNOx catalysts. Ag/Al2O3 is the most promising catalyst for the HC-SCR of NOx. Support modification, H2 co-feeding and some other strategies to improve the sulfur tolerance of Ag/Al2O3 are discussed. Some novel catalyst systems with high sulfur tolerance for NH3-SCR, H2-SCR and NSR are addressed, respectively. For NSR catalysts, developing novel sulfur resistant NOx storage systems and effective desulfation processes seem to be two avenues to improve their sulfur resistance.