Mechanism, performance and modification methods for NH3-SCR catalysts: A review

Air pollution and climate issues are becoming serious, and particularly NOx cause acid rain, ozone hole and disease of respiratory system for humans, which mainly come from automobile and industrial exhaust emissions. Selective catalyst reduction (SCR) with NH3 as reducing agent is widely employed to eliminate NOx, and the selection of catalyst has a decisive effect in the final conversion. The modification methods of catalysts, such as addition of second metal, replacement of support, optimization of structure, pretreatment and post-treatment are systematically reviewed. For zeolite catalysts, the reaction mechanism and SO2 poisoning theory are analyzed. In addition, effects of catalyst parameters on denitrification efficiency are summarized, including Si/Al ratio, Cu or Fe loading, specific surface area, coordination structure and calcination temperature. Effects of spatial structure of spinel and perovskite catalysts on catalytic effect are analyzed, and the performance of catalysts with different components is compared. Finally, the current problems of catalyst research are summarized and the development of NH3-SCR technology are prospected.