NOx reduction behaviour in copper zeolite catalysts for ammonia SCR systems: A review

This paper reviews the current copper substituted zeolite catalysts, their operating temperature ranges with NOx reduction efficiencies and their deactivation mechanisms. Different zeolite candidates suitable for NH₃-SCR are large and medium pore zeolites like ZSM-5, MOR, FER, BEA and small pore zeolites like SSZ-13 and SAPO-34, both having CHA topology. Cu substituted small pore zeolites have demonstrated low temperature NOx reduction with stability at higher temperatures. Cu/SSZ-13 and Cu/SAPO-34 are by far the best catalysts suitable for a broader temperature window and also operate well below 350 °C with good hydrothermal stability. Optimum values of Si/Al ratio (SAR) play a crucial role and hence more studies on variation in SAR and adsorbed monodentate nitrates are required to get a fundamental understanding on their impact on low temperature SCR activity of CHA based catalysts.