Research progress of hydrothermal stability of metal-based zeolite catalysts in NH₃-SCR reaction

Emission of NO_x from stationary and mobile sources had caused many environmental problems. NH₃ selective catalytic reduction technology (NH₃-SCR) is one of the most effective technologies to eliminate NO_x based on developing high-efficient catalysts. In this review, the catalytic activity for NH₃-SCR, hydrothermal stability and deactivation mechanism of metal-based zeolite catalysts (mainly Cu- and Fe-based zeolite catalysts) employed in NH₃-SCR were summarized. The main factors affecting the hydrothermal stability of Cu- or Fe-based zeolite catalysts in NH₃-SCR, such as Si/Al ratio, zeolite topological structure, metal content, particle size and preparation methods of catalysts, were systematically reviewed. The modification approaches addressed in recent researches which could effectively improve the hydrothermal stability of metal-based zeolites in NH₃-SCR, such as element modification using phosphorus, second active metal, alkali (earth) metal, and surface modification, were discussed. Hopefully, this review could provide a fundamental understanding of the deactivation behaviors of Cu- and Fe-based zeolite catalysts and pave the way towards the improvement of hydrothermal stability of zeolite catalysts in NH₃-SCR.