Recent advances and perspectives in the resistance of SO2 and H2O of cerium-based catalysts for NOx selective catalytic reduction with ammonia

Abstract

NO_x is one of the most severe air contaminants, which mainly comes from fixed sources and has a tremendous negative impact on public health and regional air quality. The treatment of NO_x has become an important issue. Among numerous NO_x emission control technologies, selective catalytic reduction using ammonia as the reducing agent (NH₃-SCR) is regarded as the most effective and mature technique with 40 years of development. Currently, commercial NH₃-SCR catalysts are mainly vanadium-based catalysts; however, V₂O₅ is identified as a biotoxic species. A cerium-based catalyst is a kind of environment friendly catalyst for NH₃-SCR. However, exhaust gas usually contains a small amount of SO₂ and H₂O vapor under actual conditions, inhibiting the NH₃-SCR reaction with cerium-based catalysts. Therefore, improving the resistance of SO₂ and H₂O of cerium-based catalysts has become a research hotspot in recent years. This review presents a unified discussion of the significant work published in the field of the resistance of SO₂ and H₂O of cerium-based catalysts for NH₃-SCR. It emphasizes the reaction mechanism and aspects of cerium-based catalysts at different levels: metal modification, preparation methods, and structures. The discussion is then extended to the essential conclusions from cerium-based catalyst modification and recommendations for future directions to develop a catalytic system that will degenerate NO_x over non-noble metal catalysts with high resistance of SO₂ and H₂O.