日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

The selective reduction reaction of NOx (NH₃-SCR) using NH₃ as a reducing agent has been commercialized as a core technology of a urea-SCR system for diesel vehicles. A recent hot topic in heterogeneous catalysis is fundamental research for understanding the high NH₃-SCR performance and high durability of Cu ion-exchanged small pore zeolites such as Cu-CHA. This paper describes our recent results on the mechanism of NH₃-SCR over Cu ion-exchanged AFX zeolite (Cu-AFX) studied by using various in situ spectroscopic methods. It is concluded that Cu²⁺-NH₃ complexes react with NO to produce N₂, H⁺ and Cu⁺ (reduction half cycle), and subsequent reaction of Cu⁺ and H⁺ with O₂ to yield water and Cu²⁺ (oxidation half cycle). The active species are Cu ions and the role of zeolites is simply to provide ion exchange sites for Cu²⁺/Cu⁺ ions and proton.