Support effect and reaction pathway for NO direct decomposition over CuMn/A (A=ZSM-5, Beta, SSZ-13) catalysts

The CuMn/ZSM-5 (CM/Z), CuMn/Beta (CM/B), and CuMn/SSZ-13 (CM/S) catalyst samples were prepared via an excess impregnation method to investigate the metal-support effect. The results show that the activity at 550 °C for NO direct decomposition follows the order of CM/Z (53.4%) > CM/B (49.2%) > CM/S (7.9%). The good activity and stability of CM/Z are attributed to a strong support effect including forming more active copper sites of the (Cu²⁺-O^2--Cu²⁺)²⁺ and (Cu⁺-□-Cu⁺)²⁺ dimers, which have higher redox activity, capacity of oxygen mobility, and NO sorption capability. The competitive adsorption between NO and O₂ on the oxygen vacancy of dimers over CM/Z results in the activity decrease from 53.4% to 40.3% at 550 °C after adding 1 vol% O₂. The reaction mechanism over CM/Z was discussed based on the in situ DRIFT and isotopic (¹⁸O₂) experiments. Two NO adsorbs firstly on (Cu⁺-□-Cu⁺)²⁺ to form N₂O^, and N₂O is activated to produce N₂, followed by the NO adsorption on (Cu²⁺-O^2--Cu²⁺)²⁺ to form nitrite and nitrate species and decomposition to NO and O₂.