Institute for Integrated Catalysis, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99352, United States.
J Am Chem Soc. 2017 Apr 5;139(13):4935-4942. doi: 10.1021/jacs.7b01128. Epub 2017 Mar 21.
Active centers in Cu/SSZ-13 selective catalytic reduction (SCR) catalysts have been recently identified as isolated Cu and [Cu(OH)] ions. A redox reaction mechanism has also been established, where Cu ions cycle between Cu and Cu oxidation states during SCR reaction. While the mechanism for the reduction half-cycle (Cu → Cu) is reasonably well-understood, that for the oxidation half-cycle (Cu → Cu) remains an unsettled debate. Herein we report detailed reaction kinetics on low-temperature standard NH-SCR, supplemented by DFT calculations, as strong evidence that the low-temperature oxidation half-cycle occurs with the participation of two isolated Cu ions via formation of a transient [Cu(NH)]-O-[Cu(NH)] intermediate. The feasibility of this reaction mechanism is confirmed from DFT calculations, and the simulated energy barrier and rate constants are consistent with experimental findings. Significantly, the low-temperature standard SCR mechanism proposed here provides full consistency with low-temperature SCR kinetics.
Cu/SSZ-13 选择性催化还原（SCR）催化剂中的活性中心最近被确定为孤立的 Cu 和 [Cu(OH)] 离子。也建立了一种氧化还原反应机制，其中 Cu 离子在 SCR 反应过程中在 Cu 和 Cu 氧化态之间循环。虽然还原半循环（Cu → Cu）的机制已经得到了很好的理解，但氧化半循环（Cu → Cu）的机制仍然存在争议。本文通过详细的低温标准 NH-SCR 反应动力学研究，并辅以 DFT 计算，提供了强有力的证据，表明低温氧化半循环通过形成瞬态 [Cu(NH)]-O-[Cu(NH)] 中间体，涉及两个孤立的 Cu 离子的参与。从 DFT 计算中证实了该反应机制的可行性，模拟的能垒和速率常数与实验结果一致。重要的是，这里提出的低温标准 SCR 机制与低温 SCR 动力学完全一致。
