Understanding Catalytic Reactions over Zeolites: A Density Functional Theory Study of Selective Catalytic Reduction of NOx by NH₃ over Cu-SAPO-34

Metal-exchanged CHA-type (SAPO-34 and SSZ-13) zeolites are promising catalysts for selective catalytic reduction (SCR) of NO x by NH 3 . However, an understanding of the process at the molecular level is still limited, which hinders the identification of its mechanism and the design of more efficient zeolite catalysts. In this work, modeling the reaction over Cu-SAPO-34, a periodic density functional theory (DFT) study of NH 3 -SCR was performed using the hybrid functional (HSE06) with the consideration of van der Waals (vdW) interactions. A mechanism with a low N–N coupling barrier is proposed to account for the activation of NO. The redox cycle of Cu 2+ and Cu +, which is crucial for the SCR process, is identified with detailed analyses. In addition, the decomposition of NH 2 NO is shown to readily occur on the Brønsted acid site by a hydrogen push–pull mechanism, confirming the collective efforts of Brønsted acid and Lewis acid (Cu 2+ ) sites. The special electronic and structural properties of Cu-SAPO-34 are demonstrated to play an essential role in the reaction, which may have general implications on the understanding of zeolite catalysis.