Revealing the mechanisms of NH3 adsorption and reactions in catalytic NOx reduction over Cux/CHA zeolites by in situ DRIFTS spectroscopy

Adsorption and activation of NH3 on Cu-SSZ-13 were essential for NOx removal, however, their important role at the molecular level remains unclear. In this work, the Al-rich Cu/SSZ-13 (Cux/CHA) catalysts were synthesized by the incipient-wetness impregnation method, and the NH3-SCR performance was investigated. It is found that high Cu content promoted the formation of Z-[Cu(OH)]+ and CuOx particles, enhanced the adsorption capacity of NOx, and increased the intra-zeolite oxolation process in the Cux/CHA catalysts. In situ DRIFTS results showed that the Z-[Cu(OH)(NH3)x]+(x<3) exhibited analogous properties to B-NH4+, but it would convert to Z-[Cu(OH)(NH3)3]+ with increasing NH3 adsorption time and exhibit L-NH3 properties. Those findings could provide a new insight into understanding the adsorption and activation of NH3 in low-temperature reactions, as well as new ideas for improving NOx conversion during cold start.