Revealing the Formation and Reactivity of Cage-Confined Cu Pairs in Catalytic NO x Reduction over Cu-SSZ-13 Zeolites by In Situ UV-Vis Spectroscopy and Time-Dependent DFT Calculation

The low-temperature mechanism of chabazite-type small-poreCu-SSZ-13zeolite, a state-of-the-art catalyst for ammonia-assisted selectivereduction (NH3-SCR) of toxic NO x pollutants from heavy-duty vehicles, remains a debate and needsto be clarified for further improvement of NH3-SCR performance.In this study, we established experimental protocols to follow thedynamic redox cycling (i.e., Cu-II & LRARR;Cu-I) of Cu sites in Cu-SSZ-13 during low-temperature NH3-SCR catalysis by in situ ultraviolet-visiblespectroscopy and in situ infrared spectroscopy. Furtherintegrating the in situ spectroscopic observationswith time-dependent density functional theory calculations allowsus to identify two cage-confined transient states, namely, the O-2-bridged Cu dimers (i.e., & mu;-& eta;(2):& eta;(2)-peroxodiamino dicopper) and the proximatelypaired, chemically nonbonded Cu-I(NH3)(2) sites, and to confirm the Cu-I(NH3)(2) pair as a precursor to the O-2-bridged Cu dimer. Comparativetransient experiments reveal a particularly high reactivity of theCu(I)(NH3)(2) pairs for NO-to-N-2 reduction at low temperatures. Our study demonstrates direct experimentalevidence for the transient formation and high reactivity of proximatelypaired Cu-I sites under zeolite confinement and providesnew insights into the monomeric-to-dimeric Cu transformation for completingthe Cu redox cycle in low-temperature NH3-SCR catalysisover Cu-SSZ-13. Thisstudy provides new insights into the strongly debatedlow-temperature mechanism of Cu-SSZ-13 zeolite as a state-of-the-artNH(3)-SCR catalyst for abating automotive NO x emissions.

Automated summary

This study reveals the low-temperature mechanism of Cu-SSZ-13 zeolite in the NH3-SCR catalysis process, identifying two transient states: O-2-bridged Cu dimers and proximately paired, chemically nonbonded Cu-I(NH3)(2) sites. It demonstrates the high reactivity of Cu(I)(NH3)(2) for NO-to-N-2 reduction at low temperatures. By providing experimental evidence, this study contributes valuable insights into the Cu redox cycle and the design of advanced catalysts for reducing automotive NOx emissions.