Mechanistic insights into the promotion of low-temperature NH3-SCR catalysis by copper auto-reduction in Cu-zeolites

The performance of Cu-chabazite (Cu-CHA) zeolite, the state-of-art catalyst for the ammonia-assisted selective reduction (NH3-SCR) of toxic NOx pollutants from heavy-duty diesel vehicles, is insufficient at low reaction temperatures and needs to be improved for meeting stringent emission regulations. Here, we demonstrate that the auto-reduction of isolated Cu sites (i.e. Cu2+[OH]-> Cu+) in Cu-CHA could promote the low-temperature NOx abatement efficiency in NH3-SCR. Combining in situ spectroscopy, steady-state/transient kinetic measurements and computational simulations, we unveiled that Cu auto-reduction, which was driven by non-oxidative thermal activation, weakened the Cu tethering to CHA framework and thus increased the Cu mobility, particularly, in the presence of NH3. More importantly, auto-reduction-induced charge redistribution favored NO activation to form intimately interacted Cu+center dot center dot center dot NO+ pairs, which enabled alternative and highly efficient pathways leading to drastically promoted NO abatement at temperatures below 250 degrees C. These mechanistic findings shed new light on tuning the speciation of Cu single-sites to promote NOx reduction catalysis over Cu-zeolites.