Strikingly distinctive NH-SCR behavior over Cu-SSZ-13 in the presence of NO.

Commercial Cu-exchanged small-pore SSZ-13 (Cu-SSZ-13) zeolite catalysts are highly active for the standard selective catalytic reduction (SCR) of NO with NH. However, their activity is unexpectedly inhibited in the presence of NO at low temperatures. This is strikingly distinct from the NO-accelerated NO conversion over other typical SCR catalyst systems. Here, we combine kinetic experiments, in situ X-ray absorption spectroscopy, and density functional theory (DFT) calculations to obtain direct evidence that under reaction conditions, strong oxidation by NO forces Cu ions to exist mainly as Cu species (fw-Cu and NH-solvated Cu with high CNs), which impedes the mobility of Cu species. The SCR reaction occurring at these Cu sites with weak mobility shows a higher energy barrier than that of the standard SCR reaction on dynamic binuclear sites. Moreover, the NO-involved SCR reaction tends to occur at the Brønsted acid sites (BASs) rather than the Cu sites. This work clearly explains the strikingly distinctive selective catalytic behavior in this zeolite system.