Prediction of Cu Zeolite NH(3)-SCR Activity from Variable Temperature (1)H NMR Spectroscopy

Selective catalytic reduction (SCR) of NO(x) by ammonia is one of the dominant pollution abatement technologies for near-zero NO(x) emission diesel engines. A crucial step in the reduction of NO(x) to N(2) with Cu zeolite NH(3)-SCR catalysts is the generation of a multi-electron donating active site, implying the permanent or transient dimerization of Cu ions. Cu atom mobility has been implicated by computational chemistry as a key factor in this process. This report demonstrates how variable temperature (1)H NMR reveals the Cu induced generation of sharp (1)H resonances associated with a low concentration of sites on the zeolite. The onset temperature of the appearance of these signals was found to strongly correlate with the NH(3)-SCR activity and was observed for a range of catalysts covering multiple frameworks (CHA, AEI, AFX, ERI, ERI-CHA, ERI-OFF, *BEA), with different Si/Al ratios and different Cu contents. The results point towards universal applicability of variable temperature NMR to predict the activity of a Cu-zeolite SCR catalyst. The unique relationship of a spectroscopic feature with catalytic behavior for zeolites with different structures and chemical compositions is exceptional in heterogeneous catalysis.