Assessing the Influence of Zeolite Composition on Oxygen-Bridged Diamino Dicopper(II) Complexes in Cu-CHA DeNOX Catalysts by Machine Learning-Assisted X-ray Absorption Spectroscopy

ABSTRACT: Cu-exchanged chabazite is the catalyst of choice for NOx abatement in diesel vehicles aftertreatment systems via ammonia-assisted selective catalytic reduction (NH3??? SCR). Herein, we exploit in situ X-ray absorption spectroscopy powered by wavelet transform analysis and machine learning-assisted fitting to assess the impact of the zeolite composition on NH3-mobilized Cu-complexes formed during the reduction and oxidation half-cycles in NH3??? SCR at 200 ??C. Comparatively analyzing well-characterized Cu-CHA catalysts, we show that the Si/Al ratio of the zeolite host affects the structure of mobile dicopper(II) complexes formed during the oxidation of the [CuI(NH3)2]+ complexes by O2. Al-rich zeolites promote a planar coordination motif with longer Cu???Cu interatomic distances, while at higher Si/Al values, a bent motif with shorter internuclear separations is also observed. This is paralleled by a more efficient oxidation at a given volumetric Cu density at lower Si/Al, beneficial for the NOx conversion under NH3???SCR conditions at 200 ??C.

Automated summary

This study investigates the mechanism of Cu-exchanged chabazite catalyst in NH3-SCR using in situ X-ray absorption spectroscopy. It is found that the Si/Al ratio of the zeolite affects the structure of Cu-complexes, thereby influencing the catalytic performance of the catalyst.