Insight into the effects of Cu ions and CuO species in Cu-SSZ-13 catalysts for selective catalytic reduction of NO by NH.

Different Cu precursors were adopted to adjust the isolated Cu ions and CuO species in the Cu-SSZ-13 catalysts. The Cu ions were mainly located at eight-member rings in the catalysts with the Cu precursors of Cu(NO) (Fresh-I) and CuSO (Fresh-II), while that located at six-member rings in the catalysts with the Cu precursors of CuCl (Fresh-III) and Cu(CHCOO) (Fresh-IV). All catalysts showed>90% of NO conversion and 100% of N selectivity at 200-680 °C. Fresh-I and Fresh-II catalysts showed an unexpected increase of the high-temperature activity after hydrothermal treatment. The characterizations revealed that the hydrothermal treatment promoted the production of CuO species, which accelerated the adsorption of NO species to enhance the high-temperature SCR activity. Moreover, the SCR reaction pathway changed from Langmuir-Hinshelwood to Eley-Rideal mechanisms for the Fresh-II catalyst after the hydrothermal treatment, which was verified by in situ DRIFTS.