Copper loading effect on active species formation over Cu/SSZ-13 catalysts for selective catalytic oxidation of high-concentration NH3

Abstract

Cu/SSZ-13 catalysts not only exhibit superior SCR performance but also possess excellent selective catalytic oxidation (SCO) ability to remove NH3 escaped from engine exhaust gas fueled by NH3. To elucidate the effect of Cu loading on Cu/SSZ-13 catalysts, a series of Cu/SSZ-13 catalysts were prepared through wet impregnation method to remove high-concentration NH3 (5000 ppm). The SCO activity test results showed that when Cu loading increased from 1% to 10%, there was an obvious improvement effect on NH3 conversion performance at low temperature. Cu10/SSZ-13 catalyst reached a high NH3 conversion of 96% at 250 °C, and N2 selectivity was higher than 86% in the whole temperature range. However, when further increasing Cu loading from 10% to 20%, there was no distinctive difference in NH3 conversion and N2 selectivity. The characterization results indicated that there were abundant active species, adsorbed oxygen species, and acid sites on the surface of Cu10/SSZ-13 catalyst. The [Cu(OH)]+ and isolated Cu2+ species in zeolite channels of Cu10/SSZ-13 catalyst rather than CuO species on the surface played a key role in NH3-SCO reactions. Since 20% Cu loading would result in a significant decrease in isolated Cu2+ species, it resulted in both [Cu(OH)]+ species in zeolite channels and superfluous Cu species on zeolite surface being main active species in NH3-SCO reactions. In-situ DRIFTS experiments suggested that NH3-SCO reactions over Cu/SSZ-13 catalysts followed the internal selective catalytic reduction (i-SCR) mechanism.