Boosting the low-temperature activity of Cu-SSZ-13 for NH3-SCR by mixing MnCeTiOx: The effect of nitrates on Cu redox cycle

Abstract

A composite catalyst was prepared by mechanically mixing Cu-SSZ-13 and MnCeTiOx to improve selective catalytic reduction (SCR) of NOx by ammonia. The optimal mass ratio of Cu-SSZ-13 and MnCeTiOx components in the composite catalysts was 1:1, where the NOx conversion was improved by around 40% in the temperature range of 150–300 °C compared with Cu-SSZ-13 alone. MnCeTiOx presented significantly stronger ability on the activation of NO to nitrates species than Cu-SSZ-13. Infrared (IR) and density functional theory (DFT) results showed that active nitrates intermediate on MnCeTiOx might migrate to Cu-SSZ-13, which assisted the oxidation of single Cu+ to Cu2+ to complete the Cu redox cycle. This avoided the rate-determining step that formation and oxidation of Cu+ dimers in low-temperature SCR over Cu-SSZ-13. The research results are beneficial to the rational design of SCR catalysts with high-performance at low temperatures.