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

A composite catalyst was prepared by mechanically mixing Cu-SSZ-13 and MnCeTiO x to improve selective catalytic reduction (SCR) of NO x by ammonia. The optimal mass ratio of Cu-SSZ-13 and MnCeTiO x components in the composite catalysts was 1:1, where the NO x conversion was improved by around 40% in the temperature range of 150-300 °C compared with Cu-SSZ-13 alone. MnCeTiO x 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 MnCeTiO x might migrate to Cu-SSZ-13, which assisted the oxidation of single Cu + to Cu 2+ 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. • Superior low-temperature performance achieved in MnCeTiO x /Cu-SSZ-13 hybrid catalysts. • NO and NH 3 were activated on MnCeTiO x and Cu-SSZ-13, respectively. • NO was activated to nitrates by lattice oxygen in MnCeTiO x . • Nitrates might transfer to the Cu-SSZ-13 and oxidize single Cu + directly. • The accelerated redox cycle of Cu ions boosts low-temperature activity.