Insight into the effect of carrier on N2O formation over MnO2/MOx (M = Al, Si and Ti) catalysts for selective catalytic reduction (SCR) of NOx with NH3

The problems of easily inactivated by SO2 poisoning and high N2O formation for MnOx based catalysts hinder its application in selective catalytic reduction (SCR) of NOx with NH3. The SO2 poisoning mechanism has been well demonstrated, but the N2O formation mechanism was still controversial due to previous limited study. Herein, MnO2 supported on MOx (Mn/M, M= Al, Si and Ti) were prepared by wet impregnation method to investigate the carrier effect on the formation of N2O. Although all of selected supports had a large amount of surface acid sites, only forming strong active-support interaction can separate the activation sites of NH3 and NO+ O-2. Accordingly, the activation of NH3 and NO+ O-2 on MnTi was respectively occurred on TiO2 and MnO2, but both NH3 and NO+ O-2 was activated on MnO2 over MnAl and MnSi samples. The over-activation (NH2 dissociated into NH) of NH3 would be effectively inhibited when NH3 activation was occurred on TiO2, thus it can significantly suppress the formation of N2O. In contrast, the NH3 species would sharply decompose into NH on MnO2 and then lead to the high amount of N2O. Finally, we proposed some methods that might effectively improve the selectivity of MnOx-based catalysts.