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 SO 2 poisoning and high N 2 O formation for MnO x based catalysts hinder its application in selective catalytic reduction (SCR) of NO x with NH 3 . The SO 2 poisoning mechanism has been well demonstrated, but the N 2 O formation mechanism was still controversial due to previous limited study. Herein, MnO 2 supported on MO x (Mn/M, M = Al, Si and Ti) were prepared by wet impregnation method to investigate the carrier effect on the formation of N 2 O. 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 NH 3 and NO + O 2 . Accordingly, the activation of NH 3 and NO + O 2 on MnTi was respectively occurred on TiO 2 and MnO 2 , but both NH 3 and NO + O 2 was activated on MnO 2 over MnAl and MnSi samples. The over-activation (NH 2 dissociated into NH) of NH 3 would be effectively inhibited when NH 3 activation was occurred on TiO 2 , thus it can significantly suppress the formation of N 2 O. In contrast, the NH 3 species would sharply decompose into NH on MnO 2 and then lead to the high amount of N 2 O. Finally, we proposed some methods that might effectively improve the selectivity of MnO x- based catalysts.
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