Selective Catalytic Reduction of NO in Excess Oxygen by Methane over Mn/ZSM-5 Catalysts

The selective catalytic reduction of NO in excess O-2 by CH4 was investigated over a series of ZSM-5-supported manganese catalysts (Mn/ZSM-5) The catalytic activity depended on preparation method and Mn loading An ion exchange method resulted in a higher activity than an impregnation method Catalytic activity increased with increasing Mn loading until a Mn loading of 2 06% that gave a maximum NO conversion of 57 3% H-2 temperature-programmed reduction results showed that the ion exchange method and low Mn loadings (<= 2 06%) restricted the formation of non-stoichiometric MnOx (1 5 < x < 2) species that have higher oxidative activity, and thus suppressed the combustion of CH4 by O-2. which increased the selectivity for NO reduction In a SO2 containing stream, a substantial decrease in NO conversion was seen at <= 550 degrees C but not at >= 600 degrees C SO2 temperature-programmed surface reaction and NO temperature-programmed desorption demonstrated that sulfur species were formed at temperature <= 550 degrees C. and these covered active sites and decreased the catalytic activity The sulfur species desorbed at >= 600 degrees C, thus the addition of SO2 did not have a significant impact on the catalytic activity