Abstract: The selective catalytic reduction of NO in excess O₂ 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%. H₂ temperature-programmed reduction results showed that the ion exchange method and low Mn loadings (≤ 2.06%) restricted the formation of non-stoichiometric MnO_x (1.5 < x < 2) species that have higher oxidative activity, and thus suppressed the combustion of CH₄ by O₂, which increased the selectivity for NO reduction. In a SO2 containing stream, a substantial decrease in NO conversion was seen at ≤ 550 ^oC but not at ≥ 600 ^oC. SO₂ temperature-programmed surface reaction and NO temperature-programmed desorption demonstrated that sulfur species were formed at temperature ≤ 550 ^oC, and these covered active sites and decreased the catalytic activity. The sulfur species desorbed at ≥ 600 ^oC, thus the addition of SO₂ did not have a significant impact on the catalytic activity.

Key words: nitrogen oxide, methane, selective catalytic reduction, manganese, ZSM-5, sulfuric dioxide