The selective catalytic reduction of NO x (NO + NO 2 ) at low temperature with ammonia has been investigated with natural manganese ore, pure manganese dioxide, and manganese dioxide supported alumina. The catalysts showed high activities for NO x reduction with NH 3 in the presence of O 2 at temperatures below 250 °C. The decrease of SCR activity without oxygen in the gas phase differed among the three catalysts in accord with their differing amounts of lattice oxygen. The SCR activity of the catalysts, in that case, decreased in the order MnO 2 > NMO > MnO 2 /γ-Al 2 O 3 . Small amounts of SO 2 deactivated the catalysts in the low-temperature range. An XRD analysis of the sulfated catalysts with differing temperature provides evidence that the formation of ammonium sulfates is the main poisoning route. These results could restrict the practical application of these catalysts to sulfur-free conditions.
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Park et al. (2001) studied this question.