Selective catalytic reduction of nitrogen oxides with NH3 over natural manganese ore at low temperature

The selective catalytic reduction of NOx (NO + NO2) at low temperature with ammonia has been investigated with natural manganese ore, pure manganese d ioxide, and manganese dioxide supported alumina. The catalysts showed high activities for NOx reduction with NH3 in the presence Of O-2 at temperature s below 250 degreesC. The decrease of SCR activity without oxygen in the ga s phase differed among the three catalysts in accord with their differing a mounts of lattice oxygen. The SCR activity of the catalysts, in that case, decreased in the order MnO2 > NMO > MnO2/gamma -Al2O3. Small amounts Of SO2 deactivated the catalysts in the low-temperature range. An XRD analysis of the sulfated catalysts with differing temperature provides evidence that t he formation of ammonium sulfates is the main poisoning route. These result s could restrict the practical application of these catalysts to sulfur-fre e conditions.