Cr-MnO_x mixed-oxide catalysts for selective catalytic reduction of NO_x with NH_3 at low temperature

摘要

Cr-Mn mixed-oxide based catalysts were prepared for the low-temperature selective catalytic reduction of NO_x with ammonia in the presence of excess oxygen. It was found that the Cr(0.4)-MnO_x showed the highest activity and yielded 98.5% NO_x conversion at 120 °C. XRD, TPR and Raman data results suggested that a crystalline phase of CrMn _(1.5)O_4 was present in the Cr-MnO_x catalysts, which contained the active species. XPS results of fresh, used and regenerated Cr(0.4)-MnO_x catalysts illustrated clearly the presence of Mn ~(2+), Mn~(3+), Mn~(4+) and Cr~(2+), Cr ~(3+), Cr~(5+) oxidation states. Efficient electron transfer between Cr and Mn in the crystal of CrMn_(1.5)O_4 was thought to be the reason for the high activity and long lifetime of the Cr(0.4)-MnO _x catalyst. In addition, the SCR activity was gradually suppressed in the presence of SO_2, while such an effect was shown to be reversible after switching off the SO_2 injection.