Preparation And Performance Of Novel Low-temperature Mn-Co Catalysts For Denitration

Nitrogen oxides emitted from thermal power plants are currently considered as one of the main sources of a series of environmental issues. Selective catalytic reduction（SCR） with NH₃ is a well-proven technique to reduce NO_x emissions. Mn-based oxides catalysts with the superiority of unique activities at low temperature and excellent redox properties have received much attention. But due to the high sulfur sensitivity of the Mn-based catalysts, which can induce a severe deactivation, researchers have been studied modified Mn-based catalysts by doping the other transition metal oxides. Cobalt oxides have long been studied widely in the field of catalysts, due to the terrific redox properties and morphology characteristics. But there have been few reports on Mn-Co mixed oxides for SCR of NO_x with NH₃. In this study, a series of Mn-Co oxide catalysts, prepared by the different preparation methods were examined,their morphology were improved and they obtained high de NO_x performance with high resistance to SO₂ poisoning.The porous Mn₂Co₁ O_x catalyst synthesized by a one-step combustion（CB） method. The effect of the calcination temperature, the calcination time, the different Mn/Co molar ratios and the GHSV on the catalyst de NO_x performance was investigated. The result displayed that the catalyst obtained the highest de NO_x activity when the calcination temperature was 450°C, the calcination time was 2h, Mn/Co molar ratio was 2 or the GHSV was 30 000h-1.The porous Mn₂Co₁ O_x catalyst prepared by a one-step combustion（CB） method displays excellent NH₃-SCR activity, achieving 100% NO_x conversion at 150-300°C. In addition, the catalyst shows high N₂ selectivity, wide operating temperature window, high stability, and high H2 O and SO₂ resistance. The Mn₂Co₁ O_x catalysts have been characterized by XRD, SEM, BET, XPS, H2-TPR and NH₃-TPD. XRD data results suggested that a crystalline phase of Co Mn₂O4 was present in the Mn₂Co₁O_x（CB） catalysts, which contained the important active species. The catalysts own porous structure and large specific surface area obtained from SEM and BET results, which is beneficial for the de NO_x activity. XPS results illustrated that the catalysts exist abundant Mn4+, Co3+ and surface adsorbed oxygen species. Meanwhile, better redox ability and plenty of acid sites attributed to the strong interaction of manganese and cobalt oxide species enhance excellent de NO_x activity.The Mn₂Co₁ O_x catalyst prepared by a hydrothemal（HT） method also obtains high NH₃-SCR activity, achieving over 90% NO_x conversion at 175-325°C and over 85% N₂ selectivity at 100-325°C. The needle-like nano-flower’ structure of the Mn₂Co₁O_x（HT） catalyst greater improved the specific surface area and provided abundant Br?nsted and Lewis acid sites. All of these provided a rich theoretical basis for excellent catalytic activity of the Mn₂Co₁O_x（HT） catalyst. In addition, the strong interaction of manganese and cobalt oxide species improved the catalytic cycle, inhibited the production of sulfate on the catalyst surface, thus H2 O and SO₂ resistance and stability of the catalyst were enhanced.