Investigation Of Mn-Y/TiO₂ For NO Selective Catalytic Reduction At Low Temperature

As the development of power industry in China, the discharge of NOx in the flue gas from coal-based power plant increase every year. Low temperature SCR can solve the problem which high concentrations of dust and SO2 can affect the life of catalysts. The paper studied performance of new Mn-Y/TiO2 catalyst, explored relative characterization to analyze the catalytic mechanism of the reaction, investigated operation conditions and kinetics of catalytic reduction reaction, which provides reference for industrial application of new catalyst in low temperature SCR of NOx.The performance of catalysts was investigated in a catalytic fixed reactor, the effect of Y doping amount and the calcination temperature on the catalytic activity to optimize the catalyst preparation conditions. The results showed that under the experimental conditions of GHSV 27000h-1,3%O2 (volume fraction), NO concentration 600×10-6, [NH3]/[NO] ratio 1.0, when [Y]/[Ti] was 1.5 (percentage), Mn loading was 5%(mass fraction), Mn-Y/TiO2 calcined at 500℃could yield about 79.9% NO conversion.The characterizations of XRD, FT-IR, BET, SEM, PL, Raman, XPS and EPR was explored to analyze the surface chemical structure, surface area, grain size, electronic structure and surface properties of catalysts. The results showed that Y doping restrained the process of transformation of anatase TiO2 and crystallization which would be conducive to the dispersion of the active component, and also reduced the hydrophilicity of TiO2 particles;Y doping could reduce the aggregation of catalyst particles, which improved the surface area; while Y3+ entering into the TiO2 lattice could partly replace the Ti4+, which caused lattice defects, lattice defects were conducive to the generation of oxygen vacancies, the latter could act as adsorption sites of oxygen to form superoxide radicals, oxidizing NO to the reactive intermediates of the SCR reaction, thereby enhancing the rate of catalytic reaction, improved the catalytic activity.The effect of operating conditions on NO conversion was studied. Under the experimental conditions of GHSV 14000h-1,O23%, NO concentration 600×10-6, [NH3]/[NO] 1.0, MnTiY1.5 could yield over 93.5% NO conversion at 180℃.4% H2O has an obvious poisoning influence, which was due to the presence of water vapor could inhibit effective NH3 adsorption on the catalyst surface, however, the rise of temperature could improve the catalytic performance. When SO2 presented, the poisoning effect of the catalysts could not be restored, mainly because ammonium sulfate and metal sulfate generated on the catalyst surface.The kinetics of catalytic reduction reaction on Mn-Y/TiO2 was revealed. Reaction series of NH3 and O2 was 0 and 1.17, respectively; when O2 concentration was below 3%, reaction series of O2 was 1.13, but when O2 concentration was above 3%, reaction series of O2 was 0, external and internal diffusion of catalytic reaction rate could be ignored.