Preparation And Performance Of Nickel-Manganese Oxides Composite For Selective Catalytic Reduction Of NO_x At Low Temperature

Nitrogen oxides are the main exhaust gases from coal-fired power plants,coal-fired boilers and motor vehicle exhaust,which are the important factors causing the imbalance of atmospheric environment.Moreover,it can cause such ecological security problems as acid rain,photochemical smog,ozone hole and greenhouse effect.Therefore,in recent years,efficient denitrification catalysts have become the focus of scientific research.Nowadays,ammonia selective catalytic reduction of nitrogen oxides（NH₃-SCR）is one of the most widely used technologies in denitrification process,which has attracted the most attention and research of scientific researchers.The NH₃-SCR catalysts used in industrial production are mainly vanadium-containing or manganese-containing composite oxide catalysts However,the denitrification process has many shortcomings,such as high cost of preparation and operation,high catalyst active temperature range（300-400 C）,complex reactor,short catalyst life and easy deactivation.The SO₂ gas in the flue gas is easy to react to form ammonium sulfate and other substances in the presence of ammonia in the temperature range of 180-300℃,which makes the exhaust pipe blocked and equipment corroded.By using low temperature catalysts and flue gas reheating technology,It could realize denitrification before desulfurization.thus reducing pipeline blockage.Therefore,the development of SCR catalysts with low cost,low reaction temperature,high degradation rate and high stability has become the most important.In this paper,a series of Ni-Mn composite oxides catalysts for low-temperature denitrification were synthesized by coprecipitation method under the same experimental conditions.The activity of NO（NH₃-SCR）degradation was tested under the same simulated flue gas conditions,and the catalytic performance of NO degradation was observed and recorded.The experimental results show that the catalysts prepared with nickel acetate and manganese acetate as precursors and ammonium carbonate as precipitators have a conversion rate of nearly 100%and a high degradation rate at 110-250℃.The catalysts prepared with oxalic acid as precipitators have a conversion rate of 76%at 80℃,the conversion rate of 100%at90℃and and maintain a high degradation rate at 90℃-250℃.Then the nickel-manganese composite oxide catalysts were tested by XRD,SEM,specific surface area and pore size analysis（BET and BJH）,XPS and other characterization techniques.The results showed that NiMnO₃,MnNiO₄,Mn₄O₃ and NiO were the main reactants in the catalytic reaction.Compared with manganese nitrate and nickel nitrate as precursors,the relative concentration of surface adsorption oxygen（Oα）and Mn⁴⁺ions is improved.Catalysts prepared with oxalic acid as precipitator have larger specific surface area and higher relative concentration of surface adsorption of oxygen（Oα）and Mn⁴⁺ions.These are the main reasons for improving the catalytic efficiency of NO degradation at low temperature.