Preparation And Performance Of Natural Manganese Oxide Composite Catalysts For Catalytic Oxidation Of NO

With the increasing air pollution and the state had issued a new emission standards for coal-fired boilers, which puts forward more stringent requirements on flue gas denitrification in China. As a result, flue gas denitrification has become one of the hotspots in the research of air pollution control.In this dissertation, several kinds of catalysts were prepared by using different treatment methods to natural manganese oxide, which were used for selective catalytic oxidation (SCO) at the same time.Using the equal volume impregnation method, with the natural manganese ore (the main components is MnO2) as the carrier, several composite catalysts including acid leaching, Ni/MnO2, Ti/MnO2, Ce/MnO2 and Ti/Ce/MnO2 were prepared. Physic-chemical properties of the catalyst were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed desorption (TPD), thermal gravimetric analysis (TG), specific surface area analysis (BET) and Fourier transform infrared spectroscopy (FTIR). Also on of the best catalyst based, the effects of the acid concentration, reaction temperature, calcination temperature, NO concentration, O2 concentration and H2O and SO2 on the oxidation activity were investigated. The results showed:The natural manganese ore was used as catalyst after the impregnation with a certain concentration of sulfuric acid has good catalytic activity for low temperature catalytic activity. When sulfuric acid was 3 mol/L, under the low temperature (1000 ppm NO, 100 ℃,3% O2), the NO conversion efficiency can exceed 90% and stable for 10 hours more, and it can resist the low concentration of H2O and SO2 (≤300 ppm), cutting off the H2O and SO2 supply resulted in activity restoration. The new catalysts were prepared by loading active component, and the results have shown that the natural manganese ore loading Ce% Ni and Ti have a poor performance. NO conversion efficiency is less than 40% in the same condition of flue gas, and the service life of catalyst is very short, unable to meet the requirements. Therefore the catalysts of loading Ce and Ti these two kinds of active components were produced, and the result shows that the catalysts have a good catalytic oxidation performance, but with a demand of high temperature. With the natural manganese ore loaded 5% Ti and 5% Ce and calcined 250 ℃ for 2 hours,1000 ppm NO conversion efficiency can reach almost 100% and stable for more than 10 hours, but when higher H2O and SO2 (≥500 ppm)were putted in, catalyst soon lost activity,cutting off H2O and SO2 supply could not to fully recover the activity. Above all three systems, the main reason of catalyst deactivation is producing a certain amount of sulfate and nitrate in the catalyst surface, especially in H2O and SO2 conditions, there are a lot of sulfate produced on the catalyst surface, resulting in deactination of catalyst.