Catalytic Properties Of The Fly-ash-supported Cr-Cu-Mn Catalysts For SCR Denitrification Of Flue Gas

In recent years,with the rapid development of China’s economy,the release of environmentally harmful emissions has become highly problematic.Coal-fired power plants release a significant amount of pollutants such as nitrogen oxides and sulfur dioxide,leading to serious environmental problems such as photochemical smog and acid rain.Therefore,the removal of NOx from flue gas is of significant importance.Ammonia selective catalytic reduction(NH3-SCR)has been recognized as an economical and effective De-NOx method.The catalyst used in the flue gas NH3-SCR process-domestically and globally is V2O5-WO3/TiO2.However,this catalyst has few setbacks,such as high operating temperature and cost.Therefore,developing a catalyst with a low price and wide operation temperature range has attracted significant attention.Herein,Cr8Cu2Mnx/FA series NH3-SCR catalysts with medium and low activation temperatures were prepared by doping Cr,Cu and Mn onto coal-based fly ash.A self-designed flue gas De-NOx experimental setup was used to test the denitrification performance of the catalyst.The effects of catalyst preparation conditions,flue gas temperature and gas space hourly velocity on the denitrification performance of the catalyst were investigated.The physicochemical properties of catalysts were characterized by specific surface area analyzer,X-ray diffractometer,temperature-programmed desorption,temperature-programmed reduction and X-ray photoelectron spectroscopy.The experimental results show that the denitrification efficiency of Cr8Cu2/FA catalyst can reach 100%at 250℃.Although CrgCu2/FA catalyst shows good denitrification performance at low-medium temperature,the denitrification temperature window of the catalyst is narrow(230-280℃).In order to widen the temperature window of Cr8Cu2/FA catalyst and meet the requirement of industrial application,Mn was added to Cr8Cu2/FA.This addition of Mn allowed for a wider operating temperature window.After the addition of Mn,the denitrification efficiency of Cr8Cu2Mn2/FA catalyst reached over 80%in the range of 180-350℃and 100%in the range of 200-250℃.Mn doping not only broadens the temperature window but also further improves the denitrification activity.The Cr-based catalysts were analyzed and characterized.The results showed that the fly ash as a carrier of the catalyst possessed a porous structure and had a large surface area,which contributed to the uniform dispersion of active sites on the carrier.The surface of the Cr-based catalyst is rich in acid sites and is dominated by medium and strong acids,which can improve the denitrification activity of the catalyst at medium and low temperatures.The addition of Mn can further improve the redox ability of the catalyst and promote the transfer of Cr and Mn ions.The conversion of Cr2++Cu2++Mn2+→Cr5++Cu++Mn4+during the catalytic reaction is beneficial for the catalytic reaction.The addition of Mn also improves the adsorption of oxygen on the surface of the catalyst and explaining the high activity of the catalyst.Also,it was found that Cr8Cu2Mn2/FA catalyst has strong surface adsorption ability and thermal stability,resulting in great water resistance,and the catalytic denitrification reaction followed L-H mechanism.In the adsorption and desorption experiments,the Cr8Cu2Mnx/FA catalyst can adsorb NH3 and NO,which indicates that there are active adsorption sites of NH3 and NO in the reaction process,which meets the requirements of L-H mechanism.Cr8Cu2Mn2/FA catalyst has excellent denitrification performance with low price and wide denitrification temperature window.The technology of preparing medium and low-temperature denitrification catalyst from fly ash is of significant importance in terms of solid waste utilization.