Study On The Removal Or Use Of Dichloromethane And CO In The Selective Catalytic Reduction Denitration Process

In Coal fired industrial boilers/furnaces,especially iron and steel smelting furnaces,iron ore sintering machines,coke furnaces and other industrial furnaces,the flue gas often contaians unconventional flue gas pollutans other than NO_x and SO₂,such as volatile organic compounds（VOCs）,CO etc.,which have a great influence on atmospheric haze and regional composite pollution.To solve the above problems,this paper systematically investigated the effects of unconventional flue gas pollutants VOCs and CO on the existing selective catalytic reduction denitration（SCR）process.The prepared Nb-doped cerium nanotubes（Ce NTs）realized denitration and removal of VOCs simultaneously.A noble metal supported silicon-based catalyst was developed for the CO-SCR denitration process under the oxygen enriched condition.The CO-SCR performance of the precious metal supported silicon-based catalyst was further optimized by doping alkaline earth metal Ba,and the influence of Ba on NO_x removal performance was also investigated.Firstly,niobium oxide-dopeded cerium nanotubes（CeNTs）and commercial VWTi catalysts were prepared and their simultaneous removal performance of NO_x and dichloromethane were investigated.Methylene chloride（CH₂Cl₂）was selected as a typical VOCs representative in this study.It was found that the Nb-Ce NTs catalyst had better NO_x removal efficiency and CH₂Cl₂degradation efficiency than that of VWTi.10 wt%Nb-Ce NTs catalyst achieved 90%NO_xremoval efficiency at 200 ^oC and exhibited nearly 100%NO_x removal efficiency in the temperature range of 230-450°C,and achieved 90%CH₂Cl₂ degradtion efficiency at 350 ^oC,and remained above 90%CH₂Cl₂ degradtion efficiency in the temperature range of 350-450°C.Furthermore,it has excellent water resistance,sulfur resistance and stabilit.Nb species can significantly improve the redox capacity and the number of acid sites of the catalyst.With the increase of Nb loading,the contents of Ce³⁺,Nb⁴⁺and chemisorbed oxygen in the catalyst also gradually increases,which helps to promote the redox cycles of Ce⁴⁺/Ce³⁺and Nb⁴⁺/Nb⁵⁺and improve the synergistic catalytic performance of the catalysts.Secondly,the noble metal supported silicon-based catalysts was prepared to investigate its CO-SCR denitration performance under the oxygen rich condition.Using ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 27 as the carrier,noble metal Ir as the active component,the loading mass percentage of Ir loade is 0.5%.When the oxygen content is 5 vol.%and the CO/NO ratio is 5,the catalyst has the best CO-SCR denitration performance.In addition,after reducing at 500 ^oC for 2 h under 5%H₂/N₂ cindition,the Ir/ZSM-5 catalyst could reach a NO_x removal rate of 39%and has good regeneration performance.Finally,different amounts of catalytic promoter Ba were added into the Ir/ZSM-5 catalyst to further improve its NO_x removal rate and stability.When the Ba/Ir molar ratio is 0.2,the Ba-doped Ir/ZSM-5 catalyst has the highest catalytic performance,with NO_x removal rate reach 47%at250℃,which is 9%higher than that of un-doped Ir/ZSM-5 catalyst.Also it has excellent cycle test performance and stability.The characterization analysis results shown that the redox performance of Ir/ZSM-5 was decreased after the alkaline earth metal Ba was doped,which was more conducive to the stability of the Ir⁰ sites.In addition,Ba-Ir/ZSM-5（0.2）catalyst has stronger NO adsorption and desorption performance,more Ir⁰ species and chemisorption oxygen,which are more conducive to improve the NO_x removal performance.