Study On Preparation Of Co-doped α-MnO₂ Low-temparature SCR Catalysts And Its Denitration Performances

Nitrogen oxides（NO_X）,as one of the major atmospheric pollutants,endanger human life and health seriously.In the field of flue gas denitrification of the fixed pollution source,the technology of low-temperature ammonia selective catalytic reduction（NH₃-SCR）with operating temperature below 250°C has attracted much attention in recent years.The traditional commercial catalysts cannot meet the process requirements due to its rather high operating temperature range（300-400°C）.Therefore,the research and development of low-temperature and high-efficiency denitration catalysts have become the working focus of scientists.Among them,manganese-based catalyst has been widely concerned by scholars owing to its excellent low-temperature catalytic denitration performance.However,the catalysts face some problems such as unsatisfactory catalytic denitration performance at low temperature and poor resistance to H₂O and SO₂,which limit industrial applications.In this work,a series of studies on manganese-based catalysts have been carried out,and the hydrothermal synthetic process with the assistance of additives was applied to prepare a series of manganese-cobalt composed oxide catalysts with different compositions.Then,the physic-chemical properties of catalysts were systematically investigated by means of X-ray diffraction（XRD）,N₂ adsorption-desorption,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,H₂ temperature programmed reduction（H₂-TPR）,NH₃ temperature programmed desorption（NH₃-TPD）and NO temperature programmed desorption（NO-TPD）.Combined with test results of catalytic denitration performance,the structure-activity relationships of the Mn-Co composed catalysts were studied systematically.Firstly,the manganese-cobalt composed oxide catalysts with different compositions were prepared by acetic acid（HAc）-assisted hydrothermal synthesis reaction,and the influence of the doping of Co on its structure and properties was investigated.The results showed that the doping of Co could improve the catalytic performance of catalysts significantly.Among them,Mn-Co-0.2-HAc catalyst exhibited the best low-temperature SCR catalytic denitrification performance,and its NO_X conversion reached 87%at 100°C and maintained above 90%in the temperature range of 120～280°C.Through the study of structure-activity relationship,it was found that the specific surface area,low-temperature reduction performance,and adsorption capacity to NH₃ and NO of catalysts were improved with the increase of Co doping amount,and the synergistic effect of above factors contributed to the modify catalytic performances of catalysts.This paper further explored the structure and properties of manganese-cobalt composite oxide catalysts prepared by the polyvinyl pyrrolidone（PVP）-assisted hydrothermal reaction.Mn-Co-0.2-PVP catalyst showed the best low-temperature SCR catalytic denitrification performance,and its NO_X conversion was 92%at 100°C and could remain above 90%in the temperature range of 100～280°C.The characterization results further proved that the increase of Co doping amount could improve the reduction strength of catalyst,increase the amount of surface Lewis acid sites and enhance the adsorption capacity to NH₃ and NO,thereby promoting the catalytic performance.Furthermore,compared with the catalysts prepared by HAc-assisted hydrothermal reaction,the catalysts prepared by PVP-assisted hydrothermal synthesis exhibited higher low-temperature SCR catalytic performance and better resistance to H₂O and SO₂.