The Influence Of Ho-modified Mn-Ce/TiO₂ Catalyst On Its Low Temperature SCR Performance

Nitrogen oxides?NO_x?are the main source of environmental problems such as acid rain,photochemical pollution,and haze effects.The control of nitrogen oxides has become a concern.However,the anti-sulfur performance,temperature window and low-temperature catalytic performance of the catalyst in the research of low-temperature SCR technology still need to be improved.This paper modified the Mn-Ce/TiO₂ catalyst based on previous research that has been conducted,and prepared the catalysts by using doping element modification method.Besides,the doping effect and the specific influence mechanism were studied.In this paper,five low-temperature SCR catalysts Mn_0.4Ce_0.07Ho_x/TiO₂?x=0,0.01,0.05,0.1,0.15?doped with different proportions of Ho were prepared by impregnation method.The low temperature denitrification performance of Ho-doped Mn-Ce/TiO₂ catalyst was investigated.The physicochemical properties of the catalyst were characterized by XPS,XRF,XRD,TPD,etc.The results show that Ho doping can affect the catalytic activity of Mn-Ce/TiO₂catalyst,and there is an optimal doping ratio.It is found by this experiment that the optimal doping ratio is Ho/Ti of 0.1.At this doping ratio,Ho-doped Mn-Ce/TiO₂ catalyst has the best low-temperature denitrification performance.Besides,it was found that Ho doping can increase the specific surface area of the catalyst to a certain extent,and provide more reaction sites for the denitrification reaction.At the same time,the inhibition of the agglomeration phenomenon also suppresses the decrease of the specific surface area of the catalyst.In the process of denitrification reaction,Ho doping can provide a higher concentration of chemical adsorption oxygen.The stronger acidity contributes to the adsorption of the reducing agent ammonia gas and promotes the redox reaction,thereby improving the denitrification performance of the catalyst.At the same time,SO₂ and H₂O can reduce the activity of the catalyst,where the effect of SO₂ on the catalyst is irreversible,and Ho doping can improve the sulfur resistance of the Mn-Ce/TiO₂ catalyst.Through characterization analysis,it was found that the sulfates formed on the surface of the catalyst after the reaction in the sulfur-containing atmosphere is the main cause of catalyst deactivation.The reason for better sulfur resistance is that it can inhibit the conversion of Mn⁴⁺ and Ce⁴⁺ to a low-valent state after doping with Ho,thereby inhibiting the oxidation of SO₂,generating less SO₃,and less sulfate formed,thereby improving the sulfur resistance of the catalyst.The regeneration of the deactivated catalyst and the low temperature denitrification performance of Ho-doped Mn-Ce/TiO₂ catalyst under high oxygen concentration and high sulfur concentration were studied.It has been found that the deactivated catalyst can be regenerated by high temperature treatment.At the same time,the different oxygen concentration and different sulfur concentration in the flue gas will affect the denitrification performance of the catalyst.The performance of the denitrification reaction of the catalyst requires the participation of an appropriate amount of O₂.Besides,the denitrification performance of Ho-doped Mn-Ce/TiO₂ catalyst decreases with the increase of SO₂ concentration in flue gas,and the higher concentration of SO₂ has greater influence on the poisoning of the catalyst.