Construction Of High Efficiency Denitration Catalyst Based On Cerium And Copper Co-doped Modified Lanthanum Manganese Perovskite

Nitrogen oxides(NOx)cause environmental problems such as smog and acid rain and harm human health.Therefore,it is necessary to take effective measures to control the emission of NOx.Ammonia selective catalytic reduction(NH3-SCR)technology is the most effective and widely used industrial denitration technology at present.However,traditional denitration catalysts cannot meet the requirements of low temperature flue gas treatment due to the narrow active temperature window.At present,the researchers focus on transition metal oxide catalysts because they have excellent redox properties and low-temperature denitration performance.Besides,perovskite oxide catalysts have attracted wide attention owing to their stable structure and variable lattice defects.Therefore,it plays an important role in the practical application of industrial denitration to prepare efficient perovskite catalysts with transition metal elements.In this paper,modified perovskite catalysts La1-xCexMnO3(x=0,0.05,0.1,0.2)and La0.9Ce0.1Mn1-yCuyO3(y=0.05,0.1,0.2,0.4)were prepared by sol-gel method for NH3-SCR denitration reaction.The effects of Ce and Cu substituted in A and B sites of La-Mn perovskite catalysts on the denitration performance were studied.The influences of structure,morphology,and redox properties of perovskite catalysts on their denitration efficiency were discussed by XRD,SEM,BET,BJH and XPS characterization methods.The low-temperature NH3-SCR denitration reaction mechanism on the catalyst surface was analysed by the DRIFT results.The Ce substitution in A site of LaMnO3 catalyst can change its physical and chemical properties and enhance the denitration performance.The results show that the modified catalyst with substitution ratio of 0.1 has the highest denitration efficiency,and the NO conversion efficiency reaches 86.7%at 350℃.Through characterization experiments,it is found that partial substitution in La of LaMnO3 catalyst by Ce leads to the lattice distortion of perovskite structure,and reduces the cell volume and average lattice size.With the increase of Ce substitution ratio,the surface morphology of catalyst gradually changes from wool-like to thinwalled associated with the increased specific surface area and surface active particles,and the average valence state of Mn gradually increases from Mn2+to Mn3+and Mn4+.Due to its large specific surface area,many mesoporous structures and active sites,high Mn average valence state and chemisorbed oxygen concentration,La0.9Ce0.1MnO3 catalyst has the best denitration efficiency among the modified LaMnO3 catalysts prepared with Ce substitution.The Cu substitution in B site of La0.9Ce0.1MnO3 catalyst can change its physical and chemical properties and enhance the denitration performance.The results show that the modified catalyst with substitution ratio of 0.2 has the highest denitration efficiency,and the NO conversion efficiency reaches 91.8%at 350℃.Through characterization experiments,it is found that partial substitution in Mn of La0.9Ce0.1MnO3 catalyst by Cu causes the changes of the average ionic radius and average valence state of Ce,Mn and Cu,and affects the tolerance factor and lattice distortion of perovskite,thus changing the cell volume and average lattice size of perovskite.With the increase of Cu substitution ratio,the aggregation degree of metal particles on catalyst surface increases,and the wool-like mesoporous structure decreases.There is a synergistic effect between Ce,Mn and Cu metal ions in the process of Cu substitution,which reduces the average valence state of Ce and Cu,and increases the average valence state of Mn.The strong interaction between the three metal ions and the change of the average valence state of each metal ion affect the redox properties and denitration performance of perovskite catalysts.Due to its many mesoporous structures and active sites,the highest contents of Ce3+and high valence Mn ion,strong interaction between metal ions and high chemisorption oxygen concentration,La0.9Ce0.1Mn0.8Cu0.2O3 catalyst has the best denitration efficiency among the modified La0.9Ce0.1MnO3 catalysts prepared with Cu substitution.According to the DRIFT spectra of La0.9Ce0.1Mn0.9Cu0.1O3 catalyst,it is found that NH3 adsorbs on the catalyst surface mainly forms coordinated NH3 and NH4+,which can be dehydrogenated into-NH2 to participate in the subsequent reaction,and NO adsorbs on the catalyst surface mainly forms monodentate nitrate and bidentate nitrate.Gaseous NO can combine with-NH2 to generate N2 and H2O,and the reaction follows the E-R mechanism.Besides,monodentate nitrate and bidentate nitrate can combine with NH4+to remove nitrogen oxides,and the reaction follows the L-H mechanism.