Study On Catalytic Performance Of Doped LaMnO₃ Perovskite And Cerium-Zirconium Solid Solution Support Catalyst For Soot Removal And CO₂ Methanation

Nitrogen oxides（NOx）,soot（Soot）,and a large amount of carbon dioxide in diesel engine exhaust have become environmental pollutants or greenhouse gases that the International Maritime Organization（IMO）strictly restricts emissions.They are used as remaining heat and achieved through catalytic conversion.NOx and Soot purification treatment and CO₂ recycling have proven to be effective and environmentally-friendly methods.In this paper,K element is used to substitute perovskite at A position,transition metals（Cu,Co,Ni）and precious metal Pt are respectively substituted at B position.The La_0.8K_0.2Mn_1-yB_yO₃ series of perovskite catalysts were prepared by the citric acid sol-gel method Through XRD,FT-IR,BET,SEM,TEM,XPS,H₂-TPR,O₂-TPD,NO-TPD,Soot-TPR and other tests,the phase structure,chemical bond composition,surface morphology,specific surface area,The pore structure,surface atomic valence state distribution,redox properties,oxygen and NO adsorption and desorption properties were characterized,the catalytic activity of the catalyst is characterized.Studies have found that transition metals have partially substituted atoms at the B position of the perovskite.When ions with a larger radius are substituted,the catalyst phase changes from a cubic phase to a tetragonal phase,and the lattice distortion increases;with the doping of similar ions,the catalyst phase maintains the cubic phase and the crystal structure is more complete.In the H₂-TPR test,the temperature of the low-temperature hydrogen consumption peak of the catalyst dropped from 418.6℃to274.2℃.The oxygen vacancy concentration of the catalyst increases with the increase of the lattice distortion of the catalyst.The adsorbed amount of NO is directly proportional to the concentration of B-site low-valent ions.In general,the increase in catalytic activity is affected by the substitution of different B-site elements（Cu>Co>Ni）and different doping amounts(y_（Cu）=0.02>0.03>0.04>0.01).Among them,La_0.8K_0.2Mn_0.7Cu_0.3O₃ has the best catalytic activity.The ignition temperature of soot is277.9℃,the maximum combustion temperature is 427.8℃,and the maximum elimination efficiency of NO is 67.27%.The noble metal Pt is substituted for the B-site of the perovskite,and the cubic structure of the catalyst is more complete,indicating that Pt successfully enters the crystal lattice,but the amount of substitution is limited,and a small amount of elemental Pt exists on the surface of the catalyst.The oxidation-reduction capacity of the catalyst is reduced,while at the same time the absorption and deactivation capacity of oxygen and NO is improved,and the catalytic activity is significantly improved.The cerium-zirconium solid solution support with macroporous structure was prepared by the colloid-crystal template method,and the Pt-Ni active components were loaded on the support by the impregnation method to obtain the Pt-Ni_x/M-Ce_0.9Zr_0.1O₂series catalyst.The activity performance of the catalyst for simultaneous removal of NOx and soot was evaluated,and the catalytic performance of the catalyst for CO₂methanation was investigated.After the cerium-zirconium solid solution was loaded with Pt-Ni bimetallic active components,the phase structure did not change significantly.Under the synergistic effect of the active components and the carrier,the reduction temperature of the catalyst H₂-TPR decreased significantly.The increase in Ni loading increases the oxidation-reduction capacity of the catalyst,and the adsorption capacity of the catalyst for oxygen,NO and CO₂ decreases.In the catalytic soot combustion activity test,the Ni loading is 12 w%,which has the most excellent catalytic activity:the soot ignition temperature is 385.6℃,the maximum soot combustion temperature is 496.8℃,and the maximum NOx elimination rate is 45.61%.The Ni component serves as the reaction site to improve the contact conditions between the soot particles and the catalyst,and the properly crystallized Ni component is conducive to the progress of the reaction.The Pt component improves the migration ability of the reactants on the catalyst surface and inhibits the excessive crystallization of the Ni component.The carrier is the main site for NO and O₂ adsorption and activation,and the synergy between the carrier and the active components improves the activation efficiency.Pt-Ni₁₂/M-Ce_0.9Zr_0.1O₂has the best catalytic activity for CO₂ methanation.At 400℃,the CO₂ conversion rate is 72%and the CH₄selectivity is 92%.