Study On The Catalytic Performance Of Cerium-zirconium Solid Solution Support Catalyst For CO₂ Methanation And NH₃-SCR Denitration

The CO₂ produced by the burning of fossil fuels is the main cause of the greenhouse effect,and the accompanying production of nitrogen oxides（NO_X）can also cause atmospheric pollution.Therefore,the treatment of CO₂ and NO_X is necessary.The phenomenon that the content of CO₂ in the atmosphere is increasing year by year is attracting more and more attention.Among various methods for reducing carbon dioxide emissions and levels in the atmosphere,the catalytic conversion process is valued because it can generate additional economic benefits in addition to reducing pollution and the carbon dioxide methanation technology that promotes the construction of clean energy has aroused great research enthusiasm.The key to fully exploiting the advantages of this technology is to prepare catalysts with high activity,high selectivity and low cost.For the treatment of nitrogen oxides,selective catalytic reduction（SCR）technology can efficiently catalyze the conversion of nitrogen oxides.The use of SCR catalysts is also the main method for industrial treatment of nitrogen oxides.In this paper,the Pt_a-Ni_b/Ce _XZr_1-XO₂ catalysts with macroporous structure were prepared by colloid-crystal template method and impregnation method to catalyze CO₂methanation reaction.XRD,SEM,BET,H₂-TPR and CO₂-TPD were used to characterize the phase,surface morphology,pore volume,pore size,redox capacity and CO₂ adsorption and desorption capacity of the catalysts.The activity and selectivity of the CO₂ methanation reaction were determined,and the reaction mechanism was investigated by in situ-IR.For the catalytic reaction of NH₃-SCR,a VO_X/TiO₂-Ce_0.9Zr_0.1O₂ catalyst with core-shell structure was prepared by precipitation method and impregnation method,and compared with commercial catalyst.The physicochemical properties and mechanism of action were analyzed by XRD,XPS and other characterization methods.Polymethylmethacrylate（PMMA）templating agent was prepared by bulk polymerization method,and a series of Ce _XZr_1-XO₂（x=0.1,0.3,0.5,0.7,0.9）carriers with macroporous structure were prepared,and Pt and Ni were loaded on Ce _XZr_1-XO₂ carrier by impregnation method.By adjusting the Ni loading,Pt loading,and different cerium-zirconium ratios of the carrier,the catalyst ratio was optimized.The results showed that when the mass fraction of Pt and Ni were 1 wt.%and 12 wt.%,the carrier composition was Ce_0.9Zr_0.1O₂,the space velocity is 14,000 h^-1,and the catalyst exhibits the best activity and selectivity at 400℃.The CO₂ methanation conversion rate and CH₄ selectivity can reach 73%and 93%,respectively.The cerium-zirconium solid solution was coated on the surface of nano-TiO₂powder by precipitation method to prepare TiO₂-Ce_0.9Zr_0.1O₂ carrier with core-shell structure.VO_X was supported on the surface of TiO₂-Ce_0.9Zr_0.1O₂ carrier by impregnation method.A VO_X/TiO₂-Ce_0.9Zr_0.1O₂ core-shell catalyst was obtained.In order to compare with the performance of the V-WO_X/TiO₂ catalyst currently used in commercial use,the loading of VO_X is the same as that of the commercial catalyst,which is 3 wt.%（calculated as V₂O₅）.The VO_X/TiO₂-Ce_0.9Zr_0.1O₂ core-shell catalyst has a higher conversion rate of NO than the commercial V-WO_X/TiO₂ catalyst at100℃-450℃and a space velocity of 40,000 h^-1.In the temperature range of 250℃to 400℃,the NO conversion of the catalyst is above 97%,and the selectivity of N₂is above 97.5%.The TiO₂-Ce_0.9Zr_0.1O₂ core-shell structure carrier contains more oxygen vacancies,which can provide more electrons with migration ability.After VO_X loading,oxygen vacancies are supplemented,and electron transfer occurs between Ce³⁺and high valence state V,resulting in an increase of the low valence state the V content.The presence of low valence V is more conducive to the NH₃-SCR reaction of NO.The presence of Ce_0.9Zr_0.1O₂ coating can effectively improve the thermal stability of the catalyst,broaden the temperature window of the reaction,and the catalyst contains more acidity.The presence of acid sites,especially medium-strong acid sites,facilitates the adsorption of NH₃,resulting in better catalytic performance of the catalyst.