Research On Catalytic Conversion Of CO₂ For The Production Of CH₄

In recent years,the sharp increase in CO₂ emission has caused severe impacts on the environment.Besides,the global energy supplies are under increasing pressure.Hydrogenation of CO₂ into clean fuel——methane,is of great significance for the sustainable development of energy and environment.In this paper,a series of systematical studies on the development and optimization of CO₂ methanation catalysts were conducted.First,the effect of Ce O₂ content on the performance of Ni-based catalysts for CO₂ methanation was studied.A series of Ni-x Ce O₂/MCM-41 catalysts with a nickel content of 20wt% were prepared through deposition precipitation method.It was found that all Ce O₂-promoted catalysts exhibited enhanced catalytic activity when compared to Ni/MCM-41.The catalyst modified with 20 wt% Ce O₂ showed the best catalytic performance under optimum condition,with CO₂ conversion and CH₄ selectivity of 85.6% and 99.8%,respectively.The synergetic effects among Ni0 active sites,the promoter and the support,including nickel dispersion improvement and increased CO₂ adsorption sites due to the addition of Ce O₂,were considered as important factors for high reactivity of the promoted catalysts.However,the addition of excess Ce O₂ will cause some Ni0 active sites to be covered,resulting in a decrease in catalyst activity.In the above study,it was found that excessive after-loading of the promoter would affect the activity of the catalyst.x Mg@MCM-41?where x = 0,0.05 0.1?functional mesoporous materials were synthesized by a novel in-situ one pot method and then were used as supports for Ni based catalysts.It turned out that when n Mg/n Si was equal to 0.05,Mg@MCM-4 with a regular and ordered mesoporous structure was synthesized where Mg was introduced into the framework of MCM-41.Introducing Mg into the framework of the support can significantly enhance the basic properties of the catalyst,thus promoting the adsorption and activation of CO₂.The catalysts prepared in the experiments all have good thermal stability and catalytic activity.In this study,Ni/0.05Mg@MCM-41 showed the best low temperature reaction activity in the CO₂ methanation reaction.Based on the above studies,it was found that the dispersion of Ni had a great influence on the performance of the catalyst.The preparation method of the catalyst can affect the distributionof the active component Ni.A new,highly active Ni-La2O₃/SBA-15?C?catalyst for CO₂ methanation was prepared using a citrate complex method,where the formed La Ni O₃ was a key precursor.Its catalytic performance was analyzed in detail and compared with catalysts prepared through a typical wet impregnation method.Ni-La2O₃/SBA-15?C?showed a high dispersion of Ni with a small particle size less than 5 nm,which is one third size of that prepared by impregnation.Decent catalytic performance was achieved with a CO₂ conversion of 90.7%together with a CH₄ selectivity of 99.5% at 320 °C.Due to the specific perovskite structure of La Ni O₃,the interaction between La and Ni was intensified,thus enhancing the synergistic effect of La2O₃ and Ni,which contributed to the high dispersion of Ni nanoparticles as well as the good anti-sintering and anti-carbon deposition properties.Density functional theory calculations also suggested that the catalyst derived from La Ni O₃ favored the adsorption and activation of CO₂.Biochar is one of the by-products of biomass pyrolysis or gasification.If high-value utilization of biochar can be realized simultaneously with the efficient conversion of biomass gas,the economics of biomass thermochemical conversion will be effectively improved.An in-situ modification and activation process was developed.The biochar modified by highly dispersed Ce O₂ was obtained from pyrolysis of Pinus sylvestris combined with in-situ activation with Na HCO₃ and Ce doping and then was assessed as a catalyst support.The Ni/Ce-ABC catalyst exhibited better activity than Ni/ABC for CO₂ methanation,achieving a CO₂ conversion of 88.6% at 360 °C together with a CH₄ selectivity of 92.3% at 1 MPa.The highly dispersed Ce species on the biochar were found to be beneficial for the dispersion of the nickel species and enhancement of the CO₂ adsorption.Finally,life cycle assessments of different catalyst preparation processere were performed.It was found that biochar-based catalysts were more environmental friendly than the metal oxides catalysts.The technology of modified biochar-based catalyst was further evaluated,which provided guidance for the optimization of the preparation process of high-performance catalyst for the reduction and valorization of CO₂.