Design Of Highly Efficiency Ni-containing Perovskite Catalysts For CO₂ Reforming Of Methane

At present,the greenhouse effect and energy shortage seriously threaten human survival and development.CO₂ reforming of methane is of great significance to solve the above environmental problems and optimize the energy structure.However,the industrial application of CO₂ reforming of methane is still limited by catalysts.The design and preparation of catalysts with high reforming performance has been the focus of research.In recent years,nickel-based perovskite catalysts have attracted extensive attention in CO₂ reforming of methane.La Ni O₃ as the catalytic precursor is conducive to controlling the particle size of nickel nanoparticles and improving their dispersion.The structure of perovskite is ABO₃,and its A and B cations can be partially replaced.Thus,the composition of perovskite is very flexible.However,the surface area of perovskite is usually lower than 10 m²/g,which has a negative impact on the activity of the catalyst.In this thesis,KOH and PVP are used as structure-directing agents,perovskite catalysts with higher specific surface area are synthesized with novel methods and the prepared Ni-based catalysts exhibited enhanced reforming activity.The structural parameters of the catalyst were characterized by XRD,N₂ adsorption,TEM,TG/DTA,H₂-TPR.The results are as follows:1.The La Ni O₃-HT catalyst with large specific surface area of 19.9 m²/g is prepared by new hydrothermal method.Then,the effects of partial substitution of A and B cations on the catalytic performance are discussed.Compared with the La_0.9Mg_0.1Ni_0.8Al_0.2O₃-SG catalyst prepared by citrate sol-gel method,the La_0.9Mg_0.1Ni_0.8Al_0.2O₃-HT catalyst shows better catalytic activity.The specific surface area of the La_0.9Mg_0.1Ni_0.8Al_0.2O₃-HT catalyst is 1.8 times that of the La_0.9Mg_0.1Ni_0.8Al_0.2O₃-SG catalyst.The large specific surface area is beneficial to the dispersion of nickel nanoparticles.Moreover,more nickel species are reduced in the catalyst prepared by hydrothermal method.Abundant active sites are the main factor accounting for the high catalytic activity of the La_0.9Mg_0.1Ni_0.8Al_0.2O₃-HT catalyst.It is note that the graphite carbon is not present in the spent La_0.9Mg_0.1Ni_0.8Al_0.2O₃-HT catalyst.Simultaneously,according to the change of particle size of nickel nanoparticles before and after the reaction,the spent La_0.9Mg_0.1Ni_0.8Al_0.2O₃-HT catalyst is only slightly sintered,which improves the stability of the catalyst.2.The La_0.7Mg_0.3Ni O₃-NSG catalyst is prepared by new sol-gel method,its specific surface area is 1.2 times that of the La_0.7Mg_0.3Ni O₃-SG catalyst prepared by the citrate sol-gel method.The characterization results indicates that the calcined La_0.7Mg_0.3Ni O₃-SG catalyst shows a large number of Ni O and La₂Ni O₄ hybrid phases,which decreases the activity of the catalyst.Moreover,the La_0.7Mg_0.3Ni O₃-NSG catalyst has more active sites after H₂ reduction at700°C,which is a crucial structural factor leading to the excellent catalytic activity.In addition,the existence of La₂O₂CO₃ inhibits the production of graphite carbon and improves the stability of the La_0.7Mg_0.3Ni O₃-NSG catalyst.