Design Of Highly Efficient Ni Catalysts For CO₂ Methanation

While promoting the development of modern industry,the use of fossil fuels such as coal,oil and natural gas has also led to problems such as energy depletion,environmental pollution and abnormal climate.The excessive emission of greenhouse gases such as carbon dioxide has become one of the important problems facing modern humans.How to effectively recover carbon dioxide and transform it into valuable products has become the focus of scientific researchers.The CO2 methanation technology is carbon dioxide(CO2)hydrogenation to methane(CH4).Its products can be used not only as chemical products but also as energy storage materials.Therefore,it is of great significance in CO2 conversion and utilization.The transition metal Ni has the advantages of good hydrogenation activity,inhibition of side reactions and low cost,becoming the most widely used active component in methanation catalysts.However,based on thethermodynamic analysis,CO2 methanation is unfavored at high temperature because the reaction is highly exothermic.Therefore,it is of great practical significance to design and prepare catalysts with high activity at low temperature.In this paper,Ni was used as the active component and SiO2 microspheres were used as support firstly.The NiCeO2/SiO2 was prepared by co-impregnation and the Ni/SiO2@CeO2 was prepared by self-assembly method which hexamethylenetetramine was as template.By comparing the activity of several catalysts,we studied the effect of the promoter CeO2 and its introduction mode on the performance of the catalysts.Secondly,the active component Ni was then immersed in nano-CeO2 three morphology(rod,cube and polyhedra)supports,and the effect of the support morphology on the activity of the catalyst was investigated.Finally,Al2O3 nanoplate and Ni were used as the support and active component,respectively.The effect of lanthanum oxide on the low-temperature activity was studied.The stabilities of the catalysts in three systems were tested respectively.The physical and chemical means such as N2 sorption,X-ray diffraction,H2 temperature programmed reduction,CO2 temperature programmed desorption,Transmission electron microscope were were carried out to characterize the catalyst.The conclusions were as follows:1.The Ni/SiO2@CeO2 prepared by self-assembly method exhibited better activity than the catalyst introduced CeO2 by co-impregnation.The characterization results showed that Ni/SiO2@CeO2 had larger specific surface area and smaller Ni particle size,which can increased the activity of the catalyst significantly.2.Among the three-morphology nano-CeO2 supported Ni catalyst systems,the activity of Ni/CeO2 nanorod was the highest.The characterization results showed that it had the largest specific surface area,pore volume and more oxygen vacancy.The result demonstrated that morphology of support can affect the support interaction with the active metal,changing the catalytic performance of the catalyst.3.The optimum content of La2O3 introducing into Ni/Al2O3 catalyst was 3wt%.The introduction of La2O3 was not conducive to the specific surface area,but it greatly changed the dispersibility of Ni and increased the weakly alkaline active sites.The weakly alkaline active site obviously benefited the sorption and conversion of carbon dioxide,increasing the low-temperature activity of the catalyst.