Study On Methanation Properties And Mechanism Of Hydrogen Storage Metal-induced Selective Hydrogenation Of Carbonate

With the development of industrialization,the concentration of carbon dioxide（CO2）in the atmosphere is getting higher and higher,which will lead to global warming,ocean acidification and threaten the safety of all living things.The use of carbon dioxide as a renewable carbon source to produce high-value fuels and chemicals has attracted worldwide attention,among which catalytic hydrogenation of carbon dioxide is the most realistic and attractive option.Metal hydrides can provide negative lattice H and exhibit high selectivity and catalytic activity during hydrogenation.In addition,carbonate can be regarded as a solid storage form of CO2,which is a rich and useful resource.Therefore,the utilization of carbonate is considered as indirect utilization of CO2.CH4-H2 fuel was prepared by hydrogen-storage metals（Ca,Mg,Ba）induced highly selective hydrogenation of carbonate.Metal hydrides（CaH2,MgH2,BaH2）formed in situ play a key role in improving the methanation performance of carbonate.On this basis,the influence of different reaction conditions on methanation performance was studied,and the methanation mechanism was explored through experimental phenomena and DFT theoretical calculation.1.Hydrogenation of carbonate provides an indirect pathway for utilizing CO2 and a sustainable method for utilizing carbonates.Here,for the first time,we report hydrogen storage metal can efficiently induce the hydrogenation of carbonate to methane under room-temperature ball milling conditions.The effects of different ball milling conditions on methanation performance were studied.The results show that the methane yield can reach 56%,and the methane selectivity is 100%.When adding metal Ni,the methane yield can be further increased and the methane selectivity remains 100%.Metal hydride formed during ball milling plays a key role in carbonate methanation because it can provide negative hydrogen（H-）with strong reducibility.DFT calculation shows that H-is more inclined to combine with the C atom of carbonate,forming a transition state with the formate structure.This work provides a novel and sustainable method to convert carbonate/CO2 to methane at room temperature.2.Based on the previous chapter,the thermochemical reduction of barium carbonate with barium hydroxide was first studied.Ba was heated in a hydrogen atmosphere to synthesize BaH2,which was mixed with BaCO3 and reacted at 500℃ for 24 h to prepare methane.The results show that the methane yield of BaH2-BaCO3 is 41.38%.With the addition of metal Ni,the maximum methane yield is 76.22%,and methane selectivity remains 100%.Increasing reaction temperature,time,and BaH2/BaCO3 ratio are beneficial to improve methanation performance.This chapter provides a novel and efficient method for the methanation of barium carbonate.3.Finally,we optimize the experimental process in the previous chapter,and report hydrogen storage metal Ba can efficiently induce the hydrogenation of BaCO3 to methane under heating conditions.The results showed that the methane production rate increased from 8.72%to 65.57%,the highest methane production rate was 85.52%,and the selectivity remained 100%when Ni was added.Methane production depends on Ni content,heating temperature,heating time,and Ba/BaCO3 ratio.The density functional theory calculation shows that Ni3-BaCO3 structure can promote the adsorption and activation of H2 molecule,and BaH2 is beneficial to provide negative lattice H for the hydrogenation of BaCO3 molecule.