Theoretical Study On The Mechanism Of The Synthesis Of Methanol From Carbon Dioxide On Ni Doped Cu Surface

Carbon dioxide is a greenhouse gas,its emergence and accumulation will bring great harm to the earth’s environment.Therefore,the use of effective methods to reduce carbon dioxide emissions and the development of carbon dioxide is a hot issue at present.Carbon dioxide is a safe and rich source of carbon and oxygen in nature.The decomposition of carbon dioxide into a new corporate chemical is a green chemistry.Researchers have used carbon dioxide to replace toxic CO to synthesize new chemicals.Carbon dioxide molecules are usually relatively stable and poor in activity.Therefore,in order to convert and utilize carbon dioxide,a variety of catalysts are first used to activate carbon dioxide to improve their reactivity.Carbon dioxide can be converted into CH4,HCO2H,HCHO and CH3OH by catalytic activation.The selective catalytic reduction of carbon dioxide into CH₃OH is a hot topic at present.NiCu alloy catalysts exhibit good catalytic activity during the catalytic reduction of CO2 to CH3OH.However,the mechanism of the conversion of CO2 into CH3OH on the NiCu catalyst has not yet been reported.Based on density functional theory（DFT）and Slab model,the adsorption of CO₂ on Ni doped Cu（110）surface has been discussed and the most stable adsorption configuration has been determined.On the basis of the most stable adsorption configuration,the reaction mechanism of catalytic hydrogenation of CO2 to CH3OH on the Cu（110）surface of a single layer of Ni was discussed.The results are summarized as follows:（1）The adsorption of carbon dioxide on Cu（110）surface with different Ni doping concentration was systematically investigated.The results show that the adsorption energy of carbon dioxide increases gradually with the increase of the concentration of Ni in the surface layer.When the Cu atoms are completely replaced by Ni atoms in the surface layer,the adsorption energy of carbon dioxide is maximum.On the surface of Cu（110）,the adsorption of CO₂ is weaker than that of physical adsorption.The Ni doped in the surface layer is the active site of CO2 adsorption.With the increase of Ni concentration,CO2 is converted from physical adsorption to chemical adsorption.In the various adsorptive structures,the most stable adsorption configuration of carbon dioxide is SB-4f on the surface of Ni doped.In this adsorption configuration,the C and O atoms in CO₂ interact with the surface active atoms,respectively.The 4σ_g、1π_u and 2π_u orbitals of CO₂ molecules interact with the d_yz and d_z²orbitals of Ni atoms on the surface respectively.Through this interaction,the surface charge is transferred to the anti bonding orbitals of CO₂,the charges on CO₂ increase,the C-O bonds increase,and the CO2 molecules are activated.（2）The decomposition mechanism of carbon dioxide on Cu（110）surface with different Ni doping concentration was studied.From the predominant adsorption configuration of CO2molecules as a starting point.Its decomposition is similar to the mechanism of CO and O,and the energy barrier of the C-O bond is gradually decreased with the increase of the concentration of Ni in the surface layer.The modification of the surface layer helps to improve the activity of its decomposition of CO₂.（3）A systematic study was carried out on the reaction mechanism of CO2 on Cu（110）surface with a single layer of Ni and gradually reduced to CH₃OH by H atoms.The following five possible CO₂ reduction paths are discussed:（1）CO₂→HOCO→CO→COH/HCO→HCOH→H2COH→CH3OH（2）CO₂→HOCO→COHOH→COH→HCOH→H₂COH→CH₃OH（3）CO₂→CO→COH→HCOH→H₂COH→CH₃OH（4）CO₂→CO→HCO→HCOH→H₂COH→CH₃OH（5）CO₂→CO→HCO→CH₂O→H₂COH→CH₃OH...