DFT Study On The Mechanism Of Char-CO₂ Gasification Catalyzed By Transition Metals

Gasification technology is a clean and efficient energy conversion technology.The greenhouse gas CO₂ can be converted into combustible gas through this technology,but it has higher requirements for reaction conditions.Using catalytic gasification technology,higher conversion efficiency can be obtained under milder conditions,and production costs can be reduced.Fe,Co,Ni and V are stable and ideal catalyst.Studying the microscopic mechanism of these four metals is of great significance for understanding their catalytic gasification mechanism.In this thesis,the reaction process of Fe,Co,Ni,V single-atom catalytic gasification is calculated under the level of PBE-D3/def2-SVP,and the wave function analysis is carried out to study the catalytic mechanism of these four transition metals.The four metals exhibit catalytic activity in the process of CO₂ adsorption,oxygen transfer,and CO desorption:in the process of CO₂ adsorption,metal atoms can deform CO₂ molecules and weaken the C-O bond,making it easier to break.In the process of oxygen transfer,metal atoms can enhance the activity of O atoms and promote the transfer of O atoms to char.During the CO desorption process,the metal will interact with the C atom,which is conducive to the cleavage of the C-C bond to generate CO.The catalytic activity of V is different in each stage of gasification.In the process of CO₂ adsorption,the V atom weakens the C-O bond in CO₂ more,so the CO₂ on V is more likely to be decomposed into CO and O atoms;while in the process of oxygen transfer,the V-O bond is stronger and the O atom is less active.Suppress the transfer of O atoms to char.The combination of Fe,Co,Ni and O is weak and will enhance the activity of O atoms,which can be transferred to char more easily.In the process of CO desorption,Fe,Co,Ni and C atoms interact more strongly,which is conducive to CO desorption.The interaction between V and C is weaker and CO desorption is more difficult.Take Fe as an example to construct VFe₃ mixed clusters to further explore the synergistic promotion mechanism of Fe-V.In the process of CO₂ adsorption,Fe atoms interact with C atoms,and V atoms interact with O atoms to greatly reduce the dissociation energy barrier.In the process of oxygen transfer,the performance of VFe₃clusters is between that of Fe₄ clusters and V₄ clusters,and there is no synergistic promotion.During the CO desorption process,the addition of V can enhance the strength of the Fe-C bond and reduce the energy barrier for CO desorption,showing a synergistic catalytic effect.