The Theoretical Study On Reduction Of CO₂ Catalyzed By Metalloradical Complex And Mg⁺/Al（Ⅰ） Lewis Acid/base Combination

In recent years,the study of CO₂ reduction has been one of the hotspots of scientific research.As a kind of abundant,cheap and non-toxic C1 raw material,the conversion to CO₂ into high value-added chemical products has attracted widespread attention.On the one hand,it can alleviate a series of environmental problems caused by excessive CO₂ emissions.On the other hand,it also relieves the energy crisis facing the world.It is of great theoretical significance and practical guidance for rational utilization of CO₂ that theoretically design new and efficient catalysts for CO₂ reduction and to gain insight into their reduction mechanism.In this thesis,two catalysts for CO₂ reduction reaction are designed theoretically:metalloradical Co-C·Ph₃ and Mg⁺/Al（Ⅰ）Lewis acid/base pair,and the reaction mechanism have been clarified.The main research contents are as follows:1.A novel strategy of CO₂ reduction by metalloradical complex was proposed in theory.In this work,we theoretically designed a metalloradical complex Co-C·Ph₃ with the triplet characters of the transition metal cobalt（Co⁰）coordinating a triphenylmethyl radical.The potential catalytic role of this novel metalloradical in the CO₂reduction in H₂/CH₄ in the gas phase was explored via density functional theory（DFT）calculations.For the CO₂ reduction reaction to H₂,there are two possible pathways:one（path A）is the activation of CO₂ by Co-C·Ph₃,followed by the hydrogenation of CO₂.The other（path B）starts from the splitting of the H–H bond by Co-C·Ph₃,leading to the transition-metal hydride complex Co H–H,which can reduce CO₂.However,for the reduction of CO₂ by CH₄ two different products,CH₃COOH and HCOOCH₃,can be generated following different reaction routes.Both route to begin with one CH₄ molecule approaching the Metalloradical Co-C·Ph₃ to form the intermediate Co H–CH₃.This work puts forward a new CO₂ reduction scheme,which is helpful to develop the research field of using small molecules（H₂ and CH₄）to reduce CO₂.2.A reaction strategy for reduction of CO₂ based on the main group cationic heterobimetallic Lewis acid/base combination was proposed.Here,we performed a proof of concept studied and used DFT computations to demonstrate that a heterobimetallic Mg⁺/Al（Ⅰ）Lewis acid/base combination without transition metal can reduce CO₂ and generate formate in gas phase.The roles of the both the Lewis acid and base of the CO₂ fixation/activation is elucidated with the block-localized wavefunction（BLW）method of the same DFT theoretical level.Lewis base plays a leading role in CO₂ fixation and activation,while Lewis acid only plays a supporting role.The reduction begins with the fixation CO₂ and the formation of complex,following by the hydrogenation to obtain the intermediate.Next,with the help of the acid（HCl）,a complex containing an HCOOH part and an Al-H type complex is formed through acidolysis action.The Al-H typed complex also has the ability to reduce CO₂.This study reveals the influence of Mg⁺/Al（Ⅰ）lewis acid/base combination on CO₂ reduction reaction.It is expected that the development of CO₂ reduction and conversion will expand new research directions through the heterobimetallic Lewis acid/base system.