Theoretical Study On The Catalytic Reduction Of CO₂ By Mn/Ru Complex

One of the most popular methods for converting CO₂ to fuel or fuel precursors is the utilization of transition metal complexes as catalysts to reduce CO₂ to CO or CH₃OH,respectively,by electrochemical reduction or catalytic hydrogenation.Although such catalysts have been studied over the years,many of these catalysts are based on expensive metals.Compared to these precious metals,low-cost,inexpensive metal catalysts have broader prospects.For electrochemical reduction of CO₂,the catalysts which use abundant metal manganese?Mn?as coordination center have attracted researchers'attention.And for the catalytic hydrogenation of CO₂,relatively inexpensive ruthenium?Ru?catalysts in platinum group metals have also been widely developed in recent years.In this thesis,we first studied the CO₂ electroreduction mechanism of weak Br?nsted acid and Lewis acid assisted Mn?mesbpy??CO?₃Br?1?by density functional theory calculations.Our results indicate that for the Lewis acid assisted cycle,an energy sink?13?,which is present owing to the interaction between Mg?OTf?₂ and activated CO₂,is disadvantageous to the apparent activation energy??G^??.Moreover,a series of substituted 13 counterparts were investigated to reduce the energy sink and decrease?G^?.Based on our study on the substituent effect,an excellent linear relationship was found between 2e reduction potentials and LUMO energies of substituted 1,and a moderate linear relationship was observed between?G^?of substituted 13 and 2e reduction potential of substituted 1 counterparts.Moreover,for the CO₂ reduction assisted by Lewis acid,the formyl-substituted complex R8 has been predicted to be a more effective catalyst with lower 2e overpotential and higher catalytic activity than its parent complex 1.Secondly,we studied the detailed mechanism of the hydrogenation of CO₂ to CH₃OH by the bifunctional catalyst Ru?PNP?by density functional theory.DMF is a key intermediate in the whole catalytic reaction.It can be generated from DMC,which is produced via the capture of CO₂ by NHMe₂,or it can be generated by the reaction between NHMe₂ and HCOOH,which is formed from the hydrogenation of CO₂.After the initial hydrogenation of DMF carbonyl group,the protonolysis of the C-N bond of the hemiaminal intermediate produces NHMe₂ and CH₂O and is further hydrogenated to form the final product CH₃OH.It is worth noting that the protonolysis of the C-N bond of the hemiaminal intermediate follows different pathways,including intramolecular proton transfer and catalyst promoted proton transfer.This depends on the nature of the substrate and expermental conditions.After calculation,we plotted the free energy profiles of the entire catalytic reaction.In the next step,we intend to study the influence of catalyst structure on the catalytic activity by changing the ligand,which provides a theoretical basis for the future catalyst design.