Design And Synthesis Of Dication Poly（ionic Liquid）s And Its Application In CO₂ Hydrogenation

Since carbon dioxide（CO₂）from fossil fuel burning has aggravated the global greenhouse effect and led to extreme environmental problems,it has been an urgent problem to make full and effective use of CO₂ resources.CO₂hydrogenation to formic acid is considered as an atomic economic reaction with 100%atomic utilization rate.The formic acid produced from catalytic hydrogenation is not only widely used in industrial production,but also can be directly used as hydrogen carrier.At present,the catalysts used for hydrogenation of CO₂ to formic acid have some problems,such as low activity and easy loss of active center.So,a series of palladium（Pd）based heterogeneous catalysts for the hydrogenation of CO₂ to formic acid were studied using poly（ionic liquid）s（PILs）as the carrier.Firstly,dication poly（ionic liquid）s（PILs）-supported palladium nanoparticles（Pd NPs）were designed to catalyze the hydrogenation of CO₂ to formic acid under mild conditions.Results indicate that due to the strong metal-support interactions in the resultant catalysts,PILs are constructed by the IL units comprising dications and hydrophobic anions（bis（trifluoromethanesulfonyl）amide,[Tf₂N^-]）that can uniformly disperse Pd NPs and enhance the catalytic hydrogenation of CO₂ to FA.It was found that the prepared catalyst showed excellent catalytic performance of CO₂ hydrogenation.Under the conditions of 80°C,1 h,2 MPa pressure of CO₂,and 0.88 M sodium borohydride aqueous solution,the amount of formic acid could be obtained 2.19 mmol,and the maximum amount of the obtained FA could reach up to 82%of the theoretical value.A possible mechanism of catalytic hydrogenation of CO₂ to FA is proposed according to the product analysis.This study highlights that PILs,as support,can promote the catalytic performance,and the resulting catalyst has potential application value for the CO₂ industry.Then,we designed two novel hydrophobic poly（ionic liquid）s（PILs）with a good affinity for CO₂.Since the abundant N atoms in the PILs can anchor palladium（Pd）nanoparticles,the designed catalyst can rapidly activate CO₂ and H₂ simultaneously,thus efficiently catalyzing the hydrogenation of CO₂ to formic acid under mild conditions.The prepared catalysts showed the best performance of CO₂ hydrogenation to formic acid due to the synergy from the[Tf₂N^-]anion with strong hydrophobicity and CO₂affinity and trimethylamine（NEt₃）as an alkaline additive with low dissociation energy.The TOF value reached 1190 h^-1 in the aqueous solution of NEt₃ at 100°C,1 h,and a total pressure of 4 MPa.The activation energy and dissociation energy during the catalytic process were carried by DFT calculation,indicating that the synergistic effect of NEt₃ is better than that of other alkaline additives.In addition,the catalytic activity of the catalyst remained stable after several cycling experiments.Combined with the experimental results,a possible reaction mechanism was proposed.Therefore,PILs have great potential as catalyst carrier material for CO₂ hydrogenation.In conclusion,the catalysts with high stability and activity in the process of CO₂hydrogenation was successfully designed and synthesized in this paper.And a new synthetic method has been provided for the synthesis of PILs with hydrophobicity and good affinity for CO₂.