Hydrogenation Of Carbon Dioxide To Formic Acid Catalyzed By MOF Supported Ru-based Catalyst

Carbon dioxide?CO₂?as a waste originated from anthropogenic activity is a direct contributor to the greenhouse effect.Therefore,the efficient and economical method of CO₂ capture and utilization is of great significance to the development of human society.Formic acid is difficult to replace in some special markets?tannery and feed industry?,and has the potential as a chemical hydrogen storage material in the future hydrogen energy economy.Therefore,CO₂ hydrogenation to formic acid is a promising green route for CO₂ utilization.In this paper,the catalytic performance of MOF supported Ru based catalysts RuNPs/MOF and RuCl₃/MOF for the catalytic hydrogenation of CO₂ to formic acid was studied.RuNPs/MOF catalysts were prepared by impregnation and sodium borohydride reduction method with four kinds of MOF such as MIL-101?Cr?,MIL-101?Cr?-NH₂and UiO-66 and UiO-66-NH₂ respectively,as supporter.The reaction properties of CO₂hydrogenation to formic acid in EtOH-H₂O-NEt₃ solvent system were investigated.The XRD,FT-IR,N₂ physical adsorption,TEM,XPS,TG characterization of the catalyst showed that the Zr based MOF supported catalyst RuNPs/UiO-66 achieved a desirable catalytic performance due to well dispersion of Ru species,and stronger interaction between the Ru species and the Zr₆O₄?OH?₄ secondary structural unit of UiO-66,which led to the bivalent distribution of species and was more conducive to the activation of H₂ heterolytic cleavage.Under the optimum reaction conditions,TON of formic acid reached 1152 over RuNPs/UiO-66 for hydrogenation of CO₂.RuCl₃/MIL-101?Cr?-NDPPB catalyst was prepared by post synthesis modification of grafting 2-?Diphenylphosphino?benzaldehyde onto MIL-101?Cr?-NH₂.It is proved that the bidentate phosphate ligand was successfully introduced to MIL-101?Cr?-NH₂by FT-IR.The characterization of XRD and TEM-EDS showed that RuCl₃ was highly dispersed on the carrier because it was coordinated with the coordination group on the MOF carrier.XPS characterization showed that RuCl₃ was introduced to MOF carrier and the binding energy of Ru3p decreased because of the role of the donor ligand on the carrier,which was beneficial to the activation of CO₂ molecules and thus increased the activity of the reaction.Using DMSO-H₂O-NEt₃ as solvent and adding PPh₃ as free ligand,the TON reached 831 after 2 h reaction.