Catalytic Hydrogenation Of Carbon Dioxide To Formic Acid Over Pd-Cu/C

Huge execution of greenhouse gas CO₂ in atmosphere is the chief origin of global warming followed by the climate change.The urgency to capture,store and convert CO₂ into variety of fuels and chemicals got abundant considerations.The catalytic hydrogenation of CO₂to formic acid is under deliberation because of broadly commercial applications of formic acid like rubber,food,leather,fertilizers,agricultural,pharmaceutical and textiles industries as well as its favorable abilities of hydrogen storage.The carbon supported Pd nanoparticles promoted by the addition of Cu metal was prepared by incipient wetness impregnation method.Series of Pd-Cu/C catalysts with the different molar ratios of Pd and Cu（1:0,1:2,1:1,2:1,3:1,0:1）was fabricated and applied for CO₂ hydrogenation to formic acid.The morphology,particle size,dispersion,crystal structure,reduction properties,electron transformations,and elemental contents were determined by means of XRD,TEM,HAADF-STEM,EDS,TPR,XPS,and ICP.The results showed that Pd-Cu/C had very small particle size of average 1.7 nm and Pd-Cu alloy was formed with the addition of Cu promoter,which is favorable for CO₂ hydrogenation to formic acid by donating electrons from Cu to Pd to improve the nucleophilicity of Pd and accelerate the dissociation and absorption of H₂during reaction.The reaction conditions including reaction temperature,reaction pressure,and solvent were also optimized.Pd₂Cu₁/C performed the best catalytic performance for hydrogenation of CO₂ to formic acid.Turnover number（TON）of formic acid reached up to 6699 with strong polarity of solvent di-methyl formamide（DMF）,water and a strong base tri-ethylamine（NEt₃）at temperature of 120°C under pressure of 8 MPa（H₂/CO₂=1:1）for 2h of reaction time.Hydrogenation activity significantly enhanced by combination of DMF with water,due to facilitation of CO₂ insertion into Pd-H bond to activate CO₂ completely for the highest activity.