Direct synthesis of formic acid from carbon dioxide and hydrogen: a thermodynamic and experimental study using poly-urea encapsulated catalysts

The present work is concerned with direct hydrogenation of CO2 to formic acid which takes into account thermodynamic feasibility and experimental studies. Poly-urea encapsulated catalysts were explored and the effect of ionic liquids under supercritical conditions was examined. The monometallic and bimetallic catalysts were prepared, characterized, screened for the hydrogenation of CO2 and also compared with a commercially available poly-urea–Pd catalyst. The effect of reaction temperature, type of the catalyst, promoter, pressure and molar ratio of the feed (H2/CO2) on the yield of formic acid has been studied and discussed in order to maximize the formation of formic acid. The highest yield of formic acid obtained in terms of turn-over frequency (TOF) was 11,900 h−1 at a total pressure of 144 bar, temperature of 70 °C, mole ratio (H2/CO2) of 1, catalyst (poly urea encapsulated Ru) loading of 0.04 g/cm3 and 3.12 × 10−5 mol/cm3 of ionic liquid (trihexyl (tetradecyl) phosphonium chloride)