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

Abstract

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).