Reaction and separation system for CO₂ hydrogenation to formic acid catalyzed by iridium immobilized on solid under base-free condition

Hydrogenation of carbon dioxide (CO2) to produce formic acid (HCOOH) in base -free condition can avoid waste producing and simplify product separation process. However, it remains a big challenge because of the unfavorable energy in both thermodynamics and dynamics. Herein, we report the selective and efficient hydrogenation of CO2 to HCOOH under neutral conditions with imidazo-lium chloride ionic liquid as the solvent, catalyzed by a heterogeneous Ir/PPh3 compound. The heterogeneous catalyst is more effective than the homogeneous one because it is inert in catalyzing the decomposition of product. A turnover number (TON) of 12700 can be achieved, and HCOOH with a purity of 99.5% can be isolated by distillation because of the non-volatility of the solvent. Both the catalyst and imidazolium chloride can be recycled at least 5 times with stable reactivity.