Selective CO₂ Hydrogenation to Formic Acid with Multifunctional Ionic Liquids

The development of simple, cost-effective, and sustainable methods to transform CO₂ into feedstock chemicals is essential to reduce the dependence of the chemical industry on fossil fuels. Here, we report the selective and efficient catalytic hydrogenation of CO₂ to formic acid (FA) using a synergistic combination of an ionic liquid (IL) with basic anions and relatively simple catalysts derived from the precursor [Ru₃(CO)₁₂]. Very high TON (17000) and TOF values have been observed, and FA solutions with concentrations of up to 1.2 M have been produced. In this system, the imidazolium-based IL associated with the acetate anion acts as a precursor for the formation of the catalytically active Ru–H species, as a catalyst stabilizer, and as an acid buffer, shifting the equilibrium toward free formic acid. Moreover, the IL acts as an entropic driver (via augmentation of the number of microstates), lowering the entropic contribution imposed by the IL surrounding the catalytically active sites. The favorable thermodynamic conditions enable the reaction to proceed efficiently at low pressures, and furthermore the immobilization of the IL onto a solid support facilitates the separation of FA at the end of the reaction

Selective Carbon Dioxide Hydrogenation Driven by Ferromagnetic RuFe Nanoparticles in Ionic Liquids

CO₂ is selectively hydrogenated to HCO₂H or hydrocarbons (HCs) by RuFe nanoparticles (NPs) in ionic liquids (ILs) under mild reaction conditions. The generation of HCO₂H occurs in ILs containing basic anions, whereas heavy HCs (up to C₂₁ at 150 °C) are formed in the presence of ILs containing nonbasic anions. Remarkably, high values of TONs (400) and a TOF value of 23.52 h^–1 for formic acid with a molar ratio of 2.03 per BMI·OAc IL were obtained. Moreover, these NPs exhibited outstanding abilities in the formation of long-chain HCs with efficient catalytic activity (12% conversion) in a BMI·NTf₂ hydrophobic IL. The IL forms a cage around the NPs that controls the diffusion/residence time of the substrates, intermediates, and products. The distinct CO₂ hydrogenation pathways (HCO₂H or FT via RWGS) catalyzed by the RuFe alloy are directly related to the basicity and hydrophobicity of the IL ion pair (mainly imposed by the anion) and the composition of the metal alloy. The presence of Fe in the RuFe alloy provides enhanced catalytic performance via a metal dilution effect for the formation of HCO₂H and via a synergistic effect for the generation of heavy HCs