A biphasic homogeneous catalytic strategy enabling simplified product separation in CO2-to-calcium formate conversion

A biphasic homogeneous catalytic route was developed for the conversion of CO₂ to calcium formate, aiming to overcome the energy-intensive separation associated with previously reported CO₂-to-formate processes using a highly water-soluble amine. The process employs a Ru–MACHO catalyst dissolved in a non-polar solvent and a water-insoluble tertiary amine as a reactive component. This phase configuration enables efficient CO₂ hydrogenation to formate while allowing spontaneous phase separation between the product-containing aqueous layer and the catalyst-containing organic phase. Subsequent addition of CaO converts the amine–formate adduct into calcium formate dissolved in the aqueous phase and simultaneously regenerates the amine without the need for energy-demanding distillation. Reaction parameters and amine selection were systematically optimized to maximize calcium formate formation, and the catalyst stability was subsequently evaluated. The results confirm that the biphasic homogeneous design effectively simplifies the product separation process compared with previously reported systems. These results highlight the sustainability of the biphasic homogeneous catalytic system for energy-efficient CO₂-to-calcium formate conversion.