Single-amine strategy for CO2 hydrogenation to formic acid: Process simplification using NBIM coupled with heterogeneous Ru-MACHO-POMP catalysis

The catalytic hydrogenation of carbon dioxide (CO 2 ) to formic acid (FA) is a promising pathway for sustainable C1 chemical production and hydrogen storage; however, practical implementation is often limited by complex separation processes associated with conventional dual-amine systems. Herein, we propose a simplified single-amine strategy in which N-butylimidazole (NBIM) functions simultaneously as both the reaction and separation amine, eliminating the amine-exchange step and reducing process complexity. To compensate for the relatively low basicity of NBIM, heterogeneous catalysts were systematically screened, and a porous polymer–immobilized Ru-MACHO catalyst (Ru-MACHO-POMP) exhibited the highest activity under NBIM-based conditions, achieving a formate productivity of 53 kg FA /kg cat. /d. at 80 °C and 80 bar. Temperature-dependent studies revealed that operation at moderate temperature enables a favorable balance between reaction productivity and acid-to-amine ratio (AAR), which is a critical parameter governing downstream separation energy. Based on the optimized reaction conditions, process simulation and techno-economic analysis (TEA) were conducted, demonstrating a levelized cost of FA of $0.583 kg⁻¹ , comparable to conventional fossil-based production routes. This work demonstrates that integrating catalyst design with process simplification enables a viable pathway toward economically competitive CO 2 -to-formic acid production using a single-amine platform.