Direct CO₂ Conversion Using Geological Carbonates as Absorbents for an Integrated Carbon Capture–Conversion Strategy

The current carbon capture and utilization (CCU) technologies suffer from energy-intensive processes due to conventional alkaline-based capture methods requiring significant energy input for regeneration and material cycling. In Earth's carbonate weathering process within Karst systems, CO₂ is sequestered and transformed through interaction with CaCO₃. Inspired by this natural process, here, we propose an integrated CO₂ capture-conversion strategy using geologically abundant carbonates as low-cost absorbents. We demonstrate that CO₂ absorbed by carbonates can be efficiently hydrogenated in situ to formate in a one-pot system at 140 °C using a nonprecious cobalt-copper (CoCu) catalyst, achieving 21% yield of formate with diluted CO₂ emissions (as low as 50 000 ppm, representative of typical industrial exhaust). Co facilitates the formation of a Cu⁺/Cu⁰ interfacial structure, leading to an enhancement of the hydrogenation efficiency. Density functional theory calculations show that the Cu⁺/Cu⁰ interface serves as the primary active site for H₂ adsorption and activation to H*, which then promotes the reduction of bicarbonate (HCO₃^-) to formate. Furthermore, the interface between Co and Cu lowers the energy barrier for HCO₃^- adsorption, leading to its enhanced reduction by H*. This work offers a new pathway for simultaneous CO₂ capture and catalytic conversion, advancing sustainable and energy-efficient CCU technologies.