Potassium-Promoted Limestone for Preferential Direct Hydrogenation of Carbonates in Integrated CO₂ Capture and Utilization

Integrated CO₂ capture and utilization (ICCU) via the reverse water–gas shift (RWGS) reaction offers a particularly promising route for converting diluted CO₂ into CO using renewable H₂. Current ICCU-RWGS processes typically involve a gas–gas catalytic reaction whose efficiency is inherently limited by the Le Chatelier principle and side reactions. Here, we show a highly efficient ICCU process based on gas–solid carbonate hydrogenation using K promoted CaO (K-CaO) as a dual functional sorbent and catalyst. Importantly, this material allows ∼100% CO₂ capture efficiency during carbonation and bypasses the thermodynamic limitations of conventional gas-phase catalytic processes in hydrogenation of ICCU, achieving >95% CO₂-to-CO conversion with ∼100% selectivity. We showed that the excellent functionalities of the K-CaO materials arose from the formation of K₂Ca­(CO₃)₂ bicarbonates with septal K₂CO₃ and CaCO₃ layers, which preferentially undergo a direct gas–solid phase carbonates hydrogenation leading to the formation of CO, K₂CO₃ CaO and H₂O. This work highlights the immediate potential of K-CaO as a class of dual-functional material for highly efficient ICCU and provides a new rationale for designing functional materials that could benefit the real-life application of ICCU processes.