In Situ CO ₂ Conversion by Hydrogenation of Red Mud‐Doped Limestone: Experimental and DFT Investigation

Abstract In conventional cement production, carbonate decomposition represents the dominant contributor to CO 2 emissions. Introducing green hydrogen into the calciner facilitates the reduction of limestone to CaO and CO, achieving in situ CO 2 utilization while decreasing the calcination temperature, thereby resulting in mitigation of carbon emissions and energy demands. Nevertheless, this approach is limited by hydrogenation conversion efficiency of limestone. This study proposes an innovative red mud doping strategy, in which cost‐effective red mud‐doped limestone composites are prepared by ball milling and evaluated for hydrogenation performance in a bubbling fluidized bed reactor. Density functional theory (DFT) calculations elucidate the catalytic mechanism of Fe 4 cluster during CaCO 3 hydrogenation. Results show that at 650 °C under 100% H 2 , a red mud/limestone mass ratio of 2:20 enhances CO selectivity by 11.83% compared to natural limestone. The hydrogenation process follows a dynamic catalytic pathway, beginning with reduced Fe species as the primary active sites, which subsequently transition to calcined CaO‐dominated catalysis. DFT analysis confirms that Fe active sites significantly enhance the interaction between H 2 and CaCO 3 surface, reducing the H 2 dissociation barrier by 94.8% and altering the rate‐limiting step. This work provides a promising approach for low‐carbon cement production while simultaneously advancing sustainable red mud utilization.