In Situ Reduction of Fe-Doped Calcium Carbonate to Perform Low-Carbon Cement Clinker Coupling with Generation of Syngas

In situ reduction of carbonates is an efficient strategy to prepare cement with lower CO2 emission and energy consumption. However, the important role of Fe species in CaCO3 still lacks comprehensive and in-depth research. Herein, we report on the preparation of a low-carbon cement clinker coupling high-value syngas via the in situ reduction process of Fe-doped CaCO3. The optimal 3 wt % Fe–CaCO3 exhibits an ultrahigh CO selectivity (99.2%) at 600 °C with a CO formation rate of 0.67 mmol min–1, which significantly reduces the decarboxylation temperature and inhibits CO2 emissions. A combination of advanced in situ characterization and density functional theory calculations has demonstrated that Fe species facilitate the hydrogen dissociation, and the process undergoes a temperature-dependent reduction mechanism. At relatively low temperatures, CO is produced via the direct hydrogenation mechanism; i.e., the active H species initially binds to O in C–2O on the carbonate, selectively cleaving Ca–O and C–O bonds to generate CO*. At elevated temperatures, the reverse water gas shift pathway with HCOO* species as intermediates is executed. This study elucidates the mechanism of Fe-doped CaCO3 hydrogenation as raw materials for cement, thereby providing a novel avenue for the practical large-scale application of low-carbon cement coupled with syngas.