Quantitative Characteristics and Microscopic Mechanism of Direct Reduction of CaCO3 with CH4 for Syngas Production.

The direct reduction of CaCO3 with CH4 emerges as a pivotal strategy to mitigate intensive carbon emissions with higher energy efficiency than conventional pyrolysis. Despite the promising industrial potential, its advancement is fundamentally hindered by the lack of quantitative metrics for key reaction behaviors and the limited mechanistic understanding of the facilitating role of CH4. To address these gaps, we quantify the onset decomposition temperature of CaCO3 and its reduction kinetics under the synergy of CH4 and the catalyst, and elucidate the underlying microscopic mechanism. Experimental results demonstrate a 29% reduction in the decomposition temperature of Ca95Ni2.5Fe2.5 in CH4 compared to Ca100 in Ar, with an empirical correlation derived for quantitative prediction, and the activation energy also decreases drastically by 35%. In situ DRIFTs and DFT calculations confirm that the promotional effect originates from the dissociation of CH4 at catalyst active sites to generate H*, which migrates to the CaCO3 surface, induces the formation of key intermediates, weakens the C─O bond strength, and lowers the decomposition energy barrier. This study quantifies core properties of the direct CaCO3 reduction with CH4 and proposes a formate-involved reaction pathway, offering vital guidance for the advanced low-carbon and high-value utilization of carbonates.