Quantitative Characteristics and Microscopic Mechanism of Direct Reduction of CaCO ₃ with CH ₄ for Syngas Production

ABSTRACT

The direct reduction of CaCO ₃ with CH ₄ 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 CH _4. To address these gaps, we quantify the onset decomposition temperature of CaCO ₃ and its reduction kinetics under the synergy of CH ₄ and the catalyst, and elucidate the underlying microscopic mechanism. Experimental results demonstrate a 29% reduction in the decomposition temperature of Ca ₉₅ Ni _2.5 Fe _2.5 in CH ₄ compared to Ca ₁₀₀ 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 CH ₄ at catalyst active sites to generate H ^* , which migrates to the CaCO ₃ 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 CaCO ₃ reduction with CH ₄ and proposes a formate‐involved reaction pathway, offering vital guidance for the advanced low‐carbon and high‐value utilization of carbonates.