Insights into metal site effects on adsorption-hydration methane storage in water-based MOF system

J Duan and J Li and KY Zhong and HY Ye and YX Yao and DY Chen and SJ Chen and MC Zi, CHEMICAL ENGINEERING JOURNAL, 519, 164907 (2025).

DOI: 10.1016/j.cej.2025.164907

Methane hydrate exhibits significant potential in gas transportation and storage, however, the industrial application of methane hydrate is hindered by slow formation kinetics and theoretical upper limits. Herein the water-based MOF system, with different metal sites that can effectively influence adsorption, is proposed to enhance methane hydrates nucleation and growth. Focusing on ZIF-67 (Co) and ZIF-8 (Zn), the regulatory roles of metal sites in methane adsorption, hydrate nucleation kinetics, and gas storage performance were investigated by experiments, GCMC and MD simulations. Hydrate experimental results demonstrated that the ZIF-67 system achieved a 31% higher methane storage capacity (0.051 mol/mol) and a faster storage rate (0.00182 mol/ mol & sdot;min) compared to ZIF-8 system. Besides, cycling tests showed a 35.5% reduction in induction time for ZIF-67 system with stable capacity retention over five cycles. The combined characterization results showed that ZIF-67 exhibited a larger specific surface area. Meanwhile, compared to the water-based ZIF-8 system, the water-based ZIF-67 system exhibited enhanced fluidity and phase transition stability at low temperatures, suggesting its superior capability in promoting adsorption-hydration methane storage. Molecular-level investigations revealed that the adsorption sites of methane in the inner cavities of ZIF-67 and ZIF-8, potential energy and adsorption heat confirmed that Co enhanced methane capture efficacy. MD results further revealed the Co sites in ZIF-67 synergistically enhanced methane-metal interactions and stabilized hydrogen-bond networks compared to the water-based ZIF-8 system, thereby accelerating the nucleation of 512 hydrate cages and ultimately achieving a higher hydrate conversion rate. Moreover, high- concentration ZIF-67 suppressed the methane nanobubbles formation, enabling sustained hydrate growth. This work elucidates the micro- mechanisms of metal site functionality in adsorption-hydration hybrid systems, providing critical insights for advancing efficient natural gas storage technologies.

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