In this study, molecular dynamics simulations were performed to investigate the effects of montmorillonite with different surface cations (i.e., Na⁺, K⁺, and Ca²⁺) on CH₄ hydrate formation. The results showed that CH₄ hydrate cages are mainly formed beyond the montmorillonite surface. The inner-sphere adsorption of K⁺ and the outer-sphere adsorption of Na⁺ and Ca²⁺ occurred on the montmorillonite surface, leading to differences in order parameters and hydrogen bond number of H₂O molecules. The number of structure I cages increased faster than that of structure II cages in different models and were in agreement with the fact that CH₄ molecules can only form sI hydrate crystals. The number of 5¹² cages increased in the order: Na–Mt < Ca–Mt < K–Mt. The aqueous environment dominated by K⁺ on the external surface of montmorillonite facilitate heterogeneous nucleation of CH₄ hydrate rather than that by Ca²⁺ or Na⁺. The abovementioned findings suggest that the coordination structure of cations on the external surface of montmorillonite plays an important role in CH₄ hydrate formation through altering the occupation of CH₄ hydrate.

中文翻译：

---

阳离子（Na ⁺，K ⁺和Ca ²⁺）对蒙脱土外表面甲烷水合物形成的影响：分子动力学模拟的启示

在这项研究中，进行了分子动力学模拟以研究具有不同表面阳离子（即Na ⁺，K ⁺和Ca ²⁺）的蒙脱石对CH ₄水合物形成的影响。结果表明CH ₄水合物笼主要形成在蒙脱石表面以外。蒙脱石表面发生K ⁺的内球吸附和Na ⁺和Ca ²⁺的外球吸附，从而导致H _2的序参数和氢键数不同O分子。在不同模型中，结构I笼的数量增长快于结构II笼的增长，这与CH ₄分子只能形成sI水合物晶体这一事实是一致的。5^个12笼的数量按以下顺序增加：Na–Mt <Ca–Mt <K–Mt。在蒙脱石外表面上以K ⁺为主的水环境促进了CH ₄水合物的异质成核，而不是由Ca ²⁺或Na ^+形成。上述发现表明，蒙脱石外表面阳离子的配位结构通过改变CH ₄的占有量在CH ₄水合物形成中起重要作用。 水合物。