Guo Dezhou, Wang Hongwei, Shen Yidi, An Qi
Department of Chemical and Materials Engineering, University of Nevada-Reno Reno Nevada 89557 USA
RSC Adv. 2020 Apr 14;10(25):14753-14760. doi: 10.1039/d0ra02393k. eCollection 2020 Apr 8.
Clathrate hydrates are ice-like crystalline substances in which small gas molecules are trapped inside the polyhedral cavities of water molecules. They are of great importance in both scientific research and the petroleum industry because of their applications in modern energy and environmental technologies. To achieve an atomistic-level understanding of the diffusion and decomposition of trapped molecules in clathrate hydrate, we used methane hydrates (MHs) as the prototype system and examined the methane diffusion and decomposition mechanism by employing quantum mechanics (QM) and quantum mechanics molecular dynamics (QMD) simulations. Our QMD simulations illustrated that the initial decomposition reaction in MHs initiates from hydrogen transfer among water molecules and attacks by fragments of O and OH on CH molecules are responsible for the destruction of the methane molecules. Next, our QM simulations revealed that the methane molecule prefers to escape from the ice cage through the hexagonal face at low temperature. To suppress the methane diffusion, we demonstrated that the diffusion barrier is significantly enhanced by adding electron or hole carriers. This is because the extra electrons and holes enhance the electrostatic interaction between methane and water molecules, leading to an increased diffusion barrier. Thus, the clathrate hydrates could be stabilized by adding extra free electron or hole carriers.
笼形水合物是一种类似冰的晶体物质，其中小的气体分子被困在水分子的多面体空腔内。由于它们在现代能源和环境技术中的应用，它们在科学研究和石油工业中都具有重要意义。为了在原子水平上理解笼形水合物中被困分子的扩散和分解，我们以甲烷水合物（MHs）作为原型系统，并通过采用量子力学（QM）和量子力学分子动力学（QMD）模拟来研究甲烷的扩散和分解机制。我们的QMD模拟表明，MHs中的初始分解反应始于水分子之间的氢转移，并且O和OH碎片对CH分子的攻击是甲烷分子被破坏的原因。接下来，我们的QM模拟表明，甲烷分子在低温下更倾向于通过六边形面从冰笼中逸出。为了抑制甲烷扩散，我们证明通过添加电子或空穴载流子可以显著提高扩散势垒。这是因为额外的电子和空穴增强了甲烷与水分子之间的静电相互作用，导致扩散势垒增加。因此，通过添加额外的自由电子或空穴载流子可以使笼形水合物稳定。
