Diffusion of CH4, CO2, and Their Mixtures in AlPO4-5 Investigated by QENS Experiments and MD Simulations

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• 作者：S茅bastien Rives ; Herv茅 Jobic ; AndrewM. Beale ; Guillaume Maurin
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：July 3, 2013
• 年：2013
• 卷：117
• 期：26
• 页码：13530-13539
• 全文大小：442K
• 年卷期：v.117,no.26(July 3, 2013)
• ISSN：1932-7455

文摘

Quasi-elastic neutron scattering (QENS) measurements in combination with molecular dynamics (MD) simulations have been performed to characterize the dynamics of CH₄, CO₂, and binary mixtures of different compositions in the zeolite-type AlPO₄-5 material. The experimental and simulated self-diffusion coefficients (D_s) for CH₄ in the presence of CO₂ are in very good agreement in a whole range of CO₂ concentrations, showing a decreasing profile when the CO₂ loading increases. Similar to the diffusion of light gases in other nanoporous materials, the experimental and simulation approaches both evidence a fast mobility for CH₄ at low loading in this zeolite. Complementary to this, the MD simulations predict a slightly faster diffusivity for CH₄ in binary mixtures with CO₂ when compared to its behavior as a single component, which is concomitant with a speeding up of the CO₂ molecules. QENS further reveals a nonmonotonous evolution of the transport diffusivity for CO₂ as a function of the loading. This peculiar behavior is reproduced by MD simulations, with the minimum being shifted to a higher concentration. A deep analysis of the MD spatial densities indicates that both CO₂ and CH₄ experience a 1D-type normal diffusion along the AlPO₄-5 channels in a hollow cylinder with a hexagonal base. Finally, QENS and MD allow the exploration of the rotational dynamics of CH₄ as a pure component and in a binary mixture.