Title: Response to Extreme Temperatures of Mesoporous Silica MCM-41: Porous Structure Transformation Simulation and Modification of Gas Adsorption Properties

Abstract

In this paper, molecular dynamics (MD) and Monte Carlo (MC) simulations were applied together for the first time to reveal the porous structure transformation mechanisms of mesoporous silica MCM-41 subjected to temperatures up to 2885 K. Silica was experimentally characterized to inform the models and enable prediction of changes in gas adsorption/separation properties. MD simulations suggest that the pore closure process is activated by a collective diffusion of matrix atoms into the porous region, accompanied by bond reformation at the surface. Degradation is kinetically limited, such that complete pore closure is postponed at high heating rates. We experimentally observe decreased gas adsorption with increasing temperature in mesoporous silica heated at fixed rates, due to pore closure and structural degradation consistent with simulation predictions. Applying the Kissinger equation, we find a strong correlation between the simulated pore collapse temperatures and the experimental values which implies an activation energy of 416 ± 17 kJ/mol for pore closure. MC simulations give the adsorption and selectivity for thermally treated MCM-41, for N₂, Ar, Kr, and Xe at room temperature within the 1–10 000 kPa pressure range. Relative to pristine MCM-41, we observe that increased surface roughness due to decreasing pore size amplifies the differencemore » of the absolute adsorption amount differently for different adsorbate molecules. In particular, we find that adsorption of strongly interacting molecules can be enhanced in the low-pressure region while adsorption of weakly interacting molecules is inhibited. Finally, this then results in higher selectivity in binary mixture adsorption in mesoporous silica.« less

Authors:

Zhang, Shenli ^[1]; Perez-Page, Maria ^[1]; Guan, Kelly ^[1]; Yu, Erick ^[1]; Tringe, Joseph ^[2]; Castro, Ricardo H. R. ^[3]; Faller, Roland ^[4]; Stroeve, Pieter ^[4]

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+ Show Author Affiliations

1. Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering. Dept. of Materials Science and Engineering
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
3. Univ. of California, Davis, CA (United States). Dept. of Materials Science and Engineering
4. Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering

Publication Date:

Mon Oct 17 00:00:00 EDT 2016

Research Org.:

Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Univ. of California, Davis, CA (United States)

Sponsoring Org.:

USDOE Office of Nuclear Energy (NE)

OSTI Identifier:

1476196

Report Number(s):

LLNL-JRNL-705740
Journal ID: ISSN 0743-7463; 840784

Grant/Contract Number:  

AC52-07NA27344; NE0000704

Resource Type:

Accepted Manuscript

Journal Name:

Langmuir

Additional Journal Information:

Journal Volume: 32; Journal Issue: 44; Journal ID: ISSN 0743-7463

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY