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Title: Surface Interactions and Confinement of Methane: A High Pressure Magic Angle Spinning NMR and Computational Chemistry Study

Characterization and modeling of the molecular-level behavior of simple hydrocarbon gases, such as methane, in the presence of both nonporous and nanoporous mineral matrices allows for predictive understanding of important processes in engineered and natural systems. In this study, we observed changes in local electromagnetic environments of the carbon atoms in methane under conditions of high pressure (up to 130 bar) and moderate temperature (up to 346 K) with 13C magic-angle spinning (MAS) NMR spectroscopy while the methane gas was mixed with two model solid substrates: a fumed nonporous, 12 nm particle size silica and a mesoporous silica with 200 nm particle size and 4 nm average pore diameter. Examination of the interactions between methane and the silica systems over temperatures and pressures that include the supercritical regime was allowed by a novel high pressure MAS sample containment system, which provided high resolution spectra collected under in situ conditions. There was no significant thermal effects were found for the observed 13C chemical shifts at all pressures studied here (28.2, 32.6, 56.4, 65.1, 112.7, and 130.3 bar) for pure methane. However, the 13C chemical shifts of resonances arising from confined methane changed slightly with changes in temperature in mixtures with mesoporousmore » silica. The chemical shift values of 13C nuclides in methane change measurably as a function of pressure both in the pure state and in mixtures with both silica matrices, with a more pronounced shift when meso-porous silica is present. Molecular-level simulations utilizing GCMC, MD, and DFT confirm qualitatively that the experimentally measured changes are attributed to interactions of methane with the hydroxylated silica surfaces as well as densification of methane within nanopores and on pore surfaces.« less
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  1. The Ohio State Univ., Columbus, OH (United States). School of Earth Sciences
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States).Environmental Molecular Sciences Lab.
  3. The Ohio State Univ., Columbus, OH (United States). School of Earth Sciences and Dept. of Chemistry
  4. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Physical and Computational Sciences Directorate
Publication Date:
Report Number(s):
Journal ID: ISSN 0743-7463; TRN: US1700967
Grant/Contract Number:
AC0576RL01830; SC0006878
Accepted Manuscript
Journal Name:
Additional Journal Information:
Journal Volume: 33; Journal Issue: 6; Journal ID: ISSN 0743-7463
American Chemical Society
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
OSTI Identifier: