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

Abstract

Characterization and modeling of the molecular-level behavior of simple hydrocarbon gases, such as methane, in the presence of both nonporous and nano-porous mineral matrices allows for predictive understanding of important processes in engineered and natural systems. In this study, 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) were observed with 13C magic-angle spinning (MAS) NMR spectroscopy while the methane gas was mixed with two model solid substrates: a fumed non-porous, 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. For pure methane, no significant thermal effects were found for the observed 13C chemical shifts at all pressures studied here (28.2 bar, 32.6 bar, 56.4 bar, 65.1 bar, 112.7 bar, and 130.3 bar). However, the 13C chemical shifts of resonances arising from confined methane changed slightly with changes in temperature inmore » mixtures with mesoporous 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

Authors:
; ; ; ; ; ; ORCiD logo; ORCiD logo
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1344636
Report Number(s):
PNNL-SA-123185
Journal ID: ISSN 0743-7463; 48394; KP1704020
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Langmuir; Journal Volume: 33; Journal Issue: 6
Country of Publication:
United States
Language:
English
Subject:
Natural gas; shale gas; confinement; porous silica; methane; NMR; high pressure; Environmental Molecular Sciences Laboratory

Citation Formats

Ok, Salim, Hoyt, David W., Andersen, Amity, Sheets, Julie, Welch, Susan A., Cole, David R., Mueller, Karl T., and Washton, Nancy M.. Surface Interactions and Confinement of Methane: A High Pressure Magic Angle Spinning NMR and Computational Chemistry Study. United States: N. p., 2017. Web. doi:10.1021/acs.langmuir.6b03590.
Ok, Salim, Hoyt, David W., Andersen, Amity, Sheets, Julie, Welch, Susan A., Cole, David R., Mueller, Karl T., & Washton, Nancy M.. Surface Interactions and Confinement of Methane: A High Pressure Magic Angle Spinning NMR and Computational Chemistry Study. United States. doi:10.1021/acs.langmuir.6b03590.
Ok, Salim, Hoyt, David W., Andersen, Amity, Sheets, Julie, Welch, Susan A., Cole, David R., Mueller, Karl T., and Washton, Nancy M.. Wed . "Surface Interactions and Confinement of Methane: A High Pressure Magic Angle Spinning NMR and Computational Chemistry Study". United States. doi:10.1021/acs.langmuir.6b03590.
@article{osti_1344636,
title = {Surface Interactions and Confinement of Methane: A High Pressure Magic Angle Spinning NMR and Computational Chemistry Study},
author = {Ok, Salim and Hoyt, David W. and Andersen, Amity and Sheets, Julie and Welch, Susan A. and Cole, David R. and Mueller, Karl T. and Washton, Nancy M.},
abstractNote = {Characterization and modeling of the molecular-level behavior of simple hydrocarbon gases, such as methane, in the presence of both nonporous and nano-porous mineral matrices allows for predictive understanding of important processes in engineered and natural systems. In this study, 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) were observed with 13C magic-angle spinning (MAS) NMR spectroscopy while the methane gas was mixed with two model solid substrates: a fumed non-porous, 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. For pure methane, no significant thermal effects were found for the observed 13C chemical shifts at all pressures studied here (28.2 bar, 32.6 bar, 56.4 bar, 65.1 bar, 112.7 bar, and 130.3 bar). However, the 13C chemical shifts of resonances arising from confined methane changed slightly with changes in temperature in mixtures with mesoporous 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.},
doi = {10.1021/acs.langmuir.6b03590},
journal = {Langmuir},
number = 6,
volume = 33,
place = {United States},
year = {Wed Jan 18 00:00:00 EST 2017},
month = {Wed Jan 18 00:00:00 EST 2017}
}
  • 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 200more » 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 mesoporous 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
  • No abstract prepared.
  • No abstract prepared.
  • Solid-state nuclear magnetic resonance (NMR) of the {sup 87}Rb has been employed to investigate the phase transitions in polycrystalline LiRbSO{sub 4}. The spin-lattice relaxation time T{sub 1} and the NMR line shape were measured using magic angle spinning (MAS) and multiple quantum magic angle spinning (MQMAS) methods between 373 and 488 K. The quadrupole coupling constant, Q{sub cc}, the asymmetry parameter, {eta}{sub Q}, and the isotropic chemical shift, {delta}{sub CS}, were determined from the analysis of MAS and MQMAS spectra. The anomalies of Q{sub cc} near the IV-III phase transition were associated with the deformation of the local environment ofmore » the Rb ions in the crystal lattice. The measurements of the spin-lattice relaxation rate as a function of temperature and Larmor frequency showed the existence of a damped soft mode near the V-IV and IV-III phase transitions.« less
  • /sup 27/Al NMR can, in principle, be very useful for following the tetrahedral/octahedral ratio in alumina supports as a function of thermal treatment as has been demonstrated previously. Even with magic-angle spinning of highly crystalline ..cap alpha..-alumina (corundum), the NMR linewidth of /sup 27/Al is quite broad. This would lead one to surmise that it would not be feasible to observe the formation of surface compounds of the alumina support or active catalytic phases since the NMR signal of the surface phase would be masked by the bulk if the two phases were of comparable linewidth and chemical shift. Whatmore » the authors demonstrate in this communication is that the surface and bulk phases of alumina need not have the same linewidth and, depending on the surface compounds formed, may have substantial chemical shifts relative to bulk Al/sup 3 +/. In the case of a NiMoP/Al/sub 2/O/sub 3/ hydrodesulfurization catalyst, at least, Al/sup 3 +/-containing surface phases are formed during calcination which can easily be distinguished from the bulk ..gamma..-Al/sub 2/O/sub 3/ support. 27 references.« less