The physical and chemical interaction of fluids with solids can be probed with various magnetic resonance techniques, particularly Magic Angle Spinning (MAS) NMR. When the fluid of interest is supercritical another level of challenge is added as the sample holder (the MAS rotor) must retain the sample at high pressure. The WHiMS rotor, developed at PNNL, allows for MAS-NMR spectra to be collected at pressures up to 400 bar and temperatures exceeding 250 C. Hyperpolarized xenon gas has been used as a probe of porous materials; it displays changes in chemical shift upon confinement and exchange techniques such as 2D-EXSY can probe the exchange rate between different environments. Here we show that when xenon is pressurized, hyperpolarization is not necessary to collect high resolution 129Xe spectra in short times. We pressurized samples of a variety of natural (shale) and artificial (porous silicates) materials with 90 bar natural abundance xenon, and collected both 1D and 2D-EXSY spectra. In addition, we have found that when at high pressure, the 13C chemical shift dispersion of methane as well as that for 17O in carbon dioxide are also sufficient to probe these materials. This has the added benefit of using the geochemically relevant supercritical fluids for the study of porous materials. The changes in the interactions of these fluids as a function of humidity will be presented as well as some preliminary results on future directions for this technique.

Supercritical fluid interactions with porous materials: Magnetic resonance techniques

2019 Spring National Meeting

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