The development of a high-pressure magic-angle spinning (MAS) rotor design (the “WHiMS” rotor) has allowed NMR data to be obtained at pressures up to 400 bar at 20 °C or 200 bar at 250 °C. These cavern rotors use a polymer bushing that snaps into position and are then locked by a retaining screw. Sealing is performed by O-rings which also form, with modification of the O-ring grooves, an integral one-way check valve. Rotor pressurization only requires them to be placed in a closed pressure vessel at pressure –mechanical manipulation of the rotor valve is not required. This rotor design has enabled experiments on a wide variety of mixed-phase (solids-liquids-gases) samples. Example data from both abiotic and biotic systems will be highlighted. These include geochemical systems, where adsorption and confinement studies of supercritical methane and carbon dioxide in clays and minerals display pressure and confinement dependent 13C chemical shifts. 2-D NMR exchange experiments of gas and supercritical fluids in confined pore spaces will also be presented. Controlled environments of biotic systems where metabolite conversion reactions using extremophilic bacteria found in subsurface systems at elevated pressures have also been studied. In addition, examples of real-time operando measurements of catalytic systems - with high resolution 1H and 13C NMR spectra will be showcased. Most recently, the temperature range of the WHiMS rotor has been extended to a new upper limit (320°C) by employing a custom designed built HT- MAS NMR probe.

In Situ Investigations of geochemical, extremophile and catalytic systems by high pressure: high temperature MAS-NMR

ACS Spring Meeting 2021

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