High temperature/pressure MAS-NMR for the study of dynamic processes in mixed phase systems

Publication date: Available online 25 October 2018

Source: Magnetic Resonance Imaging

Author(s): Ali Chamas, Long Qi, Hardeep S. Mehta, Jesse A. Sears, Susannah L. Scott, Eric D. Walter, David W. Hoyt

Abstract

A new MAS-NMR rotor (the WHiMS rotor) has been developed which can reach pressures of 400 bar at 20 °C or 225 bar at 250 °C. These rotors are ideal for mixed phase systems such as a reaction using a solid catalyst with a liquid/supercritical solvent topped with high pressure gas in the head space. After solid and liquid portions of the sample are loaded, the rotor is capped with an o-ring equipped polymer bushing that snaps into a mating groove in the rotor. The bushings incorporate a check valve into the sealing mechanism which allows for pressurization without mechanical manipulation – they will allow gas to flow in but not out. This WHiMS rotor design has enabled experiments on a wide variety of biotic and abiotic mixed-phase systems. Geochemical systems have also been studied, for example, adsorption and confinement studies of supercritical methane/CO₂ in clays and other minerals which display pressure dependent ¹³C chemical shifts. Example data from other mixed-phase chemical and microbial systems are reported. These include monitoring metabolite conversion of extremophilic bacteria found in subsurface systems at elevated pressures and real-time operando reactions in catalysis systems - with liquid-quality resolution for ¹H and ¹³C NMR spectra.

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