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The molecular structures and dynamics of solids, liquids, gases, and mixtures are of critical interest to diverse scientific fields. High-temperature, high-pressure in situ MAS NMR enables detection of the chemical environment of constituents in mixed phase systems under tightly controlled chemical environments.
Nuclear magnetic resonance (NMR) spectroscopy represents an important technique to understand the structure and bonding environments of molecules. There exists a drive to characterize materials under conditions relevant to the chemical process of interest. To address this, in situ high-temperature, high-pressure MAS NMR methods have been developed to enable the observation of chemical interactions over a range of pressures (vacuum to several hundred bar) and temperatures (well below 0 °C to 250 °C). Further, the chemical identity of the samples can be comprised of solids, liquids, and gases or mixtures of the three. The method incorporates all-zirconia NMR rotors (sample holder for MAS NMR) which can be sealed using a threaded cap to compress an O-ring. This rotor exhibits great chemical resistance, temperature compatibility, low NMR background, and can withstand high pressures. These combined factors enable it to be utilized in a wide range of system combinations, which in turn permit its use in diverse fields as carbon sequestration, catalysis, material science, geochemistry, and biology. The flexibility of this technique makes it an attractive option for scientists from numerous disciplines.
Spectroscopic analysis of samples is an analytical tool used to gain valuable information about materials of interest such as their chemical state, structure, or reactivity. In a simplistic view, nuclear magnetic resonance (NMR) is one such technique that utilizes a strong magnetic field to manipulate the spin state of atomic nuclei to better understand the chemical environment of the species of interest. The nuclear spin state refers to the relative direction of the magnetic moment induced by the motion of the spinning nucleus, a positively charged particle. In the absence of a magnetic field, the nuclear spins are randomly oriented but in the presence of a magnetic ....
The protocol is divided into four sections which specify 1) the preparation of any solid materials being used in the system or activation or clearing of undesired adsorbed species, 2) addition of the solid and liquid materials to the NMR rotor, 3) addition of gases to the rotor, and 4) conducting the NMR experiments in the spectrometer. The procedure is representative of a typical sequence but may be modified to fit the specific needs of the experiment.
1. Pretreating solid samples
The output from the NMR spectrometer takes the form of a free induction decay (FID) which is the time-domain signal from the excited spins as they relax back to thermodynamic equilibrium. Such an FID resembles Figure 3. When Fourier transformed from the time domain to the frequency domain (frequency to PPM by Equation 3, whereby the difference absolute frequency and a reference is divided by the carrier frequency of the NMR spectrometer), it represents the NMR spectrum for which each peak in.......
The method of conducting MAS NMR spectroscopic measurements outlined herein represents the state of the art for conducting high-temperature, high-pressure MAS NMR. Such methods enable the observation of interactions occurring in vacuum atmospheres up to several hundred bar and from low temperatures (well below 0 °C to 250 °C) in a reliable, reproducible fashion. The ability to probe systems containing mixtures of solids, liquids, and gases under flexible chemical environments enables a wide range of experiments.......
The review of catalyst applications was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences, and Geosciences Catalysis Program under contract DE-AC05-RL01830 and FWP-47319. The review of biomedical applications was supported by the National Institute of Health, National Institute of Environmental Health Sciences under grant R21ES029778. Experiments were conducted at EMSL (grid.436923.9), a DOE Office of Science User Facility sponsored by the Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is a multi-program national l....
Name | Company | Catalog Number | Comments |
1) Preparation of Solids Samples | |||
Gas maniforld | |||
Gas Mass Flow Controllers | |||
Vacuum Pump | |||
Tube Furnace | |||
Temperature Controller | |||
Thermocouple | |||
Quartz Tube | |||
Isolation Valves | |||
Quartz Wool | |||
2) Loading solid samples into the rotor | |||
Dry glove box | |||
High-temperature, high-pressure NMR rotor | |||
Sample funnel | |||
Sample packing rod | |||
Rotor holder | |||
Analytical Balance | |||
Microsyringe | |||
Rotor cap bit | |||
3) Addition of gases to the rotor | |||
NMR loading chamber | |||
Rotor stage and appropriately sized inserts | |||
Vacuum Pump | |||
Gas maniforld | |||
Gas Mass Flow Controllers | |||
Vacuum Pump | |||
Heating Tape | |||
Temperature Controller | |||
Thermocouple | |||
Allen wrench | |||
Threaded rod | |||
Wrenchs | |||
Pressure Gauge | |||
High-pressure syringe pump | |||
Liquid syringe pump | |||
4) Conducting the NMR experiments | |||
MAS NMR probe | |||
NMR spectrometer | |||
Computer to control the spectrometer |
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