Periodic Reporting for period 1 - DNPMAT (Studies of Materials and Catalysts by Dynamic Nuclear Polarization Enhanced Solid-state NMR)
Reporting period: 2017-05-01 to 2019-04-30
New products and devices for catalysis, energy storage or drug delivery cannot be developed without knowledge of the relationships between the structure and properties of their component materials. Molecular-level characterization is key to the rational design of new materials for technological applications with improved properties. DNP-enhanced solid-state NMR is a transformative technology offering a step-change in capability which completely overcomes the sensitivity limitations of NMR. Conventional methods for the high-resolution analysis of the surfaces of materials involve high-energy electrons or X-rays interacting with well-defined and relatively clean surfaces in a low-pressure environment. Therefore, the surface conditions during measurement differ from those prevailing in real-life applications of materials in for example catalysis or drug delivery. DNP-enhanced NMR does not suffer from these limitations, and the approach allows the power of solid-state NMR to be brought to bear for the first time on real-life technologically useful materials. The objectives of the project were the improved sample preparation protocols, new experimental approaches and proof of principle studies necessary to make DNP-enhanced solid-state NMR the method of choice for the molecular-level characterization of the surfaces of materials, including for example the catalytic converters used on vehicle exhausts.
Sample preparation is a critical aspect of DNP-enhanced solid-state NMR, but the effect on signal enhancement is not understood. For materials DNP enhancements are routinely substantially lower than the theoretical maximum limiting the utility of the technique. During the project Dr Chaudhari developed a new method of preparing samples for DNP measurements by replacing the standard glycerol/water impregnation matrix with an aqueous solution of an inorganic salt. The new matrix gave substantial improvements in DNP sensitivity via a combination of larger enhancements and reduced build-up times for a wide range of samples, including functionalized mesoporous silica materials and microcrystalline pharmaceutical compounds. A publication is in preparation about this research which will be submitted to a high-impact journal.
In addition, several proof of principle studies were carried out the demonstrate the utility of DNP, including investigations of the catalytic sites on the surface of γ-alumina which is widely used as an industrial catalyst support. Pre-treatment of the alumina surface with alkaline earth and rare earth oxides alters the availability of these sites, allowing control over the catalytic activity. The DNP-enhanced solid-state NMR results suggest that the reactive surface AlO5 environment provides a preferential nucleation site for barium, that pre-treatment does not significantly alter the local environment at the surface and possibly that the most distorted AlO5 sites are preferentially occupied. This study has been released on the Facility’s website as part of measures to disseminate the utility of DNP-enhanced solid-state NMR to a wide scientific audience.