DNP SSNMR STUDIES

Structural and Dynamics Characterization of a New Generation of Single Site Heterogeneous Metathesis Catalysts by Solid-State NMR Spectroscopy

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 Obiettivo del progetto (Objective)

'The projects outlined herein are primarily aimed at characterizing a new generation of heterogeneous catalysts with novel dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (SSNMR) experiments. DNP is an emerging technology which is designed to enhance the signal of NMR experiments. To date, most previous DNP NMR experiments have been restricted to biological systems. Before such DNP SSNMR studies can be applied to characterize single site heterogeneous catalysts it is necessary to develop methods for obtaining efficient DNP enhancement of nuclei which reside on the surface of the support material. We have suggested and previously demonstrated that a novel incipient wetting impregnation approach can be utilized to bring the radicals into close contact with the silica surface. This approach will be refined in order to obtain optimal DNP signal enhancements for the surface sites of the support materials and for molecules which are immobilized on the surface of support materials. With these methods for optimal DNP SSNMR experiments in hand, focus will be given to DNP SSNMR studies of the support materials and a new generation of flexible heterogeneous olefin metathesis catalysts. We will demonstrate that surface enhanced DNP SSNMR experiments are a straightforward and general method for probing the surface sites of a variety of support materials, such as mesoporous silicas and particulate alumina. Novel experiments designed to probe the structure and dynamics of the flexible heterogeneous catalysts will then be undertaken. This is anticipated to result in new state of the art approaches for characterizing inorganic materials and will directly aid in the development of a new generation of olefin metathesis catalysts.'

Introduzione (Teaser)

EU-funded scientists have demonstrated huge signal amplification in a powerful tool for analysis of surface structure in solids. Extension to numerous materials of industrial importance should have major impact on accelerated development.

Descrizione progetto (Article)

Solid-state nuclear magnetic resonance (SSNMR) spectroscopy is a powerful tool for studying the structure and dynamics of solid materials. However, its low sensitivity makes signal amplification a requirement for many applications. Dynamic nuclear polarisation (DNP) is an amplification technique that has been successfully applied to biological samples in fluids and, more recently, in model silica materials.

DNP surface-enhanced NMR spectroscopy (DNP SENS) has been used to characterise the surface of solids. Materials are impregnated with solutions containing radicals to bring the radicals close to the surface and enable DNP enhancement of the NMR signals. Pioneering work by EU-funded scientists and the DNP SSNMR STUDIES project advanced the current state-of-the-art. This was motivated by the need to improve the analyses of interactions between active sites and analytes. Such technology would help in the development of a new generation of catalysts, separation materials and energy conversion devices.

Scientists first addressed the issue of sample formulation. Many of the stable radicals for DNP SENS were developed to be water-soluble given the predominant application to biological samples. The team demonstrated the potential of numerous organic solvent-radical combinations to avoid issues of material hydrophobicity or reactivity in water. Researchers also developed novel chemical agents to minimise damping of the NMR signal by radicals that can negate the enhancement of DNP.

Investigators combined a newly designed chemical agent with the previously identified organic solvents for a DNP enhancement up to 100. It enabled rapid acquisition of NMR spectra and comprehensive characterisation of molecular surface species. The team demonstrated its application to the study of several other industrially important classes of materials including metal organic frameworks and pharmaceuticals.

The pioneering techniques and formulations developed by project members will foster research in the new commercial DNP instruments currently being installed throughout Europe. Accelerated development of novel materials for environmentally friendly catalysis, energy conversion and purification processes will have important benefits for industry and consumers alike.