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Solid-state nuclear magnetic resonance (NMR) spectroscopy has increasingly been used for materials characterization as it enables selective detection of elements of interest, as well as their local structure and dynamic properties. Nevertheless, utilization of NMR is limited by its inherent low sensitivity. The development of dynamic nuclear polarization (DNP) approaches, which provide enormous sensitivity gain in NMR through the transfer of polarization from electron spins, has transformed the application of solid-state NMR in materials science. In this review, we outline the opportunities for materials characterization that DNP has opened up. We describe the main DNP mechanisms available, their implementation, and the kinds of insight they can provide across different materials classes, from surfaces and interfaces to defects in the bulk of solids. Finally, we discuss the current limitations of the approach and provide an outlook on future developments for DNP-enhanced NMR spectroscopy in materials science.

α-Ga2O3, β-Ga2O3, and γ-Ga2O3 as well as the silica-supported catalysts γ-Ga2O3/SiO2, β-Ga2O3/SiO2, and Ga(NO3)3-derived Ga/SiO2 were prepared, characterized, and evaluated for propane dehydrogenat...

A silica-supported monomeric alkylaluminum co-catalyst was prepared via surface organometallic chemistry by contacting tris(neopentyl)aluminum and partially dehydroxylated silica. This system, fully characterized by solid-state 27 Al NMR spectroscopy augmented by computational studies, efficiently activates (n Bu3 P)2 NiCl2 towards dimerization of ethene, demonstrating comparable activity to previously reported dimeric diethylaluminum chloride supported on silica. Three types of aluminum surface species have been identified: monografted tetracoordinated Al species as well as two types of bisgrafted Al species-tetra- and pentacoordinated. Of them, only the monografted Al species is proposed to be able to activate the (n Bu3 P)2 NiCl2 complex and generate the active cationic species.

Single-site Ni(II) catalytic centers supported on MCM-41-type materials were prepared via surface organometallic chemistry using tailored thermolytic molecular precursors. These materials catalytic...

Low-temperature 15N dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) of adsorbed pyridine in combination with FTIR measurements and DFT calculations was applied to investigate the surface sites of γ-alumina, which can be divided into four groups: (1) groups 1 and 2, associated with less shielded 15N chemical shifts and the lowest ν(8a) frequencies of adsorbed pyridine, corresponding to weakly adsorbed H-bonding pyridine to hydroxyl group or chemisorbed water on alumina; (2) group 3, with intermediate 15N chemical shifts and ν(8a) frequencies, corresponding to pyridine coordinated to specific Lewis acid sites, namely five-coordinated (AlV) aluminum atoms of the (100) facet, as well as some H-bonded pyridine; (3) group 4, associated with the most shielded 15N chemical shift and the highest ν(8a) frequency, selectively assigned to Lewis acid Al sites located on the (110) facet and corresponding to both four- and five-coordinated aluminum atoms (AlIV and AlV). Noteworthy, a correlatio...

Angewandte Chemie. International Edition, 57 (22), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833

WOS:000447953600032; Dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (NMR) has developed into an invaluable tool for the investigation of a wide range of materials. However, the sensitivity gain achieved with many polarizing agents suffers from an unfavorable field and magic angle spinning (MAS) frequency dependence. We present a series of new hybrid biradicals, soluble in organic solvents, that consist of an isotropic narrow electron paramagnetic resonance line radical, alpha,gamma-isdiphenylene-beta-phenylallyl (BDPA), tethered to a broad line nitroxide. By tuning the distance between the two electrons and the substituents at the nitroxide moiety, correlations between the electron-electron interactions and the electron spin relaxation times on one hand and the DNP enhancement factors on the other hand are established. The best radical in this series has a short methylene linker and bears bulky phenyl spirocyclohexyl ligands. In a 1.3 mm prototype DNP pr obe, it yields enhancements of up to 185 at 18.8 T (800 MHz H-1 resonance frequency) and 40 kHz MAS. We show that this radical gives enhancement factors of over 60 in 3.2 mm sapphire rotors at both 18.8 and 21.1 T (900 MHz H-1 resonance frequency), the highest magnetic field available today for DNP. The effect of the rotor size and of the microwave irradiation inside the MAS rotor is discussed. Finally, we demonstrate the potential of this new series of polarizing agents by recording high field Al-27 and Si-29 DNP surface enhanced NMR spectra of amorphous aluminosilicates and O-17 NMR on silica nanoparticles.