ADVANCES IN ATOMIC SCALE CHARACTERIZATION OF MATERIALS SURFACES BY DNP-ENHANCED SOLID-STATE NMR

Dynamic nuclear polarization with magic angle spinning (DNP MAS) continues to revolutionize solid-state NMR spectroscopy, yielding NMR responses that are 2-3 orders of magnitude stronger than in ‘conventional’ NMR experiments. We will present several recent examples from our laboratory of applications of this technology to the studies of surfaces and interfaces of materials. These will include a coherent description of the distribution of silica-supported organic functional groups using DNP-enhanced 2D 29Si-29Si and 13C-13C homonuclear correlation experiments performed without isotope enrichment. In other studies, indirect or direct DNP measurements of 17O lineshapes, 1H-17O distances, and 2D 1H-17O spectra were used to understand the acidity and dynamics of OH groups and observe the support-metal interactions in a series of heterogeneous catalysts. The structures of surface-bound catalytic metal centers and associated ligands were determined by DNP-enhanced spectra of 195Pt, 89Y, 1H, 13C, 15N, and 29Si. We will also show how DNP-enhanced 13C-27Al, 29Si-27Al and 3D 1H-17O-dipolar correlation experiments were used to elucidate the coordination geometries of the substrates at the alumina surface and atom ordering in amorphous silica-alumina materials. Lastly, we will discuss the prospects of further sensitivity improvements using fast-MAS DNP and ultra-low temperature DNP.

Acknowledgments: This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, as well as Materials Science and Engineering Division. The Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358.