Direct Observation of Three-Dimensional Molecular Structures on Surfaces
Abstract: A fundamental challenge in surface chemistry and catalysis relates to the determination of three-dimensional structures with atomic-level precision. In fact, it is not even known whether molecular fragments at surfaces form well defined structures or if they adopt disordered conformations. For example, specific metal-surface interactions have been proposed to be essential in stabilizing active site structures in many heterogeneous catalysts, but so far it has not been possible to obtain three-dimensional structures to confirm such interactions.
We demonstrate how surface enhanced NMR spectroscopy (SENS) can be achieved by using dynamic nuclear polarization (DNP). In this approach, electron polarization is transferred from an organic radical to the rare nuclei (at natural isotopic abundance) at the surface, yielding up to a 200-fold signal enhancement for surface species in many materials.1
Combining DNP SENS with structure prediction methods and DFT chemical shift calaculations we show the full atomic-level characterization of materials including supported active single site complexes, Sn-b zeolites, and nanoparticle surfaces.
1. A. Rossini, A. Zagdoun, M. Lelli, A. Lesage, C. Copéret and L. Emsley “Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy,” Acc. Chem. Res. 46, 1942 (2013).
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