Characterizing Substrate-Surface Interactions on Alumina-Supported Metal Catalysts by Dynamic Nuclear Polarization-Enhanced Double-Resonance NMR Spectroscopy

摘要

The characterization of nanometer-scale interactions between carbon-containing substrates and alumina surfaces is of paramount importance to industrial and academic catalysis applications, but it is also very challenging. Here, we demonstrate that dynamic nuclear polarization surface-enhanced NMR spectroscopy (DNP SENS) allows the unambiguous description of the coordination geometries and conformations of the substrates at the alumina surface through high-resolution measurements of ~(13)C-~(27)Al distances. We apply this new technique to elucidate the molecular-level geometry of ~(13)C-enriched methionine and natural abundance poly(vinyl alcohol) adsorbed on y-Al_2O_3-supported Pd catalysts, and we support these results with element-specific X-ray absorption near-edge measurements. This work clearly demonstrates a surprising bimodal coordination of methionine at the Pd—Al_2O_3 interface.