Owing to the developments made during the last decade, dynamic nuclear polarization (DNP) can offer unparalleled enhancements of solid-state (SS)NMR signals, and even greater savings in experimental time of 4-5 orders of magnitude. We will highlight some of the new opportunities that DNP SSNMR brings to the studies of amorphous catalytic materials that extend far beyond the limits of conventional SSNMR. Firstly, we used DNP-enhanced 2D 29Si-29Si SSNMR experiments to elucidate the distributions of propyl (PR) and mercaptopropyl (MP) groups attached to the surfaces of MCM-41-type mesoporous silica materials by post-synthesis grafting and by co-condensation. The key findings, some of which surprised us, can be summarized as follows: (1) grafting yielded more homogeneous distributions of PR and MP functionalities on the external and internal MSN surfaces, regardless of the loading or the method used to remove the surfactant, (2) co-condensation produced partly clustered organic moieties, and (3) the most efficient, homogeneous grafting was achieved before the surfactant was removed from the pores. We used a similar technique to elucidate the differences in spatial distribution of Si species between SiOx/Al2O3 catalysts prepared using atomic layer deposition (ALD) and chemical liquid deposition (CLD). Secondly, we demonstrated the use of DNP-enhanced double-resonance 13C{27Al} experiments to obtain the unambiguous description of the coordination geometries and conformations of the substrates at the alumina surface through high-resolution measurements of 13C-27Al distances. We applied this new technique to determine the molecular-level geometry of 13C-enriched methionine and natural abundance poly(vinyl alcohol) adsorbed on γ-Al2O3-supported Pd catalysts. We described, with atomic scale detail, the formation of a bimodal coordination of methionine at the Pd-Al2O3 interface. These studies demonstrate that DNP-enhanced SSNMR opens new horizons for the design, evaluation and development of silica- and alumina-supported catalysts, so frequently used in industrial catalysis.

Studies of silica- and alumina-supported catalysts by dynamic nuclear polarization solid-state NMR

253rd National Meeting (2017)

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