The specific design of improved surface catalysts relies on knowledge of the surface structure and how this relates to function. A variety of techniques are available for the characterisation of surfaces. As always, each technique will exhibit specific benefits but will also suffer from specific limitations. So far, solid-state nuclear magnetic resonance (SSNMR) spectroscopy has been largely overlooked by the surface characterisation community. This is possibly due to the major specific limitation of NMR: the sensitivity of the technique. This deterrent is accentuated when considering surfaces, which usually constitute only a small fraction of the studied sample. However, one of the first world-wide installations of a high-field DNP-MAS NMR system, here at Inac, has facilitated the acquisition of high-resolution NMR spectra with greatly enhanced signal-to-noise ratios. DNP involves the transfer of the substantial spin-polarization of unpaired electrons to many nuclei. By this approach the net polarization of the nuclei is enlarged significantly. Since the extent of polarization relates directly to the intensity of the observable NMR signal the use of DNP heralds the imagination and implementation of previously unrealistic surface experiments.

Owing to a true sensitivity enhancement resulting from DNP experiments on mesoporous alumina, corresponding to a time-saving factor of ~32000 (compared to conventional NMR), it was possible to record NMR spectra that aided in obtaining structural information about the surface of the system. In particular, two-dimensional correlation spectra were recorded (4h with DNP, > 15 years without!) that detailed the inter-connectivity between different surface-aluminium coordination states.