For the first time researchers have found a way to study highly-dispersed metal nanoparticles and their reactions using dynamic nuclear polarization (DNP) surface-enhanced nuclear magnetic resonance spectroscopy (SENS). Nuclear magnetic resonance (NMR) spectroscopy is a researcher’s equivalent to a physician’s MRI, only in this case the patient is not a person but a material. Now researchers have demonstrated new DNP-based measurements that extend solid-state NMR well beyond its current capabilities and into the realm of probing noble metal nanoparticles. The characterization of metal nanoparticles and the reactions occurring on their disordered surfaces is extremely challenging by conventional means. Here researchers applied the DNP-SENS NMR technique to monitor the chemistry on the surface of the nanoparticle; namely the interaction between the palladium catalyst and an amino acid, methoionine, which can lead to rapid deactivation of the catalyst. Over the course of the experiment, researchers were able to monitor the formation of minor intermediates and pinpoint the sites where breakdown occurred. Demonstrating the utility of DNP-SENS NMR for studying these materials, these developments should inspire further work using this technique in understanding the chemistry at the surface of noble metal catalysts.
Schematic of interaction of methionine with Pd dispersed on alumina and the cooresponding DNP NMR signal
Identifying low-coverage surface species on supported noble metal nanoparticle catalysts by DNP-NMR