Researchers have discovered a core deactivation mechanism of noble metal catalysts that are used in biorefining and catalytic automobile converters. Much like how physicians use X-ray and magnetic resonance (MRI) images to diagnose patients, X-ray absorption spectroscopy (XAS) and nuclear magnetic resonance spectroscopy (NMR) can be combined to diagnose the ‘ailments’ of the catalysts. Using dynamic nuclear polarization (DNP) to enhance the NMR signals, the authors were able to measure the distances between carbon atoms in methionine, a compound known to be responsible for catalyst deactivation, and the surface of the alumina support. Surprisingly, it was discovered that methionine binds simultaneously to both the catalyst and the support, at the interface between the two. This bimodal coordination enhances the blocking of catalytically-important interfacial sites and exacerbates the deactivation of the catalyst. The deactivation of catalysts is a major industrial problem that leads to reduction of product output as well as the death of the catalysts. This information regarding the atomic-level mechanisms responsible for deactivation can be used to design newer catalysts or pre-treatments that would prevent this type of blocking and extend the catalysts’ lifetime.
Bimodal coordination of methionine observed on alumina in the presence of a Pd catalyst using dynamic nuclear polarization surface-enhanced NMR spectroscopy.
Characterizing Substrate–Surface Interactions on Alumina-Supported Metal Catalysts by Dynamic Nuclear Polarization-Enhanced Double-Resonance NMR Spectroscopy