¹²⁹ Xe NMR Spectroscopy of Supported Ionic Liquids

In 129Xe NMR spectroscopy, gaseous xenon is used as a sensitive probe for the structural and textural investigation of porous materials. The chemical shift is responsive to the pore sizes and surface chemistry in a wide range of industrially relevant materials. However, many applications of porous materials necessitate the interaction of a liquid with the pore surface. Little is known about the behavior of xenon in such systems. Supported ionic liquid phase (SILP) catalysts are a promising class of new catalysts, achieved by impregnating a suitable porous solid support with a combination of an ionic liquid (IL) and a catalytically active metal complex. In general, a thin, homogeneous film covering the surface is advantageous for many applications. Using 129Xe as a probe nucleus detected by 129Xe NMR spectroscopy, combined with quantitative xenon physisorption isotherms, different environments can be discerned in the SILP, namely, xenon adsorbed on the bare silica surface and xenon adsorbed on an immobilized IL phase. Moreover, we found that the behavior of xenon and its mobility depend intricately on the nature of the IL and its interactions with the support.