In the preceding decades, numerous challenges in heterogeneous catalysis have been overcome through the development and improvement of new spectroscopy techniques e.g. Microscopy, DRIFT, EXAFS, XANES and solid state NMR (SS) spectroscopy. The combination of these advanced spectroscopic tools contributed to the discovery of new field in heterogeneous catalysis including Surface Organometallic Chemistry (SOMC)[1] and more recently Single Atom Catalysis (SAC).[2] It is now well-established that the SS NMR spectroscopy enables the characterization of surface at the atomic-level whenever possible, but the low detection limit of SS NMR spectroscopy is a major issue to allow many modern heterogeneous catalysts to be examined. 

Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy (DNP SENS) is an emerging solid state technique that allows access to high-sensitivity NMR spectra from surfaces.[3]  DNP SENS requires bringing an exogenous radical solution (bulky nitroxide TEKPOL, 16 mM in o-DCB) into contact with the surface by incipient wetness impregnation (IWI). But so far, this technique has limited applications for sensitive catalytic active site to those that do not react with the radicals. At KAUST CATALYSIS CENTER (KCC), we have addressed this challenge by immobilizing sensitive organometallic complexes inside porous materials with suitable small windows which exclude a direct contact of the radical with the complexes. But, what about the case of sensitive active catalytic site supported on non-porous silica? Surprisingly, in non-porous silica some DNP characterizations are possible depending on the metal-loading and the type of substituents of the complex. This unexpected observation suggests that aggregation of the silica occurs in non-polar solvent (as o-DCB) leading to (partial) protection of the complex inside the interparticular space. Hence, a reaction with the bulky radical may be prevented. In this talk, we will present a new theory showing that we predict the possible application of DNP SENS to sensitive organometallic complexes on non-porous support by measuring the hydrophilic/hydrophobic property [by elemental analysis and Nitrogen sorption (CBET) measurements] of the heterogeneous catalyst. [5]