Solid-State NMR Probe Molecules for Catalysts and Adsorbents: Concepts, Quantification, Accessibility, and Spatial Distribution
Michael Dyballa
Abstract
The application of probe molecules is the state-of-the-art method to quantitatively determine accessibility and spatial distribution of catalytically active sites on solid materials. Knowing the spatial distribution of active sites on solid catalysts is crucial for increasing their performance and shape-selectivity. In this review, general aspects of the use of probe molecules in combination with quantitative spectroscopy are discussed. Then, the currently available families of probe molecules applied in solid-state NMR are described in detail. Properties and chemical shifts are provided for exemplary molecules interacting with active sites. Literature examples show which probe molecules can efficiently be used quantitatively on which system. Then, approaches for evaluating the spatial distribution of active sites are presented. It is shown how an intelligent combination of probe molecules and postmodification techniques provides a quantitative picture of sites in most spatial regimes. This shall lead the way for further methodological developments regarding solid-state NMR probe molecules and catalytic investigations.