Solid acid catalysts are important for condensed phase biomass conversion technologies. Understanding reactions in the condensed phase requires knowledge of the factors that influence the stability under hydrothermal conditions and probe dynamics at the solvent-solid interface. In these systems, solid-state NMR (SSNMR) can be used to determine molecular structure, measure dynamics and evaluate spatial proximity of different species. We utilized SSNMR to elucidate two key issues related to condensed phase heterogeneous catalysis. First, a detailed structural characterization was performed on a suite of sulfonated carbon materials to determine how the average molecular structure influenced the hydrothermal stability using spectral edited 13C-13C 2D experiments, quantitative 1D and spectral modeling. Second, a high-resolution magic angle spinning (HR-MAS) NMR method was developed that exploited benefits of both solution and SSNMR by wetting porous solids with small volumes of liquids (&lt; 2 ul/mg) to create an interfacial liquid that exhibited unique motional dynamics intermediate to an isotropic liquid and ridged solid. Results from these experiments provided information about the influence of the solvent mixtures on the acidic properties at a solid-liquid interface. Importantly, use of MAS led to spectra with full resolution between water undergoing rapid exchange with acidic protons and that of bulk water. This technique was able to provide a direct measurement of the relative acidity as a function of the hydration level, the distance the acidic proton was delocalized from the catalyst surface, products deposited onto catalyst surface, and, in conjunction with EXSY 1H-1H 2D experiments, the proton exchange rate between different surface sites and molecules in the liquid. In concert, these techniques can provide both a detailed molecular characterization of the catalyst materials and the reaction interface for a variety of mixed solvent systems.

Use of solid-state NMR for condensed phase catalyst applications: Hydrothermal stability and solid liquid interfaces

254th National Meeting (2017)

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