Speaker: Dr. Robert Lee Johnson Chemistry Department, King Fahd University of Petroleum and Minerals Abstract: High-resolution magic angle spinning (HR-MAS) NMR spectroscopy was used to study the effect of mixed solvent systems on the acidity at the solid-liquid interface of solid acid catalysts. A method was developed that can exploit benefits of both solution and solid-state NMR (SSNMR) by wetting porous solids with small volumes of liquids (< 2 µL/mg) to create an interfacial liquid that exhibits unique motional dynamics intermediate to an isotropic liquid and a rigid solid. Results from these experiments provide 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 in an acidic environment and that of bulk water. Using mixed solvent systems, the chemical shift of water was used to compare the relative acidity as a function of the hydration level of the d6-DMSO solvent. Non-linear increasing acidity was observed as the d6-DMSO became more anhydrous. 1H HR-MAS NMR experiments on a variety of supported sulfonic acid functionalized materials, suggest that the acid strength and number of acid sites correlates to the degree of broadening of the peaks in the 1H NMR spectra. When the amount of liquid added to the solid is increased (corresponding to a thicker liquid layer), fully resolved water phases were observed. This suggests that the acidic proton was localized predominantly within a 2 nm distance from the solid. EXSY 1H-1H 2D experiments of the thin layers were used to determine the rate of proton exchange for different catalytic materials. These results demonstrated the utility of using (SSNMR) on solid-liquid mixtures to selectively probe catalyst surfaces under realistic reaction conditions for condensed phase systems. Biography: Dr. Robert Lee Johnson started as an assistant professor at KFUPM in September 2017. His research interests focus primarily on heterogeneous catalysis for condensed phase applications, catalyst synthesis, reaction testing to compare kinetics and stability in high pressure flow reactors, and solid state NMR. Dr. Johnson has a keen interest to synthesize carbon-metal nano-composite materials to improve catalyst stability through reducing the rate of coke formation, and improve catalyst reactivity by exploiting metal-support interactions. In addition to standard NMR techniques, Dr. Johnson's use of solid state NMR is focused on developing techniques to probe metal support interactions and molecular behavior at the solid-liquid interface using high-resolution magic angle spinning (HRMAS). | 