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Solvent-Solid Interface of Acid Catalysts Studied by High Resolution MAS NMR

TitleSolvent-Solid Interface of Acid Catalysts Studied by High Resolution MAS NMR
Publication TypeJournal Article
Year of Publication2017
AuthorsJohnson, RL, Hanrahan, MP, Mellmer, M, Dumesic, JA, Rossini, AJ, Shanks, BH
JournalJournal of Physical Chemistry C
Date Published08
Type of ArticleArticle
ISBN Number1932-7447
Accession NumberWOS:000408179500023
Keywordsangle-spinning nmr, c-13 chemical-shift, chemistry, cross-linked polystyrene, hydrolysis, in-situ nmr, Materials Science, organic-reactions, Spectroscopy, strength, Technology - Other Topics, zeolite

2 mu L/mg) to create an interfacial liquid that exhibits unique motional dynarirics 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 DMSO-d(6) solvent. Nonlinear increasing acidity was observed as the DMSO-d6 became more anhydrous. H-1 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 H-1 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 H-1-H-1 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.

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