Campus Units

Chemistry, Ames Laboratory, Chemical and Biological Engineering

Document Type

Article

Publication Version

Submitted Manuscript

Publication Date

7-19-2017

Journal or Book Title

The Journal of Physical Chemistry

Volume

121

Issue

32

First Page

17226

Last Page

17234

DOI

10.1021/acs.jpcc.7b04102

Abstract

High-resolution magic angle spinning (HRMAS) 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 DMSO-d6 solvent. Nonlinear increasing acidity was observed as the DMSO-d6 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.

Comments

This is manuscript of an article published as Johnson R.L., Hanrahan M.P., Mellmer M., Dumesic J.A., Rossini A.J., Shanks B.H.* The Solvent- Solid Interface of Acid Catalysts Studied by High Resolution MAS NMR, Journal of Physical Chemistry C, 2017, Submitted for Publication.doi: 10.1021/acs.jpcc.7b04102. Posted with permission.

Copyright Owner

American Chemical Society

Language

en

File Format

application/pdf

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