Journal of Physical Chemistry C
Journal of Physical Chemistry C
5 years ago

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

Solvent–Solid Interface of Acid Catalysts Studied by High Resolution MAS NMR
Aaron J. Rossini, Max Mellmer, Michael P. Hanrahan, James A. Dumesic, Brent H. Shanks, Robert L. Johnson
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 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.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b04102

DOI: 10.1021/acs.jpcc.7b04102

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.