Carlos Bornes had the opportunity to work during his master's thesis with solid-state NMR spectroscopy in the structural characterization and study of the acid properties of zeolites.
This was a great challenge for Carlos, because he was for the first time really coming into contact with the NMR technique applied in an area that he was completely unaware of. The challenge started by discovering what a zeolite was and that a solid could be acidic.
Throughout his testimony, Carlos mentioned that although these materials are widely used, there is still a big gap in terms of describing the acidic properties of these materials.
Currently, Carlos is trying to develop a methodology that allows a complete characterization of the zeolite acid sites, such as distinguishing between Brønsted and Lewis acidity, quantifying and determining the strength of each acid site. For this, he uses several methodologies of solid-state NMR and computational chemistry, which combined with the adsorption of basic molecules allow him to study the nature of the acid-base interactions between the different acid centres and the probe molecule. This, of course, with a lot of associated electronic and computational work.
Carlos and his research group recently published an article where you can learn a little more about this technique, whose title is:
“1H–31P HETCOR NMR elucidates the nature of acid sites in zeolite HZSM-5 probed with trimethylphosphine oxide”
Zeolites have a wide range of applications as solid acid catalysts in various industrial processes, as safer alternatives to harmful and corrosive liquid catalysts.
The growing number of known structures offers new chemical properties, which can result in unique shape selection reactions.
As the catalytic activity of zeolites depends on the nature of the acidic sites (Brønsted or Lewis) and on their accessibility, number and strength, a comprehensive characterization of these characteristics is crucial for the development of more active and selective catalysts. Although several methods have been proposed to investigate the acidity of zeolites, they have several limitations. Therefore, achieving a complete understanding of zeolite and acidity remains a major challenge.
In this work, it was shown, for the first time, that two-dimensional 1H-31P heteronuclear correlation NMR (HETCOR) discriminates the 31P resonances given by the adsorbed trimethylphosphine oxide (TMPO) molecules that interact with the Brønsted and Lewis acid sites in HZSM-5 pores, an acidic zeolite with medium-pores size converted from the original NH4ZSM-5 through a two-stage calcination. In addition, quantum mechanics calculations explained the peculiarities observed in the shape of the cross-peak.
To know more about the article, click here:
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