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DFT modeling of the adsorption of trimethylphosphine oxide at the internal and external surfaces of zeolite MFI

Hernandez-Tamargo, Carlos E., Roldan Martinez, Alberto and De Leeuw, Nora H. 2016. DFT modeling of the adsorption of trimethylphosphine oxide at the internal and external surfaces of zeolite MFI. Journal of Physical Chemistry C 120 (34) , pp. 19097-19106. 10.1021/acs.jpcc.6b03448

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Abstract

The characterization of the acidity of zeolites allows a direct correlation with their catalytic activity. To this end, probe molecules are utilized to obtain a ranking of acid strengths. Trimethylphosphine oxide (TMPO) is a widely used probe molecule, which allows the sensing of solid acids by using 31P NMR. We have performed calculations based on the density functional theory to investigate the Brønsted acid (BA) sites in zeolite MFI by adsorbing TMPO as a probe molecule. We have considered the substitution of silicon at the T2 site by aluminum, both at the internal cavity and at the external surface. The different acid strengths observed in the zeolite MFI when probed by TMPO (very strong, strong, and weak) may depend on the basicity of the centers sharing the acid proton. If the proton lies between the TMPO and one of the framework oxygen atoms binding the Al, the acidity is strong. When the framework oxygen atom is not directly binding the Al, it is less basic and a shortening of the TMPO–H distance is observed, causing an acid response of very strong. Finally, if two TMPO molecules share the proton, the TMPO–H distance elongates, rendering a weak acid character.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Advanced Research Computing @ Cardiff (ARCCA)
Chemistry
Subjects: Q Science > QD Chemistry
Publisher: ACS Publications
ISSN: 1932-7447
Funders: EPSRC and Royal Society
Date of First Compliant Deposit: 14 September 2016
Date of Acceptance: 8 August 2016
Last Modified: 28 Dec 2017 21:00
URI: http://orca.cf.ac.uk/id/eprint/94530

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