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DFT Modeling of the Adsorption of Trimethylphosphine Oxide at the Internal and External Surfaces of Zeolite MFI

Hernandez-Tamargo, CE; Roldan, A; de Leeuw, NH; (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. Green open access

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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.

Type: Article
Title: DFT Modeling of the Adsorption of Trimethylphosphine Oxide at the Internal and External Surfaces of Zeolite MFI
Open access status: An open access version is available from UCL Discovery
DOI: 10.1021/acs.jpcc.6b03448
Publisher version: http://dx.doi.org/10.1021/acs.jpcc.6b03448
Language: English
Additional information: ACS AuthorChoice - This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
Keywords: Science & Technology, Physical Sciences, Technology, Chemistry, Physical, Nanoscience & Nanotechnology, Materials Science, Multidisciplinary, Chemistry, Science & Technology - Other Topics, Materials Science, INITIO MOLECULAR-DYNAMICS, TOTAL-ENERGY CALCULATIONS, SOLID-STATE NMR, AUGMENTED-WAVE METHOD, ACIDITY CHARACTERIZATION, TRANSITION-METALS, BASIS-SET, P-31 NMR, CATALYSTS, DENSITY
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1521711
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