The surface basicity of the alkaline-earth metal oxides has been investigated by studying the properties of 17O nuclear magnetic resonance (NMR). To this end, we performed density functional theory calculations and determined the 17O chemical shift and the quadrupolar coupling constants of the regular and stepped surfaces of MO (M = Mg, Ca, Sr, and Ba) oxides. The computed average chemical shift (δisoav) for 17O NMR of bulk MgO, CaO, SrO, and BaO is 46, 301, 394, and 636 ppm, respectively, in excellent agreement with the experiment. The 17O NMR chemical shifts correlate linearly with the Madelung potential in the four oxides. Next, we considered the changes in the 17O chemical shift due to the adsorption of BR3 (R = F and OCH3) and pyrrole as probe molecules. We found that the 17O NMR signal of the O ion directly bound to the probe molecule shifts considerably compared to the clean surface. This is due to a change in the polarization of the O charge distribution due to the molecular adsorption. This change is the largest for BaO, with the strongest bond and the shortest surface-adsorbate distance, and the smallest for MgO, thus showing a direct correlation between 17O NMR and surface basicity. The 17O chemical shift of the basic site correlates linearly also with several properties of the adsorbed molecules, providing a direct measure of the surface basicity.
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14 December 2019
Research Article|
December 11 2019
17O NMR as a measure of basicity of alkaline-earth oxide surfaces: A theoretical study Available to Purchase
Special Collection:
Oxide Chemistry and Catalysis
Farahnaz Maleki
;
Farahnaz Maleki
Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca
, via R. Cozzi 55, 20125 Milano, Italy
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Gianfranco Pacchioni
Gianfranco Pacchioni
a)
Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca
, via R. Cozzi 55, 20125 Milano, Italy
a)Author to whom correspondence should be addressed: [email protected]
Search for other works by this author on:
Farahnaz Maleki
Gianfranco Pacchioni
a)
Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca
, via R. Cozzi 55, 20125 Milano, Italy
a)Author to whom correspondence should be addressed: [email protected]
Note: This article is part of the JCP Special Topic on Oxide Chemistry and Catalysis.
J. Chem. Phys. 151, 224705 (2019)
Article history
Received:
October 17 2019
Accepted:
November 11 2019
Citation
Farahnaz Maleki, Gianfranco Pacchioni; 17O NMR as a measure of basicity of alkaline-earth oxide surfaces: A theoretical study. J. Chem. Phys. 14 December 2019; 151 (22): 224705. https://doi.org/10.1063/1.5131831
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