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Adsorption of Dibenzothiophene and Fluorene on TiO2(110) and Supported Ag Clusters

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journal contribution
posted on 16.12.2015, 23:54 by Elizabeth R. Webster, Aileen Park, Miranda B. Stratton, Victoria C. Park, Amber M. Mosier, Ryan S. Shine, Lauren Benz
New adsorbent materials, many of which rely on supported Ag nanoclusters or exchanged Ag+ ions, have recently been employed in petroleum processing to further reduce sulfur content in fuels following catalytic hydrodesulfurization (HDS). HDS refractory species include aromatic heterocycles, such as dibenzothiophene (DBT) and its methylated derivatives. Herein, we report a fundamental study of the adsorption of two structurally analogous petroleum-relevant molecules, DBT and fluorene, on a clean TiO2(110) surface and one with supported Ag nanoclusters. Using thermal desorption spectroscopy, we determined the desorption activation energies to be 106 ± 2 and 103 ± 2 kJ/mol for DBT and fluorene, respectively. The similar desorption activation energies imply that the interaction of DBT on TiO2 is not strongly dependent upon the S atom (which fluorene lacks). When adsorbed on supported Ag nanoparticles, both desorption activation energies shifted to 111 ± 2 kJ/mol, suggesting a non-selective binding enhancement, which likely involves the π-electron systems. After heating the Ag/TiO2(110) surface to 650 K to force agglomeration of the particles, no enhancement in binding was observed for either molecule, suggesting that the cluster size is critical for the observed enhancement. These results point to the importance of the metal particle size in addition to the oxidation state in commercially employed sorbents.