Adsorption of multiple H_2 molecules on the complex TiC_6H_6: An unusual combination of chemisorption and physisorption

摘要

The hydrogen physisorption properties of diverse examples of Ti-decorated six-membered carbocycles have been established and intensively investigated. However, fewer investigations have been devoted to the chemical reactions occurring during the process of hydrogen storage. Herein, for the first time, a variety of plausible hydrogenation intermediates and physisorption complexes involving multiple H-2 molecules on the complex TiC6H6 has been investigated simultaneously. The relative Gibbs free energies of TiC6H6-nH(2) (n = 1-4) isomers and the minimum-energy pathways of the successive hydrogenation steps show that the overall reactions to give the hydrogenation product TiC6H11-3H is exothermic by 11.07 kcal/mol in terms of Delta G (298.15 K). It indicates that a facile switch of hydrogen addition and release with superior capacity of 6.02 wt % can be quickly achieved with simply regulated by increasing/decreasing the hydrogen pressure, which is consistent with the recent experiment on hydrogen adsorption in TiC6H6 at room temperature. The physisorption processes show that three H-2 molecules can be efficiently trapped below 210 K and desorbed completely at 935 K. More importantly, chemisorption and physisorption will convert in certain circumstances, which indicates that the mechanism of the bonding of H-2 molecules on TiC6H6 is an unusual combination of chemisorption and physisorption. (C) 2019 Elsevier Ltd. All rights reserved.