Thermodynamic study of benzene and hydrogen coadsorption on Pd(111)
Résumé
Periodic Density Functional Theory (DFT) calculations have been used to evaluate the (co)adsorption of hydrogen and benzene on Pd(111). Adsorption energies and geometries are evaluated as a function of coverage with both the PW91 generalized gradient-corrected and the optPBE vdW-DF functionals. Next, surface Gibbs free energies are used to predict the most stable surface coverage as a function of the gas-phase conditions by constructing thermodynamic phase diagrams. Different conclusions are obtained compared to the common approach that neglects vibrational contributions to the Gibbs free energies, particularly for benzene coadsortion with hydrogen and due to large entropy differences in surface Gibbs free energies obtained by the two. Neglect of vibrational contributions and use of the vdW-DF method predicts lower hydrogen coverages coadsorbed with benzene, compared to the quivalent approach with the PW91 functional. Results including vibrational contributions with the vdW-DF method have not been obtained due to computational constrains, however, our results allow proposing that hydrogen coverages between 0.44 ≤ θH ≤ 1 can be expected at typical hydrogenation conditions for the coadsorption with benzene.
Domaines
Chimie
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