Dehydrogenation mechanisms of liquid organic hydrogen carriers over Pt, Pd, Rh, and Ni surfaces: Cyclohexane as a model compound

In order to make a better understanding of dehydrogenation mechanisms of liquid organic hydrogen carriers, cyclohexane was selected as a model compound to carry out its decomposition studies over Pt(1 1 1), Pd(1 1 1), Rh(1 1 1), and Ni(1 1 1) surfaces via periodic density functional theory calculations. The adsorption geometries and adsorption energies of reaction intermediates were presented. Similar linear relationships of the adsorption energies with respect to the number of hydrogen removal over these four surfaces were revealed for C(6)Hx* (x = 8-12). Seven elementary reactions for cyclohexane successive dehydrogenation to C6H5* were considered. The initial dehydrogenation of C6H12* to generate C6H11* were identified as the rate-determining steps over all surfaces, association with activation energies of 1.04, 1.06, 0.96, and 1.14 eV for Pt(1 1 1), Pd(1 1 1), Rh(1 1 1), and Ni(1 1 1), respectively. The reactivity of dehydrogenation was in the order of Rh(1 1 1) > Pt(1 1 1) > Pd(1 1 1) > Ni(1 1 1).

Automated summary

The dehydrogenation mechanisms of liquid organic hydrogen carriers were studied using density functional theory calculations on different metal surfaces, revealing linear relationships between adsorption energies and hydrogen removal. The rate-determining step of cyclohexane dehydrogenation to C6H5* was identified, with reactivity order of Rh(1 1 1) > Pt(1 1 1) > Pd(1 1 1) > Ni(1 1 1).