Density functional theory study of decalin dehydrogenation for hydrogen release on Pt(111) and Pt(211)

The catalytic dehydrogenation of organic hydrides on transition metal surfaces is of fundamental importance to hydrogen storage technologies based on organic hydrides. Density functional theory (DFT) calculations were performed to study the dehydrogenation of both trans- and cis-decalin on flat Pt(111) and stepped Pt(211) surfaces. Considering that long-range van der Waals (vdW) forces play an important role in the adsorption and reaction of large organic molecules on metal surfaces, a recently developed vdW-inclusive method (optB88-vdW) was adopted in the computational procedure for accurate adsorption results. It revealed that the adsorption energies of decalin on Pt(111) and Pt(211) have little difference due to the dominant role of vdW forces during adsorption instead of chemical interaction. The possible dehydrogenation pathways of decalin on Pt(211) and Pt(111) are found to be clearly dependent on the isomeric molecular structures of decalin and the metal crystal facets. The dehydrogenation is more favourable for cis-decalin than for trans-decalin when on Pt(211) compared to on Pt(111). Taking the Gibbs free energy calculated for the experimental conditions (500 K, 1 atm) as the descriptor, it was observed that the energy barrier for the desorption of reaction product (naphthalene) is much higher than that of every elementary dehydrogenation step. Therefore, desorption of naphthalene is critical in determining the dehydrogenation reaction rate, especially on stepped Pt surfaces. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.