Role of the OH-group in the adsorption properties of methanol, ethanol, and ethylene glycol on 15-atom 3d, 4d, and 5d transition-metal clusters

Abstract

The adsorption of alcohols on transition-metal (TM) substrates has received the attention of many researchers due to the applications of alcohols in several technological fields. However, our atomic-level understanding is still far from satisfactory, in particular for the interaction of alcohols with finite-size TM clusters, where new effects can arise due to the presence of quantum-size effects. In this work, we report a theoretical investigation of the adsorption properties of methanol, ethanol, and ethylene glycol on 12 different 3d, 4d, and 5d TM₁₅ clusters based on density functional theory calculations within the semi-empirical D3 van der Waals corrections. From the correlation analysis of all the lowest- and high-energy configurations, we identified the adsorption modes of methanol, ethanol, and ethylene glycol on the TM₁₅ clusters, in which the OH group binds to the cationic TM sites via the O–TM and H–TM interactions. Due to the relatively weak alcohol–TM₁₅ interaction, the changes induced on the TM₁₅ clusters are small, except for Au₁₅ and Ru₁₅, where the bare cluster changes its structure to a nearby minimum in the potential energy surface. The adsorption energy for the alcohol/TM₁₅ systems is correlated to the combination of several parameters, in which the main contribution is connected with the O–TM interaction and the HOTM angles. Furthermore, the TM electronegativity is an important descriptor for the methanol and ethanol adsorption energies, while charge transfer is important for ethylene glycol.