Hydrogenation of Aromatic Ethers and Lactones: Does the Oxygen Functionality Really Improve the Thermodynamics of Reversible Hydrogen Storage in the Related LOHC Systems?

Liquid organic hydrogen carrier (LOHC) compounds represent a promising option for hydrogen storage. Beyond the use of pure hydrocarbons, the incorporation of oxygen atoms offers a way to modify thermodynamic properties and potentially improve suitability for hydrogen storage. This study investigates the effect of oxygen functionalization in aromatic ethers and lactones on the reaction equilibrium of reversible hydrogenation. To address this question, reaction enthalpies and entropies are calculated using both experimental and theoretically determined pure substance data. The equilibrium position shift of the hydrogenation of furan derivatives has been shown to follow a similar trend to that of their hydrocarbon counterparts upon the addition of aromatic rings. This shift is, however, more pronounced in the case of the furan-based systems. The effect is reflected in increasing Gibbs reaction energies during the dehydrogenation process. Both the formation of lactones and the addition of a second ring to the furan core leads to a further increase in the Gibbs reaction energy. The highest value is observed for dibenzofuran, with a Gibbs reaction energy of 36.6 kJ∙mol-1 at 500 K. These findings indicate that, from a thermodynamic perspective, hydrogen release is feasible at temperatures below 500 K, which is an important feature for the potential application as a hydrogen storage system.