Direct enthalpy measurement for hydrogenation of liquid organic hydrogen carriers by Differential Scanning Calorimetry under H2 pressure

In this contribution, we report the hydrogenation enthalpy direct measurement of well-studied Liquid Organic Hydrogen Carriers (LOHC) (Dibenzyltoluene, N-Ethylcarbazole, 2-Octanone) and of a new LOHC (Acetophenone) by differential scanning calorimetry (DSC) under H2 pressure. The obtained hydrogenation enthalpies showed good correspondence with DFT predictions and the literature. Moreover, multistep hydrogenation processes were investigated, evidencing that transfer hydrogenation occurred during the reaction. The study of bifunctional LOHC such as acetophenone and its derivatives showcased the potential of direct enthalpy measurement for rapid LOHC screening. Besides, a DFT correction factor for this specific bifunctional LOHC class was experimentally obtained, enabling more precise DFT predictions for similar systems. Kinetic parameters such as the activation energies for the catalytic Ru/Al2O3 system were also determined to be in the 45-60 kJ/mol range, compatible with the H2 adsorption on the Ru surface. The detrimental effect of steric hinderance was also observed. Finally, the reaction order in H2 was experimentally estimated to ~1 for all of the studied LOHCs.