Kinetic investigation of toluene hydrogenation over Pt/Al2O3 for liquid organic hydrogen carrier (LOHC) applications

The hydrogenation kinetics of toluene to methylcyclohexane (MCH) was investigated in a semi-batch reactor to assess the toluene/MCH system as a liquid organic hydrogen carrier (LOHC). Three commercial catalysts were physically and chemically characterized and screened at 393 K and 20 bar H₂ revealing 100% selectivity to MCH. Pt/Al₂O₃ exhibited the highest intrinsic activity, with turnover frequencies approximately 34 and 125 times greater than Pd/Al₂O₃ and Pd/C, respectively. Kinetic experiments were conducted over temperatures of 353–393 K, hydrogen pressures of 10–30 bar, catalyst loading of 1–3 kg/m3, initial toluene concentrations of 0.25–4 M and stirring rates ranging from 250 to 750 rpm. The Weisz–Prater criterion confirmed negligible intraparticle diffusion limitations. A Langmuir–Hinshelwood model including competitive adsorption of toluene and hydrogen on catalyst sites was developed and fitted to experimental data, describing the non-monotonic dependence of hydrogen pressure, the inhibitory effect of toluene. The activation energy was 126 kJ/mol, with adsorption and mass transfer coefficients quantified. These results provide a comprehensive kinetic framework for toluene hydrogenation over Pt/Al₂O₃ offering quantitative insights for the design and optimization of LOHC-based hydrogen storage systems.