Kinetic Model and Mechanism of Hydrogenation of Unsaturated Carbocyclic Compounds Based on Norbornadiene

Liquid-phase hydrogenation of bicyclo[2.2.1]hepta-2,5-diene (norbornadiene, ND) proceeds in the presence of an industrial palladium catalyst Pd/γ-Al2O3 (PK-25) in an n-heptane solution at 76°C via consecutive formation of bicyclo[2.2.1]hept-2-ene (norbornene, NE) and bicyclo[2.2.1]heptane (norbornane, NA), as well as tricyclo[2.2.1.02,6]heptane (nortricyclane, NT) as a minor product. The reaction products were identified, the main routes were determined, and the material balance was studied. Preferable adsorption of ND at the active palladium site over adsorption of other components of the system was confirmed. A parallel-serial scheme of the process mechanism was proposed based on the sum of experimental and theoretical data. Zero order kinetics was observed in a wide range of initial substrate concentrations. The apparent rate constants of each stage were measured. A detailed kinetic model was developed based on the Langmuir–Hinshelwood approach, assuming multiple adsorption of substrates at a single active site of the heterogeneous catalyst. The model adequately describes the available experimental data using the proposed mechanism of ND hydrogenation. The possibility of a "cocktail" mechanism for the given reaction was discussed.