Kinetic Model and Mechanism of Heterogeneous Hydrogenation of Strained Polycyclic Compounds Derived from 5-Vinyl-2-norbornene

• Published in: Petroleum chemistry 2023-03, Vol.63 (3), p.277-288
• Main Authors: Zamalyutin, V. V., Katsman, E. A., Flid, V. R.
• Format: Article
• Language: English
• Subjects: Adsorption; Aluminum oxide; Chemical properties; Chemistry; Chemistry and Materials Science; Hydrogen; Hydrogenation; Industrial Chemistry/Chemical Engineering; Isomerization; Liquid phases; Material balance; Palladium; Palladium catalysts; Rate constants; Reaction products; Substrates; Transitional aluminas
• ISSN: 0965-5441; 1555-6239
• DOI: 10.1134/S0965544123010073

The main pathways of liquid-phase hydrogenation of 5-ethenylbicyclo[2.2.1]hept-2-ene (5-vinyl-2-norbornene, VNE) in the presence of PK-25 palladium catalyst (Pd/γ-Al 2 O 3 , 0.25% Pd) were studied. All the reaction products were identified, and the material balance was examined. The effect of the prevalent adsorption of the norbornene double bond on the Pd active site (AS) was confirmed. The parallel-consecutive scheme of the process mechanism, based on the set of experimental and theoretical data, was suggested. It involves the successive substrate hydrogenation and significant role of the isomerization of the vinyl group into the ethylidene group in intermediates on AS in a hydrogen atmosphere. The reaction is zero-order in a wide interval of initial VNE concentrations. An adequate kinetic model of the process, based on the Langmuir–Hinshelwood approach and the concept of multiple adsorption of substrates on one AS, was developed. Five steps, including two parallel steps, significantly contribute to the reaction rate. Their rate constants and the adsorption constants of AS complexes with unsaturated compounds were estimated.