MECHANISMS OF REFORMING REACTIONS ON PD/AL2O3 CATALYSTS

The influence of palladium precursor salt, calcination temperature, and metallic dispersion on the activity and selectivity of reforming reactions on Pd/Al2O3 catalysts have been investigated. Reforming reactions involve methylcyclopentane (MCP) hydrogenolysis. 2- and 3-methylpentane (2MP and 3MP) isomerization, dehydrocyclization and hydrocracking, and finally 3-methylhexane (3MH) aromatization. When necessary. 13C-labelled hexanes have been used to determine more accurately the selectivity pathways. We find that the mechanistic pathways involve metallacyclic and π olefin-σ alkyl intermediates: metallacyclobutanes and metallacyclopentanes for hydrocracking (essentially demethylation) and bond shift isomerization; 1,2π-5σ intermediates for dehydrocyclization, cyclic isomerization. hydrogenolysis of cycles, and hydrocracking of heptanes; and 1,2π-6σ intermediates for aromatization. The selectivity obtained in these reactions is discussed in terms of the relative stability of these intermediate species and the kinetic steps of the overall process. The influence of metallic dispersion, palladium precursor salt, and calcination temperature both on the selectivity and the activity is investigated. © 1993 Academic Press, Inc.