HYDROISOMERIZATION OF N-PENTANE OVER HYBRID CATALYSTS CONTAINING A SUPPORTED HYDROGENATION CATALYST

Isomerization of n-pentane to iso-pentane was studied on a series of ZSM-5 zeolite catalysts under hydrogen and nitrogen atmosphere. A H-ZSM-5 catalyst showed low n-pentane conversion and isopentane selectivity. A Pt-ZSM-5 catalyst prepared using an ion-exchange method showed high activity and high iso-pentane selectivity reaching an equilibrium conversion. A hybrid catalyst prepared by physically mixing H-ZSM-5 and Pt/SiO2 showed high activity and selectivity equal to those of Pt/ZSM-5 while Pt/SiO2 and H-ZSM-5 had a poor catalytic performance for this reaction. A hybrid catalyst containing palladium showed high activity and selectivity but a palladium ion-exchanged ZSM-5 catalyst did not. With the hybrid catalyzed reaction, the mixing state of H-ZSM-5 and Pt/SiO2 had a strong influence on the activity and iso-pentane selectivity. In the absence of hydrogen, the conversion of n-pentane was dramatically reduced and the oligomerization reaction became dominant. These results suggest that spilled-over hydrogen plays an important role in alkane activation and the stabilization of intermediates.