Catalytic cycles for isobutane isomerization over sulfated-zirconia catalysts

Abstract

Reaction kinetic studies of isobutane isomerization over sulfated-zirconia catalysts were performed at 423 K. These catalysts show sustained rates of dihydrogen production that follow the same trend with time-on-stream as the rate of hydrocarbon production. Lower rates of dihydrogen production and correspondingly lower rates of hydrocarbon production are observed for catalysts dried at 773 K compared to samples dried at 588 K. It appears that sulfated-zirconia has the ability to generate olefins under reaction conditions, and this dehydrogenation reaction appears to be reversible, because increasing levels of dihydrogen in the feed suppress catalytic activity. These kinetic data can be described by a reaction scheme involving oligomerization/β-scission, isomerization and hydride transfer steps over acid sites, combined with dehydrogenation steps that generate olefins. The values of the rate constants for oligomerization steps over sulfated-zirconia are several orders of magnitude higher than for the corresponding steps over H-mordenite, whereas the rate constants for hydride transfer steps are similar for sulfated-zirconia and H-mordenite.