Catalytic cycles for isobutane isomerization over sulfated-zirconia catalysts

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 c orrespondingly lower rates of hydrocarbon production are observed for catal ysts dried at 773 K compared to samples dried at 588 K. It appears that sul fated-zirconia has the ability to generate olefins under reaction condition s, and this dehydrogenation reaction appears to be reversible, because incr easing levels of dihydrogen in the feed suppress catalytic activity. These kinetic data can be described by a reaction scheme involving oligomerizatio n/beta-scission, isomerization and hydride transfer steps over acid sites, combined with dehydrogenation steps that generate olefins. The values of th e rate constants for oligomerization steps over sulfated-zirconia are sever al orders of magnitude higher than for the corresponding steps over H-morde nite, whereas the rate constants for hydride transfer steps are similar for sulfated-zirconia and H-mordenite.