Butane and butene isomerization over solid acid catalysts

Microcalorimetric and reaction kinetics measurements were used to investigate the catalytic activity of sulfated zirconia for butane isomerization at 423 K. The heats of ammonia adsorption on the strongest acid sites of sulfated zirconia catalyst are comparable to strong solid acids in zeolites, e.g., H-mordenite, though not superacidic. Therefore, the catalytic activity for butane isomerization at low temperatures is not strictly related to acid strength.; Isomerization of n-butane and isobutane at 423 K over sulfated zirconia involves bimolecular reactions in which two adsorbed n-C{dollar}sb4{dollar} species react reversibly, via a C{dollar}sb8{dollar} intermediate, to form a single i-C{dollar}sb4{dollar} species and in which two adsorbed i-C{dollar}sb4{dollar} species react reversibly to form a single n-C{dollar}sb4{dollar} species. The rate expression based on these reactions describes not only the observed rates of isomerization, but also the measured rates of formation of the disproportionation products (i.e., C{dollar}sb3{dollar} and C{dollar}sb5{dollar} species).; Sulfated zirconia catalysts undergo rapid initial deactivation during isomerization of n-butane at 423 K, and the longer-term deactivation rate increases with increasing n-butane pressure. The rate of catalyst deactivation is slower during isobutane isomerization. The more rapid deactivation of the catalyst during isomerization of n-butane is caused by the formation of n-C{dollar}sb4{dollar}-diene species from n-C{dollar}sb4{dollar} olefins that are present in the n-butane feed or that are produced on the catalyst under reaction conditions.; Hydrogen in the reactor effluent is detected during isobutane isomerization over sulfated zirconia, and its rate of formation appears to correlate with the rate of butane isomerization. Sulfated zirconia appears to possess the ability to generate olefins in situ. A kinetic model for isobutane isomerization is developed over H-mordenite at 473 K and contains reaction steps involving olefin adsorption/desorption, oligomerization/{dollar}beta{dollar}-scission, and hydride transfer. The kinetic model is then extended to sulfated zirconia for isobutane isomerization at 423 K with the addition of an olefin generation cycle. The rate constants for oligomerization/{dollar}beta{dollar}-scission reactions are faster over sulfated zirconia than over H-mordenite, while the rate constants for hydride transfer reactions are comparable over both catalysts. The reactive intermediates appear to follow reaction pathways similar to those exhibited in known carbenium ion chemistry.