DEACTIVATION OF SULFATED-ZIRCONIA AND H-MORDENITE CATALYSTS DURING N-BUTANE AND ISOBUTANE ISOMERIZATION

The catalytic properties of sulfated-zirconia and H-mordenite for isom erization of n-butane and isobutane were studied at temperatures near 450 K. Both catalysts showed rapid deactivation (deactivation constant k(deact) near 0.02 min(-1)) during isomerization of n-butane when ole fins were present in the feed stream. Removal of olefins from the feed decreased the rate of catalyst deactivation over sulfated-zirconia (k (deact) near 0.007 min(-1)), while removal of feed olefins eliminated the isomerization reaction over H-mordenite. Deactivation of the catal ysts during n-butane isomerization appears to be caused by the product ion of coke on the catalyst from straight-chain olefinic species eithe r present in the feed or produced on the catalyst (for the case of sul fated-zirconia) under reaction conditions. The rates of deactivation a re slower during isobutane isomerization than during n-butane isomeriz ation over sulfated-zirconia and H-mordenite catalysts in the presence of feed olefins (k(deact) near 0.006 min(-1)). Higher rates of produc tion of C-6-species are observed during isobutane isomerization than d uring n-butane isomerization. It appears that more effective hydride t ransfer during isobutane isomerization than during n-butane isomerizat ion may remove coke precursors. Isobutane isomerization may be an effe ctive probe reaction to study solid acid catalysts at pseudo-steady st ate reaction conditions. (C) 1998 Elsevier Science B.V, All rights res erved.