Deactivation of sulfated-zirconia and H-mordenite catalysts during n-butane and isobutane isomerization

The catalytic properties of sulfated-zirconia and H-mordenite for isomerization 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 olefins 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 catalysts during n-butane isomerization appears to be caused by the production of coke on the catalyst from straight-chain olefinic species either present in the feed or produced on the catalyst (for the case of sulfated-zirconia) under reaction conditions. The rates of deactivation are slower during isobutane isomerization than during n-butane isomerization over sulfated-zirconia and H-mordenite catalysts in the presence of feed olefins (k(deact) near 0.006 min(-1)). Higher rates of production of C-6-species are observed during isobutane isomerization than during n-butane isomerization. It appears that more effective hydride transfer during isobutane isomerization than during n-butane isomerization may remove coke precursors. Isobutane isomerization may be an effective probe reaction to study solid acid catalysts at pseudo-steady state reaction conditions. (C) 1998 Elsevier Science B.V, All rights reserved.