ON THE ACID-CATALYZED ISOMERIZATION OF LIGHT PARAFFINS OVER A ZRO2 SO4 SYSTEM - THE EFFECT OF HYDRATION/

Over a superacid ZrO2/SO4 system (ZS8: microcrystalline tetragonal, SO 4 content approximate to 2.6 groups per nm(2)), the isomerization of n -butane proceeds rapidly and with high yield of i-butane at 423 K, if the catalyst is calcined in dry air at approximate to 823 K. The activ e catalyst typically shows: all surface sulfates in a highly covalent form, a high concentration of strong (aprotic) Lewis acid sites, and a fairly low (though never null) concentration of(protonic) Bronsted ac id sites. A partial rehydration of the catalyst gradually converts the surface sulfates first into a less covalent form and then into an ion ic form, decreases the concentration of strong Lewis sites, and increa ses (up to a factor of approximate to 10) the concentration of Bronste d sites, while the catalytic activity is gradually extinguished. Initi al activity and initial surface features can be recovered by repeating the catalyst activation step. (C) 1994 Academic Press, Inc.