Labile sulfates as key components in active sulfated zirconia for n-butane isomerization at low temperatures

A wide variety of sulfate species exists on sulfated zirconia and many of these species have been connected to the catalytic performance. Some of these groups show strong interactions with polar molecules, indicating that they may play a role for the catalytic properties. In order to differentiate between these groups and to explore the role of labile soluble sulfate for n-butane skeletal isomerization, active sulfated zirconia was washed with water. Water washing removed around 40% of the sulfate species and led to a catalyst inactive for the alkane isomerization. This indicates that the labile sulfate plays a key role for the catalysis. The water-soluble fraction of the sulfate exists as highly covalent sulfate species characterized by an S=O vibration between 1390 and 1410 cm(-1) on the activated sulfated zirconia. Bronsted acid sites related to the sulfate groups are shown to be indispensable for activating n-butane, while Lewis acid sites do not directly participate in the alkane conversion catalysis. (C) 2004 Elsevier Inc. All rights reserved.