Sulfated zirconia and Mn-promoted sulfated zirconia (0.5 and 2.0 wt% Mn) catalysts were subjected to mechanical stress. Pressing (10 min 540 MPa), milling (10 min vibrating mill), and grinding (manually, 10 min agate mortar) effected a partial phase transformation from the tetragonal to the monoclinic phase of ZrO2. The mechanical stress also reduced the n-butane isomerization rate (1 kPa n-butane, 323-378 K, atmospheric pressure) to 30% and less of that measured for untreated catalyst. Standard sample preparation techniques for analytical methods thus alter the structural and catalytic properties of sulfated zirconia. Attempts to correlate data from different methods are futile unless the integrity of the sulfated zirconia is ensured. (C) 2003 Elsevier Science (USA). All rights reserved.