Sulfated zirconia catalysts promoted with Fe and Mn have been synthesized and the acidity characterized by IR spectroscopy of adsorbed pyridine. The catalytic isomerization of n-butane was investigated in a fixed bed reactor operated at low conversion at atmospheric pressure and 250 degrees C. The main effect of the promoters was to change the ratio Bronsted:Lewis acidity of the samples. The catalytic activity was found to be correlated with the number of strong Bronsted acid sites. (c) 2004 Elsevier B.V. All rights reserved.