Heterogeneous catalytic processes in supercritical fluids offer environmentally benign alternatives to current catalyst technologies. In the case of isomerization of light alkanes over solid acid catalysts at atmospheric pressure, the catalysts deactivate rapidly due to coke formation on the catalyst surface. To solve this problem, we studied the isomerization of n-butane over sulfated zirconia in a n-butane supercritical condition of reactant and products. Under the supercritical condition, no significant deactivation was observed, and the steady state activity was maintained. Furthermore, the active sites of sulfated zirconia were characterized by FT-IR spectroscopy: it was found that Lewis acid sites on sulfated zirconia play an important role in the isomerization of n-butane. (c) 2005 Elsevier B.V. All rights reserved.