The application of supercritical temperatures and pressures in the isomerization of n-butane is a means to avoid deactivation of the catalyst by coke and to enhance the throughputs. However, catalysts consisting of unpromoted sulfated zirconia are not sufficiently active to attain equilibrium conversions of n-butane. Through impregnation of iron salts on sulfated zirconium hydroxide, we produced catalysts containing 1 wt % iron with strongly enhanced activity. In pelletized form, these catalysts enabled the processing of n-butane at conversions close to thermodynamic equilibrium. At the preferred reaction temperature of 488 K, the yield of isobutane amounted to 43%. Catalysts manufactured by extrusion were considerably less active.