The low temperature isomerization of butane to isobutane was catalyzed by sulfated zirconia promoted with transition metals like Fe, Mn, and Pt. At 323 K, the Fe,Mn-promoted sample exhibited the usual induction period to a highly active state, followed by rapid deactivation. At the same conditions, a Pt-promoted catalyst also showed an induction period but was followed by a period of unusually stable activity, even in the absence of dihydrogen. The mechanism of the isomerization reaction, evaluated by using C-13-labeled butane over Fe,Mn-promoted at 323 K and unpromoted sulfated zirconia at 473 K, was found to be intermolecular. Because the formation of a C-8 intermediate in a bimolecular pathway most likely involves the reaction of olefins, the effect of adding trans-2-butene to the butane feed was investigated. The increase in isomerization activity that accompanied butene addition was consistent with a mechanism in which butene is protonated by acid sites of the catalyst to initiate a chain reaction that eventually produces isobutane. Since the calculated chain length (moles isobutane formed/moles butene added) was similar for all of the materials studied, the acidities of the catalysts appear to be unaffected by the presence of transition metals. Therefore, the role of transition metal promoters in sulfated zirconia is to increase the surface concentration of intermediate butenes that subsequently react to form isobutane. Due to the very different stabilities of the promoted catalysts at low temperatures, we speculate that the Fe,Mn-promoted sample forms butene non-catalytically whereas the Pt-promoted sample forms butene catalytically.