Reaction mechanism of skeletal isomerization of n-butane over Cs2.5H0.5PW12O40 catalyst was studied using C-13 MAS NMR. The reaction proceeds mainly via a monomolecular mechanism at 80degreesC. The contribution of the bimolecular mechanism becomes more significant as the reaction temperature is increased to 150degreesC. Hydrogen suppresses the bimolecular mechanism, in particular on Pt-promoted Cs2.5H0.5PW12O40 catalyst. The latter catalyst is highly selective to isobutane in the presence of H-2 even at 220degreesC. The kinetics of the monomolecular isomerization reaction and the reaction schemes of C-13 scrambling and n-butane isomerization are discussed. (C) 2003 Elsevier B.V. All rights reserved.