n-Butane isomerization was studied on nickel supported on SO42- - ZrO2 and compared with SO42- - ZrO2 and Pt/SO42- - ZrO2. Reaction conditions were 300 degrees C, WHSV = 1 h(-1), atmospheric pressure and several H-2/n-C-4 ratios. Metallic phases (Ni or Pt) do not show typical properties of supported metallic functions. The metal limits its role to the ’activation’ of hydrogen. The activated hydrogen inhibits the formation of a carbonaceous deposit which affects the strong acid sites and is the cause of SO42- - ZrO2 deactivation. Nickel has less capacity than platinum to activate hydrogen and requires greater metal loads and higher partial pressures of hydrogen in order to give stability to SO42- - ZrO2 for n-butane isomerization.