An active catalyst for the skeletal isomerization of butane to isobutane was obtained by mechanically mixing WO3/ZrO2 and Pt/ZrO2. WO3/ZrO2 was prepared by impregnation of Zr(OH)(4) with aqueous ammonium metatungstate, followed by calcination in air at 700 degrees C (15 wt% W); Pt/ZrO2 was prepared by impregnation of the hydroxide with aqueous H2PtCl6 . 6H(2)O, followed by calcination at 700 degrees C (0.5 wt% Pt). The effect of mixing was specific to Pt/ZrO2; no effectiveness was found for Pt/TiO2, Pt/SiO2, Pt/Al2O3, Pt/Fe2O3, and Pt/SnO2. Pt-WO3/ZrO2 prepared by co-impregnation of zirconia with the W and Pt materials showed quite low activity; the first impregnation with Pt followed by W gave an activity value much higher than that obtained by the reverse order. XPS of Pt/ZrO2 showed the Pt species to be cationic, while those of Pt/TiO2, WSiO2, and Pt-WO3/ZrO2 were metallic.