The effects of tin and potassium addition on the catalytic properties of Pt/SiO2 catalysts were studied by diffuse reflectance UV-vis spectroscopy, temperature programmed reduction (TPR), CO chemisorption and isobutane dehydrogenation. Pt/SiO2, Sn/SiO2 and Pt-Sn/SiO2 catalysts were prepared by incipient wetness impregnation with aqueous solutions of H2PtCl6 and SnCl2. Pt-Sn/SiO2 catalysts were prepared by coimpregnation and sequential impregnation. A part of these catalysts was then impregnated with an aqueous solution of KOH. Fresh and calcined catalysts were studied. [PtCl2(SnCl3)(2)](2-) complex was only detected in (PtSn/SiO2) and Sn(Pt/SiO2) catalysts. The proximity between Pt and Sn species favoured the formation of Pt-Sn ensembles or alloys after the reduction treatment that provided stability and selectivity for the isobutane dehydrogenation. The addition of potassium to fresh Pt-Sn/SiO2 did not change the activity, but it improved the dehydrogenation selectivity, which reached values of almost 100%. Surface Pt-Sn species changed by the calcination treatment, causing the segregation of Pt and Sn oxide species. This treatment caused a decrease of CO/Pt ratio, activity and selectivity of Pt-Sn catalysts. In calcined Pt-Sn-K catalysts, the activity seemed to be a function of K-Pt-Sn interactions. (C) 2004 Elsevier B.V. All rights reserved.