Effect of tin and potassium addition on the nature of platinum supported on silica

Abstract The effects of tin and potassium addition on the catalytic properties of Pt/SiO 2 catalysts were studied by diffuse reflectance UV–vis spectroscopy, temperature programmed reduction (TPR), CO chemisorption and isobutane dehydrogenation. Pt/SiO 2 , Sn/SiO 2 and Pt–Sn/SiO 2 catalysts were prepared by incipient wetness impregnation with aqueous solutions of H 2 PtCl 6 and SnCl 2 . Pt–Sn/SiO 2 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. [PtCl 2 (SnCl 3 ) 2 ] 2− complex was only detected in (PtSn/SiO 2 ) and Sn(Pt/SiO 2 ) 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/SiO 2 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.