Effect of Sn Addition on n-Butane Dehydrogenation over Alumina-supported Pt Catalysts Prepared by Co-impregnation and Sol-gel Methods

Abstract

n-Butane dehydrogenation was investigated over alumina-supported Pt catalysts modified with Sn. Preparation of this catalyst by conventional co-impregnation method with H₂PtCl₆ and SnCl₂ mixed solution (Pt–Sn/Al₂O₃ catalyst), resulted in considerable loss of amount of Sn during calcination. Therefore, SnO₂–Al₂O₃ was prepared by the sol-gel method and Pt was then deposited on this support (Pt/SnO₂–Al₂O₃ catalyst). This procedure prevented loss of Sn at the calcination step. In addition, Pt/SnO₂–Al₂O₃ demonstrated a remarkable promotion effect of Sn compared with Pt–Sn/Al₂O₃. CO adsorption was higher on Pt/SnO₂–Al₂O₃ than on Pt–Sn/Al₂O₃. Sn present in the oxidized state was dispersed on the support surface of Pt/SnO₂–Al₂O₃. XRD measurements suggested that an inactive PtSn₂ phase was formed and particle growth occurred in Pt–Sn/Al₂O₃. XRD peaks from Pt were not observed for Pt/SnO₂–Al₂O₃, suggesting the formation of highly dispersed Pt₃Sn. This study showed that highly dispersed tin oxides on the support surface retarded side reactions and formation of Sn-rich PtSn₂ particles, resulting in high activity for n-butane dehydrogenation.