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

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.