Effect of the addition of potassium and lithium in Pt–Sn/Al2O3 catalysts for the dehydrogenation of isobutane

Dehydrogenation of isobutane (iC₄) to isobutene has recently received considerable attention because of the increasing demand for methyl tertiary butyl ether (MTBE) and ethyl tertiary butyl ether (ETBE), as additives for gasoline to increase the octane number and to substitute lead. Among several catalysts, Pt–Sn/γ-Al₂O₃ catalyst is one of the most suitable ones. In this study, Pt–Sn, Pt–Sn–K and Pt–Sn–Li catalysts supported on γ-Al₂O₃ have been investigated. The catalysts were prepared by co-impregnation using H₂PtCl₆, SnCl₂ as the metal precursors and K₂CrO₄ and LiOH as the promoters. The obtained catalysts were characterized by TPR and XRD techniques. Reaction temperature, feed flow rate (Q), iC₄/H₂ ratio and the catalyst type were the main variables that were investigated. Initially, primary experiments were carried out for the identification of the optimum range of operating variables, then, Taguchi's algorithm was employed to design the experiment. The results revealed that the Pt–Sn–K catalyst showed higher selectivity than Pt–Sn–Li. Under the optimum operating conditions i.e. at 550 °C, feed flow rate of 50 cm³/min and iC₄/H₂ ratio of 1/3, selectivity toward isobutene of higher than 90% was achieved with the corresponding conversion values of about 15%.