In situ UV–VIS diffuse reflectance spectroscopy–on-line activity measurements Significance of Cr n+ species ( n=2, 3 and 6) in n-butane dehydrogenation catalyzed by supported chromium oxide catalysts

Abstract

The dehydrogenation of n-butane over supported chromium oxide catalysts has been investigated at 500 °C by insitu UV–VIS diffuse reflectance spectroscopy–on-line activity measurements as a function of the reaction time (0–60 min), the support composition (SiO₂:Al₂O₃ ratio) and the Cr loading (0–8 wt.%). The catalytic reaction is characterized by an initial induction period, during which the supported chromium oxides are reduced to Cr^3+/2+, and CO/CO₂ and cracking products (C₁, C₂ and C₃) are formed. After this initial induction period, but-1-ene and but-2-ene are produced with a selectivity up to 90%. The catalytic activity increases with increasing Cr content and Al₂O₃ content of the support, and is maximum after 5–15 min on stream. A relation between the dehydrogenation activity and the amount of Cr³⁺ formed upon the reduction of Cr⁶⁺ has been established.