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

The dehydrogenation of n-butane over supported chromium oxide catalysts has been investigated at 500 degrees C by in situ 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 Cr3+/2+, and GO/CO2 and cracking products (C-1, C-2 and C-3) 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.