The Role of Chemical and Structural Changes on the Surface in Deactivation of Chromia-Alumina Catalysts in Dehydrogenation of Paraffinic Hydrocarbons

The chemical and structural changes on the surface of chromia-alumina catalysts, operated for long time in dehydrogenation of paraffins hydrocarbons have been investigated. In reduced media at 500°C a gradual decrease of the number of active site associated with Cr 2+ ions was established. A loss of surface area of chromia may be considered as the main reason of this phenomenon. The process was especially pronounced at 700°C. In oxidizing media at 500°C no change in the surface area and chemical state of the chromia surface were observed, whereas at 700°C the improvement in the dispersity of chromium compounds were found. The processes of reversible, partially reversible and complete deactivation of chromia-alumina catalyst were considered.