Deactivation of VMgO x Catalysts by Coke in the Process of Isobutane Dehydrogenation with Carbon Dioxide

The process of isobutane dehydrogenation in the presence or absence of carbon dioxide was carried out over VMgO _x catalysts with different vanadium loading. The performed tests show that both the reaction atmosphere and physicochemical properties of the catalysts (related to vanadium content) have a great influence on the activity decrease and the carbonaceous deposit formation. Despite small ability of carbon dioxide to remove coke in the Boudouard reaction, the amounts of carbonaceous species deposited on the catalysts after the isobutane dehydrogenation under CO₂ atmosphere were even twice greater in comparison to those deposited in helium stream. Moreover, the rate of coke deposition during the dehydrogenation in the inert gas flow was only slightly dependent on the reaction time, in contrast to the process in carbon dioxide atmosphere. The results show that the coke formation on VMgO _x is enhanced predominantly by surface acidity of the catalysts, which grows with the vanadium content and the presence of CO₂ in the feed.