Oxidative dehydrogenation of isobutane over activated carbon catalysts

In past work, we reported on the textural and chemical modifications induced by treating an activated carbon under nitrous oxide, oxygen and hydrogen. In this work, we are reporting on the testing of surface modified activated carbons in the oxidative dehydrogenation of isobutane (ODHI). The results show that the different treatments lead to a given catalytic performance associated with the degree of oxidation. At 648 K, isobutene yields are higher in the initial stages for the activated carbons with the highest amounts of carbonyl/quinone groups on the surface, which are considered the active sites for this reaction, and the isobutene yields are lower for the catalysts with lower concentrations of these groups. As the reaction proceeds, the reactant mixture (isobutene-oxygen and argon as carrier gas) is able to introduce active sites onto the carbon surface to the point where they are stabilized for the case of treatment in H-2 and without pretreatment. For the other treatments, N2O and oxygen, the active sites are rearranged and stabilized after a while. It is observed that there is a tendency towards a similar CO/CO2 relationship as measured by TPD, corresponding to a yield of about 7% after 5 h of reaction. (C) 2006 Elsevier B.V. All rights reserved.