Transient kinetic modeling of the oxidative dehydrogenation of propane over a vanadia-based catalyst in the absence of O 2

Abstract

The oxidative dehydrogenation of propane in the absence of O 2 over the vanadia-based EL10V1 Eurocat catalyst is investigated in a Temporal Analysis of Products (TAP) reactor over a completely oxidized catalyst and at reduction degrees up to 0.47. Only CO 2 and propene are detected as reaction products at temperatures from 723 to 823 K. The reduction of the catalyst with propane occurs through the formation of propene, the consecutive oxidation of propene to CO 2 and the parallel total oxidation of propane. Four elementary reactions are considered as kinetically relevant: (1) the methyl C–H bond dissociation in propane during the formation of propene, (2) the methylene C–H bond breaking in propane to form surface isopropoxide, which finally transforms into CO 2, (3) the C C double bond breaking in propene in the formation of surface formate species and (4) the oxidation of these surface formate species to CO 2. The formation of propene via (1) is favored at the investigated conditions, while CO 2 is largely produced by the sequential oxidation of propene (3–4), and to a lesser extent by the parallel route of the direct total oxidation of propane (2). Both the oxidative dehydrogenation and the direct total oxidation of propane reaction paths involve only one kinetically relevant step, (1) respectively (2), with an activation energy of 36 and 74 kJ mol −1 over a completely oxidized catalyst and of 15 and 40 kJ mol −1 over a partially reduced catalyst. The further oxidation of propene involves two kinetically relevant steps (3–4) of which only the double bond breaking (3) is slightly activated (5 kJ mol −1) over the completely oxidized catalyst, while both steps are non-activated when the catalyst is partially reduced.