Potassium effects on kinetics of propane oxydehydrogenation on vanadia-titania catalyst

Oxidative dehydrogenation of propane (ODH) over V2O5/TiO2 and V2O5/TiO2 doped with K was carried out by measuring conversions and selectivities for various feed compositions, contact times and temperatures. The results obtained for both catalysts were interpreted on the basis of the mechanism, in which propene is formed through Eley-Rideal sequence of steps, i. e. without participation of the adsorbed propane species. Kinetic constants (activation energies, pre-exponential factors) for the model of ODH reaction of propane on these catalysts, obtained on the basis of steady-state results, are given. Addition of K to vanadia-titania catalysts leads to the decrease of total combustion of propane and consecutive combustion of propene. It has been found that the direct propane total oxidation is 5divided by9 times lower than that of the consecutive propene oxidation and is almost temperature independent for potassium doped catalyst, whereas it quickly decreases with temperature for a non-doped catalyst. Secondly, the addition of K to a vanadia-titania catalyst decreases the activation energies for propene formation (k(1)), parallel formation of COx(k(3)) and reoxidation of the catalyst (k(OS)). Potassium exhibits a stronger inhibitory effect on the secondary propene combustion, what reflects the lower acidity of V+5 cations modified by the strongly basic alkali oxide species.