Influence of reaction conditions on catalyst composition and selective/non-selective reaction pathways of the ODP reaction over V2O3, VO2 and V2O5 with O2 and N2O

The effect of reaction conditions on catalytic performance and composition of individual vanadium oxides (V2O3, VO2, and V2O5) in the oxidative dehydrogenation of propane (ODP) at 773 K was investigated by means of steady-state catalytic experiments with 16O2, 18O2 and N2O in combination with in situ XRD, in situ UV–vis, and ex situ XPS analysis. Steady-state product selectivities over these oxides are not determined by their initial (fresh) composition but a new catalyst composition created under the reaction conditions. At similar degrees of propane conversion, this steady-state composition depends on the oxidizing agent (O2 or N2O). For an oxygen (C3H8/O2 = 2) containing mixture (X(C3H8) < 5%, X(O2) < 10%), vanadium species are stabilized in penta- and tetravalent oxidation states, with the former being the main one. In the presence of N2O, the oxidation state of vanadium is lower under controlled degrees of propane and oxidant conversion (X(C3H8) < 5%, X(N2O) < 10%). It is suggested that the difference in the oxidation state of vanadium with O2 and N2O is related to the lower ability of N2O for reoxidation of reduced VOx species as compared to O2. Moreover, individual vanadium oxides poorly performing with O2 become selective in the ODP reaction using N2O. This improving effect of N2O on the catalytic performance of vanadium oxides is related to the degree of catalyst reduction under reaction conditions and to the nature of oxygen species originated from O2 and N2O.

Catalytic performance of V2O5, VO2 and V2O3 in the ODP reaction is determined by a new catalyst composition created under the reaction conditions. This steady-state composition depends on the oxidizing agent (O2 or N2O). The oxidation state of vanadium in V2O5, VO2 and V2O3 reduces from +5 to ca. +4, when O2 is replaced by N2O. This is due to the lower oxidizing ability of N2O as compared to O2. Moreover, propene selectivity is significantly improved in the presence of N2O. This improving effect of N2O is related to the degree of catalyst reduction and to the nature of oxygen species. Figure optionsDownload as PowerPoint slide