Study of surface and lattice oxygen atoms over magnesium vanadate phases by isotopic exchange with C18O2

Abstract

Different magnesium vanadate phases, V-Mg-O phases (α- Mg2V2O7, Mg3V2O8 and β- MgV2O6), MgO and V2O5 oxides have been compared with respect to their surface properties and their oxygen exchange capacities with C18O2 in the gas phase. By temperature- programmed desorption of carbon dioxide, the absence of any basic impurities (i.e., MgO or residual oxidised K impurities resulting from the preparation) has been evidenced on the surface of magnesium vanadate phases. This demonstrates that the catalytic properties of the magnesium vanadate phases for oxidative dehydrogenation of propane as previously studied cannot be explained by synergetic effects due to the presence of any basic component impurities since they are absent in this case. While on MgO an important surface exchange process occurs with C18O2 of the gas phase, this exchange is very low on V2O5 and pure V-Mg-O phases. A comparison of the different magnesium vanadate phases in the same experimental conditions indicates that the α-Mg2V2O7 phase (which exhibited the highest selectivity for oxidative dehydrogenation of propane to propene) shows the lowest lattice oxygen exchange with C18O2 of the gas phase. This is another specificity of this phase.