| The surface species on Mg3（VO4）2 catalyst prepared by citric acid complexation method,were investigated by X-ray photoelectron spectroscopy（XPS）techniques.In the oxidative dehydrogenation of cyclohexane to cyclohexene,the relationship between the catalytic performance over Mg3（VO4）2 catalyst and the surface species on the catalyst was studied.With the characterization of X ray diffraction（XRD）,scanning electron microscopy（SEM）,FT-IR spectroscopy（FT-IR） and H2-temperature programmed reduction（H2-TPR）techniques,the results indicated that well crystalline structures of Mg3（VO4）2 with a pure phase and a uniform granularity of particles of 110 nm mean size were obtained by the citric acid complexation. XPS spectra also indicated that the lattice oxygen was the main oxygen species among the three oxygen species（e.g.O-,O-2 and O2-） on the catalyst surface.Meanwhile,V4+ and V5+ species were coexisted on the catalyst surface.Although the molar amount of V5+ was a little more than that of V4+,the isolated VO4 species was the main vanadium species on the catalyst surface owing to the segregation of Mg.In the oxidative dehydrogenation of cyclohexane,gaseous oxygen participated in the reaction only after adsorption in other parts of the catalyst and then migrated through the lattice to the active sites by the reoxidation between V4+ and V5+.The characterization and the catalytic results also demonstrated that the catalytic performance was correlated to the lattice oxygen O2-and isolated VO4 species,which was beneficial to the improvement of the selectivity to cyclohexene. |