Bulk structure and catalytic properties of mixed Mo-V-Sb-Nb oxides for selective propane oxidation to acrylic acid

摘要

The bulk mixed Mo-V-Sb-Nb-O catalysts, which are a candidate catalytic system for the selective oxidation of propane to acrylic acid, were invstigated to elucidate the bulk structure and catalytic behavior of these complex materials These ,oxed pxodes were preared via a redox reaction between V~5+ and Sb~3+ in the presence of Mo~6+ and Nb~5+ and characterized by potentiometric titrations, XRD, Raman spectroscopy, electron microscopy(TEM),and bulk elemental analysis. A potentiometric titration method was used to determine concentrations of metal cations in various oxidation states. XRD and Raman spectroscopy identified Mo_6 V_9 O_40,MoO_3,SbVO_4,and a Nb-stabilized defect phase of a V-rich molybdate as the major phases present. Eicroscopy illustrated the heterogeneity of the bulk oxide phases present in the model Mo-V-Sb-Nb-O system on the submicron scale. MoO_3 comprised the bulk of this mixed metal oxide system, while the surface region of these model catalysts containde mixed Mo-V-Sb-Nb oxides. The rutile SbVO_4 phase was inefficient in propane oxidation to acrylic acid, while mixed Mo-V-Nb oxides were capable of producing acrylic acid at~20 mol% yield.