RELEVANCE OF A GLASSY NANOCRYSTALLINE STATE OF MO4VO14 FOR ITS ACTIONAS SELECTIVE OXIDATION CATALYST

The oxide Mo4VO14, in its active state, is a partly reduced material w ith an ''amorphous'' structure. Temperature-programmed methods reveal that the active lattice oxygen gives rise to a desorption signal at 50 0 K, which is at the lower end of the temperature window for activity in the selective oxidation of n-propanol. The phase is metastable with respect to oxidative crystallisation into isotropic crystals of the t itle structure occurring at 781 K. Photoemission revealed in the zero bandgap semiconductor oxide of the amorphous state the MO6 octahedra t o be distorted and the oxygen pumping activity to be related to oxidat ion-reduction cycles of metal d-states situated close to the Fermi ene rgy. Structural studies by XRD and HRTEM showed that the oxygen-pumpin g state is a nanocrystalline modification of the title structure. The relation of the structural motif to the catalytic function is discusse d for this compound and for the whole family of systems in the framewo rk of the theory of glass formation.