SOME SELECTIVITY CRITERIA IN MILD OXIDATION CATALYSIS V-P-O PHASES IN BUTENE OXIDATION TO MALEIC-ANHYDRIDE

The VPO system, active and selective in the oxidation of butene into maleic anhydride, provides an additional example of a mild oxidation catalyst, where the catalytic properties are shown to depend strongly on the intrinsic properties of the constituent phases. The structural and spectroscopic properties of VOPO4 and (VO)2P2O7, whose presence is necessary to obtain a substantial selectivity in the range P:V = 0.5:1 to 2:1, have been examined in connection with those of V2O5. Since electron diffraction patterns obtained on spent catalyst samples revealed the existence of microdomains, these results have been compared with the hysteresis loop found in kinetic and thermodynamic experiments: The excited atoms, which are located on each side of the coherent boundaries formed in steady state conditions, are assumed to influence strongly the activity and selectivity. © 1979.