MODIFICATIONS OF THE AGMO3P2O14 CATALYST IN THE OXIDATION OF PROPANE

The catalytic performances in the oxidation of propane of the AgMo3P2O 14 catalyst are quite good leading to 70% of propene selectivity at 7% of propane conversion. We have checked that, before reaction, results of XANES and EXAFS obtained at the Mo K-edge (19999 eV) confirm those obtained by X-ray spectroscopy (oxidation state and Mo number of oxyg en neighbour of 5.66, Mo=O bond length=1.72 Angstrom). After reaction, we have shown that the catalyst is partially reduced (5.66-->5.2), th e number of oxygen atoms increases to 6 and the mean molybdenyl bond l ength decreases (1.68 Angstrom) which is in agreement with the variati on of this bond length with the oxidation state of the molybdenum in m olybdenum phosphates. XPS measurements also confirmed a partial reduct ion of molybednum species and showed a migration of the silver cation to the surface, certainly participating to the surface stabilization. Moreover, a correlation between the catalytic activity and the modific ation of the catalyst is made showing that an equilibrium between Mo-V and Mo-VI species in the catalyst leading to the avrerage oxidation s tate of molybdenum of 5.2 seems to be very important.