CATALYSIS OF THE OXIDATION OF ISOBUTYRIC ACID BY VANADYL, COPPER AND MIXED VANADYL-COPPER SALTS OF H-3[PMO12O40] AND H-4[PMO11VO40]

Effects of variable amounts of vanadyl or/and copper counter-ions of t he heteropolyanions [PMo12O40](3-) and [PMo11VO40](4-) on the catalyti c oxidative dehydrogenation of isobutyric acid are reported. For the m olybdophosphate. selectivity to methacrylic acid increases continuousl y with respect to the quantity of vanadyl at the expense of both aceto ne and propene. On the opposite, copper cations does not modify the se lectivity to methacrylic acid. A synergy between the two cations is ob served, which is maximal when they are in equal quantities. For the va nadomolybdophosphate, vanadyl alone or vanadyl and copper have a posit ive effect on the selectivity to methacrylic acid only if there is les s than one metal cation per heteropolyanion. This is related to the tr ansformation of the catalyst during the first stage of the reaction: v anadium is reduced by isobutyric acid and expelled from the Keggin uni t. For high amounts of vanadyl and/or copper cations, decrease of the activity and selectivity to methacrylic acid could be related to the f ormation of oxides.