PALLADIUM SALTS OF HETEROPOLYANIONS AS CATALYSTS IN HETEROGENEOUS WACKER OXIDATION OF 1-BUTENE

Palladium salts of heteropolyanions, of the Keggin-series H3+nPVnMo12- nO40, supported on silica, have been successfully applied as catalysts in the gas-phase Wacker oxidation of 1-butene. In such catalysts the palladium reaction centre (Pd2+) and the redox component (HPA) are com bined in one complex. At 343 K and atmospheric pressure a high initial yield of more than 0.16 g butanone/g of catalyst/h, in combination wi th a very high butanone selectivity of more than 98%, can be obtained. In the steady-state, the activity of the catalysts is more than a fac tor ten lower than initially, due to slow reoxidation of reduced palla dium-heteropolyanion complexes. The rate of reoxidation increases with increasing number of vanadium atoms per Keggin unit. Under reaction c onditions the PdHPAs are reduced by approximately five electrons per K eggin unit. DRIFT spectra of the used catalyst show that the Keggin un it is not affected by this reduction and that no oxygen is removed fro m the HPA. The DRIFT spectra also show that the reduction and the reox idation at reaction temperature in the absence of water is fast in com parison with the standard reaction conditions.