PALLADIUM SALTS OF HETEROPOLYACIDS AS CATALYSTS IN THE WACKER OXIDATION OF 1-BUTENE

Palladium salts of heteropolyacids (PdHPAs) of the Keggin series Ha H3 +nPVnMo12-nO40 supported on silica, have been used successfully as cat alysts in the gas-phase Wacker oxidation of 1-butene. In such catalyst s the palladium reaction centre and the redox component are combined i n one complex. At 343 K and atmospheric pressure a high initial butano ne yield of more than 0.2 g g(cat)(-1) h(-1), in combination with a ve ry high butanone selectivity of more than 98%, can be obtained. In the steady state, the activity of the catalyst is more than a factor of 1 0 lower than the initial activity, due to slow reoxidation of reduced palladium-heteropolyanion complexes. The rate of reoxidation depends o n the composition of the HPA, the palladium loading, and the reaction conditions. The reaction order of 0.5 in the O-2 partial pressure indi cates the dissociation of dioxygen to be rate determining. The degree of hydration of the HPA appears to be important for the activity and s tability of the catalysts. Spent catalysts can be regenerated by an ox idation treatment in air at temperatures around 525 K. Regeneration be comes more difficult with high palladium loading of the catalyst. (C) 1995 Academic Press, Inc.