PERFORMANCE OF GAMMA-ALUMINA-SUPPORTED WACKER CATALYSTS IN THE OXIDATION OF 1-BUTENE

Heterogeneous Wacker oxidation catalysts, consisting of a palladium co mplex supported on a monolayer vanadium pentaoxide on gamma-alumina, h ave been tested in the oxidation of 1-butene to butanone. The steady-s tate activity of the catalysts is found to be 0.2 mmol butanone per mo l Pd per second. The oxidation of 1-butene over the heterogeneous cata lysts runs analogously to the homogeneous Wacker oxidation. The stabil ity of the catalysts depends on the structure of the vanadium pentaoxi de overlayer. Continuous reoxidation of Pd-0 is possible only if the v anadium pentaoxide is present in a molecularly dispersed overlayer and does not proceed when crystalline vanadium pentaoxide is used as a su pport. Temperature-programmed reduction measurements have shown that t his is the result of the lower reducibility of the crystalline vanadiu m pentaoxide as compared to supported vanadium pentaoxide monolayers. The stability of the supported catalysts depends strongly on the vanad ium pentaoxide coverage; due to sintering of the vanadium pentaoxide o verlayer, a rapid deactivation is observed for catalysts with coverage s below 1.5 V/nm(2). Sintering is probably caused by the poor interact ion of the partly reduced vanadium pentaoxide layer with gamma-alumina . X-ray photoelectron spectroscopy analysis revealed that under the re action conditions 35% of the vanadium pentaoxide is present as V4+ and 50% of the palladium is present as Pd-0.