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S. Buhr, K. Föttinger:
"Pd-VANADIUM OXIDE SUPPORTED ON ALUMINA FOR LOW TEMPERATURE SELECTIVE OXIDATION OF ETHYLENE";
Poster: 15. Österreichische Chemietage 2013, TU-Graz, Graz, Österreich; 09-23-2013 - 09-26-2013; in: "15. Österreichische Chemietage - Programm", (2013), PO-148.

Acetaldehyde is used in chemical industry e.g. as an intermediate of acetic acid, fuel mixtures, cosmetics and in food industry. The common synthesis by homogenous Wacker-reaction has, however, several disadvantages: high corrosivity of HCl in combination with oxygen, chlorinated byproducts and the difficult separation of solved acetaldehyde from reaction solution. This requires the development of a heterogeneous catalyst-system, application of low reaction temperatures, high selective and long lasting catalyst.

The investigated catalyst was prepared by impregnation of alumina with ammonium methavanadate at pH 4 followed by pre-calcination at 533 K. It forms a monolayer of vanadium oxide with special chemical properties. Finally, Pd nanoparticles were precipitated from an organic palladium acetate solution, followed by calcination at 533 K. Catalytic tests were performed in a plug flow reactor feeded by water, ethylene and oxygen in different ratios with followed by GC and MS analysis. The interaction between palladium, vanadium species on alumina and the reactant ethylene was studied after different pretreatments like oxidation, reduction and exposure to water vapor at
different temperatures. Investigation about the structure of catalyst has been performed by synchrotron based EXAFS. Water was found to be an essential compound in this reaction. A correlation was observed between water exposure and selectivity. No acetaldehyde was formed at the beginning of the reaction at 363 K and concentration increases to 94% after two hours on stream (ratio H2O:C2H4:O2 = 8:3:33). At the same time, the signal m/z = 18 increased steeply, indicating the saturation of the catalyst by water. Additional tests were carried out to confirm shorter activation times by higher water partial pressures and lower amounts of catalyst. Without water, the catalyst shows no selectivity for acetaldehyde formation.