Catalysis Letters, Vol.144, No.4, 702-710, 2014
Wacker-Oxidation of Ethylene Over Pillared Layered Material Catalysts
This paper concerns the Wacker oxidation of ethylene by oxygen in the presence of water over supported Pd/VOx catalysts. High surface area porous supports were obtained from layer-structured materials, such as, montmorillonite (MT), laponite (smectites), and hydrotalcite (layered double hydroxide, LDH) by pillaring. Before introduction of Pd, supports MT and LDH were pillared by vanadia. The laponite was used in titania-pillared form (TiO2-LAP) as support of Pd/VOx active component. Acetaldehyde, acetic acid and CO2 were the products with yields and selectivities, depending on the reaction conditions and the properties of the applied catalyst. Under comparable conditions the pillared smectite catalysts gave higher AcH yield than the pillared LDH catalyst. UV-Vis spectroscopic examination suggested that the pillared smectites contained polymeric chains of VO4, whereas only isolated monomeric VO4 species were present in the pillared LDH. The higher catalytic activity in the Wacker oxidation was attributed to the more favorable redox property of the polymeric than of the monomeric vanadia. The V3+ ions in the polymeric species can reduce O-2 to O2- ions, whereas the obtained V5+ ions are ready to pass over O to Pd-0 to generate PdO whereon the oxidation of the ethylene proceeds.
Keywords:Wacker oxidation;Supported Pd/VOx catalyst;Pillared layered materials;UV-Vis spectroscopy H-2-TPR