Synthesis, characterization and catalytic properties in oxidation of styrene over cobalt-substituted microporous nickel phosphate CoVSB-5

Cobalt-substituted microporous nickel phosphates VSB-5 (CoVSB-5s) employing triethylamine as an organic template have been synthesized under hydrothermal conditions. The incorporation of cobalt (II) into the framework of VSB-5 has been characterized by powder X-ray diffraction pattern, diffuse reflectance UV-vis spectroscopy, ICP-AES elemental analysis and IR spectroscopy methods. The molar ratio of Co/(Co + Ni) incorporated into the framework of CoVSB-5 is up to 20.01 mol% without changing the structure of the VSB-5 and no other phases produced. The cobalt ions coordinated in the architecture of the as-synthesized CoVSB-5 are located in octahedral and tetrahedral sites. After calcination in air at a temperature above 300 degrees C. the related absorption bands from UV-vis spectrum which are ascribed to Co(II) in a tetrahedral environment shift to high wavelengths at 510 and 586 nm and the octahedral Co(II) turns into tetrahedral Co(II) due to dehydration under calcination conditions. CoVSB-5 powders have a little lower crystallinity than that of pure VSB-5. The crystallinity reduces from 82% for 5CoVSB-5 to 53% for 20CoVSB-5 using VSB-5 as standard. The catalytic properties of those CoVSB-5s are demonstrated by the heterogeneous catalytic oxidation of styrene with dilute hydrogen peroxide. The conversion of styrene over CoVSB-5s is higher than that of VSB-5 and the primary product of the oxidation reaction is benzaldehyde. The influence factors of the catalyst's calcined condition, reaction temperature and cobalt contents on the catalytic activity have been investigated. (c) 2005 Elsevier Inc. All rights reserved.