Liquid-phase epoxidation of cyclooctene with O₂ over CoO_x/SiO₂ catalyst prepared by sol–gel method

A series of CoO_x/SiO₂ catalysts has been prepared by the sol–gel method and characterized with XRD, N₂ adsorption/desorption, diffuse reflectance UV–vis spectroscopy, Raman spectroscopy as well as TPR techniques. This type of material is highly active and selective for the epoxidation of cyclooctene with atmospheric molecular oxygen. Although all the catalysts attained at different pH values are amorphous, their catalytic activities are remarkably different because the pH values influence not only the coordination state of Co species but also the textural structures of the prepared catalysts, in which CoO_x/SiO₂ obtained at pH below 5 is highly active and selective for the epoxidation of cyclooctene with atmospheric O₂. The prepared CoO_x/SiO₂ catalysts are highly stable and can be recycled at least four times without significant loss of activity and selectivity.