Selective oxidation of cyclohexane over Co-APO-5: Effects of solvent and modification method on the catalytic performance

A series of Co-APO-5 molecular sieves were prepared and used as the catalysts in the selective oxidation of cyclohexane; the effects of solvent and modification method on the catalytic performance of Co-APO-5 were investigated. The results illustrated that polar solvents containing π-bonds are favorable for the oxidation reaction and the conversion of cyclohexane increases with the increase of solvent polarity. The introduction of Si and F leads to a decrease of the tetrahedral cobalt content in the Co-APO-5 framework. However, introducing F can improve the crystallinity of Co-APO-5, whereas adding Si may promote the oxidation and reduction of cobalt species and then enhance the catalytic activity in oxidation. In general, the activity of Co-APO-5 catalysts is related to the content of tetrahedral cobalt in the framework, suggesting that the framework Co(II) is probably the catalytically active species for the oxidation of cyclohexane.