Abstract: Cobalt substituted molecular sieves (CoAPO-5) with different cobalt content were synthesized
hydrothermally. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), thermogravimetric(TG) analysis, and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results indicated that cobalt was incorporated into the framework of AlPO4-5 molecular sieves and the as-synthesized CoAPO-5 was highly crystalline and pure. There is a good linear relationship between the crystal cell parameters and the cobalt content in CoAPO-5. The UV-Vis intensity of Co(II) is significantly reduced through calcinations as Co(II) is oxidized to Co(III) during calcinations. The as-synthesized CoAPO-5 exhibited excellent performance for the oxidation of cyclohexane using molecular oxygen as oxidant. The conversion of cyclohexane and the ratio of cyclohexanol to cyclohexanone in the product increased as the cobalt content increased in CoAPO-5. At nCo/nP=0.04 the conversion of cyclohexane was 23.3%.

Key words: Aluminophosphate molecular sieves, Hydrothermal synthesis, Cobalt incorporation, Cyclohexane oxidation, Cyclohexanone