Vapour phase oxidation of cyclohexane over CeAlPO-5 molecular sieves

Single sited CeAlPO-5 molecular sieves exhibit activity, selectivity and recyclability. In this study crystalline CeAlPO-5(Al/Ce = 25, 50, 75, 100 and 125) were synthesized hydrothermally in fluoride medium for the selective oxidation of cyclohexane. The framework incorporation of cerium in AlPO-5 and absence of separate ceria phase were verified from XRD analysis. Diffuse reflectance spectral analysis also confirmed the absence of free ceria phase in CeAlPO-5. Electron spin resonance study revealed sorption of molecular oxygen in CeAlPO-5(25). Their catalytic activity was tested in the vapour phase oxidation of cyclohexane in air. Cyclohexanone was obtained as the main product (>90% selectivity). Oxidation of cyclohexane to cyclohexanol and then to cyclohexanone was postulated to occur on the same single oxygen molecule via radical mechanism. The stability, activity and selectivity of the catalysts were verified from time on stream study. It is concluded that CeAlPO-5 may be a convenient catalyst for the selective oxidation of cyclohexane.

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► CeAlPO-5 molecular sieves were synthesized in fluoride medium.
► Cerium retained chemisorbed oxygen in CeAlPO-5 from ambient to high temperature.
► Vapour phase oxidation of cyclohexane over CeAlPO-5 gave high selectivity to cyclohexanone.
► Catalyst was not deactivated by coke formation.