The selective oxidation of cyclohexane to cyclohexanol, cyclohexanone and adipic acid using molecular oxygen as the oxidant and at moderate temperatures (403 K) has been investigated over four different cobalt-containing aluminophosphate (AlPO) molecular sieves. There is a correlation between catalytic activity and the fraction of (framework) Co(II) ions that is first oxidised to Co(III) in air. CoAlPO-36 (pore aperture 6.5 x 7.5 Angstrom) exhibits significant activity for the oxidation of cyclohexane in contrast to CoAlPO-18, which, although it has the highest fraction of oxidisable cobalt, does not show any activity chiefly because of its smaller pores.