Dawson-type POMs series of formula alpha- and beta-K6P2W18O62 isomers, alpha 1- and alpha 2-K6P2Mo5W13O62 isomers, alpha-K6P2Mo6W12O62 isomer and alpha 1-K7P2Mo5VW12O62 isomer, have been used as catalysts for the liquid phase oxidation of cyclohexanol, cyclohexanone and cyclohexanol/cyclohexanone mixture to form adipic acid in presence of hydrogen peroxide without solvent, without phase-transfer agents and without adding acid. P-31 NMR spectroscopy of different POMs after cyclohexanol oxidation showed the formation of new active species that can be attributed to "peroxo-POMox" form. An adipic acid yield of 69% was obtained from the oxidation of a mixture of cyclohexanol (50%) and cyclohexanone (50%) with alpha-K6P2Mo6W12O62 isomer. (C) 2016 Published by Elsevier B.V.