Adipic acid (AA) was synthesized from the oxidation of cyclohexanol (-ol), cyclohexanone (-one) and cyclohexanol/cyclohexanone (-ol/-one) mixture over a series of H3-2xCoxPMo12O40 (x: 0.0-1.5) Keggin-type polyoxometalates as catalysts in the presence of hydrogen peroxide (30 %) under mild conditions (90 A degrees C, 20 h) and in solvent free. The heteropolysalts were prepared from H3PMo12O40 and Ba(OH)(2) using the cationic exchange method and characterized by Infrared and diffuse reflectance UV-Vis spectroscopies, X-ray diffraction and TG analyses. The catalytic tests showed that salts are more efficient than the corresponding heteropolyacid and among the H3-2xCoxPMo12O40 (x: 0.25-1.5) series, H1Co1PMo12 exhibits the highest AA yield for whole substrates, with ca. 76, 53 and 43 % from oxidation of -one, -ol and -ol/-one, respectively.