Tin-Based Keggin-Type Phosphomolybdate and Silicomolybdate as Catalysts for the Green Synthesis of Adipic Acid

Abstract

The catalytic activity of two series of Keggin-type salts of formula Cs4-xSnxSiMo12O40 (x: 0.5 and 1) and Cs3-xSnxPMo12O40 (x: 0.25-1) was examined in the liquid phase cyclohexanone oxidation to adipic acid (AA) in the solvent absence. The materials were prepared and characterized by FTIR, UV-Vis and SEM. The adipic acid synthesis was carried out at 90°C in presence of hydrogen peroxide (30%), a green oxidant that produces only water as by-product. The effects of catalyst/substrate molar ratios and time reaction on dipic acid yields were studied. The results of this study showed that the POM-H2O2 system was found to be efficient for the production of adipic acid from the oxidation of cyclohexanone and the yields were closely dependent on the operating conditions. The highest AA yield (55%) was obtained with Cs2Sn0.5PMo12O40 using a catalyst/substrate molar ratio of 3.7×10-3 and a reaction time of 20h.