Adipic acid is a dicarboxylic acid of great industrial importance

mainly used in the production of nylon-6

6 and polyurethane. The use of nitric acid as an oxidant in the industrial production of adipic acid poses significant carbon footprint to the environment. Clean adipic acid synthesis methods using a heterogeneous catalyst with H

2

O

2

as oxidant and water as solvent have potential advantages of low catalyst cost

easy synthesis and recovery

cleanness and environmental protection. In this work

hexagonal mesoporous silicate materials were synthesized by a sol-gel method and evaluated for cyclohexanol/cyclohexanone oxidation to adipic acid. The physical and chemical properties of Fe-HMS were characterized by XRD

HR-TEM

BET and UV-Vis. The experimental results showed that Fe-HMS materials show pore sizes ranging from 2-3 nm. W- and Mo-based polyoxometalates were also evaluated and compared to the Fe-based HMS catalysts. To improve the adipic acid yield

the influence of the transition metal as well as the effect of metal loading

reaction temperature and catalyst amount on the catalytic performances of Fe-HMS have been inves

tigated in details. When Si/Fe atomic ratio = 100

Fe-HMS catalyst shows the highest activity

with a cyclohexanone conversion of 92.3% and adipic acid selectivity of 29.4%. The reaction pathway of cyclohexanone oxidation was further proposed based on experimental data.