OXIDATION OF CYCLOHEXANOL ON PHOSPHOTUNGSTIC ACID ANION INTERCALATED LAYERED DOUBLE HYDROXIDES WITH AQUEOUS H₂O₂ AS OXIDANT

The layered double hydroxides (LDH) of Mg₂AlNi and Mg₃Al pillared by Keggin-type phosphotungstic acid anion (POM), i.e. Mg₂AlNi-POM LDH and Mg₃Al-POM LDH were synthesized by an ion-exchange method. The synthesized POM intercalated LDH compounds were characterized using various techniques such as FTIR, XRD, TGA and BET. The observed results show that the obtained catalysts retain the layer structure of LDH. Compared with the binary Mg₃Al-POM LDH, the ternary Mg₂AlNi-POM LDH catalyst indicated a higher thermal and chemical stability. The catalytic activity of the resulting LDH-POM was also assessed in the green oxidation of cyclohexanol with aqueous H₂O₂ as an oxidant. The Mg₂AlNi-POM LDH showed a much higher conversion and selectivity for cyclohexanone than the corresponding Mg₃Al-POM LDH catalyst.

Keywords:
layered double hydroxides; heterogeneous catalysis; phosphotungstic acid; ion-exchange; oxidation