Abstract—Cs-and tetrabutyl ammonium (TBA) salts of Cuand Mn-polyoxotungstates were synthesized. They were loaded on MCM-41 support (by impregnation method in 20-30 wt%) to increase surface area of the catalysts. The supported catalysts were characterized by inductive coupled plasma emission (ICP), Fourier-Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD) and nitrogen adsorption-desorption. Their catalytic activities for oxidation of cyclohexane were compared using green oxidant H2O2 under mild reaction conditions. The oxidized products are cyclohexanol and cyclohexanone. The activities follow the order: TBA-CuPOM/MCM > TBA-MnPOM/MCM > Cs-CuPOM/MCM > Cs-MnPOM/MCM. The Mn containing catalysts gave higher cyclohexanone selectivity than Cu containing catalysts. The Cs salt catalysts can be reused without loss of activity due to its insolubility in the reaction medium. The 30wt%Cs-CuPOM/MCM and 30wt% Cs-MnPOM/MCM gave comparable activity (16-17 % conversion with 75-76 %selectivity using H
2O
2/cyclohexane mole ratio = 4 at 80 ˚C in 12 h. The oxidation reaction appears to be radical process, since it was inhibited in the presence of radical scavenger.
Index Terms—Polyoxotungstate, cyclohexane, oxidation, MCM-41.
Wimonrat Trakarnpruk is with the Department of Chemistry, Faculty of Science, Chulalongkorn University, Thailand (e-mail: wimonrat.t@chula.ac.th).
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Cite: W. Trakarnpruk, "Heterogeneous Catalytic Oxidation of Cyclohexane with H2O2 Catalyzed by Cs- and TBA-salts of Cu- and Mn-Polyoxotungstates on MCM-41," International Journal of Chemical Engineering and Applications vol. 6, no. 2, pp. 120-124, 2015.
