Vapor-phase oxidation of cyclohexane over supported Fe-Mn catalysts: in situ DRIFTS studies

Alumina-supported Fe-Mn oxide catalysts were synthesized by the incipient wetness impregnation method. The catalysts were characterized using various characterization techniques such as surface area, XRD, H2-TPR, and Raman spectral analysis. The adsorption (Cy-H, CO2) and oxidation of cyclohexane (Cy-H) were conducted by considering the in situ DRIFTS studies. The iron-impregnated catalyst possessed a higher surface area than the manganese-impregnated catalyst. The manganese-oxides remained dispersed in the support and the iron oxides remained in the crystalline phase in the catalyst 20Fe50Mn50/Al2O3. The reduction temperature of the catalyst decreased due to the synergistic effects of the iron-manganese oxides. The catalyst 20Fe50Mn50/Al2O3 was the most active for the vapor-phase oxidation of cyclohexane at 220 °C and 1 atm pressure. The cyclohexanolate, phenolate, and unidentate carbonate species were observed during the study. The lattice oxygen of the catalyst activates the C-H bond of cyclohexane for the formation of reactive-cyclohexanol, further decomposed by dehydration and dehydrogenation.