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

Abstract

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.