Synthesis and characterization of Fe/CeO2 catalysts: Epoxidation of cyclohexene

Oxidation of cyclohexene using aqueous hydrogen peroxide (30%, v/v) over iron–cerium oxide (x%Fe/CeO2; x = 0, 2, 5, 10 and 20 mol%) prepared by co-precipitation was conducted in this study in order to assess the performance of the catalysts of varying composition, and catalytic activity and product selectivity were found to strongly depend on catalyst composition, acidity and reducibility. The effects of varying the catalyst composition, reaction temperature and solvent were investigated. Cyclohexene epoxide and 1,2-cyclohexanediol were found to be the main reaction products, along with small amounts of other oxygenated products. A high cyclohexene conversion rate of 99 mol% and an epoxide selectivity of 98 mol% were observed over 5%Fe/CeO2 at 100 °C. The catalysts were characterized using various techniques and measures, including BET surface area, XRD, DRS UV–vis, potentiometric titration for acidity measurement, and XPS. XRD showed the formation of iron–cerium oxide solid solutions with cerianite cubic structures for all catalysts except FC4, and the DRS UV–vis results further indicated the formation of solid solutions. Analysis of Raman spectra revealed the presence of aggregate iron oxide species in case of 20%Fe/CeO2 catalyst. TPR revealed enhancement of the reducibility of the ceria upon Fe doping, and the potentiometric titration results showed an increase in the number of acidic sites with increasing iron content up to 5% and a decrease thereafter. TPR and XPS analyses revealed the presence of highly dispersed Fe species in the 2%Fe/CeO2 and 5%Fe/CeO2 samples, whereas for the 10%Fe/CeO2 and 20%Fe/CeO2 catalysts, aggregates of Fe species were observed. Catalytic activity was found to be correlated with the composition and acidic properties of the catalyst.

The activity of iron–cerium oxide catalysts in cyclohexene oxidation using aqueous H2O2 (30%, v/v) was investigated. The highest cyclohexene conversion (99 mol%) and epoxide selectivity (98 mol%) rates were observed using 5%Fe/CeO2 at 100 °C: this greater activity and selectivity was attributed to monolayer dispersion of the Fe species and enhanced reducibility of the catalyst.Figure optionsDownload high-quality image (32 K)Download as PowerPoint slide