Oxidation of vanillyl alcohol to vanillin over nanostructured cerium-iron mixed oxide catalyst with molecular oxygen

摘要

A series of cerium-iron mixed oxides (Ce0.9Fe0.1O2, Ce0.8Fe0.2O2, and Ce0.7Fe0.3O2), pure CeO2, and Fe2O3 catalysts were prepared by a facile coprecipitation method. Synthesized catalysts were characterized by various physicochemical techniques and evaluated for oxidation of vanillyl alcohol to vanillin with molecular oxygen as the oxidant. XRD results suggested the formation of solid solutions in Fe-doped ceria mixed oxides. BET analysis revealed an increase in the surface area and Raman results showed a highest amount of oxygen vacancies in the Fe2O3-doped ceria samples. TEM and XRD results confirmed the average particle size of ceria-iron mixed oxides is in the order of 5-7 nm. XPS analysis revealed the existence of Ce in +3, +4 and Fe in +2, +3 oxidation states on the surface of the mixed oxides. H-2-TPR studies confirmed a decrease in the reduction temperature of ceria after incorporation of Fe2O3. Among all the catalysts investigated, the Ce0.8Fe0.2O2 showed better activity for vanillyl alcohol oxidation with 91% conversion and 99% selectivity to vanillin. It may be due to strong interaction between CeO2 and Fe2O3 in the mixed oxides which leads to an increased BET surface area and oxygen vacancies and a decrease in the reduction temperature. The reaction parameters such as temperature, time, oxygen pressure, and the amount of catalyst were also optimized. With the optimized best reaction conditions, a complete conversion of vanillyl alcohol with 98% selectivity to vanillin is also achieved. Nature of solvent showed a remarkable effect on the vanillyl alcohol conversion without affecting the selectivity to vanillin. [GRAPHICS] .