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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. H2-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. Among cerium- and iron-based mixed oxides, the Ce0.8Fe0.2O2 combination catalyst exhibited better activity for vanillyl alcohol oxidation with complete conversion and 98% selectivity to vanillin. [ABSTRACT FROM AUTHOR]

Mesoporous ceria–cobalt (Ce0.9Co0.1O2, Ce0.8Co0.2O2, and Ce0.7Co0.3O2) mixed oxides, ceria (CeO2), and cobalt oxide (Co3O4) catalysts were prepared through modified template-assisted method and employed in oxidation of ethylbenzene with molecular oxygen (O2) without solvent and additives. Prepared catalysts were characterized by various physicochemical characterization techniques. The XRD results showed the formation of solid solutions in cobalt-doped ceria samples. The XPS results indicated the presence of more Ce3+ ions and surface adsorbed oxygen. H2-TPR profiles revealed a remarkable improvement in the redox behavior of ceria with the doping of cobalt into the ceria lattice. TEM and N2 adsorption studies showed mesoporous nature of materials. Among the prepared catalysts, Ce0.9Co0.1O2 showed far better activity for oxidation of ethylbenzene with 60% conversion and 87% selectivity toward acetophenone. This is attributed to facile redox behavior, more surface adsorbed oxygen species, and larger surface area of the catalyst and considered as crucial factors to improve the catalytic activity. Mesoporous ceria–cobalt (Ce0.9Co0.1O2) mixed oxide efficiently catalyzed the aerobic oxidation of ethylbenzene to acetophenone without solvent with good conversion and selectivity. [ABSTRACT FROM AUTHOR]