Template preparation of nanoscale CexFe1−xO2 solid solutions and their catalytic properties for ethanol steam reforming

Abstract

High-surface-area Ce_xFe_1−xO₂ solid solutions about 5 nm in size have been successfully prepared by using ultrahigh surface area carbon material as template and cerium and iron nitrates as oxide precursor. The obtained materials were characterized by means of N₂ physisorption, X-ray diffraction, Raman spectroscopy, electron paramagnetic resonance, transmission electron microscopy and energy dispersive X-ray spectroscopy. The redox and catalytic properties of the nanoscale Ce_xFe_1−xO₂ solid solutions were also evaluated by temperature-programmed reduction and ethanol steam reforming. The results confirm the formation of the nanoscale Ce_xFe_1−xO₂ cubic phase solid solutions with fluorite structure, and the process of Ce⁴⁺ substitution by Fe³⁺ gradually from the surface to the bulk of CeO₂. A small addition of Fe into CeO₂ resulted in a remarkable increase in the surface area and oxygen vacancy concentration, and decreased the particle size of the solid solution, while further Fe addition decreased the surface area and vacancy concentration of the solid solution, and increased the particle size of the solid solution. The results from temperature-programmed reduction show that addition of Fe into CeO₂ not only promotes the reduction of CeO₂, but also increases the oxygen vacancy concentration. The Ce_xFe_1−xO₂ solid solutions show significant catalytic activity toward ethanol steam reforming with above 64% selectivity to hydrogen at 550 °C. The Ce_0.90Fe_0.10O₂ sample presents superior activity and selectivity to hydrogen compared to CeO₂, Fe₂O₃ and other solid solutions. The findings show that the carbon template route may be of great potential in synthesis of other solid solutions, and the Ce_xFe_1−xO₂ solid solutions are potential materials for oxygen storage and ethanol steam reforming.