Preparation Of Oxides With High Surface Area By Carbon Template Route And Their Catalytic Properties

Nanostructured oxides with high surface area show excellent performance and great potential applications because of size effects and surface effects. Facial and controlled preparation of those materials is desired. The carbon template route is a facile route for the preparation of inorganic materials and allow an effective control of the particle size by adjusting the conditions of synthesis.In this work, nanoscale CeO₂, Fe₂O₃, ZnO, NiO, Ce_xFe_1-xO₂, and Ni_xZn_1-xO have prepared via carbon template route, in which activated carbon was used as hard template and metal nitrates were used as oxide precursors. The carbon template route involves two steps: the impregnation of ultrahigh surface area carbon materials with the metal nitrate solutions and the bum-off to remove the carbon templates in the controlled oxidation atmosphere. These oxides were characterized by 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. Reactive adsorption desulfurization was also carried out in order to investigate the adsorption properties of ZnO and Ni_xZn_1-xO.In the case of Ce_xFe_1-xO₂ solid solutions, the results confirm the formation of the nanoscale Ce_xFe_1-xO₂ solid solutions with cubic phase with fluorite structure, and the process of Ce⁴⁺ substitution by the Fe³⁺ gradually from surface to bulk of CeO₂. A small addition of Fe into CeO₂ resulted in a remarkable increase in the surface area and oxygen vacancy concentration, and decease the particle size of the solid solution, while further Fe addition decreases the surface area and vacancy concentration of the solid solution ,and increases the particle size of the solid solution. This may be due to that the formation of the solid solution makes the removal of carbon templates more facile and that Fe³⁺ in CeO₂ stabilizes nanocrystal of the solid solution. The results from temperature-programmed reduction show that addition of Fe into CeO₂ does not only promote the reduction of CeO₂, but also increase the oxygen vacancy concentration. The Ce_xFe_1-xO₂ solid solutions show a significant catalytic activity toward ethanol steam reforming with above 64% selectivity to hydrogen at 550 888888 . The Ce_0.90Fe_0.10O₂ sample presents the superior activity and selectivity to hydrogen compared to CeO₂, Fe₂O₃ and the other solid solutions. The findings exhibit 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 with oxygen storage and ethanol steam reforming.Nanostructured ZnO and Ni_xZn_1-xO have also been prepared via carbon template route. The effects of high surface area carbon template, concentration of zinc nitrate and calcining temperature were invesigated. It was found that high surface area carbon template, low concentration of zinc nitrate and low calcining temperature is benefited to the formation of ZnO with small particle size. ZnO with 10-20 nm and 50 m²/g can be obtained at the optimized conditions. The properties of the ZnO and Ni_xZn_1-xO samples were tested in reactive adsorption desulfurization, but low adsoptive capability were obtaied. This may be due to low adsorption temperature and deffect disappearance in ZnO and Ni_xZn_1-xO. However, ZnO supported on activated carbon shows higher capability than ZnO and carbon in the adsorption desulfurization.