Study On Fe₂O₃-based Catalysts For Methane Catalytic Combustion

Fe₂O₃, active compound, supported by some new supports, was used in monolith catalysts for methane combustion. In this essay, we gave emphasis to research of novel support materials and appropriate promoters in order to invent a lower-cost, higher-performance catalyst for methane combustion. Catalytic activities of the catalysts for methane combustion were evaluated in a continuous-flow micro-reactor. They were also characterized by XPS,BET,H₂-TPR,OSC,XRD methods. The discoveries coming from the results were just as follows. XPS measurement indicated addition of ZrO₂ and Y2O3 into the support decreased the interaction between Fe₂O₃ and Al₂O₃, and increased the concentration of iron species on the surface of Fe₂O₃/YSZ-Al₂O₃ catalyst, resulting in improvement of catalytic activity of the catalyst. BET results suggested treatment time of nitric acid to YSZ-Al₂O₃ support exerted an influence on catalytic activity of the catalyst by changing its BET areas, and 0.5 h was best. Fe₂O₃-based catalyst supported by Ce_0.67Zr_0.33O₂, an oxygen-storage material, possessed lower catalytic activity. Addition of Mn lowered the light-temperature of methane under lower temperature but not favored the catalytic activity and stability of the Fe₂O₃/Ce_0.67Zr_0.33O₂ catalyst under higher temperature. Addition of Stoichiometric Ce_0.67Zr_0.33O₂ into the Al₂O₃ support, improved the catalytic capability of Fe₂O₃/Ce_0.67Zr_0.33O₂-Al₂O₃ catalyst, increased the catalyst's BET areas, promoted its redox ability, and stabilized its crystal structure. In particularly, when m(Ce0.67Zr0.33O2):m(Al2O3) was 1:2, the Fe2O3/Ce0.67Zr0.33O2-Al2O3 catalyst, possessed the best catalytic capability and the best resistance to high temperature. By contrasting catalytic properties of four Fe2O3-based catalyst supported by Al2O3, Ce0.67Zr0.33O2, ZrO2-Al2O3, Ce0.67Zr0.33O2-Al2O3 respectively, we found that the causes resulting in the best catalytic activity of Fe2O3/Ce0.67Zr0.33O2-Al2O3 catalyst rooted in that addition of Zr lowered the light temperature, and addition of Ce replacing Zr partly into the Al2O3 support shortened the range of light temperature and total conversion temperature. 8 % Fe2O3 loading was enough for the catalytic activity of Fe2O3/Ce0.67Zr0.33O2-Al2O3 catalyst. H2-TPR profiles showed, after beyond 8% Fe2O3 loading, there almost was no increasement of the area of Fe2O3 ruduction peak for the fresh samples, but obviously rise of the reduction-peak temperature and decreasement of the ruduction peak area for the aging samples, which was according with their catalytic activity for methane combustion. XRD spectras showed, the superfluous Fe2O3 species would activate the interaction between Fe2O3 and Al2O3 that should have been restrained by the addition of Ce-,Zr-species into the support, which lowered catalytic activity of the Fe2O3-based catalyst. Different promoters exercised different influence on catalytic activity of Fe2O3/Ce0.67Zr0.33O2-Al2O3 catalyst for methane combustion. Under being calcined at 600℃for 2 h, addition of La,Sr,Zr or Y did not exercise their influence on catalytic activity of the Fe2O3-based catalyst, but addition of Mn did help to the catalyst's lower-temperature activity. Noticeably, while addition of Zr or Y did harm to the catalyst's activity for methane combustion, under aging at 1000℃for 5 h, addition of La,Sr or Mn did favor not only improving its resistance to high temperature but also promoting the catalyst's activity for methane combustion.