CeO2-ZrO2 mixed oxide （Ce0.6Zr0.402） prepared by microwave-assisted heating co-precipitation was used as a support to prepare a series of CuO/Ce0.6Zr0.402 catalysts with various CuO contents （0 wt.%-1 5 wt.%） via the method of incipient-wetness im- pregnation. The obtained CuO/Ce0.6Zr0.402 samples were characterized by N2 adsorption, XRD, Raman, TEM and H2-TPR technolo- gies, and their catalytic activities for CO oxidation were investigated. The results showed that the activity of CuO/Ce0.6Zr0.402 catalyst was strongly influenced by the content of CuO, and the catalyst with 10 wt.% CuO exhibited the best catalytic activity in CO oxida- tion, which could be attributed to the high dispersion and reducibility of CuO, and high oxygen vacancy concentration in the catalyst.
Rare earth elements possess 4f orbitals without full electron occupancy and lanthanide contraction.This characteristic results in their unique catalytic performance when they are used as active components or as catalyst supports.Research into and the development of rare earth catalytic materials will significantly promote the high-efficiency utilization of abundant rare earth elements,such as lanthanum and cerium.Currently,rare earth catalytic materials play an important role in such areas as the petroleum chemical industry,the catalytic combustion of fossil fuels,automotive emissions control,the purification of industrial waste air,and solid solution fuel cells.In this paper,we review the application of and recent research progress that has been made on rare earth catalytic materials,including relative theoretical research.The effects of rare earth elements on the structure,activity,and stability of the catalysts of interest are described.
Wangcheng ZhanYun GuoXueqing GongYanglong GuoYanqing WangGuanzhong Lu
Mesoporous CeO2-MnOx binary oxides with different Mn/Ce molar ratios were prepared by hydrothermal synthesis and characterized by scanning electron microscopy （SEM）, N2 sorption, X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and H2 temperature-programmed reduction （H2-TPR）. The characterization results indicated that the CeO2-MnOx catalysts exhibited flower-like microspheres with high specific surface areas, and partial Mn cations could be incorporated into CeO2 lattice to form solid solution. The CeO2-MnOx catalysts showed better catalytic activity for CO oxidation than that prepared by the coprecipitation method. Furthermore, the CeO2-MnOx catalyst with Mn/Ce molar ratio of 1 in the synthesis gel （Ce-Mn-1） exhibited the best catalytic activity, over which the conversion of CO could achieve 90% at 135 ℃. This was ascribed to presence of more Mn species with higher oxida- tion state on the surface and the better reducibility over the Ce-Mn-I catalyst than other CeO2-MnOx catalysts.
Pd-only three-way catalyst （TWC）, Pd supported on washcoating （the mixture of alumina and Ce-Zr solid solution）/cordierite, was prepared and its catalytic performance and the operation window （2-value） at 450 ℃ were evaluated with the simulated automotive exhaust feed gas. Surfactants such as Tween-80 and Span-20 were added in the process of preparing the catalyst in order to improve the thermal stability and catalytic performance of Pd-only TWC. The fresh and aged catalysts at 1000 ℃ for 4 h were characterized by low-temperature N2 adsorption, XRD, XPS, and H2-TPR techniques. The results show that the presence of surfactants in the synthesis slurry could influence the physicochemical properties of the final Pd-only TWC. The FTS catalyst prepared with the mixed surfactant of Tween-80 and Span-20 exhibited excellent three-way catalytic performance. After being aged at 1000℃ for 4 h, the catalytic performances of Pd-only TWCs slightly decreased, but the FTS catalyst still demonstrated higher catalytic performance and better thermal stability compared with the Pd-only catalysts prepared with single surfactant or without any surfactant. And the FTS catalyst has a wider 2 value （operation window） than other catalysts, even after being aged at 1000℃.
Yutao RenQun ShenYun GuoYanqin WangYanglong GuoXueqing GongGuanzhong Lu
A modified CuO/CeO2 catalyst was prepared by surfactant-assisted impregnation method and showed better catalytic activity for low temperature CO oxidation than that from conventional impregnation method. The physicochemical properties of different CuO/CeO2 catalysts were characterized by thermogravimetrie and differential scanning calorimetric measurements （TG-DSC）, X-ray diffraction （XRD）, N2 adsorpti0n-desorption, Raman spectroscopy, H2 temperature-programmed reduction （H2-TPR）, tern- perature-programmed desorption of 02 （O2-TPD）, and diffuse reflectance infrared Fourier transform spectroscopy （DRIFTS）. The re- sults suggested that the addition of hexadecyl trimethyl ammonium bromide （CTAB） into the impregnation solution could improve the dispersion of CuO species, which could facilitate Cu2＋ incorporating into CeO2 lattice and strengthened the synergistic effects between CuO and CeO2, making the lattice oxygen more active, and eventually resulting in enhanced activity for CO oxidation.
