共查询到20条相似文献,搜索用时 15 毫秒
1.
N.M. Deraz 《Applied Surface Science》2009,255(6):3884-3890
Pure and Li2O-doped CuO/CeO2 catalysts calcined at 500 °C were prepared by impregnation method. The catalysts are characterized by DTA, TG-DTG, XRD, IR, TEM, nitrogen adsorption at −196 °C and the catalytic decomposition of hydrogen peroxide at 30 °C.The effects of molar ratio, heat treatment time and the doping on the structural, surface and catalytic properties of nanocrystalline Cu/Ce-mixed oxides system have been studied. It was found that the catalytic activity of ceria-supported copper oxide catalysts increased by increasing both the heat treatment time and dopant content. However, the pure Cu/Ce-mixed oxide solids containing 10 wt.% CuO exhibited the best performance. The characterization results indicated that the higher surface area, the formation of solid solution between copper and cerium oxides, and the high dispersion of copper species on the ceria were responsible for the high catalytic activity of the CuO/CeO2 catalysts. 相似文献
2.
TiO2 microspheres with mesoporous textural microstructures and high photocatalytic activity were prepared by hydrothermal treatment of mixed solution of titanium sulfate and urea with designed time. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N2 adsorption-desorption measurements. The photocatalytic activity was evaluated via the photocatalytic oxidation of acetone in air at room temperature. The results show that the hydrothermal time significantly influences on the morphology, microstructure and photocatalytic activity of the as-prepared samples. With increasing hydrothermal time, specific surface areas and pore volumes decrease, contrarily, the crystallite size and relative anatase crystallinity increase. The photocatalytic efficiency of the as-prepared samples is obviously higher than that of commercial Degussa P25 (P25) powders. Especially, the as-prepared TiO2 powders by hydrothermal treatment for 7 h shows the highest photocatalytic activity, which exceeds that of P25 by a factor of more than 2 times. 相似文献
3.
Mono-disperse spinel Ni0.5Zn0.5Fe2O4 nanosized particles have been synthesized via a hydrothermal method at low temperature. X-ray diffraction (XRD), transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) analysis indicated that the synthesized nanocrystals were of pure cubic spinel structure with the size about 6-20 nm. The activation energy of grain growth is 35.06 kJ/mol experimented by the Arrhenius equation. A primary experimental model was put forward to shed light on the growth mechanism of crystallined spinel Ni-Zn ferrite nanosized particles under hydrothermal conditions. The magnetic measurements shows that the prepared Ni0.5Zn0.5Fe2O4 nanoparticle possess good superparamagnetic behavior. 相似文献
4.
Xian-Ming Liu Wen-Liang Gao Jun Zhang 《Journal of Physics and Chemistry of Solids》2011,72(12):1472-1476
CeO2 nanostructures were successfully prepared by a facile and environmentally friendly mixed-solvothermal method under mild conditions. The X-ray diffraction (XRD) and transmission electron microscope (TEM) results indicated that the as-synthesized products were cubic CeO2 polycrystalline structures with uniform diameters in the range of 10–20 nm and lengths up to 80 nm. X-ray photoelectron spectroscopy (XPS) spectra and EDX data demonstrated that stoichiometric CeO2 was formed. A possible growth mechanism of the CeO2 nanostructures was proposed. Moreover, ultraviolet absorption measurement revealed the band gap of the CeO2 nanorods was estimated to be 3.85 eV, which is larger than the reported value for the bulk CeO2 (Eg=3.2 eV). Enhancement of the band gap of the CeO2 nanorods is attributed to the well-known quantum size effect. 相似文献
5.
Nanocrystalline CeO2-doped (5, 7.5, 10, and 15 mol%) Gd2O3 powders, with a particle size of about 17 nm, were synthesized through the combustion of glycine/nitrate gels. Dense nanocrystalline
materials were obtained by hot uniaxial sintering. Optical microscopy, scanning electron microscopy and transmission electron
microscopy examinations, as well as X-ray diffraction analyses, have allowed us to characterize these polycrystals. The grain
sizes, included between ∼10 and 80 nm, depend on both the sintering temperature and the amount of dopant. A comparison of
the transport properties of these nanocrystalline samples to the values obtained with coarsened grained materials of same
composition shows that the ionic conductivity passes through a maximum for mean grain sizes included between 300 and 500 nm.
Furthermore, an enhancement of the ionic conductivity is observed when the amount of dopant increases. This was attributed
to a grain-size-dependent gadolinium segregation at the periphery of the grains confirmed by X-ray photoelectron spectroscopy
characterizations.
Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, France, 9–15 Sept. 2007. 相似文献
6.
Influence of the physico-chemical properties of CeO2-ZrO2 mixed oxides on the catalytic oxidation of NO to NO2 总被引:1,自引:0,他引:1
Idriss Atribak 《Applied Surface Science》2010,256(24):7706-1365
Commercial and home-made Ce-Zr catalysts prepared by co-precipitation were characterised by XRD, Raman spectroscopy, N2 adsorption at −196 °C and XPS, and were tested for NO oxidation to NO2. Among the different physico-chemical properties characterised, the surface composition seems to be the most relevant one in order to explain the NO oxidation capacity of these Ce-Zr catalysts. As a general trend, Ce-Zr catalysts with a cerium-rich surface, that is, high XPS-measured Ce/Zr atomic surface ratios, are more active than those with a Zr-enriched surface. The decrease in catalytic activity of the Ce-Zr mixed oxided upon calcinations at 800 °C with regard to 500 °C is mainly attributed to the decrease in Ce/Zr surface ratio, that is, to the surface segregation of Zr. The phase composition (cubic or t′′ for Ce-rich compositions) seems not to be a direct effect on the catalytic activity for NO oxidation in the range of compositions tested. However, the formation of a proper solid solution prevents important surface segregation of Zr upon calcinations at high temperature. The effect of the BET surface area in the catalytic activity for NO oxidation of Ce-Zr mixed oxides is minor in comparison with the effect of the Ce/Zr surface ratio. 相似文献
7.
The adsorption of NO on the (1 1 1) and (1 1 0) surfaces of ceria (CeO2) was studied using projector-augmented wave (PAW) method based density-functional theory within the generalized gradient approximation (GGA). Several adsorption sites for NO on the stoichiometric surfaces are found, all with weak molecule-surface interaction. The adsorption on the reduced surfaces is much stronger. The O-ends of the adsorbed NO molecules fill the oxygen vacancies and the N-O bonds are elongated. If two such adsorbed NO molecules, residing at neighbouring sites, meet, their N-ends will form a strong N-N bond with little or no barrier. This is an intermediate step towards dissociation of free N2 which is calculated to be strongly thermodynamically driven. 相似文献
8.
9.
Shaobo Dun Youwen Hu Liuqi Yu Ningkang Huang Bin Tang Lev Resnick 《Journal of luminescence》2008,128(8):1363-1368
Samples of nanocrystalline 74Ge embedded in amorphous SiO2 film were prepared by 74Ge ion implantation and subsequent primary thermal annealing. These samples were irradiated by neutron flux in a nuclear reactor then the second annealing followed. Irradiation with thermal neutrons leads to doping of nanocrystalline 74Ge with As impurities due to nuclear transmutation of isotope 74Ge into 75As. Transmission electron microscope, X-ray fluorescence, X-ray photoelectron spectroscopy, laser Raman scattering and photoluminescence of the obtained samples were measured. It was observed that with the increase in As-donors concentration, photoluminescence intensity first increased but then significantly decreased. An explanatory model of this non-monotonic behavior was discussed. 相似文献
10.
We have determined the electronic structure of CeO2 and PrO2 by performing SCF band calculations. We find that in both systems there are metal f- and d- electrons in the oxygen 2p bands. We discuss the question of valency and ionicity in these systems. 相似文献
11.
Jianhong Peng Mirabbos HojamberdievYunhua Xu Baowei CaoJuan Wang Hong Wu 《Journal of magnetism and magnetic materials》2011,323(1):133-137
CoFe2−xGdxO4 (x=0-0.25) nanoparticles were synthesized via a simple hydrothermal process at 200 °C for 16 h without the assistance of surfactant. The as-synthesized powders were characterized by X-ray diffraction, transmission electron microscopy, and a vibrating sample magnetometer. The X-ray diffraction results showed that the as-synthesized powders were in the pure phase with a doping amount of ≤0.25, and the peaks could be readily indexed to the cubic spinel cobalt ferrite. Transmission electron microscopy and high resolution transmission electron microscopy observations revealed that the gadolinium-doped cobalt ferrite nanoparticles were single crystal, roughly spherical, uniformly distributed, and not highly agglomerated. The room temperature magnetic field versus magnetization measurements confirmed a strong influence of gadolinium doping on the saturation magnetization and coercivity due to large lattice distortion and grain growth of small particles. 相似文献
12.
Qingyao WangXiuchun Yang Junwei HouMin Huang Yuhua Zhao 《Applied Surface Science》2011,257(13):5857-5862
Sb2O3 nanorod-bundles with length of about 4 μm were fabricated in the presence of polyvinyl alcohol (PVA) by a simple hydrothermal method. The composition, morphology, microstructure and optical property of the as-prepared bundles were characterized by XRD, XPS, SEM, TEM and Raman spectrum. The results showed that the nanorod-bundles were composed of massive orthorhombic phase Sb2O3 nanorods grown along [0 0 1] direction. It was speculated that the nanorod-bundles developed through self-assembly of initially scattered nuclei into microdisks and subsequent oriented attachment process. PVA played a crucial role in the formation of Sb2O3 nanorod-bundles. 相似文献
13.
A comparative study of the thermoluminescence (TL) emission between beta-irradiated lithium aluminosilicates, Li2O-Al2O3-SiO2 (LAS), and beta-irradiated CeO2-doped lithium aluminosilicates, Li2O-Al2O3-SiO2-CeO2 (LAS:Ce), grown by sol-gel technique and preannealed at 1250 °C is presented. It is found that doping reinforces the result of preannealing the sample; the incorporation of CeO2 at low concentrations shifts the TL curves towards higher temperatures and increases the total intensity with respect to samples without the dopant. This behavior, together with the fact that CeO2 is a good densification agent, suggests the possibility of using CeO2 to improve the technological properties of LAS. Deconvolution analysis of the thermoluminescence glow curves of doped materials under general order kinetics shows that the relevant temperatures at which the component signals appear are virtually the same as for pure samples. This suggests that CeO2 does not introduce new types of traps, but only changes the population and distribution of impurities responsible for the TL in the original matrix of LAS. Finally, the kinetic parameters for the deconvoluted curves are reported. They corroborate that changes in CeO2 concentration only vary the depth and distribution of the same kind of original traps. 相似文献
14.
Deposition and characterization of YBCO/CeO2/YSZ/CeO2 multilayers on biaxially textured Ni substrates
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CeO2/YSZ/CeO2 buffer layers were deposited on biaxially textured Ni substrates by pulsed laser deposition. The influence of the processing parameters on the texture development of the seed layer CeO2 was investigated. Epitaxial films of YBCO were then grown in situ on the CeO2/YSZ (yttria-stabilized ZrO2)/CeO2-buffered Ni substrates. The resulting YBCO conductors exhibited self-fleld critical current density Jc of more than 1 MA/cm^2 at 77K and superconducting transition temperature Tc of about 91K. 相似文献
15.
Tomáš Skála František Šutara Michal Škoda Vladimír Matolín 《Applied Surface Science》2008,254(21):6860-6864
The interaction of gallium with CeO2(1 1 1) layers was studied using standard and resonant photoelectron spectroscopy, by means of both a laboratory X-ray source and tunable synchrotron light. Firstly a 1.5-nm thick CeO2 film was grown on a Cu(1 1 1) substrate. Secondly Ga was deposited in six steps up to a thickness of 0.35 nm, at room temperature. The interaction of gallium with the oxide layer induced partial CeO2 reduction, and gallium oxidation. The photoemission data suggest that a mixed Ga-Ce-O oxide was established similarly to the Sn-Ce-O case for Sn deposited on cerium oxide layers. As a consequence, gallium-induced weakening of Ce-O bonds provides a higher number of active sites on the surface that play a major role in its catalytic behaviour. 相似文献
16.
Shengsong Ge Qingyao Wang Qian ShaoYuhua Zhao Xiaokun YangXiaojie Wang 《Applied Surface Science》2011,257(8):3657-3665
Hollow spindle-like and cobblestone-like Sb2O3 microstructures, have been successfully synthesized via a hydrothermal method by using cetyltrimethylammonium bromide (CTAB) as soft-templates. Results from XRD, SEM, TEM, Raman and BET showed that experimental parameters, such as the reaction temperature and time, played crucial roles in the respective morphological control of Sb2O3 microstructures. On the basis of these results, possible growth mechanisms for the formation of hollow spindle-like and cobblestone-like microstructures are presented and discussed. 相似文献
17.
Gd-doped SnO2 nanoparticles were chemically prepared doping 0-12.5% Gd into SnO2 and calcined at 600 °C. X-ray diffraction and Fourier transformed infrared spectroscopy measurements show the formation of single phase of Sn1−xGdxO2 up to x=0.0625 while at x=0.125, an additional secondary phase of tetragonal GdO2 (not cubic Gd2O3) is detected. The transmission electron microscopy studies show that the individual particles are single crystalline with an average size in the range of 10-12 nm. Magnetization measurements show the absence of ferromagnetic and antiferromagnetic ordering in all samples; however surface spin effects and enhanced Gd-O-Gd interactions are proposed to account for the observed magnetic properties of the samples. 相似文献
18.
Magnetic MFe2O4 (M=Co, Ni, Zn) nanocrystals with a diameter about 30 nm and a nearly spherical shape were synthesized via a simple hydrothermal approach. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy have been used to investigate the as-prepared magnetic MFe2O4 (M=Co, Ni, Zn) nanocrystals. Magnetic properties of the as-prepared samples have been detected by a vibrating sample magnetometer at room temperature and the results show that the as-prepared magnetic MFe2O4 nanocrystals are a type characteristic of superparamagnetic materials. These superparamagnetic nanocrystals are believed to be promising for wide engineering applications, such as drug delivery, bioseparation, and magnetic resonance imaging. 相似文献
19.
Carbon nanotubes (CNTs) were controllably coated with the uninterrupted CuO and CeO2 composite nanoparticles by a facile pyridine-thermal method and the high catalytic performance for CO oxidation was also found. The obtained nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction as well as X-ray photoelectron spectroscopy. It is found that the CuO/CeO2 composite nanoparticles are distributed uniformly on the surface of CNTs and the shell of CeO2/CuO/CNT nanocomposites is made of nanoparticles with a diameter of 30-60 nm. The possible formation mechanism is suggest as follows: the surface of CNTs is modified by the pyridine due to the π-π conjugate role so that the alkaline of pyridine attached on the CNT surface is more enhanced as compared to the one in the bulk solvent, and thus, these pyridines accept the proton from the water molecular preferentially, which result in the formation of the OH− ions around the surface of CNTs. Subsequently, the metal ions such as Ce3+ and Cu2+ in situ react with the OH− ions and the resultant nanoparticles deposit on the surface of CNTs, and finally the CeO2/CuO/CNT nanocomposites are obtained. The T50 depicting the catalytic activity for CO oxidation over CeO2/CuO/CNT nanocomposites can reach ∼113 °C, which is much lower than that of CeO2/CNT or CuO/CNT nanocomposites or CNTs. 相似文献
20.
The interaction of deuterium with Ce0.6Zr0.4O2, synthesised by a co-precipitation technique, is discussed on the basis of the sample's bulk and surface composition and the presence of trace amounts of silicon. Redox cycling resulted in surface cerium enrichment, which, however, only moderately affected the interaction of the material with D2. Addition of a trace amount of chloride ion to the oxide surface promoted both H/D scrambling and vacancy creation. Chloride ion was also found to prevent the surface cerium enrichment induced by redox cycling. 相似文献