The surface properties and the activities in catalytic wet air oxidation over CeO2-TiO2 catalysts

No-noble metal CeO₂-TiO₂ catalysts prepared by sol-gel method were developed and examined for catalytic wet air oxidation (CWAO) of acetic acid. The structure of the catalysts was measured by BET, SEM, XRD, XPS and DTA-TG. We investigated the effect of the interactions of Ce and Ti on the structure of CeO₂-TiO₂ catalysts. The mechanisms of the relationships between the different content of Ti and the activity of CeO₂-TiO₂ catalysts were discussed. The results showed that the average crystal size of CeO₂ decreased and the surface areas increased; the low valence of Ce³⁺ increase, and the chemisorbed oxygen slightly decreased with the increase of Ti content on the surface of CeO₂-TiO₂ catalysts. The order of the activity in CWAO of acetic acid followed: Ce/Ti 1/1 > Ce/Ti 3/1 > Ce/Ti 1/3 > Ce/Ti 5/1 > CeO₂ > TiO₂ > no catalyst. In CWAO of acetic acid, the optimal atomic ratio of Ce and Ti was 1, and the highest COD removal was over 64% at 230 °C, 5 MPa and 180 min reaction time over Ce/Ti 1/1 catalyst. The excellent activity and stability of CeO₂-TiO₂ catalysts was observed in our study.     

Influence of the physico-chemical properties of CeO2-ZrO2 mixed oxides on the catalytic oxidation of NO to NO2

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.     

Preparation and photocatalytic property of CeO2 lamellar

A novel room temperature solid-state chemical synthesis was introduced to successfully fabricate CeO₂ samples, coupled by a polyethylene glycol 400 (PEG 400)/cetyl trimethylammonium bromide (CTAB)/sodium dodecyl sulfate (SDS). The as-prepared products were characterized by XRD, TEM, SEM, BET and UV. A study of photocatalytic degradation of the methylene blue MB under UV illumination has been carried out. It is indicated that the samples exhibit excellent photocatalytic activity. Besides, the samples assisted with surfactants possess higher photocatalytic activity than the sample without any surfactants, wherein the sample with SDS as an additive shows the highest photocatalytic activity, which is able to reach 89.6% MB degradation ratio within 60 min illumination. Moreover, the effects of important operational parameters such as initial MB concentration, catalyst loading and pH were also investigated. The above sample under the optimum conditions obtained the maximum MB degradation ratio up to 96.5%, which is higher than that of the commercial TiO₂ P25 under the same conditions. It can be concluded that CeO₂ will be a potential photocatalyst in the application of organic pollutant.     

Response improvement for In2O3-TiO2 thick film gas sensors

In₂O₃ is introduced into TiO₂ by sol-gel method to improve the response/recovery rate and expand the operating temperature, when the In₂O₃-TiO₂ mixed system is exposed to H₂/O₂. The sensor is fabricated by thick film technology. Influence of In₂O₃ on the film phase composition, microstructure and sensing characteristics is discussed. Dynamic response properties show that the operating temperature of the mixed system is at 500-800 °C, which is about 600-800 °C for pure TiO₂. Response time of the sensor is about 200-260 ms (millisecond) while recovery time is in a narrow range of 60-280 ms at 600-800 °C. The promoting mechanism is suggested to arise from the introduction of In₂O₃ and grain size effect of the sensing film. Then In₂O₃-TiO₂ thick films are surface-modified by Pt using chloroplatinic acid. The promoting effect of Pt dispersed on the mixed system is also investigated.     

Preparation and characterization of visible light responsive Fe2O3-TiO2 composites

In this study we present the effects of iron oxide (Fe₂O₃) on titanium dioxide (TiO₂) in synthesising visible-light reactive photocatalysts. A Fe₂O₃-TiO₂ composite photocatalyst was synthesized from Fe₂(SO₄)₃ and Ti(SO₄)₂ by a ethanol-assisted hydrothermal method. The preparation conditions were optimized through the investigation of the effects of hydrothermal temperature and time as well as molar ratio of Ti to Fe on the photocatalytic activity. The visual, physical and chemical properties of the Fe₂O₃-TiO₂ composites were investigated. The results showed that α-Fe₂O₃ and anatase TiO₂ were present in the composites. The Fe₂O₃-TiO₂ synthesized under optimum condition consisted of mesoporous structure with an average pore size of 4 nm and a surface area of 43 m²/g. Under visible and solar light irradiation, the photocatalytic activity of optimized sample was significantly higher than that of pure TiO₂. This sample led to a photodegradation efficiency of 90% and 40% of auramine under visible light and solar light, respectively.     

Research on CeO2 cap layer for YBCO-coated conductor

Two groups of coated conductor samples with different thicknesses of CeO2 cap layers deposited by pulsed laser deposition （PLD） under the same conditions have been studied. Of them, one group is of CeO2 films, which are deposited on stainless steel （SS） tapes coated by IBAD-YSZ （IBAD-YSZ/SS）, and the other group is of CeO2/YSZ/Y2O3 multilayers, which are deposited on NiW substrates by PLD for the fabrication of YBCO-coated conductor through the RABiTS approach. YBCO film is then deposited on the tops of both types of buffer layers by PLD. The effects of the thickness of the CeO2 film on the texture of the CeO2 film and the critical current density （Jc） of the YBCO film are analysed. For the case of CeO2 film on IBAD-YSZ/SS, there appears a self-epitaxy effect with increasing thickness of the CeO2 film. For CeO2/YSZ/Y2O3/NiW, in which the buffer layers are deposited by PLD, there occurs no self-epitaxy effect, and the optimal thickness of CeO2 is about 50 nm. The surface morphologies of the two groups of samples are examined by SEM.     

溶胶-凝胶ZrO2-TiO2高折射率光学膜层的抗激光损伤性能研究

采用溶胶-凝胶方法制备了ZrO₂-TiO₂(Ti含量为0—100mol%)高折射率光学薄膜. 借助激光动态光散射技术研究溶胶微结构. 采用傅里叶变换红外光谱、原子力显微镜、薄膜光学常数分析仪、漫反射吸收光谱及强激光辐照实验，对膜层的结构、光学性能及抗激光损伤性能进行了系统表征. 结果显示，溶胶-凝胶工艺可以在部分牺牲折射率的情况下，使膜层的抗激光损伤性能得到大幅度提升. 随Ti含量从0mol%增加至100mol%，膜层的平均损伤阈值呈下降趋势，当Ti含量从0mol%增加至60mol%时，平均损伤阈值从57.1J/cm²下降到21.1J/cm²(辐照激光波长为1053nm，脉冲宽度为10ns，“R/1”测试模式)，当Ti含量从60mol%增加至100mol%时，平均损伤阈值变化很小. 综合溶胶微结构、膜层光学性能和损伤实验结果可以推断，强激光诱导多光子吸收是引起膜层损伤的主要原因. 不同配比的复合膜之间光学带隙的显著差异导致相同辐照激光情况下多光子吸收的概率发生变化，从而导致损伤阈值的规律性变化. 关键词： 2-TiO₂薄膜')" href="#">ZrO₂-TiO₂薄膜 溶胶-凝胶 激光诱导损伤 光学带隙     

SnO2/TiO2 mixed oxide particles synthesized in doped premixed H2/O2/Ar flames

SnO₂/TiO₂ mixed oxides with primary particle size ranging between 5 nm d_p 12 nm were synthesized by doping a H₂/O₂/Ar flame with Sn(CH₃)₄ and Ti(OC₃H₇)₄ co-currently. The effects of “flow coordinate,” concentration and flame configurations were investigated with respect to particle size and morphology of the generated mixed oxides. In situ characterization of the mixed oxides was performed using the particle mass spectrometer (PMS), while XRD, TEM, BET and UV–Vis were performed ex situ. Results obtained showed that primary particle size of mixed oxides can be controlled by varying experimental parameters. The mixed oxides have interesting properties compared to those of the pure oxides of TiO₂ and SnO₂, which were also synthesized in flames earlier. Band gap tuning opportunities are possible using mixed oxides.     

Effects of oxygen vacancies on the room-temperature ferromagnetism of Co-doped polycrystalline CeO2

Pure and Co-doped single-phase CeO₂ crystals were synthesized by a solid-state reaction method. Samples of different oxygen vacancy concentration were studied, including (1) as-sintered crystals, (2) powders ground from the same crystal, and (3) a cold-pressed pellet from the ground powder that was unannealed and annealed at 800 °C. By analyzing the magnetic behaviors, surface/volume ratio and O vacancy concentration, the effects of oxygen vacancies on the room-temperature ferromagnetism (RT-FM) of Co-doped CeO₂ were systematically investigated. The results confirm that the RT-FM observed in Co-doped CeO₂ has a direct relationship with the oxygen vacancy concentration, and support the oxygen vacancy mediated FM mechanism.     

蓝宝石衬底上Gd2O3掺杂CeO2氧离子导体电解质薄膜的生长及电学性能

采用反应磁控溅射方法,在(0001)蓝宝石单晶衬底上,制备了纳米多晶Gd₂O₃掺杂CeO₂(GDC)氧离子导体电解质薄膜,采用X射线衍射仪(XRD)、原子力显微镜(AFM)对薄膜物相、结构、粗糙度、表面形貌等生长特性进行了表征,利用交流阻抗谱仪测试了GDC薄膜不同温度下的电学性能;实验结果表明,GDC薄膜为面心立方结构,在所研究的衬底温度范围内,均呈强(111)织构生长;薄膜表面形貌随衬底温度发生阶段性变化：衬底温度由室温升高到300℃时, 关键词： 2O₃掺杂CeO₂电解质薄膜')" href="#">Gd₂O₃掺杂CeO₂电解质薄膜 反应磁控溅射 生长特性 电学性能     

Preparation, structures and photoluminescent enhancement of CdWO4-TiO2 composite nanofilms

For the first time, Cadmium tungstate (CdWO₄)-TiO₂ composite nanofilms on a glass substrate were prepared by means of the dip-coating technique, in which collodion was used as a dispersant and film-forming agent. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo gravimetric and thermal analyses (TG/DTA), FTIR and photoluminescence (PL) methods, respectively. SEM and XRD characterization of these films indicated that CdWO₄ particles crystallized in a monoclinic wolframite-type structure whereas TiO₂ particles were Anatase phase; and both of them were well distributed in the nanofilms. FTIR spectra proved the presence of CdWO₄ on the nanofilms. Photoluminescent results showed that the emitting peak of CdWO₄ films blue shifted slightly relative to that of CdWO₄ crystal. Moreover, the PL intensity of CdWO₄-TiO₂ composite nanofilm was much higher than that of CdWO₄ nanofilm. We ascribed that the introduction of TiO₂ should be responsible for the PL enhancement.     

Selective CO oxidation in hydrogen-rich gas over CuO/CeO2 catalysts

A series of CuO/CeO₂ catalysts with different Cu-Ce compositions were synthesized by co-precipitation method and characterized by X-ray diffraction, H₂-TPR, CO-TPD, SEM and X-ray photoelectron spectroscopy (XPS) techniques. The effects of Cu-Ce composition and water vapor on the catalytic properties for the selective CO oxidation in the hydrogen-rich gas were investigated. The results indicated that CuO (10%)/CeO₂ catalyst remained the maximum CO conversion and selectivity at 140 and 160 °C, while the performance of CuO/CeO₂ catalysts deteriorated with the CuO molar ratio further increased. The interfacial CuO and CeO₂ interaction and synergistic effect enhanced the redox properties of CuO/CeO₂ catalyst and the highly dispersed copper species were proposed as the active sites for the selective CO oxidation. The blockage of catalytic active sites by absorbed water and the formation of CO-H₂O surface complexes reduced the activity of CuO (10%)/CeO₂ catalyst. The decreasing of surface lattice oxygen and absorbed oxygen species and the agglomeration of copper particles were the plausible interpretations for the deactivation of CuO (10%)/CeO₂ catalyst.     

Nanosized iron and chromium oxides supported on mesoporous CeO2 and SBA-15 silica: Physicochemical and catalytic study

Mesoporous ceria and SBA-15 silica were modified with iron and chromium oxide nanoparticles and characterized by XRD, N₂-physisorption, FTIR, UV-vis, Moessbauer spectroscopy and TPR-TG in hydrogen. Their catalytic behaviour in methanol decomposition to CO and hydrogen was also studied. Stabilization of mono- and bi-chromate species, FeO_x patches or isolated iron ions as well as Fe₂O₃ and Cr₂O₃ nanoparticles in different ratio depending on the nature of the porous matrix was observed. The simultaneous presence of iron and chromium oxides lead to change in their dispersion, providing easier reducibility, higher catalytic activity and stability of the obtained materials in comparison with the corresponding mono-component ones. The “intimate contact” at the interface of both loaded metal oxide nanoparticles and the support was discussed with respect to explain the differences in the state of the active ingredient and its specific catalytic behaviour.     

Synthesis and characterization of the Pd/InVO4-TiO2 co-doped thin films with visible light photocatalytic activities

Novel Pd/InVO₄-TiO₂ thin films with visible light photocatalytic activity were synthesized from the Pd and InVO₂ co-doped TiO₂ sol via sol-gel method. The photocatalytic activities of Pd/InVO₄-TiO₂ thin films were investigated based on the oxidative decomposition of methyl orange in aqueous solution. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectroscopy (UV-vis). The results indicate that the Pd/InVO₄-TiO₂ thin films are compact, uniform and consist of sphere nanoparticles with diameters about 80-100 nm. The UV-vis spectra show that the Pd/InVO₄-TiO₂ thin films extend the light absorption spectrum toward the visible region. XPS results reveal that doped Pd exist in the form of metallic palladium. The photocatalytic experiments demonstrate that Pd doping can effectively enhance the photocatalytic activities of InVO₄-TiO₂ thin films in decomposition of aqueous methyl orange under visible light irradiation. It has been confirmed that Pd/InVO₄-TiO₂ thin films could be excited by visible light (E < 3.2 eV) due to the existence of the Pd and InVO₄ doped in the films.     

Ferromagnetism in diluted magnetic Zn-Co-doped CeO2−δ

Several oxides doped with transition metals can be used in spintronics devices due to their conductive and magnetic properties at room temperature. In this work, samples of Ce_1−2xZn_xCo_xO_2−δ were obtained by an alternative sol–gel proteic process for x=0.01, 0.05 and 0.1. The structural properties of samples were analyzed by XRD and Raman spectroscopy. Magnetization measurements revealed a ferromagnetic behavior at room temperature probably induced by oxygen vacancies.     

Emission features of Ho ion in Nb2O5, Ta2O5 and La2O3 mixed Li2O-ZrO2-SiO2 glasses

Li₂O-ZrO₂-SiO₂: Ho³⁺ glasses mixed with three interesting d-block elemental oxides, viz., Nb₂O₅, Ta₂O₅ and La₂O₃, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb₂O₅ and Ta₂O₅ mixed Li₂O-ZrO₂-SiO₂ glasses (free of Ho³⁺ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta⁵⁺ and Nb⁵⁺ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho³⁺ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β_r and the radiative lifetime τ_r, for ⁵S₂ emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for ⁵S₂ level of Ho³⁺ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La₂O₃ mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho³⁺ ions.     

掺杂CeO2的75TeO2-25Nb2O5-5ZnO飞秒激光诱导瞬态光栅的研究

用泵浦探测技术研究了掺杂CeO₂的75TeO₂-25Nb₂O₅-5ZnO玻璃在飞秒激光诱导的瞬态光栅多级自衍射。从拉曼和吸收光谱中研究了玻璃的结构特性，并证明了此玻璃中存在Ce3+离子。这种瞬态光栅起因于光克尔效应，并通过Ce3+离子中1S0?1F3电子能级跃迁形成的激发态粒子数光栅而改善，一级衍射信号的转换效率可达到11%。这些实验结果显示了掺杂CeO₂的75TeO₂-25Nb₂O₅-5ZnO飞玻璃在全转换开关中具有广泛应用。     

Au在Zr掺杂的CeO2(110)面吸附的第一性原理研究

采用基于广义梯度近似的投影缀加平面波(projector augmented wave)雁势和具有三维周期性边界条件的超晶胞模型,用第一性原理方法,计算并分析了Au在CeO₂(110)和Zr掺杂的CeO₂(110) 面的吸附能,吸附结构和电子结构等特征.从而得出Zr掺杂对Au/CeO₂(110)吸附体系的影响.结果表明：Zr的掺杂增大了Au在CeO₂(110) 面的吸附能,并改变了最强吸附位置,且导致了吸附体系中衬底结 关键词： Au Zr掺杂 2')" href="#">CeO₂ 吸附     

利用脉冲激光沉积技术在双轴织构的Ni基带上外延CeO2薄膜

利用脉冲激光沉积技术在氢还原气氛下成功地在双轴织构的Ni基带上外延了高质量的CeO₂薄膜. x射线衍射θ—２θ扫描和ω扫描结果表明，CeO₂薄膜在Ni基带上呈c轴方向生长，存在很强的平面外织构；极图和φ扫描显示它具有良好的平面内织构. Ni基片上织构的CeO₂薄膜为进一步在其上外延高质量的YBa₂Cu₃O_7-x超导薄膜提供了很好的模板. 关键词： 双轴织构的Ni基带 2薄膜')" href="#">CeO₂薄膜 脉冲激光沉积     

Cu-Zn-Al mixed metal oxides derived from hydroxycarbonate precursors for H2S removal at low temperature

One series of Cu-Zn and two series of Cu-Zn-Al hydroxycarbonate precursors with varying metal molar ratios were prepared via co-precipitation or multi-precipitation method, and the mixed metal oxides obtained by calcination of the precursor materials were used as adsorbents for H₂S removal in the range of 25-100 °C. The results of H₂S adsorption tests showed that these mixed oxides, especially two series of Cu-Zn-Al mixed metal oxides exhibited markedly high breakthrough sulfur capacities (ranging from 4.4 to 25.7 g S/100 g-sorbent with increase of Cu/Zn molar ratio) at 40 °C. Incorporation Cu and/or Al decreased the mean crystalline sizes of ZnO and CuO species in the Cu-Zn and Cu-Zn-Al mixed metal oxide adsorbents by decreasing of mean crystalline sizes of hydroxycarbanate phases mainly including hydrozincite, aurichalcite and malachite, segregation of Al phase, etc. Higher breakthrough sulfur capacity of each adsorbent in two ternary series than that of the corresponding adsorbent in binary series should be ascribed to the enhancement of the dispersion of ZnO and/or CuO species with incorporation of aluminum, thereby increasing the overall rate of reaction between the adsorbent and H₂S by reducing the thickness of potential sulfide shell on the outer layer of the oxide crystalline grains and increasing the area of the interface for the exchange of HS⁻/S²⁻ and O²⁻. For each series of adsorbents, the breakthrough sulfur capacity increased with the increase of Cu/Zn molar ratio regardless of changes of the dispersion of CuO and/or ZnO. This phenomenon might be mainly attributed to faster rate of the lattice diffusion of HS⁻, S²⁻ and O²⁻ or exchange of HS⁻/S²⁻ and O²⁻ during the sulfidation of CuO than that during the sulfidation of ZnO due to less rearrangement of the anion lattice.