High-temperature transport properties, thermal expansion and cathodic performance of Ni-substituted LaSr2Mn2O7−δ

The substitution of manganese with nickel in LaSr₂Mn₂O_7−δ, where the solubility limit corresponds to approximately 25% Mn sites, enhances the Ruddlesden-Popper phase stability at elevated temperatures and atmospheric oxygen pressure. The total conductivity of LaSr₂Mn_2−yNi_yO_7−δ (y=0-0.4) decreases with nickel additions, whilst the average thermal expansion coefficients calculated from dilatometric data in the temperature range 300-1370 K increase from (11.4-13.7)×10⁻⁶ K⁻¹ at y=0 up to (12.5-14.4)×10⁻⁶ K⁻¹ at y=0.4. The conductivity and Seebeck coefficient of LaSr₂Mn_1.6Ni_0.4O_7−δ, analyzed in the oxygen partial pressure range 10⁻¹⁵-0.3 atm at 600-1270 K, display that the electronic transport is n-type and occurs via a small polaron mechanism. Reductive decomposition is observed at the oxygen pressures close to Ni/NiO boundary, namely ∼2.3×10⁻¹¹ atm at 1223 K. Within the phase stability domain, the electronic transport properties are essentially p(O₂)-independent. The steady-state oxygen permeability of dense LaSr₂Mn_1.6Ni_0.4O_7−δ membranes is higher than that of (La,Sr)MnO_3−δ, but lower if compared to perovskite-like (Sr,Ce)MnO_3−δ. Porous LaSr₂Mn_1.6Ni_0.4O_7−δ cathodes in contact with apatite-type La₁₀Si₅AlO_26.5 solid electrolyte exhibit, however, a relatively poor electrochemical performance, partly associated with strong cation interdiffusion between the materials.     

Synthesis, structural and electrical characterizations of DySr5Ni2.4Cu0.6O12−δ

A new compound DySr₅Ni_2.4Cu_0.6O_12−δ has been prepared by sol gel method and annealed at 1473 K in 1 atm of Ar gas flow. The X-ray diffraction (XRD) is used for phase identification. The sample shows to adopt the K₂NiF₄-type structure based on tolerance factor calculation. XRD analysis using the Rietveld method was carried out and it was found that DySr₅Ni_2.4Cu_0.6O_12−δ (Dy_0.33Sr_1.67Ni_0.8Cu_0.2O_4−δ′) compound crystallizes in tetragonal symmetry with space group I4/mmm (Z=2). The lattice parameters are found to be at room temperature a=3.7696(5) Å and c=12.3747(2) Å. The final reliability indices were: R_B=5.219% and χ²=3.47. Four probe electrical resistivity measurements were performed versus temperature in the range 294–579 K. A semiconducting behaviour over the whole range of temperature, with a conductivity maximum of 0.4 S cm⁻¹ is observed at 510 K.     

Microdomain texture and microstructures of Fe-containing CaTi0.4Fe0.6O3−δ

A study of the structure of Fe^IV CaTi_0.4Fe_0.6O_3−δ is presented and compared to data on the Fe^III counterparts. The powder XRD pattern was dominated by a simple cubic perovskite unit cell; however, some small peaks indicated an orthorhombic distortion. All peaks could be indexed using a space group analogous to the Fe^III phase Ca₃TiFe₂O₈. From HRTEM the strong cubic peaks are well explained by the superposition of three equivalent and mutually perpendicular orthorhombic unit cells. TEM analysis further revealed a microdomain structure consisting of disordered intergrowths of CaTiO₃- and Ca₃TiFe₂O₈-like phases. Mössbauer spectra show that ca. 4% of the Fe cations are in the 4+ oxidation state. Results suggest that the Fe⁴⁺ cations are associated with octahedral coordination and hence are associated with the CaTiO₃-like regions, transition regions between the CaTiO₃- and Ca₃TiFe₂O₈ intergrown phases and the domain boundaries. Structural models for the intergrowths are proposed based on HRTEM image simulations.     

Preparation and Characterization of Storage and Emission Functional Material of Cs2O-doped 12CaO·7Al2O3

We provides a novel approach to generate low-temperature atomic oxygen anions (O^-) emis-sion using the cesium oxide-doped 12CaO·7Al₂O₃ (Cs₂O-doped C12A7). The maximal emis-sion intensity of O^- from the Cs₂O-doped C12A7 at 700 oC and 800 V/cm reached about 0.54 μA/cm², which was about two times as strong as that from the un-doped C12A7(0.23 μA/cm²) under the same condition. The initiative temperature of the O^- emission from the Cs₂O-doped C12A7 was about 500 oC, which was also much lower than the initiative temperature from the un-doped C12A7 (570 oC) in the given field of 800 V/cm. High pure O^- emission close to 100% could be obtained from the Cs₂O-doped C12A7 under the lower temperature (<550oC). The emission features of the Cs₂-doped C12A7, including the emis-sion distribution, temperature effect, and emission branching ratio have been investigated in detail and compared with the un-doped C12A7. The structure and storage characteristics of the resulting material were also investigated via X-ray diffraction and electron paramag-netic resonance. It was found that doping Cs₂ to C12A7 will lower the initiative emission temperature and enhance the emission intensity.     

Luminescence enhancement of Eu, Ce co-doped Ba3Si5O13−δNδ phosphors

Host lattice Ba₃Si₅O_13−δN_δ oxonitridosilicates have been synthesized by the traditional solid state reaction method. The lattice structure is based on layers of vertex-linked SiO₄ tetrahedrons and Ba²⁺ ions, where each Ba²⁺ ion is coordinated by eight oxygen atoms forming distorted square antiprisms. Under an excitation wavelength of 365 nm, Ba₃Si₅O_13−δN_δ:Eu²⁺ and Ba₃Si₅O_13−δN_δ:Eu²⁺,Ce³⁺ show broad emission bands from about 400-620 nm, with maxima at about 480 nm and half-peak width of around 130 nm. The emission intensity is strongly enhanced by co-doping Ce³⁺ ions into the Ba₃Si₅O_13−δN_δ:Eu²⁺ phosphor, which could be explained by energy transfer. The excitation band from the near UV to the blue light region confirms the possibility that Ba₃Si₅O_13−δN_δ:Eu²⁺, Ce³⁺ could be used as a phosphor for white LEDs.     

Ni/Al2O3 catalysts for CO methanation: Effect of Al2O3 supports calcined at different temperatures

The correlation between phase structures and surface acidity of Al2O3 supports calcined at different temperatures and the catalytic performance of Ni/Al2O3 catalysts in the production of synthetic natural gas(SNG) via CO methanation was systematically investigated. A series of 10 wt% NiO/Al2O3 catalysts were prepared by the conventional impregnation method, and the phase structures and surface acidity of Al2O3 supports were adjusted by calcining the commercial γ-Al2O3 at different temperatures(600–1200 C). CO methanation reaction was carried out in the temperature range of 300–600 C at different weight hourly space velocities(WHSV = 30000 and 120000 mL·g-1h-1) and pressures(0.1 and 3.0 MPa). It was found that high calcination temperature not only led to the growth in Ni particle size, but also weakened the interaction between Ni nanoparticles and Al2O3 supports due to the rapid decrease of the specific surface area and acidity of Al2O3 supports. Interestingly, Ni catalysts supported on Al2O3 calcined at 1200 C(Ni/Al2O3-1200) exhibited the best catalytic activity for CO methanation under different reaction conditions. Lifetime reaction tests also indicated that Ni/Al2O3-1200 was the most active and stable catalyst compared with the other three catalysts, whose supports were calcined at lower temperatures(600, 800 and 1000 C). These findings would therefore be helpful to develop Ni/Al2O3 methanation catalyst for SNG production.     

Ammoxidation of 3- and 4-picolines over V2O5?SnO2/γ?Al2O3 catalyst

The ammoxidation of 3- and 4-picolines has been studied over V₂O₅–SnO₂/–Al₂O₃ catalysts prepared by surface impregnation technique. Best results were obtained for the generation of cyanopyridines in the temperature range 400–450°C and sub-stoichiometric value with respect to O₂. Catalysts that were calcined above 700°C showed no activity.

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3- 4- V₂O₅–SnO₂/–Al₂O₃, . 400–450°C O₂. , 700 K, .

     

Doping of CoMo?Al2O3 catalyst with Mg and Zn

Effect of Mg (Zn) addition to CoMo–Al₂O₃ catalyst on its activity in hydrogenation of toluene and HDS of thiophene has been determined. These additives decrease the catalyst activity and modify the mechanism of thiophene HDS.

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Mg (Zn) CoMo/Al₂O₃ () . .

     

Fe2O3/Al2O3氧载体制备方法的研究

采用溶胶-凝胶法、共沉淀法、水热合成法、低热固相合成法、机械混合法、燃烧合成法和冷冻成粒法制备铁基氧载体Fe₂O₃/Al₂O₃,并通过物理和化学表征手段来筛选和优化制备方法和制备工艺。对煅烧后的氧载体进行硬度测试,结果表明,溶胶-凝胶法、共沉淀法、机械混合法、燃烧合成法和冷冻成粒法制备的氧载体硬度较高;载体的X射线衍射(XRD)谱图表明,各种制备方法均能制得物相组成为Fe₂O₃/Al₂O₃的氧载体,且随着煅烧温度的提高、煅烧时间的延长,氧载体的结晶度、晶体粒径逐渐增大,煅烧温度1 200℃的氧载体的机械性能、晶体结构、晶相组成更稳定。借助化学吸附仪的程序升温还原(TPR)实验表征氧载体的反应活性,并计算氧载体活性度。综合物理和化学表征实验结果表明,最优制备方法为溶胶-凝胶法和冷冻成粒法。     

Catalytic performance in hydrodesulfurization of thiophene and ir investigation of Co and no adsorption over Co?Mo/Al2O3 and Ru?Co?Mo/Al2O3 catalysts

A new Ru–Co–Mo/Al₂O₃ catalyst has been prepared by impregnation of Ru salt as a secondary promoter onto Co–Mo/Al₂O₃ catalyst, and it was found that the Ru–Co–Mo/Al₂O₃ exhibited higher activity than Co–Mo/Al₂O₃ in hydrodesulfurization of thiophene to hydrocarbons. Ir studies on Ru–Co–Mo/Al₂O₃ revealed that the Co and NO adspecies increased significantly in intesnities and displayed a bathochromic shift in frequencies, as compared with Co–Mo/Al₂O₃.

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Ru–Co–Mo/Al₂O₃ Ru, , Co–Mo/Al₂O₃. Co–Mo/Al₂O₃. CO NO, Co Mo, Co–Mo/Al₂O₃. , Mo , Mo³⁺ Mo³⁺ Co Ru–Co–Mo/Al₂O₃.

     

Ni/Al2O3催化甲烷裂解

分别通过浸渍法和共沉淀法制备了不同Ni负载量的Ni/Al2O3催化剂。考察了Ni负载量、制备方法以及反应温度对Ni/Al2O3催化甲烷裂解性能的影响。结果表明,在550℃,浸渍法制备的Ni/Al2O3催化剂,当Ni负载量为20%(质量分数)、Ni金属平均粒径为11.25 nm时,具有最佳的甲烷催化裂解效果,其每摩尔Ni的氢气产量和每克Ni碳产量分别为164 mol和15.30 g。催化剂制备方法对Ni/Al2O3甲烷催化裂解反应有显著影响,相同Ni负载量共沉淀法制备的Ni/Al2O3甲烷催化裂解总体效果要好于浸渍法制备的Ni/Al2O3,而且反应过程中生成的碳纤维较长,管径也较均一。550℃时,共沉淀法制备的Ni负载量为41.2%(质量分数)的Ni/Al2O3催化剂在反应至350 min时,仍保持着30%以上的转化率。     

MoO3/Al2O3催化氧化选择性合成亚砜

采用浸渍法制备了不同负载量的MoO3/Al2O3催化剂,讨论了MoO3,Al2O3和MoO3/Al2O3负载的催化剂作用下,利用H2O2进行硫醚氧化制亚砜的反应.结果显示MoO3/Al2O3催化剂负载量为20%时催化活性最高,原料转化率达100%,且没有副产物生成.将该方法应用到兰索拉唑前体的氧化反应中,收率达到80%.催化剂重复使用6次不失活.     

Formation and properties of the new Al8V10W16O85 and Fe8?xAlxV10W16O85 phases with the M–Nb2O5 structure

A new, previously unknown phase Al₈V₁₀W₁₆O₈₅ has been obtained from reaction taking place in the solid state. It forms continuous solid solution with Fe₈V₁₀W₁₆O₈₅ of the Fe_8−x Al _x V₁₀W₁₆O₈₅ general formula. All these phases are isostructural with M–Nb₂O₅ and (W_0.35V_0.65)₂O₅ and belong to a block structure phases with ReO₃ type blocks of 4 × 4×∞ dimensions. Al₈V₁₀W₁₆O₈₅ is tetragonal and has the lattice constants a = b = 1.9487(1) nm and c = 0.36706(4) nm. It melts incongruently at 1,183 K depositing Al₂(WO₄)₃ and WO₃. The increase of the Al³⁺ ions content in the crystal lattice of Fe₈V₁₀W₁₆O₈₅ causes the melting point increasing, and decreasing of a = b unit cell parameters with c being almost constant. IR spectra of Al₈V₁₀W₁₆O₈₅ and Fe_8−x Al _x V₁₀W₁₆O₈₅ phases have been recorded.     

Ce0.67Zr0.33O2对CH4燃烧催化剂Fe2O3/Al2O3的改性作用

固定n(Ce)/n(Zr)比为0.67/0.33, 用共沉淀法制得一系列CeO2-ZrO2-Al2O3固溶体. 采用这些固溶体作载体, 以Fe2O3为活性组分, 用浸渍法制备了一系列催化剂. BET结果显示, 将适量Ce0.67Zr0.33O2引入到Al2O3载体中有助于催化剂保持较高的比表面积. TPR结果显示, 载体中引入适量的Ce0.67Zr0.33O2可以改善催化剂的氧化还原性能. XRD结果表明, Fe2O3在CeO2-ZrO2-Al2O3载体上呈现出良好的分散状况, 老化前后催化剂的晶相结构基本无明显变化. 特别是当载体中m(Ce0.67Zr0.33O2)∶m(Al2O3)的值为1∶2时, Fe2O3/CeO2-ZrO2-Al2O3催化剂在甲烷催化燃烧中显示出最佳的催化性能和抗高温老化性能.     

Ce0.67Zr0.33O2对CH4燃烧催化剂Fe2O3/Al2O3的改性作用

固定n(Ce)/n(Zr)比为0.67/0.33,用共沉淀法制得一系列CeO2-ZrO2-Al2O3固溶体.采用这些固溶体作载体,以Fe2O3为活性组分,用浸渍法制备了一系列催化剂.BET结果显示,将适量Ce0.67Zr0.33O2引入到Al2O3载体中有助于催化剂保持较高的比表面积.TPR结果显示,载体中引入适量的Ce0.67Zr0.33O2可以改善催化剂的氧化还原性能.XRD结果表明,Fe2O3在CeO2-ZrO2-Al2O3载体上呈现出良好的分散状况,老化前后催化剂的晶相结构基本无明显变化.特别是当载体中m(Ce0.67Zr0.33O2)∶m(Al2O3)的值为1∶2时,Fe2O3/CeO2-ZrO2-Al2O3催化剂在甲烷催化燃烧中显示出最佳的催化性能和抗高温老化性能.     

Modelling, refinement and analysis of the “Type III” δ-Bi2O3-related superstructure in the Bi2O3-Nb2O5 system

The structure of the “Type III” δ-Bi₂O₃-related superstructure phase in the system Bi₂O₃-Nb₂O₅ is presented. A starting model was constructed by considering the crystal-chemistry of the system in the context of symmetry constraints determined by electron diffraction. After applying initial distortions, this could be Rietveld-refined against a combination of synchrotron X-ray and time-of-flight neutron powder diffraction data. The undistorted starting model was independently optimized using solid-state ab initio energy calculations, giving a fully optimized structure in excellent agreement with that obtained by Rietveld refinement. This dual approach both validates the structure and demonstrates the value of combining accurate total energy calculations with traditional refinement techniques for the solution of complex structures using powder diffraction data. The structure (Bi₉₄Nb₃₂O₂₂₁, Z=1, (#119), a=11.52156(18), ) consists of interacting corner-connected strings of NbO₆ octahedra along 〈110〉_F directions of the FCC subcell, and can be described as a hybrid of fluorite and pyrochlore types.     

p(O2)-stability of LaFe1−xNixO3−δ solid solutions at 1100 °C

LaFe_1−xNi_xO_3−δ (x=0.1−1.0) perovskites were synthesized via citrate route. The p(O₂)-stability of the perovskite phases LaFe_1−xNi_xO_3−δ has been evaluated at 1100 °C based on the results of XRD analysis of powder samples annealed at various p(O₂) and quenched to room temperature. The isothermal LaFeO_3−δ-“LaNiO_3−δ” cross-section of the phase diagram of the La-Fe-Ni-O system has been proposed in the range of oxygen partial pressure −15<log p(O₂)/atm≤0.68. The unit cell parameters of orthorhombic perovskites O-LaFe_1−xNi_xO_3−δ increase with decrease in p(O₂) at fixed composition x. This behavior is explained on the basis of size factor. The decomposition temperatures of rhombohedral phases R-LaFe_1−xNi_xO_3−δ for x=0.7, 0.8, 0.9 and 1.0 in air were determined as 1137, 1086, 1060 and 995 °C, respectively.     

Reduction of an amorphous NiO?Al2O3/SiO2 catalyst by different olefins and hydrogen

By static magnetic measurements it was found that the ability to reduction of an amorphous NiO–Al₂O₃/SiO₂ catalyst decreases in the order: but-2-eneshydrogen isobutene>but-1-ene>propeneethene. The reduction temperatures are significantly higher than the dimerization reaction temperatures.

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, NiO–Al₂O₃/SiO₂ : -2>-1> . .