Catalytic application of niobium compounds

Salient examples of catalytic application of niobium compounds and materials are demonstrated. Niobium oxides, when small amounts are added to known catalysts, markedly enhance catalytic activity and selectivity and prolong catalyst life for various reactions. Moreover, niobium oxides exhibit a pronounced effect as supports of metal or metal oxide catalysts. Hydrated niobium pentoxide (niobic acid, Nb₂O₅·nH₂O) and niobium phosphate which are unusual solid acids show high catalytic activity, selectivity, and stability for acid-catalyzed reactions. Layer compounds containing niobium combined with metal show peculiar photocatalytic activity. These characteristic features of niobium compounds as catalysts and catalyst components are discussed, their potential significance being emphasized.     

Preparation of mesoporous In–Nb mixed oxides and its application in photocatalytic water splitting for hydrogen production

A series of mesoporous In–Nb mixed oxides was synthesized using NbCl₅ and In₂O₃ as the starting material and triblock copolymer P123 as template. We investigated the influence of indium content on the synthesis and characteristics of the mesoporous In–Nb mixed oxides, and their photocatalytic activities for water splitting. The materials were characterized by small angle X-ray scattering, powder X-ray diffraction, extended X-ray absorption fine structure, transmission electron microscopy, scanning electron microscopy, energy dispersive spectrometer, N₂ sorption and UV–vis spectroscopy. The surface area of mesoporous In–Nb mixed oxides was greater than 90 m²/g with a wormhole framework. The optimization of synthesis condition of the mesoporus In–Nb oxides catalyst contained a small fraction of highly dispersed indium (In/Nb = 0.13) species intercalated into the framework of mesoporous niobium oxides and exhibited a high photocatalytic activity for water splitting reaction which was about 2.7 times as compared to mesoporous Nb₂O₅ and was about 19 times higher than commercial bulk Nb₂O₅.     

Oxidation–reduction processes in halide and oxohalide niobium containing melts. Part I: Interaction of fluoride–chloride and oxofluoride–chloride Nb(V) melts with niobium oxides

The interaction between the K2NbF7–KCl–NaCl melt widely used for niobium electrolysis and niobium oxides of higher (Nb2O5) and lower (NbO2 and NbO) oxidation states was studied by linear sweep voltammetry and analysis of the dissolution time dependences. Three monooxofluoride complexes, NbOF4–, NbOF2–5 and NbOF63–, may form at the mole ratio of Nb2O5:K2NbF7=1:3. No significant difference was found in the electrochemical behaviour of the complexes, but their discharge potentials become more negative with increasing number of fluorine anions in the complex. Due to the interaction of K2NbF7 with NbO2 and NbO, oxofluoride Nb(v) and fluoride Nb(iv) complexes form simultaneously in the KCl–NaCl melt. Thus, the content of the latter increase until the molar ratios in the melt become NbO2dissolv.:K2NbF7init.=1:2 and NbOdissolv.:K2NbF7init.=1:3 and decrease with further dissolution of oxides in the melt. Dissolution of lower niobium oxides in melts containing oxofluoride Nb(v) complexes was also studied.     

纳米金属氧化物去除水体重金属的研究进展

简要介绍了用于吸附水体重金属的几种纳米金属氧化物,包括:纳米铁氧化物、纳米锰氧化物、纳米铝氧化物、纳米钛氧化物、纳米锌氧化物、纳米镁氧化物、纳米铈氧化物以及纳米金属氧化物复合材料,讨论了各种纳米金属氧化物处理水体重金属的优缺点,并展望了其应用前景。     

Supertetragonal Phases of Perovskite Oxides: Insights from Electronic Structure Calculations

We review some of the insights that electronic-structure calculations has brought about the properties of the materials with the largest electric polarization known – supertetragonal perovskite oxides. These are materials whose structure corresponds to a perovskite that has been substantially strechted along one of its pseudocubic axes. They grow in different forms: bulk crystals (such as BiCoO₃), epitaxial films (such as BiFeO₃), nanowires whose inside is under negative pressure (such as PbTiO₃), and others. Electronic structure calculations based on density-functional theory have revealed that supertetragonality potentially exist for many perovskite oxides under the right conditions, and they have helped explain why some of those conditions are easy to reach for some of the materials of the family, but not for others.     

高熵氧化物的制备及应用研究进展

高熵氧化物作为近几年发展起来的新型氧化物体系，打破了传统掺杂氧化物的设计理念，由五种及以上氧化物以等摩尔或近等摩尔构成，因其具有简单的结构和优异的性能等受到国内外研究人员的广泛关注。高熵氧化物由于多主元且主元之间混乱排列，易形成岩盐型、氟化钙型、尖晶石型或钙钛矿等固溶体结构，从而表现出优异的性能，尤其在能源存储材料和磁性材料方面有十分广阔的应用前景，但目前对高熵氧化物应用研究较少。本工作介绍了国内外高熵氧化物的制备方法，主要包括固相法、热解法、共沉淀法、水热合成法和液相燃烧合成法等，比较了各方法的优缺点和发展前景；归纳了高熵氧化物作为锂离子电极材料、巨介电材料、磁性材料和催化材料等方面的应用；指出了高熵氧化物目前研究存在的问题，讨论了解决措施，展望了高熵氧化物未来的发展趋势。     

生物炭负载铁氧化物复合材料的制备及在水处理中的应用

纳米铁氧化物能够更高效地去除水中多种有机和无机污染物质,但易团聚失活、易流失等问题限制了其在水处理中的实际应用。生物炭（biochar,BC）作为一种新型的多孔材料具有比表面积大、碳结构稳定、原料来源广、成本低等优点,是负载纳米铁氧化物的理想载体。近年来,BC负载铁氧化物复合材料（铁氧化物/BC）在水处理领域表现出巨大的应用潜力而备受关注。本文重点介绍和总结了铁氧化物/BC的制备方法,及其吸附、催化氧化去除水中磷、有机污染物、重金属及砷的应用、机理和影响因素;并介绍了其在污泥脱水、光催化消毒等水处理环节的应用。在此基础上,从进一步提高去除污染物性能、实际应用经济和技术可行性、扩展材料应用范围等方面提出了今后研究的方向。     

Reactive flash sintering and electrical transport properties of high-entropy (MgCoNiCuZn)1-xLixO oxides

In this paper, high-entropy (MgCoNiCuZn)_1-xLi_xO oxides (x = 0, 0.1, 0.15, 0.2, and 0.3) were synthesized via reactive flash sintering (RFS), and the effect of RFS process on the microstructure and electrical property of the materials were studied. The Li-doped materials exhibited a mixed ionic–electronic transport behavior. The oxidation of Co²⁺ into Co³⁺ upon Li incorporation into the materials synthesized via the conventional solid-state reaction route was not evidenced in the flash sintered materials. Instead, the charge unbalance in the Li-doped materials synthesized via RFS was compensated by oxygen vacancies and holes in the valence band of the oxides, which were accounted for the ionic conduction and electronic conduction, respectively. The ionic conductivity increased upon increasing the Li concentration as more oxygen vacancies were formed. The attraction between defects with different charges (Li_M^/ and V_O^••), which formed defect complexes, led to a decrease in the mobility of the defects, thus resulting in a less pronounced increase in the ionic conductivity at high Li concentrations. The change in the charge compensation mechanism of the materials indicates that the microstructure of such kind of oxides could be altered through RFS, and thus the property may be manipulated.     

Surfactant-assisted growth of anodic nanoporous niobium oxide with a grained surface

Nanoporous niobium oxide film with a maximum thickness of 520 nm was prepared by anodizing niobium in a mixture of 1 wt% HF, 1 M H₃PO₄, and a small amount of Sodium Dodecyl Sulfate (SDS) surfactant. The porosity of the anodic niobium oxide prepared without SDS is irregular with the surface of the oxide suggesting a grained surface pattern rather than an ordered porous structure. A proper amount of SDS addition can prepare a pore arrangement with stripe patterns. The pore depth and surface pattern were strongly affected by the concentration of SDS and bath temperature. We found that the addition of SDS surfactant facilitated improvement in the chemical resistance of niobium oxide, leading to the formation of pores with a longer length compared to those prepared without a SDS surfactant. This can be in part ascribed to the protection of the surface by the physical adsorption of SDS on the surface due to a charge-charge interaction and be in part attributed to the formation of NbO bonding on the outermost oxide layer by SDS. When anodization was carried out for 4 h, the surface dissolution of niobium oxide was observed, which means that the maximum tolerance time against chemical dissolution was less than 4 h.     

复杂氧化物载氧体的调变策略及在过程强化中的应用

CO₂减排已经成为各国发展的重要议题之一。化工产业的传统分离过程由于?效率过低,往往会导致大量的能源浪费及CO₂排放。作为一种典型的、耦合分离与反应的过程强化策略,化学链技术有利于实现产物分离、能量梯级利用,从而显著提升系统?效率。高通量计算与化学链技术的结合,可以针对不同化学反应,指导相应的化学链载氧体热力学性质的调变策略。以化学链空气分离、氧化脱氢和热化学储能三个典型过程为例,简述化学链过程中复杂载氧体热力学性质的调变策略。热力学分析表明,不同化学链流程中载氧体性质的优化方向和最优区间均存在显著差异。因此,未来化学链技术发展的重要方向之一,是针对不同的化工流程进行载氧体的精确调变,从而实现化工流程的最优化。     

稀土纳米氧化物的研究进展

介绍了稀土氧化物纳米材料的制备、性质及其应用方面的研究进展，并介绍了稀土纳米氧化物的发展趋势。     

碳球@纳米片状钴镍金属氧化物核壳型复合材料的制备及其电化学性能

以葡萄糖为碳源，采用水热炭化法制备碳球，然后以氯化钴和氯化镍为钴源和镍源，六次甲基四胺为沉淀剂，采用水热法和高温处理合成一种核壳结构的碳球@钴镍金属氧化物纳米复合材料，并研究其作为超级电容器电极材料的储能性能。借助X射线衍射、扫描电镜和低温氮气吸附/脱附等对材料的形貌和结构进行表征。采用循环伏安、恒电流充放电及交流阻抗等对材料的电化学性能进行研究。结果表明：碳球的加入能有效改善钴镍金属氧化物的分散性，同时降低材料的电子转移阻力，进而提高其电化学性能。当电流密度为1A/g时，所得碳球@钴镍金属氧化物核壳型复合材料的比电容为984.8F/g；当电流密度增大10倍（10A/g）时，仍保留86.3%的初始比电容值。当电流密度为15A/g时，经过2000次恒电流充放电后复合材料的比电容量保持率为94.6%，体现出较好的循环稳定性能。     

超疏水金红石型纳米钛硅复合氧化物的制备与表征

以正硅酸乙酯为硅源、钛酸异丙酯为钛源，采用改进的溶胶-凝胶法制备了不同钛硅摩尔比的复合气凝胶，在不同温度下进行煅烧，得到金红石型钛硅（TiO₂-SiO₂）复合氧化物纳米颗粒，然后通过三甲基氯硅烷（TMCS）改性，制得超疏水金红石型TiO₂-SiO₂纳米材料。探讨了钛硅摩尔比和煅烧温度对钛硅复合氧化物纳米颗粒晶型的影响，并通过XRD、XPS、BET、SEM和FTIR等手段对产物进行了表征，采用水接触角测试（WCA）对纳米材料改性后的疏水性能进行了表征。结果表明：当钛硅摩尔比为5：1时制得的气凝胶在1100℃煅烧及TMCS改性后，所制备的超疏水金红石型纳米钛硅复合氧化物的比表面积大，疏水性能优异，其比表面积达348 m²·g^-1，水接触角达到154.7°，在构建具有纳微分层结构的外墙装饰材料的面漆方面具有潜在的应用前景。     

非硅系介孔材料及其应用

介孔材料孔容存贮高、表面凝缩特性优良,在光、电、磁、传感、催化等领域有着广阔的应用,是近年来国内外跨学科研究的热点。文章介绍了近几年来国际上颇为关注的非硅系介孔材料的主要研究动向及其应用方面的最新成果,内容包括介孔铝磷酸盐(AlPOs)、介孔碳、介孔金属氧化物等。     

Design principles for spray-roasted iron oxides for the manufacturing of ferrites

A range of high purity iron oxides are prepared by varying basic operation parameters of an industrial spray roasting process. These iron oxides are investigated in relation to their morphology and subsequently evaluated as raw materials for MnZn-ferrite preparation. It appears that the most important morphological parameters for determining the reactivity (defined as firing shrinkage at equal compaction density) of the high purity iron oxide, and consequently the final density and magnetic properties of the ferrite specimens, are the primary particle size and the number of primary particles per aggregate. As found, the specific surface area of the iron oxide is of no predictive value for the behavior of the iron oxide in a MnZn-ferrite manufacturing process. A small primary particle size is important for a high reactivity; however, when particles are packed together in large aggregates, they are not available for the prefiring reactions. As a result, reactive sintering takes place leading to high porosity and bad microstructure. As found by the characterization methods employed in this article, the optimum iron oxides for MnZn-ferrite preparation should have a primary particle size between 0.45 and 0.55 μm with an aggregate size below 1.60 μm.     

Crossflow filtration of oils on metal oxides. Influence of chemical composition of the layer

A new technique of fat fractionation was described in which butter oil and a formulated oil (olive, grapestone, coconut, and linseed) have been submitted to crossflow percolation at 45°C on different metal oxides layers (Al₂O₃, TiO₂, ZrO₂) of various thickness. The metal oxides layers were used in order to highlight the interaction between triglycerides (TG) and filtering materials. Experiments have been checked by high-performance liquid chromatography and by differential scanning calorimetry. Partition number was used to take the double bonds into account, and nonpolarity index was used to estimate the relative hydrophobicity of TG molecules. Results point out a two-step complex partition phenomenon: The filtering layer that is initially hydrophilic is coated by less hydrophobic TG acting as a second interface with hydrophobic characteristics. The three tested metal oxides did not provide comparable patterns. The specific property of aluminum oxide is related to a better polarizability of the Al−O bond.     

锂离子电池用Na-Mn-O材料的合成及应用

Na-Mn-O材料可作为离子交换法制备层状LiMnO2的前体,同时也可以直接作为锂离子电池的正极材料,被认为是锂二次电池研究中很有前景的新型材料。本文重点介绍了Na-Mn-O材料的晶体结构、制备方法,以及以该材料为前体,通过离子交换法合成的LixMnO2正极材料的结构与电化学性能。同时讨论了Na-Mn-O材料在锂二次电池、钠离子电池以及其它一些方面的应用,分析了Na-Mn-O材料作为未来锂二次电池正极材料的发展趋势。     

超级电容器中石墨烯基复合电极材料研究进展

主要介绍了石墨烯与多种过渡金属氧化物构筑的复合材料在超级电容器方面的研究进展,其中列举了最为常见的金属氧化物如氧化锌、氧化镍、二氧化锰、氧化钴等。从各种复合材料的制备方法、电化学性能等方面进行了阐述和说明。     

介孔半导体化氧化物和硫化物的研究进展

非硅组成的介孔金属氧化物和硫化物半导体材料在光、电、催化和传感等诸多领域展示了独特的应用前景.介绍了最近几年来国内外有关半导体介孔材料合成和应用的研究动向及最新研究成果,内容包括半导体金属氧化物和硫化物等.     

Solid state chemistry of bulk mixed metal oxide catalysts for the selective oxidation of propane to acrylic acid

Syntheses of Mo–V–Sb–Nb–O bulk materials, which are candidate catalyst systems for the selective oxidation of propane to acrolein and acrylic acid, were made using soluble precursor materials. The products were characterized by X-ray powder diffraction and Raman spectroscopic studies. The objectives of this work were to explore the utility of liquid phase automated synthesis for the preparation of bulk mixed metal oxides, and the identification of the oxide phases present in the system. This is the first published study of the phase composition for these materials. After calcination of these bulk oxides under flowing nitrogen at 600°C, and using stoichiometric ratios of Mo–V–Sb–Nb (1:1:0.4:0.4) and Mo–V–Sb–Nb (3.3:1:0.4:0.4) it was demonstrated that a mixture of phases were obtained for the syntheses. X-ray powder diffraction studies distinguished SbVO₄, Mo₆V₉O₄₀, MoO₃, and a niobium-stabilized defect phase of a vanadium-rich molybdate, Mo_0.61–0.77V_0.31–0.19Nb_0.08–0.04O_x, as the major phases present. Complementary data were provided by the Raman spectroscopic studies, which illustrated the heterogeneity of the phases present in the mixture. Raman also indicated bands attributable to the presence of phases containing terminal M=O bonds as well as M–O–M polycrystalline phases. Previous studies on this system have identified SbVO₄ and niobium-stabilized vanadium molybdate species as the active phases necessary for the selective oxidation of alkanes.