Novel nanocasting method for synthesis of ordered mesoporous metal oxides

Novel one-step high vacuum nanocasting method is developed to prepare ordered mesoporous rare earth and transition metal oxides with high-surface area using mesoporous KIT-6 as hard templates. Characterization of these mesostructured materials was performed by the X-ray powder diffraction, high resolution transmission electron microscopy and N₂ adsorption–desorption isotherms. In this synthesis method, metal oxide precursors are effectively filled into the channels of hard templates by a one-step high vacuum impregnation, and the excess precursors can be removed through vacuum filtration. It is a very effective nanocasting method and has the wider application in the preparation of mesoporous metal oxides with high surface area and high purity.     

介孔过渡金属氧化物的合成研究进展

介孔过渡金属氧化物作为一种非硅基介孔材料,在光、电、磁、传感、催化等领域有着潜在的应用价值,是近年来研究的热点。本文主要从合成角度对几种典型的介孔过渡金属氧化物的最新研究进展作了总结,其中包括Ti、W、Nb、Mn、Mo、Ni、Co等。详细阐述了其合成方法、合成过程,也涉及了少量的应用研究,并根据目前合成该类材料所面临的难题,提出了介孔过渡金属氧化物以后的研究方向,即合成具有高热稳定性、孔壁高度结晶以及长程有序的介孔材料。     

介孔金属有机框架材料吸附水中重金属离子研究进展

介孔金属有机框架材料（介孔MOFs）相较于传统吸附剂具有孔径大、孔隙率可调、比表面积大、官能团丰富,便于功能化改性修饰等优点,可高效地吸附水体中重金属污染物。本文介绍介孔MOFs的特性、合成策略及四种合成介孔MOFs的方法,重点分析四种方法的介孔形成机理及其所面临的问题,并将四种合成方法的优劣进行了比较。详述介孔MOFs吸附去除水中重金属离子、类重金属阴离子以及放射性金属离子的研究进展;介绍了介孔MOFs在吸附去除重金属离子方面的可重复利用性;阐述介孔MOFs吸附去除水中重金属污染物的作用机理。对介孔MOFs成本高昂、合成条件苛刻、回收利用难等问题提出了优化方向,指出提高介孔MOFs的水稳定性、易回收利用、简便绿色合成技术以及痕量去除将是未来的研究方向。     

Preparation and Characterization of Novel Mesoporous Lanthanide–Transition Metal Mixed Oxides

We report a cationic supramolecular templating route to prepare thermally stable mixed oxides of lanthanides–transition metals, and characterization of such materials. The materials have three-dimensional wormhole-like mesoporosity with a partly crystalline lanthanide phase but an X-ray diffraction-invisible transition metal oxide phase that are probably finely dispersed as <3 nm crystallites. The materials had high surface areas with a narrow pore-size distribution in the mesoporous range after calcination up to 973 K. The materials were active for volatile organic compounds (toluene) removal at room temperature, with mesoporous ceria–titania showing the highest activity. These results suggest that these mesoporous mixed oxides are promising for air-purification applications.     

晶态介孔金属氧化物的合成研究进展

晶态介孔金属氧化物与相应的无定形材料相比具有更加优异的催化、光学、电学、磁学和力学等性能,具有较宽的应用范围,是近年来介孔材料合成的热点。本文主要对晶态介孔金属氧化物的制备方法,包括非晶晶化法、蒸发诱导自组装法和硬模板法进行了介绍,并对这些方法的优缺点进行了比较。     

表面活性剂引导合成非硅基介孔材料的研究进展

非硅基介孔材料由于其突出的结构特性和特殊的光、电、磁性质,广泛应用于许多研究领域,使该类材料的合成逐渐成为研究者关注的焦点。本文综述了国内外近年来表面活性剂引导合成非硅基介孔材料的研究进展,阐述了离子型表面活性剂和非离子型表面活性剂作为模板剂及混合模板剂合成介孔碳、介孔金属氧化物等非硅基介孔材料的现状,归纳了合成该类介孔材料的最佳工艺条件,总结了不同模板剂引导合成的非硅基介孔材料特点,同时列表对比了不同类型表面活性剂合成该类材料的性能参数和应用领域,并对其发展进行了展望,即表面活性剂的绿色化、材料的功能化、合成过程的共模板化是未来发展的主流方向。     

硬模板法合成晶态介孔金属氧化物研究进展

晶态介孔金属氧化物材料因具有窄的孔径分布、大的比表面积、有序的孔道结构以及高度晶化的孔壁而在工业催化、光电等领域有着广泛的应用.在各种制备方法中,硬模板法因制备方法简单、条件温和、产物孔道结晶度高而受到了广泛关注.对硬模板法中介孔硅模板和介孔碳模板进行了介绍;总结了近年来硬模板法合成氧化铬、氧化铁、氧化铈、氧化镁和氧化钴等晶态介孔材料的研究进展;概述了该材料的发展趋势和应用前景.     

MCM-41介孔分子筛合成与改性的研究进展

简要介绍了MCM-41介孔分子筛的特点,应用和改性原因.综述了MCM-41介孔分子筛的合成方法,主要包括水热合成法,室温合成法,微波合成法等,列出了每种合成方法的优缺点和合成过程中的影响因素,pH值、晶化时间、晶化温度、模板剂的种类及用量等都会对MCM-41介孔分子筛的结构和孔径产生很大影响.阐述了MCM-41介孔分子筛的改性方法,包括金属杂原子取代法,如主族金属、过渡金属、稀土金属等,有机修饰或功能化法,负载型改性法,如负载金属氧化物、无机酸、杂多酸、有机碱、金属的配合物等.最后就MCM-41介孔分子筛的应用前景做了展望.     

Synthesis of cyclic carbonates from urea and diols over metal oxides

Several metal oxides were used for synthesis of ethylene carbonate from urea and ethylene glycol. ZnO showed high activity towards the reaction. TPD, FTIR and reaction test indicated that the catalysts with appropriate acid and base properties were favorable to the synthesis of cyclic carbonate. Furthermore, the reaction of urea with various diols revealed that the selectivity of five-membered cyclic carbonates was higher than that of six-membered cyclic carbonates.     

Preparation of propylene carbonate by alcoholysis of urea from the perspective of homogeneous reaction: Influence of dissolution and precipitation of metal oxide catalysts

The dissolution process of metal oxide catalysts in the alcoholysis of urea by 1, 2-propylene glycol (PG) to the synthesis of propylene carbonate (PC) was investigated. It was found that the reaction was mainly catalyzed by homogeneous catalysts. The metal oxide reacted with ammonia and isocyanate acid, the decomposition products of urea, to form a complex and dissolved into the reaction system. The dissolved amount of catalyst was positively correlated with the PC yield by using different oxides and salts as catalysts. The Fourier-transform infrared spectroscopy (FTIR) result of the catalysts reacting with urea showed that the dissolution-precipitation process of the catalysts was related to the decomposition of urea. The results of catalytic test indicated that both the dissolved amount of catalysts and the structure of the complex affected PC yields. A reaction mechanism was proposed based on the results. From the mechanism, a complex catalyst with at least two ammonia ligands is better for this reaction.     

Ammonium dicyanamide as a precursor for the synthesis of metal nitride and carbide nanoparticles

We designed a highly efficient, fast and facile route for the syntheses of both metal nitrides and carbides starting from an organic reagent ammonium dicyanamide and the corresponding metal oxides, respectively. Four technologically important metal nitrides and four carbides including cubic VN, CrN, NbC, TaC, hexagonal GaN, AlN, WC, MoC were synthesized successfully at moderate temperatures. It is interesting to find that ammonium dicyanamide is not only a highly efficient nitridation reagent but also a highly efficient carburization reagent. The metal oxides are completely converted into the corresponding metal nitride and carbide nanoparticles at relatively low temperatures. A possible mechanism is proposed to explain the results of the reactions between the organic reagent and metal oxides. It is found that highly active carbon nitride materials condensed by ammonium dicyanamide play the crucial roles in the reduction, nitridation and carburization processes. This novel route may provide new insights into the synthesis of other metal nitrides and carbides.     

Effects of reduction of metal oxide sorbents on reactivity and physical properties during hot gas desulphurization in IGCC

In this study, the changes of physical properties and reactivity of the metal oxide sorbents were investigated under the reducing conditions of coal gas. Metal oxide sorbents are converted into metal sulphides as a result of reaction with H₂S in synthesis gas. This could cause the reduced reactivity of sorbents if the metal oxides were converted into metallic elements due to the reduction by either hydrogen or carbon monoxide. In this experiment, the changes of physical properties and reactivity of the metal oxides were investigated over the temperature range 480-700 °C. It is confirmed that the reactivity of sulphidation and the reduction of metal oxide increased with increasing temperature. Even though the sulphur capacity of the sorbents in the early stage was high, it reduced rapidly due to the progressive reduction of metal oxides as the sulphidation/regeneration process was repeated. The reduction of metal oxide and the extent of reduction were verified by measuring the amount of oxygen consumed and the amount of SO₂ produced during the regeneration of sulphidated sorbents with the aids of a gas analyser. It was concluded that the reactivity of the metal oxide sorbents was influenced by reduction with coal gas at high temperature.     

非硅基介孔材料的合成和研究进展

主要介绍了介孔碳、介孔金属氧化物、介孔金属等几种主要类型的非氧化硅基介孔材料的合成及研究进展,包括合成方法、材料表征以及这些材料的应用等,同时指出这类材料的研究热点和发展趋势.     

几种稀土介孔复合材料合成方法

介绍以水热合成法制备含稀土金属化合物的介孔分子筛的方法。确定了分子筛的制备条件对介孔材料结构的影响,其主要影响因素为模板剂用量,晶化温度以及pH值,考察了稀土金属化合物用量,晶化时间,陈化时间,焙烧气氛以及加料方式等制备条件对分子筛的特征结构的影响。指出了根据实际的需要控制介孔材料的组织结构的方法,找到几种高效的稀土金属化合物,方便修饰替代到介孔材料中,又不引起介孔材料结构的破坏。     

生物模板法制备金属氧化物及其催化应用研究进展

自然环境中长期进化形成的多层次、多维和多尺度天然硬模板结构和一些具有多层次多维结构的天然“软”生物分子可为多级结构纳米材料的设计与制备提供了新的思路。金属氧化物通常作为催化剂的重要组成部分,其制备与催化应用得到广泛关注,生物模板法为金属氧化物的制备提供了一条简单、绿色、有效的合成路线。本文从基于生物模板的制备方法、生物模板在氧化物制备过程中的作用和生物模板在金属氧化物催化应用时的作用方面总结近十年来的研究进展。基于硬模板的制备方法简单高效,可完美地复制结构类似的金属氧化物材料,而软模板能够灵活地调控金属氧化物颗粒的尺寸和分散性。基于生物模板制备金属氧化物的过程往往经历“吸附-成核-生长-组装”多步骤,生物模板起着表面吸附、空间限域、导向等重要作用。就所得金属氧化物的催化应用而言,生物模板法的优势在于能够实现氧化物材料元素的自掺杂、有效改善传质以及特殊的表面结构赋予催化剂优异的催化性能。     

三维金属氧化物纳米材料的研究进展

三维金属氧化物纳米材料（3D-MONs）具有独特的连续多孔网络结构特点,不仅使其保留了金属氧化物特有的化学性质,而且表现出低密度、高比表面积、高孔隙率、低热导率等优异的物理性能,是近年来纳米材料领域一个新的研究热点。综述了3D-MONs制备方法的研究进展,重点介绍了水热合成法、溶胶-凝胶法、模板法、溶液喷射法、直接发泡法,并对其共性与差异进行了讨论;探讨了3D-MONs在污水治理、空气净化、储能、隔热领域应用的研究进展;在此基础上,提出了合成3D-MONs需要解决的问题及其应用展望。     

Cyclic extrusion synthesis of mesoporous carbon-supported metal catalysts for selective hydrogenation

The mesoporous carbon-supported metal catalysts are important materials in heterogeneous catalysis. From the standpoint of process intensification, the current synthesis methods still suffer from several issues, such as the excessive use of toxic solvents, the time-consuming self-assembly process, and the difficulty of continuous production. Herein, we report a solvent-free and continuous route to synthesize mesoporous carbon-supported metal catalysts. Interestingly, the use of cyclic extrusion could promote mixing, coordination, and assembly of catalyst precursors (tannin-metal salts-additives) by shearing and squeeze force. The as-made mesoporous carbon-supported nickel materials showed high surface areas (up to 512 m² g⁻¹), narrow pore size distribution (~10 nm), and good performance in the selective hydrogenation of nitrobenzene to aniline (Conv. >99%; Sel. >99%). In addition, the fluid property of catalyst precursors and the geometry of the twin-screw extrusion channel were studied, and the essence of this cyclic extrusion process is also discussed.     

尿素和苯酚直接合成水杨酰胺

以CaO、MgO、La2O3、Al2O3、ZrO2等5种金属氧化物为催化剂,以尿素和苯酚为原料直接合成了水杨酰胺。在相同条件下,发现MgO对该反应的催化性能最佳。考察了反应温度、反应时间、催化剂用量、原料配比等因素对水杨酰胺收率的影响,最佳反应条件为:反应温度245℃,反应时间12h,MgO的用量0.2g,n(苯酚)∶n(尿素)=15∶1,水杨酰胺的收率达45.1%。     

Synthesis and characterization of transition metal and metal oxide nanoparticles inside mesoporous carbon CMK-3

Transition metal oxides were synthesized inside the pore system of mesoporous carbon CMK-3. By a wet impregnation, drying and calcination procedure iron, copper, nickel, cobalt, manganese and zinc oxides were formed almost exclusively within the mesopores. A reduction into the metal forms with regard to structural array in the case of zinc oxide and a reduction to manganese(II) oxide for manganese(IV) oxide was accomplished by hydrogen. Powder X-ray diffraction (PXRD), Raman spectroscopy and transmission electron microscopy (TEM) proved the preservation of the host structure during impregnation and reduction procedures. The formation of nanosized metal oxides inside the mesopore system was confirmed with PXRD and TEM. Nitrogen physisorption measurements still revealed micro- and mesoporosity for the host/guest compounds. A reduction of the surface areas and pore sizes in contrast to the host structure being an indication of the coating of the inner surfaces of the carbon walls is shown as well. Infrared and X-ray absorption spectroscopy (XAS) carried out in fluorescence mode confirm the formation of the respective oxides and metals. Furthermore, the existence of small, disordered nanoparticles was proved by XAS investigations and information on the local structure of the metals and metal oxides was obtained from these measurements.     

High-throughput syntheses of nano-scaled mixed metal sulphides

The use of metal and mixed metal sulphides as heterogeneous catalysts is often hampered by an undefined composition formed by in situ sulphidation of oxides. Controlled synthesis methods are serial and thus slow, because high-throughput (HT) methods for the well-directed syntheses of exactly defined metal sulphides and especially mixed metal sulphides are still lacking. The present contribution presents the development of HT synthesis methods for a broad range of nano-scaled sulphides for various applications, such as heterogeneous catalysts or photocatalysts. The nano-scale regime for the particle sizes offers the possibilities of high surface area, appearance of quantum size effects and the possibility of modification of their properties as well as stabilisation of the particles by surface coating. Several precursor molecules have been tested, which hydrolyse under specific conditions and release sulphide ions for metal and mixed metal sulphide precipitation. Particle size confinement was achieved by w/o microemulsions using non-ionic surfactants. In a first step for the parallel synthesis of sulphides a 9-fold reactor assembly was developed, which offers the possibility of synthesis by precipitation and separation of the resulting materials by filtration in one setup.