一锅法制备磁性Ni-Ag纳米合金催化剂 及其催化还原对硝基苯酚

采用液相共还原一锅法制备了不同[Ni]∶[Ag]比例的磁性Ni-Ag纳米合金催化剂。利用XRD、SEM、TEM表征了催化剂的物相和形貌,利用XPS测试了催化剂表面元素价态,采用SQUID分析了催化剂的磁学性能;以对硝基苯酚的催化还原反应作为模型反应,研究了[Ni]∶[Ag]比例对磁性Ni-Ag纳米合金催化剂催化性能的影响,并考察了其循环使用性能。结果表明,磁性Ni-Ag纳米合金催化剂由直径50 nm左右的Ni-Ag合金颗粒组成,催化还原对硝基苯酚的催化活性随Ag含量的增加先增强后减弱,[Ni]∶[Ag]=1∶1的催化剂催化性能最好。该Ni-Ag纳米合金催化剂的饱和磁化强度为15.43 emu·g~(-1),具有很好的磁学性能,可实现磁回收和循环利用,循环使用5次后依然保持高催化活性和稳定性。     

磁性纳米催化剂制备生物柴油研究进展

磁性纳米催化剂是一类具有磁响应特征的催化剂,由于具有较高的催化活性、良好的反应选择性及优良的磁响应性等优点,克服了纳米催化剂活性高但难分离的缺点,是生物柴油制备过程良好的甲酯化反应催化剂,为生物柴油催化剂研究的重要方向。本文综述了磁性纳米催化剂的结构特点、制备方法及其在制备生物柴油过程中的应用,并展望了其应用前景。     

纳米四氧化三铁化学法制备及其应用

纳米磁性材料作为一种新兴功能材料,由于其独特的物理化学性质,使其在物理、化学等方面表现出与常规磁性材料不同的特殊用途。纳米四氧化三铁就是其中一种多功能磁性材料,在磁记录材料、磁流体、催化、医药、颜料等方面具有广泛的应用。综述了近年来纳米磁性四氧化三铁的液相化学制备方法：共沉淀法、微乳液法、溶胶-凝胶法、溶剂热法等的研究现状以及最新的研究成果,对上述各种制备方法的优缺点进行了分析和比较。介绍了磁性纳米四氧化三铁在磁性液体、磁记录材料、催化、生物医药、微波吸收材料等方面的具体应用以及发展趋势,并提出其今后发展方向。     

Fe3O4纳米晶表面裹负SiO2的制备研究

纳米材料又称超微颗粒材料,是由纳米粒子组成,具有纳米尺寸效应。纳米材料用于化学反应会呈现出不同寻常的反应性能。磁性纳米材料作为一种新型的纳米材料,具有不同于常规材料的独特效应,如量子尺寸效应、表面效应、小尺寸效应、宏观量子隧道效应及顺磁效应等,这些效应使磁性纳米粒子具有不同于常规材料的光、电、声、热、磁敏感特性。近年来有关磁性纳米材料的研究备受瞩目。特别是Fe3O4纳米晶,由于其优异的磁性和表面活性及其在磁流体、微波吸收材料、水处理、催化、生物医药、生物分离等方面的应用前景,正在成为众多领域研究的热点。基于Fe3O4纳米晶的磁性纳米催化剂兼有了磁性纳米材料的所有独特性能,将其应用于催化领域,会呈现出常规催化材料所不具备的催化性能。目前液相制备Fe3O4纳米晶的液相方法主要有沉淀法、水热法、溶胶-凝胶法、微乳液法、微波超声法等。这几种方法制得的Fe3O4纳米晶有较大的差异,往往因其在不同领域的应用而采用不同的方法制备Fe3O4纳米晶。结合前人研究成果,笔者采用共沉淀法在无氮气保护的条件下制备出了粒径分布在15 nm±4 nm之间的Fe3O4纳米晶。考察了n(Fe^2+)/n(Fe^3+)、晶化时间、晶化温度、pH值对Fe3O4纳米颗粒粒径分布的影响,并在Fe3O4纳米晶表面裹负SiO2,提高了其抗氧化性能并增强其表面修饰性能,为进一步表面裹负金属活性组分制备磁性纳米催化剂打下基础。     

磁性钯催化剂的制备及催化聚苯乙烯加氢的动力学研究

采用原位法制备了以四氧化三铁为磁核的磁性钯催化剂,进行了VSM、TEM、ICP-AES、XRD等表征与测试,并考察了磁性钯催化剂催化聚苯乙烯加氢制备聚环己基乙烯的反应动力学。在消除内外扩散影响的情况下,通过测定不同反应温度时反应过程中聚苯乙烯浓度随反应时间的变化关系,得到聚苯乙烯催化加氢动力学模型,其中对聚苯乙烯呈一级反应,而对氢气呈零级反应,反应活化能为51.4 kJ/mol。磁性钯催化剂具有很好的磁分离性能。     

磁性纳米SO_4~(2-)/Fe_3O_4-ZrO_2固体超强酸催化合成己二酸二正辛酯

利用磁性对纳米固体超强酸组合,制备出磁性纳米SO42-/Fe3O4-ZrO2固体超强酸催化剂,并用TEM、IR、Ham-m ett指示剂检测磁性纳米固体超强酸催化剂性能。将其用于己二酸二正辛酯(DOA)的合成反应中。得到最佳反应条件为负压下,反应温度155℃,n(正辛醇)∶n(己二酸)=3.2∶1,反应时间2 h,w(催化剂)=1.5%,己二酸的转化率达99%。利用催化剂的磁性可将纳米颗粒催化剂迅速分离,回收率达93.8%,并能重复使用。     

磁性纳米SO4^2-／Fe3O4-ZrO2固体超强酸催化合成己二酸二正辛酯

利用磁性对纳米固体超强酸组合，制备出磁性纳米SO4^2-／Fe3O4-ZrO2固体超强酸催化剂，并用TEM、IR、Hammett指示剂检测磁性纳米固体超强酸催化剂性能。将其用于己二酸二正辛酯（DOA）的合成反应中。得到最佳反应条件为负压下，反应温度155℃，n（正辛醇）：n（己二酸）=3．2：1，反应时间2h，w（催化剂）=1．5％，己二酸的转化率达99％。利用催化剂的磁性可将纳米颗粒催化剂迅速分离，回收率达93．8％，并能重复使用。     

磁性水滑石负载纳米钯催化剂的制备及催化Suzuki反应的研究

采用化学沉淀法将磁性基质与二维层状水滑石组装制备了磁性的水滑石,再利用浸渍法和滴加吸附的负载方法制备了磁性水滑石负载纳米钯催化剂。通过XRD、ICP—AES、TG、氢气脉冲吸附等分析手段对磁性催化剂晶型结构、形貌及金属分散度进行了表征,考察了用磁性水滑石负载纳米钯催化剂对不同碱、溶剂、溶剂与水比例、时间、温度、催化剂用量等条件对Suzuki反应的影响。实验结果表明,水滑石赋予磁性后结构并没有改变,仍然具有较高的催化活性。反应的最佳条件为：碳酸钾作碱、溶剂为乙醇、与水比例为1：5、反应温度为60℃、反应1h、催化剂用量分别为3．6×10^-3mmol和4．8×10^-3mmol,催化剂重复三次产物收率仍可保持在90％以上。     

形貌可控的Pt纳米催化剂的制备及其应用进展

铂纳米催化剂由于其高效的还原和氧化作用,在催化和电催化领域的应用非常的广泛.在反应中除了尺寸外,Pt纳米晶体的形貌对催化和电催化的活性和选择性也起到了关键的作用.调变合成单一形貌催化剂的条件,如稳定剂、还原剂和表面活性剂等,对于调控纳米粒子的形貌至关重要.目前形貌可控的铂纳米催化剂已被应用到加氢、氧化和Suzuiki偶...     

纳米复合材料

(续 2 0 0 1年第 3期 )3　实际应用3 1　工业催化由于纳米粒子本身性质稳定 ,表面活化中心多 ,比表面积大 ,作为催化剂无细孔 ,无其他成份 ,能自由选择组分 ,使用条件温和、方便 ,具有优良的催化活性和催化反应选择性。在高分子聚合物氧化、还原及合成反应中用纳米粒子如纳米态铂、银、氧化铝、氧化铁等作为催化剂 ,可大大提高反应效率 ,控制反应速度 ,甚至使原来不能进行的反应得以快速进行。纳米粒子具有许多奇异的物理和化学性能 ,如金属为导体 ,但纳米金属微粒在低温下呈现电绝缘性 ,纳米磁性金属的磁化率是普通金属的 2 0倍。将金属铂…     

磁性催化剂的研究进展

磁性催化剂是一类具有磁响应特性的催化剂,它不仅具有较高的催化活性,而且在外加磁场作用下,容易分离回收。根据磁载催化剂的核壳之间是否包覆结合层,将其分为直接包覆和非直接包覆催化剂,从上述两个方面综述了近年来可分离磁性催化剂的研究进展,同时提出了目前磁载催化剂研究的热点和发展趋势。     

Simple synthesis of mesoporous carbon with magnetic nanoparticles embedded in carbon rods

Magnetically separable ordered mesoporous carbon containing magnetic nanoparticles embedded in the carbon walls was synthesized using a simple synthetic procedure. The resulting magnetically separable mesoporous carbon was denoted as M-OMC (magnetically separable ordered mesoporous carbon) poly(pyrrole) with residual Fe²⁺ ions in the mesoporous channel was converted to carbon material containing superparamagnetic nanoparticles. The size of the magnetic nanoparticles obtained was restricted by the channel size of the SBA-15 silica template, which resulted in the generation of superparamagnetic nanoparticles embedded in the carbon rods. The blocking temperature of M-OMC is 110 K. Pore size and textural property of M-OMC is similar to that of hexagonally ordered mesoporous carbon fabricated using SBA-15 silica as a template. The saturation magnetization of M-OMC is ca. 30.0 emu/g at 300 K, high enough for magnetic separation.     

磁性可回收钯催化剂催化Suzuki反应的研究进展

钯催化剂催化卤代芳烃和芳基硼酸生成碳一碳键的Suzuki偶联反应是合成联苯化合物的最重要的途径之一。相比于传统均相钯催化剂的利用率低,污染产品等缺点,磁性钯催化剂易回收,可重复利用,具有工业化应用前景,受到了广泛的关注。综述了近年来无配体磁性钯催化剂、无包裹磁性钯配体催化剂以及以碳、氧化硅、聚合物包裹的具有核壳结构的磁性钯配体催化剂的制备及其催化Szuki偶联反应的研究进展。     

磁性纳米TiO2/SiO2/Fe3O4光催化剂的制备及光催化性能研究

以化学共沉淀法制备的纳米铁氧体Fe₃O₄ 为磁载体,采用溶胶-凝胶法制备易于固液分离回收的新型磁性纳米TiO₂/SiO₂/Fe₃O₄ 光催化剂。采用X射线衍射、透射电镜、扫描电镜、傅立叶红外变换光谱和紫外可见漫反射光谱等对催化剂进行表征。以酸性大红3R为目标降解物,对催化剂的光催化性能进行了研究。结果表明,磁性纳米TiO₂/SiO₂/Fe₃O₄ 光催化剂样品混晶中,锐钛矿相TiO₂ 占90%以上,制备的催化剂样品为层状结构,平均颗粒粒径约为(50~80) nm,呈现顺磁性,在外加磁场的作用下,催化剂可与液相迅速分离。同时,磁性纳米TiO₂/SiO₂/Fe₃O₄ 光催化剂具有较强的光催化活性,在光催化剂用量0.5 g·L^-1 、溶液初始浓度100 mg·L^-1 和光催化反应120 min条件下,酸性大红3R降解率达95%。     

Structure and photocatalytic performance of magnetically separable titania photocatalysts for the degradation of propachlor

A magnetic photocatalyst was prepared by modification of TiO₂ nanoparticles (Degussa P25) with nanocrystalline γ-Fe₂O₃ nanoparticles through a protective lining made up of two oppositely charged polyelectrolytes. As-prepared magnetically separable photocatalysts differing in γ-Fe₂O₃ loading (3, 8, 13, 20 and 30 wt.%) were characterized by XRD, TEM, thermal analysis, Mössbauer and magnetic measurements. The photocatalytic efficiency of the nanocomposite catalysts was evaluated using a chloroacetanilide herbicide (propachlor) in water as model compound. The primary degradation of propachlor followed pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. Generally, all magnetic photocatalysts exhibit good catalytic activity towards organic pollutants, do not suffer from photodissolution and can be reused several times without any decrease in their photocatalytic activity.     

Graphene‐supported nickel ferrite: A magnetically separable photocatalyst with high activity under visible light

A straightforward strategy is designed for the fabrication of a magnetically separable NiFe₂O₄‐graphene photocatalyst with different graphene content. It is very interesting that the combination of NiFe₂O₄ nanoparticles with graphene sheets results in a dramatic conversion of the inert NiFe₂O₄ into a highly active catalyst for the degradation of methylene blue (MB) under visible light irradiation. The significant enhancement in photoactivity under visible light irradiation can be ascribed to the reduction of GO, because the photogenerated electrons of NiFe₂O₄ can transfer easily from the conduction band to the reduced GO, effectively preventing a direct recombination of electrons and holes. The results of the kinetic study indicated that the rate‐determining stage is the adsorption process of MB molecules. NiFe₂O₄ nanoparticles themselves have a strong magnetic property, which can be used for magnetic separation in a suspension system, and, therefore, the introduction of additional magnetic supports is no longer necessary. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

A simple route for the preparation of anatase titania-coated magnetic porous carbons with enhanced photocatalytic activity

A method is described for the production of a magnetically separable photocatalyst, which consists of porous activated carbon, iron oxide particles and anatase titania particles. The prepared samples were characterized by XRD, TEM, SEM and vibrating sample magnetometry. The photocatalytic activity of the samples was determined by degrading model contaminated water, a phenol aqueous solution. The results were compared with a commercial titania, Degussa P25, and enhanced photocatalytic activities were obtained with all the samples prepared here. An additional advantage of these composite photocatalyst is their recyclability, because it can be easily magnetically separated by an external magnetic field. The degradation rate of phenol by a titania-coated magnetic activated carbon with an Fe content of 20% and a calcination temperature for the support of 450 °C, was still higher than 85% after the photocatalyst was used for 5 cycles.     

Preparations and photocatalytic properties of magnetically separable nitrogen-doped TiO2 supported on nickel ferrite

A magnetically separable nitrogen-doped photocatalyst TiO_2−xN_x/SiO₂/NiFe₂O₄ (TSN) with a typical ferromagnetic hysteresis was prepared by a simple process: the magnetic SiO₂/NiFe₂O₄ (SN) dispersion prepared by a liquid catalytic phase transformation method and the visible-light-active photocatalyst TiO_2−xN_x were mixed, sonificated, dried, and calcined at 400 °C. The prepared photocatalyst is photoactive under visible light irradiation and easy to be separated from a slurry-type photoreactor under the application of an external magnetic field, being one of promising photocatalysts for wastewater treatment. Transmission electron microscope (TEM) and X-ray diffractometer (XRD) were used to characterize the structure of the TSN photocatalyst. The results indicate that the magnetic SiO₂/NiFe₂O₄ (SN) nanoparticles adhere to the surface of TiO_2−xN_x congeries. The magnetic photocatalyst TSN shows high catalytic activity for the degradation of methyl orange in water under UV and visible light irradiation (λ > 400 nm). SiO₂ coating round the surface of NiFe₂O₄ nanoparticles prevents effectively the injection of charges from TiO₂ particles to NiFe₂O₄, which gives rise to the increase in photocatalytic activity. Moreover, the recycled TSN exhibits a good repeatability of the photocatalytic activity.     

Synthesis of magnetically separable adsorbents through the incorporation of protected nickel nanoparticles in an activated carbon

We present a simple and versatile route to prepare magnetically separable porous carbons from commercial activated carbons. The magnetic properties of the composite are provided by nickel nanoparticles (around 8-15 nm), which are produced within the porous network by means of the thermal treatment at 600 °C of an activated carbon impregnated with a nickel salt and sucrose. This synthetic strategy allows the magnetic nanoparticles to be protected against acid attack. The magnetic composite thus obtained exhibits a large surface area and a high pore volume. An important advantage of this composite is that exhibits, at room temperature, low coercivity (∼0.1 kOe), allowing it to be easily manipulated by means of low external magnetic fields.     

Optimization of reactors with catalyst decay and the constant conversion policy

For continuous stirred-tank and plug-flow catalytic reactors in which the catalyst activity decreases with time, Szepe [1] showed that the optimal temperature-time policy can lead to a policy of constant exit conversion under specific conditions. These conditions included a single irreversible reaction with a separable rate equation and a rate of decay of catalyst activity also separable and independent of composition.It is the purpose of this paper to extend the results of Szepe and to establish: (a) A necessary and sufficient condition for a constant-conversion optimal policy in a continuous stirred-tank reactor, and (b) A proof of the constant-conversion policy for a plug-flow reactor with distributed control of temperature for a general irreversible reaction with separable kinetics.In both cases, the rate of decay is assumed to depend on composition.