ZnFe2O4 nanoparticles: A green and recyclable magnetic catalyst for fast and regioselective conversion of epoxides to vicinal hydroxythiocyanates using NH4SCN under solvent-free conditions

ZnFe₂O₄ nanoparticles were synthesized and used as recyclable magnetic catalyst in the solvent-free conversion of different epoxides to vicinal hydroxythiocyanates with NH₄SCN at room temperature. The reactions were carried out by grinding in a mortar with perfect regioselectivity within short times (2-25 min) and with high to excellent yields (75–95%). The nanocatalyst was separated easily using an external magnet and reused for four consecutive cycles without any noticeable loss of efficiency or magnetic property.     

Study of the selectivity of a V2O5?ZrO2 catalyst for partial oxidation ofo-xylene at high temperatures

It has been established that at high temperatures (above 450°C) the V₂O₅−ZrO₂ catalyst exhibits a higher selectivity in the oxidation ofo-xylene to phthalic anhydride than does the conventional V₂O₅−TiO₂(a) catalyst. The catalyst selectivity is found to increase with respect to partial oxidation ofo-xylene, the valuable by-product maleic anhydride being obtained. Studies by different physicochemical methods have shown that V₂O₅−ZrO₂ undergoes no significant phase and structural changes under high-temperature conditions.     

铁酸钴纳米粒子:室温下点击合成亚芳基巴比妥酸衍生物的高效可磁性分离多相催化剂(英文)

A coprecipitation method was used to synthesize superparamagnetic CoFe2O4 nanoparticles without using any capping agents/surfactants. The prepared nanoparticles were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, a vibrating sample magnetometer (VSM), N2 adsorption and thermogravimetric/differential thermal analysis/differential thermal gravimetry techniques. The synthesized spinel CoFe2O4 nanoparticles had an average size of 2-8 nm with a high surface area (140.9 m2/g). The field-dependent magnetization, demonstrated by VSM and saturation magnetization, was found to be 1.77 emu/g. An efficient method was used for the synthesis of arylidene barbituric acid derivatives using CoFe2O4 magnetic nanoparticles as a magnetically separable and reusable catalyst in aqueous ethanol. The attractive features of this synthetic protocol were very short reaction time, high yields, high turnover frequency, simple work-up procedure, economy, a clean reaction methodology, and chemoselectivity, as well as provision of an ecofriendly and green synthesis.     

Synthesis of magnetic CuFe2O4 nanoparticles as green catalyst for toluene oxidation under solvent-free conditions

A green method was developed for the synthesis of CuFe₂O₄ magnetic nanoparticles using a Neem leave extract. The prepared nanoparticles with an average size of 19.7 nm were used as an effective catalyst for the oxidation of various aryl alkanes in moderate to excellent yields under solvent-free conditions. The catalyst was characterized by powder- XRD, SEM and TEM study. The key advantages of this protocol are simple preparation, a recyclable heterogeneous catalytic system, and benign reaction condition with good to excellent yields with high selectivity toward acid (42–87%).     

Oxidation of thiols to disulfides using H2O2 catalyzed by recyclable chromic potassium sulphate at room temperature

Chromic potassium sulphate is found to be an efficient and recyclable catalyst for the selective oxidation of thiols to disulfides. The reaction was carried out in 60% methanol (v/v) using 30% H₂O₂ at room temperature. Cr(III) forms a complex with thiol which was then oxidized by H₂O₂ to produce disulfide in excellent yield after a simple workup procedure.     

聚乙烯基胺包裹Fe3O4@SiO2磁性微球用于Knoevenagel缩合（英文）简

Polyvinyl amine coated Fe₃O₄@SiO₂ composite microspheres with a core-shell structure were prepared and employed as a magnetic catalyst for Knoevenagel condensation under mild conditions. The catalyst can be readily recovered using a magnet and reused several times without loss in activity or selectivity. The performance of the magnetic base catalyst was compared with that of polyvinyl amine functionalized mesoporous SBA-15, which showed that the magnetic nanoparticles gave improved reaction rate and yield.     

多孔SiO_2·xH_2O负载RuB纳米粒子催化喹啉加氢反应

通过水解,聚乙烯吡咯烷酮(PVP)保护,NaOH刻蚀等方法制备了多孔及富含表面羟基的SiO2·xH2O负载的RuB催化剂RuB/SiO2·xH2O,并用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、傅里叶变换红外(FT-IR)光谱和BET(Brunauer-Emmett-Teller)等手段对该催化剂进行了表征.结果表明该催化剂具有良好的抗中毒能力,在3.0MPa的H2压力和80℃的温和反应条件下,喹啉的转化率高于95%,生成1,2,3,4-四氢喹啉的选择性高于97%.并系统研究了表面羟基和溶剂对催化剂性能的影响,发现以水为溶剂时,RuB/SiO2·xH2O对喹啉加氢反应展示出较高的活性和对1,2,3,4-四氢喹啉较高的选择性,催化剂能够多次循环使用.这一体系的优异催化性能归属于载体表面羟基和水的协同作用.     

V2O5/C catalyst for liquid phase oxidation of glyoxal to glyoxylic acid

A study of the catalytic activity of V₂O₅/C catalyst for the oxygen oxidation of glyoxal has been made, showing that glyoxylic acid can be formed without control of pH value and there is little oxalic acid from the excessive oxidation of glyoxylic acid. The studies of XRD and TEM have shown that V₂O₅ diffraction peaks gradually strengthen with the increase of the content of V₂O₅. With the content of 3% V₂O₅ and the calcination temperature of 573 K, V₂O₅/C catalyst displayed the best activity and selectivity. The conversion of glyoxal and the selectivity of glyoxylic acid reached 18.76% and 77.70% after 5 h, respectively. Moreover, V₂O₅/C catalyst showed small deactivation after recycling three times, which indicates that V₂O₅/C has a higher stability than noble metal catalysts in the reaction medium. Supported by the Technology Research and Development Project for University of Shanxi Province of China (Grant No. 20051272)     

Cr掺杂的丙烷选择氧化制丙烯酸高效催化剂

在丙烷选择氧化制丙烯酸催化剂MoVTeNbOx的活性相M1基础上掺杂一定量的Cr,当Cr/Nb摩尔比为0.002时,催化剂具有很高的丙烯酸选择性(78.3%)和收率(50.7%);并采用X射线衍射、X射线光电子能谱、程序升温还原、O2程序升温脱附、NH3程序升温脱附和异丙醇氧化等手段对催化剂的构效关系进行了探讨.结果表明,适量Cr的添加可调节催化剂表面Mo6+,V5+和Te4+等物种含量,提高催化剂的氧化能力,使丙烷转化率增加.同时,适量Cr的添加使得催化剂表面酸强度下降,酸性位点数量减少,从而抑制丙烯酸的深度氧化,提高了丙烯酸选择性.     

Selective oxidation of octadecan-1-ol to octadecanoic acid over Co3O4/SiO2 catalysts

Factors (reaction temperature, reaction time, flow rate of oxygen, amount of catalyst, etc.) influencing the catalytic properties of Co₃O₄/SiO₂catalyst in the oxidation octadecan-1-ol to octadecanoic acid were investigated. The catalysts were characterized by means of XRD, FT-IR and N₂-adsorption. The experimental results indicate that under the optimal condition the selectivity to octadecanoic acid reached 97.5 % over 5 % Co₃O₄/SiO₂ catalyst.This revised version was published online in December 2005 with corrections to the Cover Date.     

EtOAc-dispersed magnetic nanoparticles (DMNPs) of γ-Fe2O3 in the single-pot domino preparation of 5-oxo-2-thioxo-3-thiophenecarboxylate derivatives

EtOAc-dispersed magnetic nanoparticles (DMNPs) of γ-Fe₂O₃ represent a straightforward and green catalyst for the rapid three-component synthesis of 5-oxo-2-thioxo-3-thiophenecarboxylate derivatives as rhodanine skeletons via a single-pot domino process. The rhodanines were prepared over magnetic nanoparticles of γ-Fe₂O₃ without any salt or additives. Dispersed nano-γ-Fe₂O₃ have many advantages, such as stability in air, reusability, reactions with high efficiency, simple separation with magnetic external field from mixture reactions, chemical stability, and also low toxicity.     

溶胶-凝胶新方法合成介孔铁酸铜纳米粉体催化剂上CO低温氧化(英文)

Mesoporous CuFe2O4 solid solution nanopowders with high specific surface areas were synthesized by a novel, very simple and inexpensive sol-gel route using propylene oxide as gelation agent, and used as the catalyst in low temperature CO oxidation. The samples were characterized by X-ray diffraction, N2 adsorption-desorption, thermogravimetric/differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and temperature-programmed reduction. The results revealed that the samples have a nanocrystalline structure with crystals in the range of 10 to 25 nm, and that all the catalysts have mesoporous pores. The addition of Cu into iron oxide affected its structural and catalytic properties. The sample containing 15 mol% Cu showed the highest specific surface area and catalytic activity, and showed high catalytic stability in low temperature CO oxidation.     

WS2纳米颗粒的合成及摩擦学性能研究

将自制的WO₃纳米颗粒前驱体与S粉混合,在自制的反应装置氢气氛中,于550～750 ℃下煅烧得到二硫化钨纳米颗粒,反应中用H₂代替H₂S以减少对周围环境的污染。该合成路线简单且产物纯度高。用XRD、SEM、TEM和HRTEM对二硫化钨纳米结构进行了表征和分析,并将WS₂纳米颗粒作为添加剂添加到N40基础油中,在MS-T3000摩擦磨损仪测试其摩擦学性能。结果显示:制备的二硫化钨颗粒平均粒径在50 nm以内,其形状为球形或类球形。WS₂纳米颗粒作为普通润滑油的纳米级固体添加剂表现出了较优异的摩擦学性能。     

自组装型Pt/γ-Al2O3催化剂用于低温去除挥发性有机物

分别通过自组装法(AS)和浸渍法(WI)制备得到纳米催化剂Pt/γ-Al₂O₃-AS和Pt/γ-Al₂O₃-WI, 并用于评价甲苯、异丙醇、丙酮、乙酸乙酯等易挥发性有机物(VOCs)的氧化性能. 通过各种表征手段探究了催化剂形态、结构及表面性质与催化剂氧化活性的关系. 结果表明, Pt/γ-Al₂O₃-AS在低温下即可实现VOCs的完全氧化. 在气体浓度(体积分数)为1000×10^-6, 空速为18000 mL·g^-1·h^-1的条件下, 甲苯、异丙醇、丙酮、乙酸乙酯被Pt/γ-Al₂O₃-AS催化剂完全氧化的温度分别为130、135、145、215℃, 展现出了优异的氧化性能, 且具有很好的稳定性. 该催化剂较高的比表面积、较小的Pt纳米粒径、较好的Pt纳米颗粒分散度、更好的低温还原效果及丰富的表面羟基是具有较高催化活性的重要因素.     

EU-1分子筛的合成及其在正己烷异构化反应中的催化性能

在不同硅铝比(nSiO₂/nAl₂O₃)的合成凝胶(含纯硅凝胶)中引入晶种,合成了纯相的EU-1分子筛。研究了铝源、模板剂和晶种添加量对EU-1分子筛的结晶度、形貌尺寸等的影响;重点研究了不同硅铝比对样品结晶度、晶粒尺寸、酸性、比表面积和孔容等的影响。将合成结果绘制成了纯相EU-1分子筛的合成条件三元图,从三元图可看出,晶种法可显著扩大纯相EU-1分子筛的合成区域。将Pt/H-EU-1用于正己烷异构化反应,结果表明,该催化剂具有优异的正己烷异构化活性及稳定性,对异构烷烃有较高的选择性。     

Picolinimidoamide-Cu(II) complex anchored on Fe3O4@SiO2 core–shell magnetic nanoparticles: an efficient reusable catalyst for click reaction

A Cu(II) complex supported on Fe₃O₄@SiO₂ core–shell magnetic nanoparticles (MNPs) was prepared and characterized by FT-IR, XRD, SEM, EDX, TEM, VSM, TGA, and AAS analysis. The load of Cu on picolinimidoamide ligand anchored on Fe₃O₄@SiO₂ core–shell MNPs was determined as 1.22, 1.54, and 1.70 wt% using AAS, EDX and TGA analyses, respectively. Synthesized Cu(II) complex on Fe₃O₄@SiO₂ MNPs efficiently catalyzed a click reaction between alkyl halides, alkynes, and sodium azide to synthesize corresponding triazoles in high to excellent yields. The catalyst was recovered using an external magnetic field, and recycled for subsequent reactions without substantial loss of efficiency.     

An efficient ‘on-water’ synthesis of 1,4-dihydropyridines using Fe3O4@SiO2 nanoparticles as a reusable catalyst

An ‘on-water’, efficient, high yielding, expeditious method has been developed for the synthesis of 1,4-dihydropyridine (1,4-DHP) derivatives via an one-pot multi-component condensation of dimedone or 4-hydroxycoumarine, aldehydes, and ammonium acetate using Fe₃O₄@SiO₂ nanoparticles as a recyclable heterogeneous catalyst. This method takes advantage of the fact that water, a green solvent is used in combination with Fe₃O₄@SiO₂ nanoparticles as catalyst which can be easily recovered magnetically and reused for further runs.     

Magnetic CuFe2O4 nanoparticles: a retrievable catalyst for oxidative amidation of aldehydes with amine hydrochloride salts

The application of magnetic CuFe₂O₄ nanoparticles for the oxidative amidation of aldehydes with amine hydrochloride salts is described. A wide range of amides have been synthesized in good to excellent yields under mild conditions. Chiral amide also synthesized from its corresponding chiral amine salt with retention of the stereochemistry. In particular, the performance of the magnetic separation of the catalyst was very efficient and an alternative to time, solvent and energy-consuming separation procedures. The catalytic activity of the catalyst remains unaltered after five consecutive cycles, making it environmentally benign and widely applicable due to its efficiency, ease of handling and cost effectiveness.     

Effect of 3% Re2O7/60%Al2O3 - 40%SiO2 Catalyst Alkylation Time and Temperature Using Et4Pb on Methyl Erucate Conversion

A study of the alkylation of 3% Re₂O₇/60%Al₂O₃-40%SiO₂ catalyst using tetraethyllead (Et₄Pb)(TEL) shows that the reaction time and temperature affect the catalyst activity and selectivity in the methyl erucate metathesis reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis of Chitosan-La2O3 Nanocomposite and Its Utility as a Powerful Catalyst in the Synthesis of Pyridines and Pyrazoles

Recently, the development of nanocatalysts based on naturally occurring polysaccharides has received a lot of attention. Chitosan (CS), as a biodegradable and biocompatible polysaccharide, is considered to be an excellent template for the design of a hybrid biopolymer-based metal oxide nanocomposite. In this case, lanthanum oxide nanoparticles doped with chitosan at different weight percentages (5, 10, 15, and 20 wt% CS/La₂O₃) were prepared via a simple solution casting method. The prepared CS/La₂O₃ nanocomposite solutions were cast in a Petri dish in order to produce the developed catalyst, which was shaped as a thin film. The structural features of the hybrid nanocomposite film were studied by FTIR, SEM, and XRD analytical tools. FTIR spectra confirmed the presence of the major characteristic peaks of chitosan, which were modified by interaction with La₂O₃ nanoparticles. Additionally, SEM graphs showed dramatic morphological changes on the surface of chitosan, which is attributed to surface adsorption with La₂O₃ molecules. The prepared CS/La₂O₃ nanocomposite film (15% by weight) was investigated as an effective, recyclable, and heterogeneous base catalyst in the synthesis of pyridines and pyrazoles. The nanocomposite used was sufficiently stable and was collected and reused more than three times without loss of catalytic activity.