Heterogeneously catalyzed efficient hydration of alkynes to ketones by tin-tungsten mixed oxides

The Sn–W mixed oxide prepared by calcination of the Sn–W mixed hydroxide precursor with a Sn/W molar ratio of 2:1 at 800 °C (SnW2‐800) acts as an efficient heterogeneous catalyst for the hydration of alkynes. Structurally diverse terminal and internal alkynes, including aromatic, aliphatic, and double‐bond‐containing ones, can be converted into the corresponding ketones in moderate to high yields. The catalytic activity of SnW2‐800 is much higher than those of previously reported heterogeneous catalysts and commonly utilized acid catalysts. The observed catalysis was truly heterogeneous, and the retrieved catalyst can be reused at least three times with retention of its high catalytic performance. The reaction rate for the SnW2‐800‐catalyzed hydration was decreased by addition of 2,6‐lutidine and the hydration hardly proceeded in the presence of an equimolar amount of this compound with respect to that of the Brønsted acid sites in SnW2‐800. Therefore, the present hydration is mainly promoted by the Brønsted acid sites in SnW2‐800.     

Preparation of supported metal catalysts starting from hydrotalcites as the precursors and their improvements by adopting “memory effect”

Hydrotalcite-like compounds (HTlcs) can be used as the catalysts as it is since they contain various transition metal cations as the catalytically active species well dispersed on the basic support materials. Moreover, increasing numbers of the applications of HTlcs after the heat treatment have been found since the oxides with very small crystal size, stable to thermal treatments, are obtained after the calcination. The oxides possess interesting properties such as high surface area, basic properties and further form small and thermally stable metal crystallites by reduction. Moreover, the calcined oxides show a unique property, i.e., “memory effect,” which allows the reconstitution of the original hydrotalcite structure. We have developed the catalytic applications of hydrotalcites as it is and moreover the mixed oxides derived from hydrotalcites for various catalytic reactions, i.e., oxidation, dehydrogenation and reforming of hydrocarbons, and even for the reforming of methanol and the CO shift reaction. Aerobic oxidation of alcohols, Baeyer−Villiger oxidation of ketones and O₃ oxidation of oxalic acid have been successfully carried out with the Mg−Al hydrotalcites containing Ni, Fe and Cu, respectively, as the catalysts in liquid phase. In the O₃ oxidation of oxalic acid, the catalytic activity was enhanced by the “memory effect,” i.e., Mg(Cu)–Al hydrotaclite was reconstituted on the surface of Mg(Cu,Al)O periclase particles and oxalic acid was incorporated as anions in the hydrotalcite layer, resulting in an enhanced oxidation of oxalic acid. As the catalysts in the vapor phase reactions, Mg/Fe/Al mixed oxides prepared from Mg–Al(Fe) hydrotalcites and effectively catalyzed the dehydrogenation of ethylbenzene. Supported Ni metal catalysts have been prepared from Mg(Ni)–Al hydrotalcites and successfully used in the steam reforming and the oxidative reforming of methane and propane. Moreover, the Ni catalysts have been improved by combining a trace amount of noble metals by adopting the “memory effect” and used in the production of hydrogen for the PEFC under the daily startup and shutdown operation. Also starting from aurichalcite or hydrotalcite precursor as the precursor, Cu/Zn/Al catalysts with high Cu metal surface area have been prepared and successfully applied in the steam reforming of methanol and dimethyl ether, and moreover in the CO shift reaction.     

Baeyer-Villiger oxidation of ketones with hydrogen peroxide catalyzed by Sn-palygorskite

Palygorskite-supported Sn complexes were prepared by a simple procedure. Cyclic ketones and acyclic ketones were oxidized by hydrogen peroxide in a reaction catalyzed by palygorskite-supported Sn complexes, affording corresponding lactones or esters with selectivity for the product of 90-100%. The catalysts can be recycled for several times without significant decline in catalytic activity.     

Effect of the Preparation Methodof Al–Mg–O Catalysts on the Selective Decomposition of Ethanol

Summary.  Selective decomposition of ethanol was used as a test reaction at 350°C to evaluate the catalytic activity of two Al–Mg–O mixed oxides prepared by two different methods (wet impregnation and coprecipitation). The catalyst precursors were examined by TG and DTA and were calcined between 500–900°C for 5 h in air. The surface area of all catalysts was measured by N₂ sorption using the BET method. The total acidity and basicity were determined by TPD using pyridine and formic acid. The catalysts were characterized by XRD analysis. It was found that the preparation method of Al–Mg–O catalyst has a great effect on the selective decomposition of ethanol. Al–Mg–O (I) catalysts, prepared by wet impregnation, were more selective towards ethene formation during dehydration of ethanol. This is ascribed to their high total surface acidity. On the other hand, Al–Mg–O (II) catalysts, prepared by coprecipitation, were highly selective in the oxidative dehydrogenation of ethanol to yield acetaldehyde. This could be attributed to their high concentration of basic sites. In addition, the production of traces of diethyl ether was also observed (three times more for Al–Mg–O (II) than for Al–Mg–O (I)). Corresponding author. E-mail: shalawy99@yahoo.com Received October 12, 2001. Accepted (revised) January 7, 2002     

Sn-Mo混合氧化物的缺陷结构及催化性能的研究

本文以1-丁烯在水蒸汽存在下选择性氧化制甲乙酮为典型反应, 利用XRD, ESR,IR, XPS, TEM和SEM研究了Sn-Mo氧化物的结构与活性的关系。制备了8个样品, A, B,C,D,E,F,G和H的Mo/(Mo+Sn)分别为0,0.1,0.2,0.4,0.6,0.8,0.9,1.0。     

Molecular approaches towards mixed metal oxides and their behaviour in mixed oxide support Au catalysts for CO oxidation

We herein report a water-based sol-gel approach towards porous mixed Si/Ti oxides using co-precipitated glycol-modified precursors. By adjusting synthesis parameters such as the pH value and the Si/Ti ratio of the precursor, the morphology as well as the Si/Ti-composition of the resulting mixed oxide particles can be varied in a wide range. The behaviour of the mixed oxides as substrates for Au catalysts and the performance of the resulting catalysts in the CO oxidation reaction was investigated and compared to catalysts supported on mesoporous anatase and rutile synthesized analogously. For comparable Au particle sizes and Au loadings, the composition of the mixed oxide support was found to significantly affect the reactivity and reaction behaviour, with mixed oxide supported Au catalysts synthesized at pH=5 or 10 and with a Si/Ti-ratio of 1:19 and 1:34 exhibiting the maximum activity. In contrast to the enhanced activity, the mixed oxide supports do not lead to a significant improvement in deactivation behaviour and catalyst stability.     

Preparation of Novel Materials for Catalysts Utilizing Metal-Containing Silsesquioxanes

Recent progress of the preparation of novel materials for catalysts utilizing metal-containing silsesquioxanes are reviewed in the following categories: (i) activities of vanadium or titanium-containing silsesquioxanes as homogeneous catalysts for oxidative reactions, (ii) preparation of immobilized or polymeric catalysts, and (iii) preparation of porous oxide catalysts utilizing metal-containing silsesquioxanes. The present authors found that the liquid phase photo-oxidation of cyclohexane in the presence of a vanadium-containing silsesquioxane as a homogeneous catalyst selectively afforded cyclohexanol and cyclohexanone in high yields. Facile synthetic methods for group 4 metal-containing silsesquioxanes with functionalized silyl (or germyl) groups are presented. Remarkably, titanocene(IV)-containing silsesquioxanes have been synthesized for the first time. The presence of alkenylsilyl substituents shows a promotional effect on the epoxidation of cycloalkenes, which was found to be more significant for titanium-bridged silsesquioxanes. By utilizing these silsesquioxanes, polymeric, starburst-like, and dendritic silsesquioxanes were prepared as well as novel caged or macrocyclic molecules with organic–inorganic hybrid structures. The controlled calcination of these metal-containing silsesquioxanes at around 823 K produces porous oxides with high BET surface areas of 300–520 m²g⁻¹ and uniformly-controlled micropores of 0.5–0.6 nm diameter. The oxides are found to include a well-dispersed metallic oxide species. From group 13 elements-containing silsesquioxanes Br?nsted acidic oxides are produced. Among them, aluminum-containing oxides show excellent activities for the cracking of cumene even at low temperature, 523 K, in spite of their amorphous nature.     

Kinetics of reduction of supported nanoparticles of iron oxide

A series of catalysts prepared by dispersing iron oxide on supports of different nature and acidity has been studied. Silica (S) and silica-zirconia mixed oxides (SZ) with different ZrO₂ content (from 5 to 45 mass%) were used as supports for the iron oxide phase which was deposited over them by an equilibrium-adsorption method. The red-ox properties of the Fe-catalysts were studied by temperature programmed reduction (TPR) technique. The two well defined and narrow TPR peaks observed could be associated with the reduction steps: I) Fe₂O₃→FeO and Fe₂O₃→Fe(0) (at ca. 400°C) and II) FeO→Fe(0) (at ca. 800–900°C). The temperature of the second-step-peak increased with the zirconia content in the support, likely because of the stronger interaction of the iron oxide phase with the support. Activation parameters for the two step-reduction processes were obtained by a simple computation procedure applied to the TPR profiles.     

Preparation of nanoparticles of oxides by the citrate–nitrate process

This paper reports preparation of nanoparticles of oxides by the citrate–nitrate process and the effect of metal ions on the thermal decomposition characteristics of the corresponding citrate–nitrate gel precursors. In order to understand the effect of metal ions on the thermal decomposition characteristics of the precursors, we have prepared a series of single component oxides such as MO, where M = Zn, MO₂, where M = Sn, Ce, Zr, and M₂O₃ where M = Al, Fe, Bi. In all the cases the citrate to nitrate ratio was fixed at 0.3. In order to ascertain the decomposition characteristics of the gel samples, TG/DTA studies were performed on the dried gel samples. After complete physico-chemical characterization of the precursors and the calcined products, it could be concluded that the nature of decomposition of the precursors depends largely on the nature of the metal ions. Finally, the advantages of the citrate–nitrate process such as its high degree of reproducibility, its potential for large-scale production of nano-crystalline ceramic oxide powders and its lower cost could be established based on a series of experiments and examples.     

Synthesis of Ni／Mg／Al Layered Double Hydroxides and Their Use as Catalyst Precursors in the Preparation of Carbon Nanotubes

Ni/Mg/Al layered double hydroxides(LDHs) with different n(Ni) : n(Mg) : n(Al) ratio values were prepared via a coprecipitation reaction. Then Ni/Mg/Al mixed oxides were obtained by calcination of these LDHs precursors. Carbon nanotubes were produced in the catalytic decomposition of propane over the Ni/Mg/Al mixed oxide catalysts. The quality of as-made nanotubes was investigated by SEM and TEM. The nanotubes were multiwall with a high length-diameter ratio and appeared to be flexible. The catalytic activities of these mixed oxides increased with increasing the Ni content. The Ni/Mg/Al mixed oxide with the highest Ni content [ n( Ni)/n( Mg)/n(Al) = 1/1/1 ] showed the highest activity and the carbon nanotubes grown on its surface had the best quality.     

稀土氧化物上SO2和NO的催化还原 Ⅰ.催化剂的活化特性和机理

以稀土系列氧化物作为ＣＯ还原ＳＯ２和ＮＯ的催化剂,考察了催化剂的活化过程以及催化剂体相结构的变化,发现稀土系列的活化与其水合性能密切相关,而活化之后活性相为相应的稀土氧硫化物,探讨了稀土系列氧化物的活性机理。     

负载型P-Mo-V/SBA-15催化剂上的甲烷选择氧化反应

以磷钼钒杂多酸(H₅PMo₁₀V₂O₄₀)为前驱体、介孔SBA-15为载体, 采用浸渍法制备不同负载量的P-Mo-V氧化物催化剂. 在甲烷选择氧化反应中, 考察了负载量、反应温度、空速等对甲烷转化率和产物选择性的影响. 结果表明, 催化剂对甲烷选择氧化制甲醛具有较高活性, 甲烷转化率随负载量的增大和反应温度的升高而提高, 甲醛的选择性随负载量的增大先升后降. 反应温度为640 ℃、空速为48300 L•kg^－1•h^－1、氧化物负载量w＝2.89%时, 甲醛的时空产率最高(295 g•kg_cat^－1•h^－1). 多种表征表明, 氧化物负载量w≤2.89%时, P-Mo-V氧化物在载体介孔孔道内以高分散形式存在. 催化剂的酸性和氧化还原性质与负载量相关, NH₃-TPD和H₂-TPR的测试结果表明, 较弱的酸性位和较低还原温度的活性组分有利于甲烷选择氧化制甲醛.     

柠檬酸法制备复氧化物材料的配位结构化学

柠檬酸法在复氧化物材料制备中占有重要地位,它具有分散均匀、制备温度低、产物粒径小的特点.以特定组成和结构的柠檬酸络合物为前驱体,直接分解可得到纯度较高的复氧化物,从中可以了解复氧化物的形成过程.本文从配位结构化学的角度,评述以钛、钒、钼和钨柠檬酸络合物为前驱体制备复氧化物材料的研究进展.     

费-托合成Co/ZrO2-Al2O3催化剂反应性能的研究

以ZrOCl2·6H2O和AlCl3为原料,采用共沉淀方法制得一系列不同ZrO2质量分数的ZrO2-Al2O3混合氧化物载体;并以该混合氧化物为载体,采用初湿浸渍法制得钴质量分数为12％的Co/ZrO2-Al2O3催化剂。XRD、NH3-TPD、TPR和原位IR等表征结果表明,随着混合载体中ZrO2质量分数的增加,载体比表面积先增加后减少,混合载体的平均孔径则小于单一氧化物ZrO2和Al2O3的平均孔径。ZrO2和Al2O3载体混合后会导致氧化物的比表面积和酸性增大并且有新的物相生成。当混合氧化物用作载体时,能够抑制载体表面金属钴的分散,改变催化剂的还原行为,降低催化剂对CO物种的吸附能力。CO加氢反应表明,与单一金属氧化物相比,钴负载ZrO2-Al2O3混合氧化物催化剂的加氢活性和重质烃选择性有所降低。     

Synthesis and characterization of nano-structured Th1?x Ce x O2 mixed oxide

GEL combustion technique was applied to obtain oxides of thorium and cerium from their respective nitrate solutions using citric acid as the gelating agent. The dried samples were characterized by IR and TG studies. Intermediate and final products during TG studies have been isolated and characterized by XRD studies. All the TG runs during heating of thorium and cerium nitrate with citric acid dried Gels showed a two step process. The weight loss at each step and the X-ray data of the product at each step, helped in suggesting a possible mechanism. Kinetic study was carried out independently for each step. The reaction mechanism as observed during interactive procedure was found to be diffusion controlled. The kinetic parameters (activation energy and pre-exponential factor) for each step in all reactions have been calculated. Observations from XRD studies show that with increase in cerium concentration in the oxides, the lattice parameter values have shown a decreasing trend for all the five compositions studied. It was observed that in TG studies with increase in cerium concentration, the final temperature of the reactions have shown a decreasing trend. SEM studies of the powders reveal that synthesized oxides have a tendency to form agglomerate of varying size ranging from 50 to 100 μm in case of mixed oxides but the size of thorium oxide powder so synthesized have pore size 10–100 μm. SEM images shows that GEL combustion may result in agglomeration, if the temperature is not properly controlled to the desired value. SEM studies also reveal that each agglomerate contains approximately 10–100 individual particles. Surface area of the mixed oxide powders were determined using Gas adsorption technique. The surface area was found to be in the range of 3–17 m²/g in all cases. Specific surface area of thorium oxide was found to be lesser than cerium oxide but in case of mixed oxides surface area decreases with increase in cerium content. Majority of pores, indicating the particle size are in the range of 0.01–0.04 cm³/g.     

Effect of the nature of the support for copper-cerium oxide catalysts on selective oxidation of CO in hydrogen-rich mixtures

We have studied the catalytic properties of copper-cerium oxide catalysts, supported on zirconium, aluminum, titanium, and manganese oxides, in the reaction of selective oxidation of CO in hydrogen-rich mixtures. We have shown that the high activity and selectivity of catalysts supported on zirconium and aluminum oxides is connected with the presence of (in addition to divalent copper) higher amounts of copper in the (+1) oxidation state in the catalysts. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 2, pp. 119–124, March–April, 2006.     

Anodic oxide-film of the Co—Sn—O composition

Properties and electrocatalytic activity of thin-film (∼2 μm) oxide coatings on aTi support are considered by the example of the anodic chlorine evolution reaction. The coatings are obtained by thermally decomposing Co and Sn chloride solutions of different compositions on a Ti plate. The Co and Sn oxides are present in all studied compositions as individual phases and form no compounds or solid solutions. The oxide coating containing 70 at. % Co and 30 at. % Sn reveals a maximum electrocatalytic activity. The existence of the optimum composition is attributed to a favorable effect tin dioxide has on the formation of a transition layer between the Ti support and oxide coating. Tin dioxide hampers the Ti diffusion in the main coating and its subsequent oxidation, thus diminishing the negative impact titanium oxides have on the coating     

有氧气氛中碱金属改性CuAl复合氧化物催化分解N2O的活性

合成了Cu/Al原子比分别为2.0、3.1、4.1的CuAl类水滑石样品,焙烧得到CuAl复合氧化物。在Cu/Al原子比为3.1的CuAl氧化物表面浸渍碱金属盐溶液,制备改性CuAl复合氧化物,用AES、XRD、FT-IR、BET、H₂-TPR、XPS等技术对催化剂进行了结构表征,考察了CuAl复合氧化物组成、碱金属助剂类型和K的前驱物对改性催化剂在有氧气氛中催化分解N₂O活性的影响。结果表明,Na、K、Cs改性CuAl复合氧化物均提高了催化剂活性,但K助剂的增强效应最显著;钾的不同前驱物改性CuAl复合氧化物的催化活性有显著差异,加入碳酸钾、草酸钾提高了催化剂的活性,而加入醋酸钾、硝酸钾反而降低了催化剂活性。优化出的K改性CuAl复合氧化物催化剂在含氧含水气氛的N₂O分解反应中表现出了较高的活性。     

Synthesis of ZrO2–SiO2 mixed oxide by alcohol-aqueous heating method

The preparation of ZrO₂–SiO₂ mixed oxide has been carried out simply by heating an alcohol-aqueous mixture. Preparation conditions such as volume ratio of alcohol to water and prehydrolysis time of tetraethoxysilane had more important effect on the homogeneity of mixed oxide. A self-catalytic effect on the resultant Zr–O–Si formation is observed. By employing FT-IR, XRD, NH₃-TPD and pyridine adsorption FT-IR techniques, the mixing homogeneity of the mixed oxides in terms of the amount of Zr–O–Si hetero-linkages has been investigated in detail. The results indicate that the amount of Zr–O–Si hetero-linkages increases with the increase of ZrO₂ content in mixed oxides. Moreover, the phase segregation and acidity generation of mixed oxides are studied and factors responsible for good mixing are also discussed. Using this approach, a series of highly homogeneous mixed oxides with ZrO₂ content of 20–70 mol% are obtained at the optimized preparation condition.     

Differential pulse voltammetric determination of tin in the presence of noble metals

A voltammetric method for the determination of tin is proposed to minimise interferences from noble metals that are commonly encountered with other analytical techniques. Strong distortions of voltammetric peaks are observed in the presence of platinum. On the basis of a full investigation, the formation of an intermediate Sn(II)–Pt mixed chloro-complex at the electrode surface is identified as being responsible for the platinum interference, as it competes with the normal Sn(IV)→Sn(0)_Hg reduction. The use of a higher scan rate prevents the relatively low reaction kinetics and thus gets rid of this interference. No problems are encountered with other noble metals such as Pd, Ir, Re, Rh and Ru when using the modified method, although a baseline subtraction is necessary for the latter one. The proposed method is validated with real Pt–Sn catalysts.