三种碳材料上原位电沉积AuPt合金的催化性能

在碳纸（CP）及涂覆了碳粉科琴黑（KB）或石墨烯纳米片（GNs）的碳纸上,原位电沉积了AuPt合金,制备成CP/AuPt、CP/KB/AuPt、CP/GNs/AuPt三种空气电极。对比研究发现,以石墨烯纳米片为载体的CP/GNs/AuPt空气电极上,AuPt合金载量高,颗粒分散均匀,粒径约为100 nm左右,Au和Pt的含量分别为78.84%（n/n）和21.16%（n/n）。在0.1 mol·L^-1 KOH溶液中氧还原反应的起峰电势为0.93 V,催化活性和稳定性优于其他两种空气电极。分析认为,石墨烯纳米片具有高导电性、高比表面积以及较多的缺陷活性位点,有利于AuPt合金在其上均匀电沉积且沉积载量较高,同时GNs本身具有一定的催化活性,两者能够产生协同催化作用,提高了CP/GNs/AuPt电极的催化性能。     

三种碳材料上原位电沉积AuPt合金的催化性能

在碳纸(CP)及涂覆了碳粉科琴黑(KB)或石墨烯纳米片(GNs)的碳纸上,原位电沉积了Au Pt合金,制备成CP/Au Pt、CP/KB/Au Pt、CP/GNs/Au Pt三种空气电极。对比研究发现,以石墨烯纳米片为载体的CP/GNs/Au Pt空气电极上,Au Pt合金载量高,颗粒分散均匀,粒径约为100 nm,Au和Pt的含量分别为78.84%(n/n)和21.16%(n/n)。在0.1 mol·L-1 KOH溶液中氧还原反应的起峰电势为0.93 V,催化活性和稳定性优于其他两种空气电极。分析认为,石墨烯纳米片具有高导电性、高比表面积以及较多的缺陷活性位点,有利于Au Pt合金在其上均匀电沉积且沉积载量较高,同时GNs本身具有一定的催化活性,两者能够产生协同催化作用,提高了CP/GNs/Au Pt电极的催化性能。     

磁性纳米颗粒负载钯催化剂对Heck反应的催化活性

采用水热法合成了碳包埋磁性纳米复合颗粒C/(Au@Fe),并以之为载体制备了纳米钯催化剂,利用透射电镜、X射线光电子能谱和振动样品磁强计等手段对催化剂进行了表征,评价了催化剂对Heck反应的催化活性.结果表明,催化剂的平均粒径约为300nm,表面覆盖着一层粒径为12nm的钯颗粒,整个催化剂呈现超顺磁性.对于碘代苯与丙烯酸之间的Heck反应,在乙酸钠或三乙胺碱性条件下反应4h,碘代苯转化率可达95%以上.催化剂重复使用10次时仍可保持很高的催化活性(碘代苯转化率88%).对于其他不同反应底物之间的Heck反应,催化剂同样显示有较高的催化活性.催化剂可稳定分散于反应体系中,并可在外磁场作用下快速与反应体系分离.     

Catalysis of SO42--ZrO2/TiO2 nanometer solid superacid

Superacid catalyst SO42--ZrO2/TiO2 was applied in esterification of Acetic Acid and Butanol. The particle size of ZrO2 in the catalyst was about 12.5 nm. In catalyst preparation conditions, the effect factor order on catalytic activity is H2SO4 concentration ＞ calcination temperature ＞ ZrO2 supported content. The optimum preparation condition is as follows: ZrO2 content 3.5g/g; calcination temperature 600℃, and H2SO4 concentration 0.5mol/L. The catalytic activity is 96.5 vol%.SO42-/MxOy solid superacid is a kind of green catalyst, whose application perspective is bright. In this paper, SO42--ZrO2/TiO2 solid superacid was prepared with nanometer compound carrying method. The acidic strength of catalysts was measured with the following Hammett indicators, 2,4-dinitrofluorobenzene (H0=-14.52) and p-nitrochlorobenzene (H0=-12.70). Catalytic activity was evaluated with esterification reaction of Acetic Acid and Butanol. Reaction temperature was at 105℃, and reaction time was only 1h. The conversion rate of Acetic Acid was analyzed by a gas chromatograph (GC-14C SHIMADZU in Japan)The experimental results showed that H2SO4 concentration had more influences on catalytic activity than other two factors, calcination temperature and ZrO2 supported content. Since sulfur absorbed on the surface of metal oxides is necessary to the acidity of SO42-/MxOy solid superacid,H2SO4 concentration in impregnation solution is needed enough high. But, it can't be too much high,otherwise, Zirconium sulfate formed on the catalyst surface will be harmful influences on catalytic activity. In researched cover, 0.5mol/L H2SO4 concentration is the most suitable, and the catalyst prepared with this concentration has very strong acidity.The optimum preparation condition is as follows: ZrO2 content 3.5g/g; calcination temperature 600℃, and H2SO4 concentration 0.5mol/L. In the catalyst prepared with above conditions, the acidic strength (H0) of the catalyst is smaller than ＜-14.52, and catalytic activity is 96.5 vol%. When it was re-used in esterification reaction, catalytic activity decreased gradually with re-used times increasing(seen in Table 1). But after catalyst is used repeatedly up to five times, catalytic activity (84.3 vol %)is still higher than that of H2SO4 catalyst.The X-ray diffraction patterns showed that ZrO2 supported in TiO2 belonged tetragonal zirconia phases. Through the calculation of Scherrer formula, the particle size of ZrO2 in the catalyst is about 12.5 nm. After SO42- promoted nanometer ZrO2/TiO2 compound carrier, the diffraction peaks of tetragonal zircoma become broader and the strength weaker. It shows that adding SO4 ions restrains the crystallization of ZrO2, diminishes the size of particles. This might be why SO42--ZrO2/TiO2 has high catalytic activity and stability in acidic catalysis reaction.     

V（acac）3—AI（i—BU）2CI催化体系相态的研究

研究了V(acac)3-AI(i-BU)2CI催化体系的相态。通过Tyndall效应、电镜观察和超过渡实验,证明了在溶有丁二烯的甲苯溶剂中V(acac)3-AI(i-BU)2CI催化体系以小颗粒分散,粒径在1－100nm之间,为胶体催化剂,属于高度分散的多相催化体系。催化剂颗粒是无定形的,其活性中心位于胶粒表面,以较佳配比所得到的催化剂颗粒较小、分布均匀,对丁二烯聚合反应具有较高的催化活性。     

N<Subscript>2</Subscript>O catalytic decomposition — effect of pelleting pressure on activity of Co-Mn-Al mixed oxide catalysts

The effect of pelleting pressure (0–10 MPa) during the preparation of Co-Mn-Al mixed oxide catalyst on its texture and activity for N₂O catalytic decomposition was examined for small grain sizes used in laboratory experiments, and for model industry catalyst particles. Adsorption/desorption measurements of nitrogen, mercury porosimetry and helium pycnometry were used for detail characterization of porous structure. A volume of micropores of about 20 mm³ g⁻¹ was evaluated using modified BET equation. This value did practically not change with the increasing pelletization pressure except that of the sample formed at the pressure of 10 MPa. Although an increase of pelleting pressure caused an increase in bulk density and a decrease in pore size and pore volume of the prepared catalyst (resulting in lower values of N₂O effective diffusion coefficient), no direct correlation between pelleting pressure used and catalyst activity has been found. In contrary, estimation of the internal diffusion limitation according to the Weisz-Prater criterion indicated that even laboratory experimental data obtained for catalyst grains with particle size lower than 0.315 mm pelletized at higher pressures could be influenced by internal diffusion. Estimation of the internal mass transfer limitation in industrial catalyst particles described by the effectiveness factor showed that effectiveness factor of about 0.07 and 0.2 can be obtained for spheres with the radius of 1.5 mm and 0.5 mm, respectively, if pelleting pressure of about 6 MPa was used for the catalyst preparation. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

Effect of electrode size on catalytic activity

In the field of catalyst research, synthesis innovations have allowed for the production of nanoparticle catalysts less than 2 nm in size. With this decrease in catalyst size, new questions have arisen with respect to the overall effect of size on catalytic activity. It is generally accepted that as catalyst particles decrease in size, the surface area to volume ratio of the catalyst is increased, resulting in higher catalytic performance. This paper introduces a novel technique for producing electrode structures with specific catalyst sizes. Through the use of electrochemical impedance spectroscopy and chronoamperometry, these different electrode sizes are compared with respect to the hydrogen evolution reaction. From this work, it is shown that for the given reaction, there exists a critical size at which catalytic activity begins to increase. A proposed explanation for the observed change in catalytic performance is introduced.     

负载型纳米Ni催化剂用于对氯硝基苯选择加氢

以TiO2为载体,N iB为诱导剂,粉末化学镀法制备了负载型纳米N i催化剂.通过TEM、HRTEM、XRD和ICP技术对催化剂物性进行了表征.结果表明,碱性镀液可使载体表面均匀负载微晶结构纳米N i团簇,尺度为35nm左右.该负载型纳米N i在对氯硝基苯选择加氢反应中表现出很高催化加氢活性,并能有效抑制脱氯,达到了工业骨架镍水平.由酸性镀液得到的负载型非晶态纳米N i-P合金具有较弱的催化对氯硝基苯加氢活性.反应温度对反应时间和脱氯率有明显影响.     

电气石粉对制备纳米TiO2及光催化氧化甲苯气相污染物的影响

用浸渍、烧结方法制备了不锈钢网(3×15cm)负载催化剂:由溶胶-凝胶法制备含(400目)电气石粉的二氧化钛催化剂,并与直接混合电气石粉、P-25 TiO₂的复合负载催化剂进行对照;利用X射线衍射、扫描电镜、透射电镜等表征催化剂结构;研究了催化剂在反应器(14L)中由20W紫外杀菌灯照射下光催化氧化去除气相甲苯污染物的效果.结果表明,在制溶胶过程中添加微米级电气石粉,得到催化剂粒径较小,其负载量和催化活性均有提高,平均催化比活性达到1.90mg·m^-2·min^-1或0.11mg·g^-1·min^-1,该催化剂在静态条件下反应4h,对初始浓度为180mg·m^-3和70mg·m^-3的甲苯去除率分别达到87%和82%;而同样的高初始浓度下,负载P-25仅可去除21%甲苯,复合负载P-25、电气石可去除58%甲苯,其催化比活性达到1.35mg·m^-2·min^-1或0.18mg·g^-1·min^-1.     

Size-dependent catalytic behavior of platinum nanoparticles on the hexacyanoferrate(III)/thiosulfate redox reaction

Platinum nanoparticles prepared in reverse micelles have been used as catalysts for the electron transfer reaction between hexacyanoferrate(III) and thiosulfate ions. Nanoparticles of average diameter ranging between 10 and 80 nm have been used as catalysts. The kinetic study of the catalytic reaction showed that for a fixed mass of catalyst the catalytic rate did not increase proportionately to the decrease in particle size over the whole range from 10 to 80 nm. The maximum reaction rate has been observed for average particle diameter of about 38 nm. Particles below diameter 38 nm exhibit a trend of decreasing reaction rate with the decrease in particle size, while those above diameter 38 nm show a steady decline of reaction rate with increasing size. It has been postulated that in the case of particles of average size less than 38 nm diameter, a downward shift of Fermi level with a consequent increase of band gap energy takes place. As a result, the particles require more energy to pump electrons to the adsorbed ions for the electron transfer reaction. This leads to a reduced reaction rate catalyzed by smaller particles. On the other hand, for nanoparticles above diameter 38 nm, the change of Fermi level is not appreciable. These particles exhibit less surface area for adsorption as the particle size is increased. As a result, the catalytic efficiency of the particles is also decreased with increased particle size. The activation energies for the reaction catalyzed by platinum nanoparticles of diameters 12 and 30 nm are about 18 and 4.8 kJ/mol, respectively, indicating that the catalytic efficiency of 12-nm-diameter platinum particles is less than that of particles of diameter 30 nm. Extremely slow reaction rate of uncatalyzed reaction has been manifested through a larger activation energy of about 40 kJ/mol for the reaction.     

Highly stable,active and recyclable solid acid catalyst based on polymer-coated magnetic composite particles

Sulfonic acid-functionalized polymer-coated magnetic composite particles were prepared and applied as highly stable, active and recyclable magnetic solid acid catalyst for biodiesel preparation and biomass transformation.     

Highly stable,active and recyclable solid acid catalyst based on polymer-coated magnetic composite particles

A facile approach has been adopted for coating cross-linked polystyrene(PS) shells on the surface of Fe304 magnetic clusters using reflux-precipitation polymerization(RPP).Treating the PS shell with chlorosulfonic acid yields magnetic composite particles with acid functionality.By adjusting the amount and proportion of monomers(styrene and divinylbenzene),the obtained magnetic composite particle solid acid(MPM-5 S) exhibits a saturation magnetization value of 18 emu/g,a specific surface area of 243 m~2/g and an acid density of 2.113 mmol/g.The MPM-5 S magnetic solid acid catalyst was evaluated for esterification of oleic acid with methanol to prepare biodiesel.Under mild conditions,the conversion of oleic acid reached 91%,which was much higher than the catalytic activity of Amberlyst-15 and close to the catalytic activity of concentrated H_2 SO_4.The solid acid catalyst can be recovered by magnetic separation and reused three times maintaining over 95% of its initial catalytic activity.Additionally,the solid acid can be used to catalyze the dehydration of fructose to 5-hydroxymethylfurfural.     

Structure and catalytic properties of nanosized alumina supported platinum and palladium particles synthesized by reaction in microemulsion

Mixtures of nanosized platinum and palladium particles have been prepared by reduction of salt-containing microemulsion droplets using hydrazine as the reducing agent. To avoid possible negative effects of the presence of sulfur compounds during the preparation the microemulsion was made using the sulfur-free nonionic polyoxyethylene 4 lauryl ether surfactant. Transmission electron microscopy showed that the as-prepared mixtures contained crystalline platinum particles of fairly homogeneous size (20 to 40 nm) with adsorbed amorphous palladium particles 2 to 5 nm in size. Catalyst samples were prepared by depositing the nanoparticles on a gamma-Al(2)O(3) support followed by heating in air at 600 degrees C. Alloyed particles of platinum and palladium with sizes ranging from 5 to 80 nm were obtained during the heating. The majority of the particles had the fcc structure and their compositional range was dependent upon the Pt:Pd molar ratio of the microemulsion. A catalyst prepared from a microemulsion with a 20:80 Pt:Pd molar ratio showed the highest catalytic activity for CO oxidation, while pure platinum and palladium catalysts showed higher sulfur resistance. These results differ from the performance of conventional wet-impregnated catalysts, where a 50:50 Pt:Pd molar ratio resulted in the highest catalytic activity as well as the highest sulfur resistance.     

Synthesis,Characterization and Self-assembly of Gold-coated Iron Nanoparticles

Due to their small size (1-100 nm), nanoparticles exhibit novel materials properties that differ considerably from those of the bulk solid state. Especially in recent years, the interests in nanometer-scale magnetic particles are growing based on their potential application as high density magnetic storage media. A unique reverse micelle method has been developed to prepare gold-coated iron nanoparticles. XRD, UV/vis, TEM and magnetic measurements are used to characterize the nanocomposites. XRD only gives FCC paterns of gold for the obtained nanoparticles. There is a red shift and broadening of Au@Fe colloid relative to pure gold colloid in the absorption spectra. TEM results show that the average size of Au@Fe nanoparticle is about 10 nm. These nanoparticles self-assembled into wires in micron level under a 0.5 T magnetic field. Magnetic measurements show that the particles are superparamagnetic with a blocking temperature of 42 K. Coercivity of the obtained nanoparticles decreases with the measuring temperature, which are 730 Oe,320 Oe and 0 at 2 K, 10 K and 300 K, respectively.     

Electrooxidation of Methanol on Platinum–Ruthenium Catalysts Applied to a Cation-Exchange Membrane

Possibilities for production of active Pt–Ru electrodes for the direct methanol fuel cell with a decreased content of platinum-group metals in them are studied. Platinum and ruthenium are electrodeposited on a thin layer of carbon black applied to a Nafion 117 membrane. The deposition potential effect on the specific surface area of the catalyst and its electrochemical activity in the methanol oxidation is studied. The oxidation currents are related to unit true surface area or unit catalyst mass. The dependence of activity on the Pt : Ru ratio in the plating solution and in the deposit is studied. The effect of the catalyst amount deposited and the particle size on the activity is studied. It is shown that the catalytic activity decreases at the average diameter of Pt–Ru particles less than 4 nm. The results are compared with the size effects observed earlier.     

Influence of pH values in the preparation of CuO-CeO2 on its catalytic performance for the preferential oxidation of CO in excess hydrogen

CuO-CeO2 catalyst prepared with co-precipitation showed high catalytic performance for the preferential oxidation of CO in excess hydrogen (PROX). Influence of pH values in the preparation of CuO-CeO2 on its catalytic performance was investigated in this work. The CuO-CeO2 catalyst prepared at pH = 13.03 had the smallest particle size (5.4 nm), the largest surface areas (138 m2/g) and the highest activity with CO conversion of 99.6% at 130 ℃. The CuO-CeO2 catalyst was characterized using BET, XRD and TPR techniques. The results showed that when the pH value of the mixed solution containing Cu and Ce species was properly adjusted, both the adsorption layers and diffusion layers of the formed colloidal particles in hydroxide precursor of CuO-CeO2 were modified, resulting in the better catalytic performance for PROX on the final CuO-CeO2 catalyst.     

Magnetic applications of polymer gels

In this paper we report results of both, material preparation and magnetic characterisation, on CoFe₂O₄ particles of nanometric size formed by in‐situ precipitation within polymer gels. The size of the particles was controlled within a very narrow volume distribution and its average value was shifted from 2 to 10 nm. The existence of nanoparticles showing, at room temperature, coercive field values between 500 and 900 Oe and saturation magnetisations of about 500 emu/cm³, suggest to use these systems to get magnetic recording media with ultra high density. Poly(vinyl alcohol) (PVA) and Polystyrene (PS) films were prepared from this nanocomposite material. After a magnetic field treatment nanoparticles within the PVA films are free to rotate in response to an applied magnetic field. This PVA based nanocomposite film portends a new class of magnetic material with very little or no electrical and magnetic loss.     

Catalytic activity of platinum nanoparticles on highly boron-doped and 100-oriented epitaxial diamond towards HER and HOR

Platinum nanoparticles supported on boron-doped single-crystalline diamond surfaces were used as a model system to investigate the catalytic activity with respect to the influence of particle morphology, particle density and surface preparation of the diamond substrates. We report on the preparation, characterization and activity regarding hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) of these Pt/diamond electrodes. Two kinds of diamond layers with boron doping above 10(20) cm(-3) were grown epitaxially on (100)-oriented diamond substrates; post-treatments of wet chemical oxidation and radio frequency (rf) oxygen plasma treatments were applied. Electrochemical deposition of Pt was performed using a potentiostatic double-pulse technique, which allowed variation of the particle size in the range between 1 nm and 15 nm in height and 5 nm and 50 nm in apparent radius, while keeping the particle density constant. Higher nucleation densities on the plasma processed surface at equal deposition parameters could be related to the plasma-induced surface defects. Electrochemical characterization shows that the platinum particles act as nanoelectrodes and form an ohmic contact with the diamond substrate. The catalytic activity regarding HER and HOR of the platinum nanoparticles exhibits no dependence on the particle size down to particle heights of ～1 nm. The prepared Pt on diamond(100) samples show a similar platinum-specific activity as bulk platinum. Therefore, while keeping the activity constant, the well-dispersed particles on diamond offer an optimized surface-to-material ratio.     

NADH Oxidase Activity of Gold Nanoparticles in Aqueous Solution

Nanoparticles of Au(0) stabilized by Triton X-100 in water catalyze NADH oxidation. Oxygen and potassium ferricyanide can serve as electron acceptors from NADH. The NADH oxidase activity of Au(0) (normalized to gold concentration) is 0.08 turnover/min in air and 0.32 turnover/min in argon in the presence of K₃FeCN₆ (2 × 10⁻⁴ mol/l). The catalytic activity decreases with increasing gold concentration in the solution used for particle preparation and, accordingly, with increasing size of gold particles.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 399–401.Original Russian Text Copyright © 2005 by Kulikova.     

环烷酸钴-氯二异丁基铝催化体系相态的研究

研究了Co(naph) 2 Al(i Bu) 2 Cl催化体系的相态 .通过Tyndall效应、电镜观察和超过滤实验 ,证明了Co(naph) 2 Al(i Bu) 2 Cl催化体系在溶有丁二烯的苯溶剂中以纳米级小颗粒分散 ,在较佳配比时 ,粒径在 1～10 0nm之间 ,为胶体催化剂 ,属于高度分散的多相催化体系 .催化剂的活性位位于胶粒表面 ,催化剂颗粒是无定形的 .以较佳配比得到的催化剂颗粒较小、分布均匀 ,催化丁二烯聚合反应活性高 .归纳出胶体催化剂的制备特点为外观类似于均相催化体系 ,但是制备方法 (各组分配比、加入顺序、陈化等 )对催化活性有明显的影响 .并给出将胶体催化动力学作均相动力学近似的条件 ,在聚合反应初期 ,且单体浓度比烷基铝以及其他填加物浓度大 2～ 3数量级