Electrooxidation of hydrogen at Pt/carbon nanotube catalysts for hydrogen–air fuel cell

A possibility for application of the method of thin-layer rotating disk electrode (RDE) for investigation of kinetics of hydrogen electrooxidation on highly dispersed platinum catalysts formed on the carbon nanotubes (CNT) is studied. It is shown that the polarization curves of hydrogen oxidation on the studied catalysts approach the calculated curves for the diffusion overpotential of hydrogen reaction both in the acidic and alkaline electrolytes. This is the evidence, on the one hand, for a high activity of proposed catalysts in the hydrogen oxidation reaction and, on the other hand, for incorrect use of the Koutecky–Levich equation for calculating the kinetic currents in the case under consideration. The characteristics of hydrogen–oxygen fuel cell (FC) with anode based of synthesized 40Pt/CNT catalysts are highly comparative with the characteristics of FC containing commercial 60Pt catalyst (HiSPEC 9100) on the anode.     

甲烷低温氧化Pd催化剂的研究进展

环保意识和污染物排放标准的提高,使天然气汽车尾气减排成为了亟待解决的问题.催化氧化被认为是消除稀燃天然气汽车尾气中强温室效应气体甲烷最为有效的途径之一,而Pd催化剂被认为是甲烷低温氧化的首选催化剂.通过对Pd催化剂制备中的前驱体、载体、助剂、制备方法各制备要素综述,总结了各要素对催化剂低温氧化活性、稳定性和抗硫中毒性能的影响,并系统介绍了Pd催化剂制备的最新发展.基于对当前研究的认识,提出了开发低成本高性能催化剂的措施.     

Molecular complexes in water oxidation: Pre-catalysts or real catalysts

Artificial photosynthesis is considered a promising method to produce clean and renewable energy by sunlight. To accomplish this aim, development of efficient and robust catalysts for water oxidation and hydrogen production is extremely important. Owing to the advantages of easily modified structures and traceable catalytic processes, molecular water oxidation catalysts (WOCs) attract much attention during the past decade. However, the transformation of molecular WOCs to metal oxides/hydroxides or metal ions may occur under the harsh catalytic conditions, making the identification of true active species difficult. In this article, recent progress on molecular complexes acting as real catalysts or precursors toward water oxidation was briefly reviewed. We summarized the commonly used physical techniques and chemical methods that enable to distinguish homogeneous catalysts from heterogeneous catalysts. The factors that affect the nature of WOCs, such as reaction conditions, transition metal centers, and supporting ligands were discussed as well.     

Magnetically separable polyoxometalate catalyst for the oxidation of dibenzothiophene with H2O2

Two types of polyoxometalate-functionalized magnetic nanoparticles catalysts consisting of H(3)PW(12)O(40) supported on surface-modified Fe(3)O(4) magnetite nanoparticles were prepared using an easy synthetic route and successfully applied for the oxidation of dibenzothiophene. The magnetic catalysts showed a catalytic performance in the oxidation of dibenzothiophene in acetonitrile with hydrogen peroxide, and high conversions were obtained. The catalysts could be easily separated from the reaction solution by applying an external magnetic field and recycled several times.     

Effect of the Nature of the Precursor on the Activity of Copper-Containing Catalysts Based on Erionite in Oxidation of CO

We have studied the catalytic activity of copper-containing zeolite catalysts based on erionite (ERI) in oxidation of CO. We have established that the activity of Cu-ERI systems is due to isolated coordination unsaturated Cu²⁺ cations which are stabilized in the catalyst on sites with strong tetragonal distortion and are reduced to Cu⁺ during catalysis. According to X-ray photoelectron spectroscopy (XPS), diffuse reflection electronic spectra, and temperature programmed reduction by hydrogen (TPR-H₂) spectra, activity differences between 3% Cu-ERI catalysts obtained from different precursors are determined by the different numbers of Cu²⁺ cations capable of being reduced during the reaction at T < 400 °C: the higher the content of such cations in the samples, the higher the activity of the Cu-ERI systems. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 317–322, September–October, 2005.     

Effect of the nature of carbonaceous supports on the bioelectrocatalytic activity of peroxidase, immobilized on the supports, in the hydrogen peroxide reduction reaction

Electrochemical properties of such disperse carbonaceous materials as acetylene black AD-100, finely divided colloidal graphite (FCG), ultradisperse diamond (UDD), and carbon nanotubes (CNT) are examined. Effect of the nature of disperse carbonaceous supports on bioelectrocatalytic activity of adsorbed peroxidase (POD) in the hydrogen peroxide reduction reaction is investigated. It is shown that the hydrogen peroxide reduction on the biocatalysts studied proceeds in conditions of direct bioelectrocatalysis independently of the disperse-support type. It is also demonstrated that the biocatalysts’ activity depends on the structure and properties of the surface of the supports defining the magnitude of the POD adsorption in an orientation favorable for direct bioelectrocatalysis. Maximum activity is inherent in the catalysts manufactured on the basis of materials with moderate hydrophobic and hydrophilic properties. By the magnitude of the activity in the hydrogen peroxide reduction reaction, depending on the nature of the carbonaceous support, the fabricated catalysts (carbonaceous material with adsorbed POD) form the series AD-100, CNT > FCG > UDD.     

碳纳米管纯化对Pt/CNTs催化甲醇电化学氧化活性的影响

探索了一种适用于Pt/CNTs催化剂的纯化方法.利用比表面积测定、X射线衍射(XRD)、透射电子显微镜(TEM)和电化学等手段进行了表征.研究结果表明,经该方法纯化的CNTs作为载体制备的阳极催化剂表现出明显优于相应的混酸氧化法纯化的CNTs为载体的催化剂催化性能.     

Effect of ZrO<Subscript>2</Subscript> morphology in copper–cerium–zirconium oxide systems on their catalytic properties in the reaction of co oxidation in hydrogen-rich mixtures

We studied the catalytic properties of copper–cerium oxide systems, deposited on supports obtained by calcination of yttrium-stabilized zirconium dioxide at 300-1000 °C, in the reaction of selective oxidation of CO in a stream of hydrogen. We have shown that the catalytic activity of the samples obtained correlates with the activity of the original supports in the reaction of CO oxidation: the highest CO conversion is observed on catalysts with the highest and the lowest specific surface area. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 115-120, March-April, 2009.     

Tantalum(V) or niobium(V) catalyzed oxidation of sulfides with 30% hydrogen peroxide

Tantalum(V) and niobium(V) are effective catalysts for the oxidation of sulfides with 30% hydrogen peroxide. The reaction of sulfides with 30% hydrogen peroxide catalyzed by tantalum(V) chloride or niobium(V) chloride in acetonitrile, i-propanol or t-butanol selectively provided the corresponding sulfoxides in high yields. The corresponding sulfones are efficiently obtained from the reaction of sulfides with 30% hydrogen peroxide in methanol catalyzed by tantalum(V) or niobium(V).     

Carbon nanotubes as a support for Pt-and Pt-Ru-catalysts of reactions proceeding in fuel cells

Comparative study of two types of single-wall carbon nanotubes and standard carbon black Vulcan XC-72 as supports for catalysts of reactions proceeding in fuel cells is carried out. The nanotubes were prepared by arc method; they differed in the degree of their purifying from amorphous carbon and metal impurities. The structure and hydrophobic-hydrophilic properties of these carbon supports are studied by etalon porosimetry. The effect of the supports’ specific surface area on the deposited catalyst particles size and specific surface area is studied. The catalysts (Pt-Ru and Pt) were deposited from aqueous solutions of their salts. Platinum was also deposited by thermal decomposition of ethoxy clusters. It is shown that in methanol oxidation reaction at the Pt-Ru catalysts the current values per unit true surface area do not depend on the support nature, provided the catalyst loading is equal and the particle size is similar. When oxygen is reduced at platinum deposited onto purified nanotubes and the carbon black Vulcan XC-72, specific kinetic currents also are close to each other. It is shown that the degree of nanotubes purification and their structure affect the kinetics of this reaction significantly.     

由不同镍盐前体制备高分散Ni/SBA-15催化剂：活化氛围的影响

以硝酸镍和乙酸镍为镍前体,用浸渍法分别在空气和氢气氛围活化制得系列Ni/SBA-15催化剂,通过XRD、H₂-TPD、N₂物理吸附和在线质谱等物理化学手段对催化剂进行了表征,并结合微型高压反应釜萘加氢反应,评价了催化剂的加氢性能。结果表明,氢气氛围活化对硝酸镍为镍前体所制Ni/SBA-15催化剂的镍分散度和活性有显著促进作用,而空气氛围活化对乙酸镍为镍前体所制催化剂有明显促进作用。根据催化剂前体在不同氛围活化时的热分解产物,提出了活化氛围对不同镍前体制得Ni/SBA-15催化剂所产生的作用机理。     

Catalytically active platinum blacks prepared by magnetron sputtering in vacuum and their using in fuel cells with solid polymer electrolyte

Highly disperse platinum film were vacuum-plasma-deposited onto titanium foil and gas-diffusion layers. The platinum deposits have complicated structure. By measuring hydrogen desorption peaks, the catalysts’ active specific surface area was determined and the roughness factor calculated. The electrochemical activity of the electrodes on gas-diffusion layers in the oxygen reduction and hydrogen oxidation reactions was determined. It was shown that the catalysts’ specific activity depends on the platinum content and the Nafion-ionomer additive. The high-activity electrodes were tested in Membrane Electrode Assemblies of low-temperature fuel cells.     

水滑石衍生的复合氧化物催化氧化挥发性有机气体的研究进展（英文）

挥发性有机化合物(VOCs)是大气颗粒污染物(PM2.5)和臭氧污染的主要前体物,来源于工业活动(如溶剂使用过程)、汽车尾气以及植物排放等,具有毒性,对人类和自然生命产生危害.催化氧化技术是在催化剂表面,在较低的操作温度(200-450℃)下,将VOCs非均相催化氧化成CO2和H2O,是一种最为有效的分解VOCs的方法,具有副产物少,能耗低的优点.VOCs分解用催化剂主要分为贵金属和金属氧化物两大类.贵金属催化剂活性高,但价格昂贵.因此科研工作者一直在诸多方面调控过渡金属氧化物,例如制备方法、组分协同、结构缺陷等,期望获得高活性、低成本的催化剂.水滑石(LDHs)是一种层状双金属氢氧化物,由带正电荷的金属氢氧化物层板和层间阴离子组成,可以表示为[M1-x^2+Mx^3+(OH)2](An-)x/n·mH2O.鉴于LDHs特有的结构特点,层板元素可调、比例可调等,其在一定温度下煅烧可以得到过渡金属复合氧化物(MMO)材料.由于LDHs的拓扑焙烧转变得到的MMO材料显示出许多利于多相催化反应的优点,如大表面积和多孔性、高热稳定性、良好的金属氧化物分散性等.水滑石基催化材料用于VOCs催化分解也引起了科研工作者的持续关注和研究,文献大多选择苯、甲苯、乙酸乙酯等工业活动中常用的挥发性有机溶剂作为探针分子来评估催化剂的活性、稳定性等参数.本综述将LDHs衍生的VOCs降解催化剂分为4类,整理了其近10年的研究进展:(1)含过渡金属的LDHs焙烧转变成MMO催化剂:系统论述了层板元素组成、层板元素比例、焙烧温度、制备方法等条件对催化活性的影响规律,阐明了不同处理条件下催化剂的物理化学特性(比表面积、孔结构、表面元素价态、氧缺陷、还原性)与催化活性的关联;(2)贵金属/MMO催化剂:比较了贵金属种类、LDHs载体种类、负载方式等因素对催化活性的影响规律,总结了贵金属负载在LDHs载体的优势;(3)核壳型MMO催化剂:分析了在氧化铝球、MOF等载体上原位负载LDHs的方法构筑多级结构的MMO催化剂,利于促进VOCs分解活性;(4)整体型MMO催化剂:满足VOCs分解实际应用,提出铝片基底上原位生长-煅烧制备高活性位点暴露的整体式催化剂的优点.在催化活性基础上着重介绍了水蒸气对活性的影响以及VOCs分解催化机理.同时提出了3点仍需努力的方向:LDHs向MMO拓扑转变机制认识不足;LDHs衍生的催化剂的VOCs分解机制研究不深入;催化剂活性降低-再生研究不透彻.     

Study of the selective catalysis of metalloporphyrins for 2-methyl-butane oxidation with PhIO under mild conditions

Nine ironporphyrins and eight manganeseporphyrins were synthesized, and their selective catalysis for the oxidation of the secondary and tertiary carbon–hydrogen bonds of 2-methyl-butane with PhIO was studied. The proportion of the oxidation product of tertiary carbon–hydrogen bond to the one of secondary carbon–hydrogen bond was 3:1 when ironporphyrins were used as catalysts, and 2.3:1 when manganeseporphyrins were used as catalysts. The research showed that the substituting groups on the porphyrin rings influenced the catalytic selectivity of metalloporphyrins for the oxidation of the secondary and tertiary carbon–hydrogen bonds as well as the reaction yields. The electron-attracting groups on benzene rings of ironporphyrins increased the catalytic selectivity of ironporphyrins for the tertiary carbon–hydrogen bond oxidation and the reaction speeds, and the electron-releasing groups increased the catalytic selectivity for secondary carbon–hydrogen bond oxidation and reduced the reaction speeds. Both electron-attracting and -releasing groups on benzene rings of manganeseporphyrins enhanced the catalytic selectivity of manganeseporphyrins for the secondary carbon–hydrogen bond oxidation.     

Co/Fe催化剂乙醇裂解和部分氧化制氢研究

采用共沉淀法制备的Co/Fe催化剂催化乙醇裂解和部分氧化制氢反应，考察了反应温度对两种途径反应的影响。结果发现，Co/Fe催化剂对乙醇部分氧化制氢显示出较高的氢选择性，且稳定性较好；该催化剂对乙醇裂解制氢也具有较高的氢选择性，但其稳定性很很差。XRD表征结果表明，在催化乙醇部分氧化反应后，Co70Fe30催化剂中存在CoFe合金和CoO相；而催化乙醇裂解反应后，Co70Fe30催化剂中仅存在CoFe合金，即CoFe合金可能是裂解反应的活性组分。     

Ultradisperse catalytic layers supported by nanotubes and poly(diallyldimethylammonium)chloride polymer

A catalytic system consisting of carbon nanotubes, poly(diallyldimethylammonium)chloride, and a very thin layer of platinum or platinum-ruthenium is assembled layer-by-layer (LbL) on a glassy carbon (GC) electrode. Deposits of platinum metals are studied by electrochemical methods, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Such catalyst layers are shown to exhibit much higher activity in the methanol oxidation reaction as compared with commercial and electroplated catalysts. The currents compared are calculated per the surface area of deposited metals determined with respect to hydrogen adsorption.     

FePO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> Catalysts for Propylene Glycol Oxidation

FePО₄/SiO₂ supported catalysts with a different content of iron phosphate are prepared. The properties of the catalyst are changed by the introduction of alkali metal compounds (Na or Cs) on its surface. The samples obtained are characterized by X-ray diffraction, low-temperature nitrogen adsorption, temperatureprogrammed reduction by hydrogen, and temperature-programmed desorption of ammonia. The catalytic properties are investigated in the reaction of gas-phase propylene glycol oxidation. It is shown that the selectivity of methylglyoxal formation on the unmodified catalysts is determined by the state of the supported active component and by its reduction–oxidation ability under the action of a reaction mixture.     

孤岛渣油超临界水-合成气中悬浮床加氢裂化反应研究 Ⅰ. 催化剂的影响

利用超临界水-合成气为替代加氢氢源对孤岛渣油悬浮床加氢裂化反应进行了研究，设想利用超临界水中发生的水-气转化反应（CO+H2O→H2+CO2）为渣油加氢反应提供氢源，报道了孤岛渣油超临界水-合成气中悬浮床加氢裂化反应催化剂影响的研究结果。结果表明，催化剂在该反应中具有十分重要的作用，加入催化剂可以明显改善加氢裂化产物的分布和裂化反应产物的性质，降低裂化气体和抑制缩合生焦反应的发生。     

Selective oxidation of sulfide catalyzed by peroxotungstate immobilized on ionic liquid-modified silica with aqueous hydrogen peroxide

Two kinds of catalysts of peroxotungstates immobilized on ionic liquid-modified silica have been synthesized and characterized. By comparing with other heterogeneous catalysts, the most characteristic of these heterogeneous catalysts is the catalyst formed from the combination of catalytic active center peroxotungstate with an ionic liquid. Thereinto, ionic liquid-modified supported catalysts provide the hydrophobic environment for organic reactions. We presume that the heterogeneous catalyst would display excellent catalytic ability depending on the additive effect of an ionic liquid and peroxotungstate. Their catalytic properties in oxidation of sulfides to sulfoxides and sulfones were investigated with 30% aqueous hydrogen peroxide at room temperature. These recoverable catalysts both exhibit high catalytic activities in the oxidation reaction of sulfoxides and provide excellent chemselectivities towards sulfur groups with unsaturated double bonds when the aqueous hydrogen peroxide was greatly in excess. The yields of methyl phenyl sulfoxide were still satisfied when the catalyst was reused for a sixth time.     

金属核及氧化铈的物理化学性质对一氧化碳氧化的影响

氧化铈独特的氧化还原性能使其适合用作氧化反应中的催化剂或载体.氧化铈负载的过渡金属纳米粒子或孤立的单原子提供了金属-载体界面,从而降低了去除界面氧原子的能耗,提供了可以参与ManVanKulvian氧化过程的活性氧物种.CO氧化是测试氧化铈负载催化剂还原性的主要探针反应,并且它常见于在相对低温下消除CO的各种应用中.在过量H2中优先氧化CO(PROX)反应可控制CO浓度达到超低水平,以防止氢氧化电催化剂中毒.催化剂在CO氧化反应中的活性和在PROX反应中对CO和H2的选择性取决于金属物种的种类和分散性、CeO2的结构和化学性质以及催化剂的合成方法.在这篇综述中,我们总结了最近发表的关于CeO2负载的金属纳米粒子和单原子催化CO氧化和PROX反应的相关工作;以及不同的负载金属和同种金属在普通CeO2表面上的反应性.我们还总结了密度泛函理论计算中提出的最可能的反应机理;并且讨论了各种负载型金属在PROX反应中影响CO氧化选择性的因素.