In situ FTIRS studies of the electrocatalytic oxidation of ethanol on Pt alloy electrodes

Ethanol oxidation on Pt–Os and Pt–Ru–Os alloy electrodes was investigated by electrochemical and spectroelectrochemical techniques. Cyclic voltammetry and chronoamperometric results showed that the Pt–Os alloy has the highest current density at lower potentials. Linear CO_ads, acetic acid, acetaldehyde, and CO₂ were identified as reaction intermediates and/or products by single potential alteration infrared reflectance spectroscopy and subtractively normalized interfacial Fourier transform infrared reflectance spectroscopy techniques. The in situ Fourier transform infrared spectroscopy results showed that the electrooxidative adsorption of ethanol was dissociative providing CO_ads at low potentials. Dedicated to our friend Professor Francisco Carlos Nart (in memorium), IQSC-USP, Brazil.     

Effect of Ru addition on the structural characteristics and the electrochemical activity for ethanol oxidation of carbon supported Pt–Sn alloy catalysts

Binary Pt–Sn/C (1:1) and ternary Pt–Sn–Ru/C (1:1:0.3 and 1:1:1) catalysts were synthesized by reduction of precursors with formic acid, and their activity for ethanol oxidation was compared with that of commercial Pt/C and Pt–Ru/C catalysts. Linear sweep voltammetry measurements at 40 and 90 °C showed that for potentials higher than 0.3 V vs. RHE, the Pt–Sn–Ru/C (1:1:0.3) catalyst presents the highest activity for ethanol electro-oxidation, while the electrochemical activity of the Pt–Sn–Ru/C (1:1:1) catalyst was lower than that of both the binary Pt–Sn/C and Pt–Ru/C catalysts. Tests in a single direct ethanol fuel cell confirmed the superior performance of the Pt–Sn–Ru/C (1:1:0.3) electrocatalyst. The positive effect of the Ru presence in the Pt–Sn–Ru/C (1:1:0.3) catalyst was ascribed to the interactions between Sn and Ru oxides.     

A new approach to achieving a pure M1 phase catalyst for the selective oxidation of propane

A pure M1 phase catalyst was originally obtained by treatment of the multi-phase Mo–V–Te–Nb–O catalyst in the reaction atmosphere and was systematically studied by some physico-chemical techniques. The results showed that the reaction treatment played an important role in improving the performance of the catalyst.     

Improved kinetics of ethanol oxidation on Pd catalysts supported on tungsten carbides/carbon nanotubes

Pd nanoparticles on tungsten carbides modified multiwalled carbon nanotubes (Pd-WC/MWCNT) catalysts have been prepared by an intermittent microwave heating (IMH) technique for the first time. The Pd-WC/MWCNT catalysts are evaluated and show an improved kinetics for the ethanol oxidation. It is recognized that the significant increase in the catalytic activity for ethanol oxidation on Pd-WC/MWCNT is attributed to both the synergistic effect between Pd nanoparticles and the WC support and the structure effect of the MWCNT. This type catalyst can be universally used as the oxygen reduction catalyst in fuel cells and sensors both in alkaline and acidic solutions.     

Enhanced electrochemical activity for ethanol oxidation on the carbon-supported Pt3Te nanocatalysts by addition of Ru

Ternary Pt–Te–Ru catalysts with different atomic ratios were synthesized by reducing the precursor with formic acid. The physical and electrochemical characterization of the Pt₃TeRu_0.25/C catalyst was performed by transmission electron microscopy (TEM), X-ray diffraction, energy-dispersive X-ray spectroscopy equipped with TEM (TEM-EDX), X-ray photoelectron spectrometer, ethanol oxidation, and CO stripping. In TEM images, the Pt₃TeRu_0.25/C nanoparticles with an average particle size of around 2.9 nm were well dispersed on the carbon support. The Pt₃TeRu_0.25/C catalyst was superior to the Pt₃Te/C catalyst in respect of catalytic activity, durability, and CO tolerance. The positive effect of the Ru presence in the Pt₃TeRu_0.25/C catalyst was ascribed to the interactions of Ru or Ru oxides.     

活性炭和石墨混合载体的Pt催化剂(Pt/CG)对乙醇氧化电催化活性的影响

用化学沉积法制备炭载Pt(Pt/C)和以活性炭与石墨作混合载体的Pt(Pt/CG)催化剂。实验结果表明,活性炭与石墨质量比影响Pt/CG催化剂对乙醇氧化的电催化活性。当活性炭与石墨的质量比为15∶1时,制得的Pt/CG催化剂对乙醇氧化的电催化活性最高。     

Effect of thermal treatments on surface chemical distribution and catalyst activity in nickel on silica systems

The reducibility of several nickel on silica systems prepared by incipient wetness impregnation and precipitation-deposition has been studied using TPR and TG. The analysis of the results has allowed us to determine the minimum drying and reduction temperatures for both impregnation and precipitation catalysts. From an analysis of the obtained results, together with X-ray diffraction and the study of the reduction degree, dispersion and nickel particle size of catalysts activated at different reduction temperatures, conclusions on the nickel surface chemical distribution have been derived. An optimal reduction temperature for the catalysts has been determined from activity considerations in the hydrogenation of sunflower seed oil.     

Effect of silica-type sol-gel carrier’s structure and morphology on a supported Ziegler-Natta catalyst for ethylene polymerization

Silica xerogels with different structures and morphology, synthesized using a sol-gel procedure, were used as a carrier of vanadium catalysts (VOCl₃/AlEt₂Cl) for ethylene polymerization. Two techniques of catalyst synthesis were applied: slurry impregnation and gas-phase adsorption and the relevant polymerization methods were then employed. The effect of the carrier structure and morphology on the vanadium loading in the catalysts, the catalyst’s activity and kinetic stability were investigated.     

The effect of electrochemically treated glassy carbon on the activity of supported Pt catalyst in methanol oxidation

Effect of electrochemical oxidation of glassy carbon on deposition of platinum particles and electrocatalytic activity of platinum supported on oxidized glassy carbon (Pt/GC_OX) were studied for methanol oxidation in H₂SO₄ solution. Platinum was potentiostatically deposited from H₂SO₄ + H₂PtCl₆ solution. Glassy carbon was anodically polarised in 0.5 M H₂SO₄ at 2.25 V vs. saturated calomel electrode (SCE) during 35 s. Electrochemical treatment of GC support, affecting not significantly the real Pt surface area, leads to a better distribution of platinum on the substrate and has remarkable effect on the activity. The activity of the Pt/GC_OX electrode for methanol oxidation is larger than polycrystalline Pt and for more than one order of magnitude larger than Pt/GC electrode. This increase in activity indicates the pronounced role of organic residues of GC support on the properties of Pt particles deposited on glassy carbon.     

预处理条件对Ag/SBA-15催化剂上甲苯催化氧化反应性能的影响

甲苯是一种典型的挥发性有机污染物.近年来,催化氧化法是一种广泛使用并具有开发潜力的有效去除挥发性有机污染物的方法,而贵金属催化剂一直是首选.介孔二氧化硅材料SBA-15具有规则孔道和较高的比表面积因而在催化领域中具有较大的应用潜力.本课题组已对一系列的SBA-15负载的纳米银催化剂的制备和低温催化氧化性能进行了研究,本文则通过研究不同预处理处理气氛对Ag/SBA-15催化剂结构以及甲苯催化氧化性能的系统研究,获得纳米银催化剂结构与甲苯催化氧化性能间的构效关系,对新催化剂的结构优化以及甲苯催化净化的低温催化剂开发具有重要的科学意义.研究表明,处理气氛明显影响了银物种和氧物种的状态,进而影响了催化剂的催化活性,先氧气(500℃)后氢气(300℃)处理的O500-H300催化剂对甲苯的反应活性明显优于在500℃氧气处理样品O500及氢气处理样品H500.由X-射线衍射和O2-程序升温脱附(TPD)可知,氧气500 oC处理使催化剂上形成大颗粒银粒子和氧化银粒子,以及大量次表层氧物种.氢气处理使催化剂形成较大的银粒子,由于未经过氧气处理,该催化剂上并没有次表层氧的生成.先氧气处理再氢气处理后催化剂上形成高分散的小粒径银粒子以及次表层氧物种,这表明低温氢气处理可以降低银粒子的尺寸并使催化剂上的银粒子得到再分散,同时不会影响次表层氧物种的形成.从催化剂的甲苯吸附和TPD实验中看出,大尺寸银粒子对甲苯具有较强的吸附性能,从而有利于甲苯在低温的催化氧化,但是在高温反应中没有优势;小尺寸银粒子虽然对甲苯的吸附能力不强,但是对分子氧有较好的吸附作用,进而增强自身与甲苯的相互作用,而且也促进了分子氧的活化,预处理中形成的次表层氧有效增强了甲苯和银粒子的相互作用,因此,先氧气后氢气处理的O500-H300样品在反应中显示出最好的甲苯催化活性.     

Palladium-based supported liquid phase catalysts: influence of preparation variables on the activity and enhancement of the activity on recycling in the Heck reaction

Supported liquid phase catalysts (SLPC) were prepared using a porous silica, ethylene glycol, palladium acetate, and triphenylphosphine trisulfonate sodium salt (TPPTS). The SLPC samples prepared were used for Heck reaction of iodobenzene and butyl acrylate with triethylamine base in toluene and the influence of catalyst preparation conditions was examined. The rate of reaction depends on the concentration of palladium–TPPTS complexes in the dispersed phase of ethylene glycol but not on the quantity of the dispersed liquid used. The SLPC sample can be easily separated by simple filtration and it is recyclable; interestingly, the rate of reaction is promoted on the repeated runs, due to the formation and accumulation of Et₃NHI adduct in the dispersed phase.     

Electrodeposition of a nickel-based hydrotalcite on Pt nanoparticles for ethanol and glucose sensing

Two different substrates, GC and graphite electrodes, have been coated with electrodeposited Pt nanoparticles (PtNPs) of different morphologies and sizes (from 2 μm to 20 nm). The electrochemical behavior of the platinised GC electrodes has been mainly evaluated in terms of the increase of the real surface area. A nickel-based hydrotalcite-like compound (HT) has been electrosynthesised on the GC platinised electrodes, by the cathodic reduction of a 0.03 M Ni and Al nitrates solution, and the cyclic voltammetric responses to these electrodes have been measured in a 0.1 M NaOH solution. Finally, the electrocatalytic performances of the GC–PtNPs–HT electrodes to ethanol and glucose have been investigated and compared with the performances of HT electrodeposited onto bare Pt, in the same conditions.     

载体硫酸化对柴油机尾气催化剂Pt/Ce-Zr活性和稳定性的影响

近年来,随着大气环境污染问题日益严重,汽车尾气排放受到政府越来越严苛的控制.柴油车排气成分主要包括碳氢化合物(HC)、一氧化碳(CO)、氮氧化物(NOx)、微粒(PM)和二氧化硫(SO2),因此常用的尾气后处理系统有颗粒捕获器(DPF)、氧化型催化转换器(DOC)以及NOx选择还原系统(SCR),在处理尾气时三者联合使用.其中柴油机氧化型催化剂(DOC)是汽车尾气后处理装置的重要组成部分,主要用于氧化CO,HC和NO,可以将CO和HC氧化成无害的CO2和H2O,将NO氧化成NO2,为后续SCR反应提供条件.柴油机排气温度一般较低(150?400°C),特别是在冷启动阶段,排气温度可降低到100°C左右,要求催化剂具有良好的低温催化活性.此外,由于柴油中存在少量含硫有机化合物,经过燃烧分解,使得柴油机尾气中含有少量SO2,对催化剂又有钝化作用,因此催化剂的抗硫性也是需要关注的重点.本文采用浸渍法制备Pt/Ce-Zr-SO42?催化剂,考察了催化剂载体硫酸化以及Pt和H2SO4的负载顺序对催化剂催化氧化C3H6和CO的活性及抗硫性的影响,并且对Pt/Ce-Zr-SO42?催化剂进行了一系列表征,探究其物理化学性质.结果表明,SO42?的添加能有效提高催化剂活性.Pt/CZ-10S对C3H6和CO的T90(转化率为90%时的温度)相较于Pt/CZ催化剂降低了约75°C,另外,Pt/CZ-10S催化剂也表现出较好的抗硫稳定性,在含硫尾气中240°C反应20 h后,其对C3H6和CO的转化率仍保持在95%以上.CO-TPD和XPS分析结果显示,Ce-Zr-SO42?载体上Pt的分散度增加,增加的Pt颗粒可以产生更多新的活性位点(Pt&+-(SO42?)&?couples),从而表现出优异的催化活性.此外,硫酸化后催化剂表面酸性的变化也是其抗硫性能提高的原因.     

碳纳米管负载的纳米Pd-Ag催化剂对乙醇和丙醇氧化的电化学活性

在乙二醇和水混合溶剂中,采用硼氢化钠还原的方法制备了多壁碳纳米管（MWCNT）负载的Pd和Pd-Ag纳米颗粒催化剂;在碱性介质中,用循环伏安法测试了这些催化剂对乙醇、正丙醇和异丙醇的电氧化性能。结果表明,Pd和Pd-Ag纳米颗粒均匀地分散在MWCNT表面;Pd/MWCNT、Pd₄Ag₁/MWCNT、Pd₂Ag₁/MWCNT和Pd₁Ag₁/MWCNT催化剂上金属颗粒的平均粒径分别为7、4、7和11 nm。相比乙醇和异丙醇,所制备的催化剂对正丙醇的氧化表现出较大的电流密度。与Pd/MWCNT催化剂相比,双金属Pd_nAg₁/MWCNT（n=4、2、1）催化剂,尤其是Pd₄Ag₁/MWCNT上的电流密度更大,表明Ag的加入提高了Pd催化剂对醇氧化的电化学活性,其原因是因为醇氧化过程所产生的中间体物种在双金属Pd-Ag/MWCNT催化剂上的吸附力有所减弱。     

In situ time-resolved XAFS study on the structural transformation and phase separation of Pt3Sn and PtSn alloy nanoparticles on carbon in the oxidation process

The dynamic behavior and kinetics of the structural transformation of supported bimetallic nanoparticle catalysts with synergistic functions in the oxidation process are fundamental issues to understand their unique catalytic properties as well as to regulate the catalytic capability of alloy nanoparticles. The phase separation and structural transformation of Pt(3)Sn/C and PtSn/C catalysts during the oxidation process were characterized by in situ time-resolved energy-dispersive XAFS (DXAFS) and quick XAFS (QXAFS) techniques, which are element-selective spectroscopies, at the Pt L(III)-edge and the Sn K-edge. The time-resolved XAFS techniques provided the kinetics of the change in structures and oxidation states of the bimetallic nanoparticles on carbon surfaces. The kinetic parameters and mechanisms for the oxidation of the Pt(3)Sn/C and PtSn/C catalysts were determined by time-resolved XAFS techniques. The oxidation of Pt to PtO in Pt(3)Sn/C proceeded via two successive processes, while the oxidation of Sn to SnO(2) in Pt(3)Sn/C proceeded as a one step process. The rate constant for the fast Pt oxidation, which was completed in 3 s at 573 K, was the same as that for the Sn oxidation, and the following slow Pt oxidation rate was one fifth of that for the first Pt oxidation process. The rate constant and activation energy for the Sn oxidation in PtSn/C were similar to those for the Sn oxidation in Pt(3)Sn/C. In the PtSn/C, however, it was hard for Pt oxidation to PtO to proceed at 573 K, where Pt oxidation was strongly affected by the quantity of Sn in the alloy nanoparticles due to swift segregation of SnO(2) nanoparticles/layers on the Pt nanoparticles. The mechanisms for the phase separation and structure transformation in the Pt(3)Sn/C and PtSn/C catalysts are also discussed on the basis of the structural kinetics of the catalysts themselves determined by the in situ time-resolved DXAFS and QXAFS.     

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.     

UiO-66-NH2负载铜催化剂的制备及其对醇的催化氧化

通过溶剂热法成功制备了一种基于金属有机骨架(MOF)的复合材料Cu-Cu₂O/UiO-66-NH₂,采用傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)对材料进行全面表征。在空气作氧化剂条件下,以苯甲醇氧化为苯甲醛作为模型反应,系统地考察了溶剂、温度、催化剂各组分用量等因素对催化效果的影响。研究结果表明,该复合催化剂在醇选择性氧化反应中表现出优异的催化性能,60℃下反应5 h便可将苯甲醇定量转化为苯甲醛,并对其他苄基醇、烯丙基醇和杂芳基醇等底物也展现出良好活性。此外,循环利用3次后,该催化剂活性几乎不变,表明其具有良好的稳定性和重复使用性。     

UiO-66-NH2负载铜催化剂的制备及其对醇的催化氧化

通过溶剂热法成功制备了一种基于金属有机骨架(MOF)的复合材料Cu-Cu₂O/UiO-66-NH₂,采用傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)对材料进行全面表征。在空气作氧化剂条件下,以苯甲醇氧化为苯甲醛作为模型反应,系统地考察了溶剂、温度、催化剂各组分用量等因素对催化效果的影响。研究结果表明,该复合催化剂在醇选择性氧化反应中表现出优异的催化性能,60℃下反应5 h便可将苯甲醇定量转化为苯甲醛,并对其他苄基醇、烯丙基醇和杂芳基醇等底物也展现出良好活性。此外,循环利用3次后,该催化剂活性几乎不变,表明其具有良好的稳定性和重复使用性。     

Change in carbon content on the surface of a multicomponent catalyst during its reduction, oxidation and due to action of the reaction medium

The change in the carbon content on the surface of Fe, Cu, Ni containing catalysts has been studied by X-ray Photoelectron Spectroscopy (XPS) under different treatments. It has been concluded that the superficial carbon content affects the content of an active element,e.g. copper, on the catalyst surface.     

Effect of preparation of Ag/Co composite oxide on characteristic and activity for carbon monoxide oxidation

We report our results on the development of 1:1 in molar Ag/Co composite oxide prepared by co-precipitation, and the effect of different rates of precipitation and heat treatment on the surface area, pore size and also catalytic activity for CO oxidation. It was observed that slow precipitation of the catalysts gave small pore sizes, high surface area and high activity for CO oxidation at low calcination temperatures. This revised version was published online in June 2006 with corrections to the Cover Date.