Oxidation of CO on hydrogen-loaded palladium

The oxidation of CO adsorbed on the surface of palladium electrodes loaded with different amounts of hydrogen was studied by single potential alteration infrared reflectance spectroscopy (SPAIRS). In the absence of hydrogen, only CO₂ was detected during anodic oxidation of CO. Adsorption of CO in the presence of hydrogen in palladium led to a more negative onset of its electrooxidation, and the formation of other products, such as ethanol and formaldehyde, as well as CO_{_2}. The results indicate that hydrogen occluded in palladium contributes to the displacement of carbon monoxide from the interface; this may assist in the continual electrooxidation of organic compounds at palladium electrodes.     

Coke deposition on supported palladium catalysts

Palladium/silica catalysts of varying dispersities were submitted to the coking reaction with cyclopentane at 500°C. Temperature programmed oxidation curves reveal the presence of two peaks for carbon deposition on the metallic function: the first one near 250°C would correspond to coke deposited on palladium atoms of high coordination and the second one near 400°C would involve palladium atoms of low coordination.     

Acetylene hydrogenation using palladium zeolite catalysts

Catalysts consisting of low concentrations of palladium on several zeolite carriers were used in the hydrogenation of acetylene in low concentrations in the presence of ethylene in high concentrations. The objective was to maximize the conversion to ethylene and minimize further hydrogenation to ethane or oligomerization. Data for the rate of both acetylene disappearance and conversion to oligomers were correlated by simple first-order relationships in hydrogen partial pressure and palladium concentration over a range of temperatures from 24 to 80°C. The relationship between reaction rate and temperature was described by an Arrhenius-type equation with an effective activation energy of 13-14 kcal/g mol. Reaction rates and selectivities for palladium on silicalite and palladium incorporated into ZSM-5 during synthesis compared favorably with a commercial reference catalyst.     

Oxidation of ferrous hydroxide suspensions. I

Ferrous hydroxide suspensions, obtained by the addition of calcium hydroxide to ferrous sulphate solution have been oxidised at room temperature (28 ± 3 °C). The extent of oxidation and the rate of oxidation were studied as a function of time by varying the air flow rate, concentration of calcium hydroxide (stoichiometry) and the concentration of ferrous sulphate. Expressions have been obtained giving the relation between velocity constant, k, and the air-flow rate as well as between k and concentration of ferrous sulphate.     

Oxidation of ferrous hydroxide suspensions. II

Ferrous hydroxide suspensions, obtained by the addition of sodium carbonate to ferrous sulphate solutions, have been oxidised. The rates and extents of oxidation have been studied at room temperature (28±3°C) as a function of time by varying the air flow rate, concentration of sodium carbonate and concentration of ferrous sulphate. Expressions have been obtained giving the relation between the velocity constant, k, and the air flow rate as well as k and the concentration of ferrous sulphate.     

Study of polymer-bound mixed valence palladium catalysts. I. Preparation and characterization of polymer-bound mixed valence palladium catalysts

Polymer-bound palladium catalysts of different valence have been prepared by reducing PdCl₂ with a proper reductant, i.e., hydrazine hydrate, under certain conditions. ESR, XPS and IR were used to characterize the catalysts. Pd ⁺ was prepared for the first time and found to be stable on the polymersupport. The authors also investigated the influences of the reducing conditions, the surface properties of polymer supports and the effectsof reducing agents on the degree of reduction of divalent palladium bound onto the polymers, and the state of the palladium after reduction. The experimental results showed that the coexistence of different valence states of palladium in the supports may be Pd ²⁺, Pd^O; Pd²⁺, Pd⁺ (or Pd^δ+); Pd^O and Pd²⁺ Pd⁺ (or Pd^δ+), Pd^O. The method of preparing catalysts of mixed valence is described.     

Comparison of homogeneous and heterogeneous palladium hydrogenation catalysts

Mechanistic and kinetic studies of Pd-catalyzed hydrogenation at atmospheric pressure and 30–100 C were carried out with methyl sorbate, methyl linoleate and conjugated linoleate. Homogeneous Pd catalysts and particularly Pd-acetylacetonate [Pd(acac)₂] were significantly more selective than Pd/C in the hydrogenation of sorbate to hexanoates, mainlytrans-2-hexenoate. Relative rate constants for the different parallel and consecutive reactions, determined by computer simulation, indicated that the low diene selectivity of Pd/C can be dattributed to a significant direct reduction of sorbate to hexanoate. The similar behavior of PdCl₂ to that of Pd/C suggests that Pd(II) was initially reduced to Pd(O). Valence stabilization of PbCl₂ by adding DMF or a mixture of Ph₃P and SnCl₂ increased the diene selectivity but decreased the activity. Stabilization of Pd(acac)₂ with triethylaluminum (Ziegler catalyst) resulted in increased activity but decreased selectivity. The kinetics of methyl linoleate hydrogenation showed that although Pd(acac)₂ was only half as active as Pd/C, their respective diene selectivity was similar (10.4 and 9.6). The much greater reactivity of conjugated compared with unconjugated linoleate toward Pd(acac)₂ suggests the possible formation of conjugated dienes as intermediates that are rapidly reduced and not detected in the lipid phase during hydrogenation.     

硫化钯催化剂的合成及其应用研究进展

在非均相催化反应中,硫化钯作为催化剂的应用具有重要意义。综述了负载型和非负载型硫化钯的合成方法,重点讨论在气相或液相条件下前驱体、反应温度、反应气氛及载体对合成硫化钯晶相的影响,初步分析硫化钯在催化领域中的应用及未来的发展趋势。     

Oxidation of alcohols using RuMnCe catalysts

The combination of ruthenium, manganese as well as cerium oxides formed an active catalytic system for the oxidation of 2-octanol and other alcohols. The addition of manganese species as promotors resulted in more active catalysts than comparable cobalt-doped oxidic materials. The application of RuMnCe oxides on redox-active supports, such as TiO₂ or CeO₂, by deposition–precipitation caused a further improvement of catalytic activity. A tolerance to nitrogen-containing substrates was observed.     

XPS analysis of the oxidation of palladium model catalysts

The oxidation of 5 and 8 nm palladium particles supported on SiO₂/Si(1 0 0) has been studied with XPS. During oxidation the thickness of the oxide layer increases linearly with time. The lattice rearrangement needed for the formation of a new oxide layer at the metal–oxide interface is probably the rate-determining step. There were no significant differences between the oxidation of the 5 and 8 nm particles. The rate of the oxidation is strongly temperature-dependent. The activation energy for the oxidation is at least 100 kJ/mol. For comparison the oxidation and reduction of a 8 wt% Pd/SiO₂ catalysts was studied. The results indicated that oxidation and reduction of the Pd/SiO₂ catalyst proceeds in a similar way as on the Pd/SiO₂/Si(1 0 0) model catalysts.     

ZnAl水滑石负载钯催化剂的制备及催化性能

采用离子交换-还原法制备了系列锌铝水滑石负载钯催化剂Pd/ZnAl-LDH,通过XRD、TEM和ICP对该系列催化剂进行了表征,并对其在低毒溶剂乙醇或水中苯甲醇氧化反应的催化性能进行了详细考察。研究结果表明,反应溶剂、Pd负载量、氧气压力、反应时间等对催化剂的催化性能有很大的影响,当Pd负载质量分数为2%,反应压力为0.2MPa时,Pd/ZnAl-LDH在乙醇溶剂中表现出最佳的催化性能,苯甲醇转化率和苯甲醛选择性可分别达到93.3%和93.6%。     

Oxidative dimerisation of methane on supported palladium oxide catalysts

Supported palladium oxide catalysts are able to convert CH₄ to C₂H₆, CO, CO₂, H₂ and H₂O at temperatures 315 °C. Catalysts did not show any support effect when TiO₂, Al₂O₃, ZrO₂, La₂O₃ and MgO were used as supports. With sequential O₂ pulsing the catalyst showed long term activity when used at temperatures below 400 °C. Addition of Pt increased selectivity whereas with Ga it decreased. Results indicate participation of lattice O₂ from catalyst in the reaction pathway.     

Deuteration isomerization and exchange of cycloolefins over palladium catalysts

The deuteration, exchange, and isomerization of cyclopentene and of several disubstituted cycloolefins with four- and five-membered rings are studied over palladium films and over palladium-pumice catalysts at very low conversions.     

Recent advances in selective acetylene hydrogenation using palladium containing catalysts

Recent advances with Pd containing catalysts for the selective hydrogenation of acetylene are described. The overview classifies enhancement of catalytic properties for monometallic and bimetallic Pd catalysts. Activity/selectivity of Pd catalysts can be modified by controlling particle shape/morphology or immobilisation on a support which interacts strongly with Pd particles. In both cases enhanced ethylene selectivity is generally associated with modifying ethylene adsorption strength and/or changes to hydride formation. Inorganic and organic selectivity modifiers (i.e., species adsorbed onto Pd particle surface) have also been shown to enhance ethylene selectivity. Inorganic modifiers such as TiO₂ change Pd ensemble size and modify ethylene adsorption strength whereas organic modifiers such as diphenylsulfide are thought to create a surface template effect which favours acetylene adsorption with respect to ethylene. A number of metals and synthetic approaches have been explored to prepare Pd bimetallic catalysts. Examples where enhanced selectivity is observed are generally associated with decreased Pd ensemble size and/or hindering of the ease with which an unselective hydride phase is formed for Pd. A final class of bimetallic catalysts are discussed where Pd is not thought to be the primary reaction site but merely acts as a site where hydrogen dissociation and spillover occurs onto a second metal (Cu or Au) where the reaction takes place more selectively.

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负载型钯催化剂上甲烷催化燃烧的研究进展

概述了负载型钯催化剂对甲烷完全氧化的催化机理,以及钯催化剂在甲烷催化燃烧中的性能特点。     

用X射线荧光光谱法测定催化剂中铂钯含量

X射线荧光光谱法是一种无损检测的方法,对于粉末样品,可以通过直接压片的方式进行测量,无需对样品进行消解。它具有分析速度快、测定范围广、自动化程度高的特点。采用X射线荧光光谱法,模拟样品制备的工艺条件和组分含量自制了一系列标样,绘制了标准曲线,并利用经验系数方程矫正基体效应,测定了催化剂中钯、铂含量。通过与电感耦合等离子体发射光谱法和分光光度法进行实验方法的比对,得到的测试结果基本一致,表明此方法具有很好可靠性。     

氯代芳烃偶联反应中钯催化剂的研究进展

在合适的钯催化作用下,可将廉价易得、低活性的氯代芳烃应用于C—C键和C杂键形成的偶联反应。对偶联反应用钯催化剂的研究进行了综述。通过选择合适的配体,钯催化剂可有效地催化带有多种体取代基的氯代芳烃或氯代杂芳烃,发生Suzuki、Negishi、Stille和Heck等多种偶联反应,获得较高的收率和很高的选择性。     

环境友好催化剂催化葡萄糖水解的研究

研究了n(SiO₂)∶n(Al₂O₃)=20～25的ZRP-5分子筛（催化剂1）、n(SiO₂)∶n(Al₂O₃)=30的ZRP- 5分子筛（催化剂2）、甲酸、液态水四种催化剂分别催化葡萄糖水解。研究发现,葡萄糖水解机理复杂,产物众多,水解主产物为乙酰丙酸(LA),同时还有5 羟甲基糠醛(HMF)、果糖、乳酸、甲酸、呋喃甲醛等副产物生成。不同的催化剂对葡萄糖的转化率影响不大,但各个反应产物收率相差很大。HMF的生成比较容易,而LA的生成相对困难。ZRP-5分子筛催化剂对LA具有良好的选择性。     

Application of electroless procedures to the preparation of palladium catalysts

The influence of various (laser, UV lamp and thermal) activation treatments on the diffuse reflectance and ESR spectra of CeO₂ are examined. Ceria-supported palladium catalysts are prepared by electroless deposition of the metal from palladium chloride and hydrazine hydrate solutions. The atomic defects induced in ceria by the activation procedures appear to initiate the palladium deposition.On leave from the General Physics Institute of the Russian Academy of Sciences.