Preparation of methanol oxidation electrocatalysts: ruthenium deposition on carbon-supported platinum nanoparticles

Methanol oxidation electrocatalysts were prepared from Ru electrochemical or spontaneous deposition on commercial-grade carbon-supported Pt nanoparticles (Pt-Vulcan XC72, E-TEK). The resulting Ru coverage was estimated by cyclic voltammetry in supporting electrolyte. The maximum electrocatalytic activity for methanol oxidation at room temperature was observed at lower Ru coverage for spontaneous deposition than for electrodeposition; _Ru 10% vs 20%, respectively. On the other hand, higher current densities for methanol oxidation were obtained in the case of electrodeposited Ru. These two results were related to the presence of non-reducible ruthenium oxides in the spontaneous deposit. The present work provides evidence that (i) efficient DMFC electrocatalysts can be achieved by Ru deposition on Pt nanoparticles, and (ii) formation of a PtRu alloy is not a required condition for effective methanol electrooxidation.     

过渡金属对Ru/海泡石催化剂加氢性能及表面性质的影响

用浸渍法制备了一系列含不同助剂Mo、Co、Mn、Cu、Zr等的Ru/海泡石催化剂，以CO₂及苯加氢为探针反应，以TPD和CS₂中毒为手段研究了助剂对Ru/海泡石催化剂加氢、反应物吸附及活化性能的影响。结果表明，助剂的加入显著地影响Ru/海泡石催化剂的催化活性，且随着反应分子的加大，这种影响随之增大；助剂对催化反应中反应物的吸附、活化过程的影响是其影响催化活性的重要原因。另外，结果还表明，助剂的加入还调整了Ru/海泡石催化剂的表面性能，但并没有改变活性中心的类型。     

Methanation of carbon dioxide over Ru/Titania at room temperature: explorations for a photoassisted catalytic reaction

The methanation of CO₂ has been investigated over a special Ru/TiO₂ catalyst suggested by Thampi, Kiwi and Graetzel [4]. This paper deals with the analysis of the material and the investigation of the reported photoenhancement of the activity. The catalyst is characterised by in situ UV-VIS spectroscopy and by XPS. Conversion experiments at atmospheric pressure were carried out with and without UV light irradiation. The irradiation increases the conversion significantly. From various experiments it can be shown, however, that this effect is due to a thermal effect and does not involve an intrinsic photochemical step. Localised Ti³⁺ states sensitise the support to convert visible light into heat resulting in the observed increase in conversion.     

Performance of Methanol Oxidation Catalysts with Varying Pt:Ru Ratio as a Function of Temperature

This paper describes the effects of varying the Pt to Ru ratio in carbon-supported catalysts for methanol oxidation as a function of temperature. Previously these effects were studied in isolation, but now it is shown that the composition of a given catalyst as a function of temperature is extremely important for its activity towards methanol oxidation. Platinum rich 3:2 atomic ratio catalysts perform better than a 1:1 catalyst at 25 °C, where only Pt is believed to be active towards methanol dehydrogenation, since this process is a highly thermally activated process on Ru sites. This result is reversed at 65 °C, where the 1:1 catalyst displays much higher currents across the entire range of polarization. This may result from methanol dehydrogenation occurring on both Ru and Pt sites at higher temperatures. At an intermediate temperature, 45 °C, the 3:2 catalyst is seen to perform better at lower current values, while the 1:1 catalyst is superior at higher current densities, with the crossover occurring at 62 A g^–1. As a consequence, when designing fuel cell catalysts, the composition of the catalyst employed should be tailored with respect to the exact operating conditions, in order to promote optimum fuel cell performance.     

Deactivation of metal catalysts in liquid phase organic reactions

The paper gives a general survey of the factors contributing to the deactivation of metal catalysts employed in liquid phase reactions for the synthesis of fine or intermediate chemicals. The main causes of catalyst deactivation are particle sintering, metal and support leaching, deposition of inactive metal layers or polymeric species, and poisoning by strongly adsorbed species. Weakly adsorbed species, poisons at low surface coverage and solvents, may act as selectivity promoters or modifiers. Three examples of long term stability studies carried out in trickle-bed reactor (glucose to sorbitol hydrogenation on Ru/C catalysts, hydroxypropanal to 1,3-propanediol hydrogenation on Ru/TiO₂ catalysts, and wet air oxidation of paper pulp effluents on Ru/TiO₂) are discussed.     

Preparation of three-dimensional ordered macroporous SiCN ceramic using sacrificing template method

Three-dimensional (3D) long range well ordered macroporous SiCN ceramics were prepared by infiltrating sacrificial colloidal silica templates with the low molecular weight preceramic polymer, polysilazane. This was followed by a thermal curing step, pyrolysis at 1250 °C in a N₂ atmosphere, and finally the removal of the templates by etching with dilute HF. The produced macroporous SiCN ceramics showed high BET surface areas (pore volume) in the range 455 m²/g (0.31 cm³/g)–250 m²/g (0.16 cm³/g) with the pore sizes of 98–578 nm, which could be tailored by controlling the sizes of the sacrificial silica spheres in the range 112–650 nm. The sphere-inversed macropores were interconnected by 50 ± 30 nm windows and 3–5 nm mesopores embedded in the porous SiCN ceramic frameworks, which resulted in a trimodal pore size distribution. The surface of the achieved porous SiCN ceramic was then modified by Pt–Ru nanoparticle depositing under mild chemical conditions.     

Catalytic combustion of trichloroethene over Ru/Al2O3: Reaction mechanism and kinetic study

The performance of 0.5% Ru/Al₂O₃ for the deep oxidation of trichloroethene (1000–2500 ppmV, WHSV = 55 h⁻¹) in air was studied in this work. Experiments were carried out both at dry and wet (20,000 ppmV of H₂O) conditions. Catalytic performance was studied in terms of activity and selectivity for the different reaction products (CO₂, HCl, Cl₂, C₂Cl₄, CCl₄ and CHCl₃). Both the activity and the selectivity for total combustion are higher than other catalysts suggested in the literature for this process (especially Pd and Pt).The main organic by-products are CCl₄ and CHCl₃, whereas in all the other catalysts tested in the literature, tetrachloroethene is the main organic by-product. This fact suggests that the mechanism of the combustion reaction, involving a double-bond scission, is essentially specific for this catalyst.Kinetic data was fit to a pseudo-first order kinetic expression, providing fairly good fit.     

4-甲基苯甲酸催化加氢合成4-甲基环己基甲酸的研究

以钌/炭为催化剂,在氢氧化钠水溶液介质中,4-甲基苯甲酸(4-MPA)催化加氢制备4-甲基环己基甲酸(4-MHA).实验条件下,无脱羧副反应产生,4-甲基环己基甲酸的选择性为100%.碱液种类对转化率有一定影响,与氢氧化钠水溶液相比,氢氧化钾水溶液具有较高的转化率;碱液浓度对转化率有较大影响,当n(氢氧化钠):n(4-甲基苯甲酸)大于等于1.25时,转化率达到最大值,120℃,2 MPa条件下,反应95 min后,4-甲基苯甲酸转化率为97.82%.反应速率随载体比表面积的增大而增大.     

Direct conversion of methane to higher hydrocarbons via an oxygen free,low-temperature route

The direct conversion of methane to higher hydrocarbons over a silica-supported Ru catalyst has been investigated via an oxygen free, two-step route. The reaction consists of decomposition of methane over a 3% silica-supp orted Ru catalyst at temperatures between 400 and 800 K to produce surface carbonaceous species followed by rehydrogenation of these species to higher hydrocarbons at of 368 K. It was found that the Ru/SiO₂ catalyst exhibits a trend similar to that for single-crystal Ru catalysts. However, the temperature at which a maximum in ethane selectivity occurs shifts toward a higher temperature. It was also found that the ethane yield can be optimized by changing the surface carbon coverage. Under optimum conditions a net ethane yield of about 13–15% has been realized. For this two-step reaction sequence, only a few reaction cycles could be operated without intermediate high temperature rehydrogenation and without significant loss in ethane yield. This is attributed to large amounts of inactive carbon that could not be hydrogenated at 368 K. Higher methane partial pressures were found to be desirable for this reaction. The activity of the catalyst could also be maintained at total pressures up to 10 atm.     

Ag-Pd-5Ru-Gd四元系部分相图的700℃等温截面

在Ag Pd Gd ,Ag Pd Ru ,Ag Ru Gd和Pd Ru Gd三元系合金相图的基础上 ,采用X射线衍射 ,差热分析、扫描电镜和显微金相分析等方法研究了Ag Pd Ru Gd(x(Ru) =5 % ,x(Gd) <2 5 % )四元系相图的 70 0℃等温截面。结果表明 :该截面上包含有 2个单相区 ,即Pd(Ag)和Pd3 Gd ;4个两相区 ,即Pd(Ag) (Ru) ,Pd(Ag) Pd3 Gd ,(Ru) Ag51Gd14 ,(Ru) Pd3 Gd ;3个三相区 ,即Pd(Ag) Pd3 Gd (Ru) ,Pd(Ag) Ag51Gd14 (Ru) ,Pd3 Gd Ag51Gd14 (Ru) ;1个四相区 ,即Pd(Ag) Pd3 Gd Ag51Gd14 (Ru)。未发现新的四元中间相