New gold catalysts for liquid phase oxidation

A pre-requisite for good catalytic activity with supported gold is that the metal is present as nanoparticles, but no suitable method for depositing gold on carbon as nanoparticles has previously been reported. The deposition precipitation method which has been used successfully for catalyst preparation with other supports, produces large aggregates with carbon. It is now shown, however, that pre-reduced gold sol is a satisfactory method for preparing gold on carbon catalysts as long as an appropriate choice of sol is made. In this paper the activity of gold on carbon catalysts prepared in a number of different ways is compared in a standardized liquid phase organic oxidation reaction. The activity for Au/C catalysts prepared by the sol method can show a two-fold increase compared with a similar catalyst prepared by deposition precipitation.     

Hydrogenation over gold catalysts: The interaction of gold with hydrogen

Gold is active in various hydrogenation reactions and often shows exceptional high chemoselectivity when multiple functional groups are present. All hydrogenation reactions have in common, that the hydrogen molecules have to adsorb and dissociate before they react. Recent insights in the interaction of gold with hydrogen and simple reactions involving hydrogen are described.     

Catalytic performance of gold catalysts in the total oxidation of VOCs

Catalysts for the oxidation of volatile organic compounds (VOCs) were prepared by supporting 1% gold on cerium and zirconium oxides (CeO2, Ce_0.5Zr_0.5O₂, ZrO₂) using a simple impregnation method followed by reduction of gold in the presence or absence of ammonia (N). The catalysts were tested in model reactions, namely the total oxidation of benzene, hexane and chlorobenzene, using a micro flow reactor at atmospheric pressure in the temperature range 100–500°C and their activity was compared to that of Au/TiO₂ and Au/Fe₂O₃ reference catalysts supplied by the World Gold Council (WGC). Benefits on the light-off temperatures were observed by adding gold to cerium-containing oxides: 100% conversion of hexane was obtained with Au/Ce_0.5Zr_0.5O₂ at the lowest temperature (300°C). Full conversion of benzene was reached at only 250°C with Au/CeO₂ (N), at 290°C with Au/Fe₂O₃ (WGC) and at 300°C with Au/Ce_0.5Zr_0.5O₂. In the case of chlorobenzene oxidation, the addition of gold was of even greater relevance because of a drop in the light-off temperature of over 100°C for Au/Ce_0.5Zr_0.5O₂ and Au/CeO₂, with respect to the gold-free oxide supports; but in this case rapid deactivation took place.     

Homogeneous gold catalysts and alkynes: A successful liaison

The use of the combination of homogeneous gold-catalysts and alkynes in organic synthesis is reviewed from its beginnings in C-N-bond formation to the newest developments in C-C-bond formation. The common basic principle of these reactions is discussed. Special attention is devoted to the question where the gold catalysts are superior to either other catalysts or more traditional synthetic approaches to the product molecules.     

A review of the use of gold catalysts in selective hydrogenation reactions Lynsey McEwana

The field of gold catalysis has been a lively area of research for the past two decades and gold catalysts are now an established ‘best choice’ for many oxidation reactions. Most well known for its performance in selective and preferential oxidation reactions, gold has more recently found potential in selective hydrogenation reactions. In this work the recent developments using gold and gold-promoted catalysts for selective hydrogenation reactions are reviewed: the use for chemoselective hydrogenation of α,β-unsaturated aldehydes and, in particular, the excellent selectivity exhibited for the selective partial hydrogenation of alkyne, alkadiene and alkene C₂–C₆ hydrocarbon streams.     

Synthesis, processing, assembly and activation of core-shell structured gold nanoparticle catalysts

This paper describes recent progress of an investigation of the synthesis, processing, assembly and activation of gold nanoparticles that are of potential interest to fuel cell catalysis. Core-shell type gold nanoparticles of a few nanometer core size with organic monolayer encapsulation are highlighted. The activation of the core-shell nanoparticle assemblies towards nanostructured catalyst for potential fuel cell catalytic reactions is discussed. The understanding of the control factors in terms of nanocrystal size and interparticle spatial properties has important implications to the design of highly active nanogold catalysts for practical applications.     

Supported gold catalysts for selective hydrogenation of 1,3-butadiene in the presence of an excess of alkenes

Supported gold catalysts were investigated in the selective gas phase hydrogenation of 1,3-butadiene in an excess of propene (0.3% butadiene, 30% propene and 20% hydrogen), in order to simulate the process required for the purification of industrial alkenes streams to prevent poisoning of the polymerisation catalysts used for polyalkene production. Gold catalysts containing small gold particles (between 2 to 5 nm in average) are less active than commercial palladium catalysts, but they are much more selective. Under our experimental conditions, 100% of butadiene can be converted at ≈170°C into 100% butenes with 1-butene as the main product, and with only very small amount of alkanes formed (≈100 ppm). The absence or presence of propene does not drastically modify the rate of hydrogenation of butadiene.     

银精矿加石灰焙烧过程中银的化学物相变化

采用化学物相分析方法,定量研究了石灰和焙烧气氛对银精矿加石灰焙烧过程中银的化学物相及其相对含量变化的影响,并借助热力学分析手段初步探讨了石灰在主要载银矿物的氧化、解离过程中的作用机制。结果表明：添加石灰能够大大地降低焙砂中的氧化物包裹银含量,如焙烧2h后的氧化物包裹银含量由直接焙烧时的11．08％降到有石灰存在时的4．15％,而与焙烧气氛的关系不大。     

The effect of evaporation on size and shape evolution of faceted gold nanoparticles on sapphire

We studied the size and shape evolution of about 180 faceted gold nanoparticles attached to a sapphire substrate during annealing at 950 °C in air. We employed the scanning force microscopy and interrupted annealing techniques to track the changes in size and shape of individual nanoparticles. The height of all single-crystalline nanoparticles was constant up to the longest cumulative annealing time of 65 h. The lateral dimensions of ∼20% of all nanoparticles shrunk during anneals, while all three dimensions of the remaining 80% of nanoparticles remained constant. Only the nanoparticles with the height below the average (for all particles) were laterally shrinking. We formulated a kinetic model relating the lateral shrinkage of the nanoparticles to the evaporation of Au atoms adsorbed on sapphire. We also assumed that the process controlling particles shrinkage is the slow self-diffusion of Au atoms along the lateral facets of the nanoparticles toward the substrate. The model predicted a power law dependence of the shrinkage rate on the particle height, with the exponent n = 3. The corresponding exponent determined from the experimental data was n = −2.9 ± 0.3, in excellent agreement with the theory. The low value of the effective self-diffusion coefficient along the lateral facets determined with the aid of our model (3.2 ± 0.2 × 10⁻¹⁷ m² s⁻¹) was attributed to the difficulties of step nucleation on atomically flat facets.     

Study of the sorption-kinetic properties of carbon molecular sieves

To elucidate the role of the electron-exchange properties of arene molecules that form the pore walls of carbon molecular sieves in their interactions with sorbate molecules, the correlation between the electronexchange and sorption-kinetic properties was studied. The electron-exchange properties were estimated by using quantum-chemical modeling based on the energies of formation of singly charged anions and cations and neutral (both oxidized and reduced) molecules.     

基于GMAW焊接快速制造的控形研究新进展

GMAW焊接快速制造是低成本金属零件层制造的重要研究方向,成形精度是评判零件成形质量的重要指标。阐述了单道焊缝截面形态控制中焊接工艺、数学建模、数值模拟以及截面形态表征体系等方面的国内外研究现状,总结了单层多道成形堆积路径规划理论与方法的新进展,回顾了多层多道堆积策略及极限堆积的新实践,并对控形研究中的存在问题进行了分析,最后对未来焊接控形研究内容和发展方向提出了建议。     

Effect of the oxidation state of gold on the complete oxidation of isobutane on Au/CeO2 catalysts

Catalysts of highly dispersed gold supported on ceria were prepared by deposition precipitation method. Au is dispersed as Au⁰, Au⁺ and Au³⁺ species on ceria. The content of Au⁺ and Au³⁺ was highest on catalyst prepared on uncalcined ceria, which possess least ordered surface. It is inferred that oxygen vacancy on disordered ceria surface is essential for the preparation of highly dispersed gold catalysts and in stabilizing monolayer surface Au⁺ clusters while cationic vacancies are sites for substitutional Au³⁺. Au/CeO₂ catalysts showed low-temperature isobutane oxidation activity with maximum conversion at 150–180°C. Ex-situ XPS results demonstrated that the low temperature isobutane oxidation activity was closely related to the content of Au⁺ which we interpreted as surface gold oxide formed under reaction conditions. Isobutane oxidation activity associated with ceria at temperature above 300°C was enhanced by substitutional Au³⁺.     

New In–Pd mechanical loss peak in ternary gold alloys

A point defect relaxation peak has been observed in a ternary 18-carat gold alloy with the composition Au_62.5Pd_32.5In₅. It shows a Curie–Weiss dependence on the temperature, as is commonly observed for a Zener peak. However, the peak is absent in the binary alloys AuPd and AuIn and therefore it is a new type of relaxation that is due to In–Pd pairs. The relaxation strength shows a linear dependence on the indium concentration. We have developed a model of elastic dipoles containing one palladium and one indium atom in a gold matrix. The model is based on the reorientation under stress of InPd dipoles in a gold matrix and takes into account the atom ordering. The model accounts for a linear dependence of the relaxation strength on the indium concentration in a dilute alloy and is also valid for more concentrated alloys.     

汽车用交流发电机磁极的净形加工新工艺

论述了国内外制造交汉发电机转子磁极的锻造工艺，介绍了热、冷复合精密锻造新工艺和分流式反挤压模具。该工艺和模具在生产应用中优质、高效、节材、节能，降低生产成本，社会社会效益显。     

Co-MCM-41介孔分子筛的水热合成与稳定性

以硅酸钠、氯化钴等无机盐为原料,通过水热法合成含有不同Co含量的六方介孔分子筛Co-MCM-41.采用X射线粉末衍射、红外光谱、等离子发射光谱、程序升温还原、透射电子显微镜和N2吸附-脱附等技术对样品的物化性能进行表征,研究所合成的Co-MCM-41的稳定性.研究结果表明:在水热条件下合成4种不同Co含量的Co-MCM-41介孔分子筛,其比表面积为809.8～1257.2 m2/g,平均孔径为2.7～2.8 nm.随着介孔分子筛中Co含量的增加,介孔分子筛的比表面积、孔体积变小,介孔有序性变差.所合成的含Co介孔分子筛经750 ℃焙烧3 h后介孔结构被破坏,经100 ℃水热处理5 d后样品虽然具有介孔结构,但介孔有序性差.     

Characterizing gold in refractory sulfide gold ores and residues

Gold is present in refractory sulfide gold ores mainly in arsenian pyrite and arsenopyrite, where it occurs in both the chemically bonded state and as nano-size grains of metallic gold. During roasting or pressure oxidation, the sulfide matrix is destroyed and essentially all the gold is converted to the metallic form. The liberated gold is readily dissolved in conventional cyanide media, although a few residual gold particles, commonly encapsulated by films of silica-rich gel or by calcium sulfate, are detected. Chloridecontaining gold ores can generate soluble gold chlorocomplexes during hydrometallurgical processing and the dissolved gold can be sequestered on the surfaces of associated carbon particles, resulting in reduced gold recoveries.     

介孔AlPO4分子筛前驱体的原位焙烧

采用热重(TGA)-差热(DTA)、原位X射线衍射(XRD)、原位红外光谱(FT-IR)和扫描电镜(SEM),对介孔AlPO4分子筛前驱体焙烧过程中的多种变化进行实验研究。TGA-DTA和原位FT-IR结果表明,前驱体脱除主要分为两步:模版剂中N—H键首先断裂,然后甲基(CH3)和亚甲基(CH2)被氧化除去;从原位XRD分析结果可以看出,焙烧过程受温度的影响表现为结晶度的变化,当焙烧温度超过650℃时,AlPO4分子筛会转化成磷石英相和无定形相;SEM照片清楚表明,焙烧使无定型的前驱体转化成柱状分子筛。另外升温速率高于10℃.min-1,会造成分子筛颗粒破碎。     

Mechanisms of change of shape in deforming and heating titanium alloys with the shape memory effect

Alloys with the shape memory effect based on titanium nickelide are well known and used quite widely in medicine, aircraft and spacecraft engineering, and other fields of mschine building. These alloys are used in creating thermomechanical parts of structures, temperature-sensitive gauges, and thermoregulators. Titanium alloys with the shape memory effect that posses high damping properties are used when vibrations and noise have to be limited in order to provide effective operation of machine parts and engineering systems as a whole. Commercial titanium-base alloys have lower characteristics of shape regeneration than alloys based on titanium nickelide. However, commercial alloys are much less expensive and are used to produce a wide range of semifinished products. In these materials the characteristics of shape regeneration and damping are often determined by the mechanism of change of shape in deformation, which has not yet been studied appropriately. The present work is devoted to the mechanisms of inelasticity in titanium alloys in various stages of the action of the shape memory effect. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 12–16, April, 1998.