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排序方式: 共有9185条查询结果,搜索用时 93 毫秒
71.
Gang Li Dan I. Enache Jennifer Edwards Albert F. Carley David W. Knight Graham J. Hutchings 《Catalysis Letters》2006,110(1-2):7-13
The oxidation of benzyl alcohol to benzaldehyde has been investigated in the absence of solvent using zeolite-supported Au
and Au–Pd catalysts. Three zeolites were investigated, ZSM-5, zeolite β and zeolite Y, and these were contrasted with the
titanoslicalite TS-1 and TiO2 as supports. For the Au catalysts the best results are obtained with zeolite β as the support and the conversions were comparable
or better than those observed with TiO2 in terms of turn over frequencies. However, the selectivities observed with the acidic zeolites were lower than the non-acidic
TS-1 and TiO2. This is due to the subsequent reaction of benzaldehyde via acid catalysed reactions to give benzyl benzoate and its dibenzyl
acetal, and, in some cases dibenzylether. Initial catalysts were evaluated with a gold loading of 2 wt% and increasing this
to 4 wt% showed the expected increase in activity, indicating that there is scope to improve the performance of these catalysts.
The most active catalysts were prepared by impregnation and catalysts prepared by deposition precipitation were considerably
less active. Introduction of Pd into the catalyst improved the activity without significantly affecting the selectivity. 相似文献
72.
Using a Debye function analysis, the presence of icosahedral and face centered cuboctahedral gold in a 1 1 ratio has been found in freshly prepared Au/Mg(OH)2 catalyst. The results support earlier studies which suggest the icosahedral form to be more stable at small nanometer sizes. Interactions between the gold and the Mg(OH)2 support appear to be weak, with the gold rapidly coagulating over a period of three months. Re-analysis of the aged sample shows the gold to be mainly in the form of truncated decahedra. 相似文献
73.
Saleh Al-Sayari Albert F. Carley Stuart H. Taylor Graham J. Hutchings 《Topics in Catalysis》2007,44(1-2):123-128
The preparation of Au/ZnO and Au/Fe2O3 catalysts using two coprecipitation methods is investigated to determine the important factors that control the synthesis
of high activity catalysts for the oxidation of carbon monoxide at ambient temperature. In particular, the factors involved
in the preparation of catalysts that are active without the need for a calcination step are evaluated. The two preparation
methods differ in the manner in which the pH is controlled during the precipitation, either constant pH throughout or variable
pH in which the pH is raised from an initial low value to a defined end point. Non-calcined Au/ZnO catalysts prepared using
both methods are very sensitive to pH and ageing time, and catalysts prepared at a maximum pH = 5 with a short ageing time
(ca. 0–3 h) exhibit high activity. Catalysts prepared at higher pH give lower activity. However, all catalysts require a short
operation period during which the oxidation activity increases. In contrast, the calcined catalysts are not particularly sensitive
to the preparation conditions. Non-calcined Au/Fe2O3 catalysts exhibit high activity when prepared at pH ≥ 5. Calcined Au/Fe2O3 prepared using the controlled pH method retain high activity, whereas calcined catalysts prepared using the variable pH method
are inactive. The study shows the immense sensitivity of the catalyst performance to the preparation methods. It is therefore
not surprising that marked differences in the performance of supported Au catalysts for CO oxidation that are apparent in
the extensive literature on this subject, particularly the effect of calcination, can be expected if the preparation parameters
are not carefully controlled and reported. 相似文献
74.
Laura Prati Alberto Villa Francesca Porta Di Wang Dangsheng Su 《Catalysis Today》2007,122(3-4):386-390
The liquid phase oxidation of glycerol with oxygen has been studied using mono and bimetallic catalysts based on Au and Pd metals supported on activated carbon, in order to study the effect of the metal on the distribution of the products and on activity of catalysts. It was found that by using bimetallic catalysts (Au–Pd) a strong synergistic effect was shown. By using a preformed nucleating centre we were able to obtain a single alloyed phase, which allowed us to address the synergistic effect to the presence of alloyed Au/Pd. The advantage of using this latter catalyst lies not only in the high activity but also in a prolonged catalyst life. Although a partial leaching of palladium and assembling of the particles have been revealed by ICP and HRTEM respectively, activity after 10 re-cycles decreased less than expected (about 10%). 相似文献
75.
77.
Ruojun Lao Lihua Wang Ying Wan Jiong Zhang Shiping Song Zhizhou Zhang Chunhai Fan Lin He 《International journal of molecular sciences》2007,8(2):136-144
In this work, we reported the investigation on the interaction between DNA strands self-assembled at gold electrodes and an electron transfer protein, cytochrome c. We observed that cytochrome c exhibited well-defined electrochemistry in both double-stranded and single-stranded DNA films. This suggested that the electron transfer reaction of cytochrome c arose possibly due to the electron hopping along DNA strands rather than wiring along the double helix. We also compared the heterogeneous electron transfer rate of cytochrome c with that of a ruthenium complex, which further confirmed this mechanism. 相似文献
78.
J. A. Rodriguez X. Wang P. Liu W. Wen J. C. Hanson J. Hrbek M. Pérez J. Evans 《Topics in Catalysis》2007,44(1-2):73-81
Synchrotron-based techniques (high-resolution photoemission, in-situ X-ray absorption spectroscopy, and time-resolved X-ray diffraction) have been used to study the destruction of SO2 and the water-gas shift (WGS, CO + H2O → H2 + CO2) reaction on a series of gold/ceria systems. The adsorption and chemistry of SO2 was investigated on Au/CeO2(111) and AuO
x
/CeO2 surfaces. The heat of adsorption of the molecule on Au nanoparticles supported on stoichiometric CeO2(111) was 4–7 kcal/mol larger than on Au(111). However, there was negligible dissociation of SO2 on the Au/CeO2(111) surfaces. The full decomposition of SO2 was observed only after introducing O vacancies in the ceria support. AuO
x
/CeO2 surfaces were found to be much less chemically active than Au/CeO2(111) or Au/CeO2−x
(111) surfaces. In a separate set of experiments, in-situ time-resolved X-ray diffraction and X-ray absorption spectroscopy were used to monitor the behavior of nanostructured {Au + AuO
x
}–CeO2 catalysts under the WGS reaction. At temperatures above 250 °C, a complete AuO
x
→ Au transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au
nanoparticles supported on rough ceria films or a CeO2(111) single crystal corroborate that cationic Auδ+ species cannot be the key sites responsible for the WGS activity at high temperatures. The active sites in {Au + AuO
x
}/ceria catalysts should involve pure gold nanoparticles in contact with O vacancies of the oxide. 相似文献
79.
采用混合组装技术,利用植酸胶束(IP6micelles)的磷酸酯键络合辣根过氧化物酶(HRP)和金纳米粒子(GNPs),形成了具有生物亲和性的纳米复合材料,保持了辣根过氧化物酶的生物活性,并利用金纳米粒子的高电子密度、介电特性和催化性能,实现了HRP与玻碳电极(GCE)表面的直接电子转移。Nafion膜的滴加能提高电极的选择性和稳定性。实验过程中借助紫外-可见吸收光谱和透射电子显微镜进行表征,实验结果证明:GNPs的高导电和高催化性能,结合植酸胶束的优良生物相容性和对酶的高负载量的特点,使得吸附在其上的HRP保持活性,制备的生物传感器能对H2O2进行电催化还原。Nafion/HRP-IP6micelles-GNPs/GCE对H2O2的线性浓度范围为5×10-7~1.15×10-5mol/L(线性相关系数r=0.993,n=9),最低检测限为0.1μmol/L(信噪比S/N=3),米氏常数为0.002 4 mmol/L。 相似文献
80.
Thiosulfate has been considered as one of the most promising of the non-toxic alternatives to cyanide for the leaching of gold and much work has been carried out with the aim of understanding and improving the ammoniacal thiosulfate leaching process. In particular the behaviour of gold in thiosulfate solutions containing copper in the absence of ammonia has received little attention. It has been shown in this study involving electrochemical and leaching tests that copper ions catalyze not only the oxidation of thiosulfate but also the dissolution of gold in alkaline thiosulfate solutions. Electrochemical studies have shown that copper has a positive effect on the anodic dissolution of gold with increasing concentrations of copper resulting in higher dissolution rates of gold at a potential of 0.3V. Studies on the dissolution of gold powder in alkaline oxygenated thiosulfate solutions containing low concentrations of copper have shown that the role of copper in enhancing the dissolution rate of gold is possibly associated with the formation of a copper–thiosulfate–oxygen intermediate which is more reactive in terms of cathodic reduction than dissolved oxygen. The electrochemical experiments have been complemented by a leaching study which has shown that milling of gold powder in the presence of copper (added as ions, metal, or oxide) assists with the dissolution of gold in thiosulfate solutions. 相似文献