| 查看: 3892 | 回复: 23 | |||
| 当前主题已经存档。 | |||
hejin04c荣誉版主 (著名写手)
小木虫乐乐虫
|
[交流]
【专题】每日文献一篇
|
||
|
Nature Nanotechnology 5, 5 - 7 (2010) doi:10.1038/nnano.2009.463 A golden opportunity Owain Vaughan1 -------------------------------------------------------------------------------- AbstractGold has risen from relative obscurity to command a place at the forefront of catalysis research, but when will nanoscale gold catalysts be ready for industrial applications? -------------------------------------------------------------------------------- Catalysts have many guises and numerous uses. They can be homogeneous or heterogeneous, biological or synthetic, and they are widely used in the chemical industry and in energy production. A catalyst increases the rate of a chemical reaction without being consumed in the process, and it can allow reactions to occur in ways that would otherwise be impossible. Chemical reactions can, for example, be steered towards different products, and a wide variety of chemicals can be produced efficiently. Catalysis — and in particular heterogeneous catalysis — is also a subject that is benefiting from our ability to probe and control matter at the nanoscale. In heterogeneous catalysis, the catalyst is in a different phase to the reacting molecules: in general the catalyst is composed of metal particles on a solid support, and the reactant molecules — supplied from the gas or liquid phase — adsorb on the surface of the catalyst particles, where they react to form the chosen product or products. By reducing the size of the metal particles, the overall surface area increases relative to the bulk, which increases the number of sites on the surface that are available for catalytic action. Moreover, the surface structure and electronic properties of the particles can also change in ways that improve catalytic performance. “The key point will be durability of the catalysts under real conditions.” Graham Hutchings, Cardiff University. However, many other factors need to be considered before nanoscale catalysts can be transferred from the laboratory to industry. First, according to David Barton of Dow Chemical Company, the catalyst must meet a number of criteria related to, for example, product selectivity, reaction rates and lifetime. “Assuming that the laboratory-scale catalyst meets all of these economic criteria,” says Barton, “the biggest challenge of catalyst scale-up is to translate the synthetic approach used in a laboratory into an economically viable method that can be used to produce catalysts that have similar performance when used in industrial reactors.” Such catalysts will need to be in the form of pellets or some other structured shape, rather than fine catalyst particles, which are typically used in laboratory tests. The research breakthrough Annular dark-field scanning transmission electron microscopy image of a gold-palladium nanoparticle with a diameter of around 40 nm supported on TiO2 (top left), and the corresponding energy-dispersive X-ray maps for gold (top right) and palladium (bottom left)7. A reconstructed composition map is shown in the bottom right image (Au, blue; Pd, green; Ti, red). Such nanoparticles can be used as catalysts for the direct synthesis of hydrogen peroxide from hydrogen and oxygen. Image reproduced with permission from ref. 7 (© 2008 RSC). Until the 1980s, gold was an inert metal, prized for its beauty rather than its chemical reactivity. In 1987, however, Masatake Haruta, then at the Government Industrial Research Institute of Osaka, and colleagues reported that gold supported on semiconducting transition-metal oxides, such as iron oxide, could efficiently catalyse the oxidation of carbon monoxide to carbon dioxide, even at temperatures as low as −77 °C (ref. 1). At first Haruta thought that he had discovered a new composite metal oxide catalyst, but with the help of the electron microscopist Sumio Iijima, he was able to show that the catalyst was in fact made up of gold nanoparticles with diameters in the range of 2–4 nm dispersed across the support material. Although this is widely recognized as the decisive breakthrough, other studies had also hinted there was more to gold than the chemistry textbooks of the day might have suggested2. In 1973, for instance, it had been reported that gold could catalyse hydrogenation reactions3. And in 1988 Graham Hutchings and co-workers at the University of Witwatersrand in South Africa showed that gold could catalyse the hydrochlorination of ethyne to form vinyl chloride4 — a molecule used to make the polymer polyvinyl chloride — confirming previous predictions made by Hutchings in 1985 (ref. 5). Since these initial discoveries, there has been an explosion of interest in gold catalysis. The field has grown into an extensive research topic where nanoscale gold particles have been shown to be active for a range of reactions. A fundamental understanding of why nanoscale gold is special, and the various reaction mechanisms at play, has also slowly begun to emerge, although there are still many open questions. But as the papers and patents stack up, when and where are the commercial applications going to appear? Commercial developments Gold has in fact been used in an industrial process since the 1970s: the production of vinyl acetate from ethene, acetic acid and oxygen relies on a palladium–gold alloy catalyst. The monomer vinyl acetate is used to make emulsion-based paints, wallpaper paste and wood glue, and has a worldwide capacity of around five million tonnes a year6. Although gold is only a minor component of this alloy7, it has an important role, which has only more recently become clearer. It has, for example, been proposed that the role of gold is to isolate palladium sites, a process that prevents unwanted side-reactions from occurring8. “Within ten years people will recognize the applicability of gold for hydrogenation reactions.” Masatake Haruta, Tokyo Metropolitan University. Beyond this, gold has had a limited impact on industrial catalysis, although new commercial applications have started to emerge. For example, a pilot plant for a liquid-phase oxidation process in which ethylene glycol and methanol react to produce methyl glycolate (a molecule used in industries as diverse as semiconductors and cosmetics), with the assistance of a gold catalyst, has been run by Nippon Shokubai in Japan6. A supported gold catalyst has also been used commercially as a deodorizer in Japanese toilets. A number of companies have also filed or obtained patents related to gold nanocatalysts. The most active companies have been BASF, Celanese Corporation, Toyota and Dow Chemical Company, and areas of particular interest have included exhaust-gas cleaning, fuel cells, and the production of alkenes and hydrogen peroxide6. In addition, companies have started to market gold catalysts. 3M Company, for example, sells a gold catalyst under the name NanAucat™, while Project AuTEK — a collaboration between three mining companies and the Mintek research organization in South Africa — sells kilogram quantities of their AUROlite™ catalyst9. Moreover, and as Jason McPherson of Mintek explains, “Project AuTEK supplies shape-formed materials, which are necessary in most flow-type industrial/emission control applications, as opposed to powdered materials.” So what are the major challenges involved in taking gold catalysts from the laboratory to industry? “The key point will be durability of the catalysts under real conditions,” says Hutchings, who is now at Cardiff University. Wayne Goodman of Texas A&M University agrees: “Developing a catalyst that is sufficiently stable while maintaining acceptable activity and selectivity is a major challenge.” This issue is confounded by the fact that although it is relatively straightforward to assess the selectivity and activity of a catalyst in the laboratory, it is more difficult to determine its long-term performance. “For many bulk chemical processes very long testing is required,” says Chris Hardacre of the Queen's University of Belfast. “This is not possible in the lab in general and we use accelerated ageing techniques to do it. The question is, are these tests relevant on the large scale?” Furthermore, he notes that “the preparation of gold catalysts can be tricky and requires very specific conditions which, at times, are difficult to reproduce at the bulk scale.” Significant financial issues are of course also at stake. “In general, a new industrial process requires years of industrial effort and lots of money to undergo the transformation from discovery to application,” says Bruce Gates of the University of California, Davis. “There would need to be a demonstration of stable catalyst performance for a reaction that was economically viable.” The industrial breakthrough? The oxidation of carbon monoxide to form carbon dioxide — the subject of Haruta's breakthrough paper in 1987 — is still the most widely studied reaction in research labs, partly because gold's role in this reaction is still not fully understood, and partly because it is relatively easy to use this process as a test reaction. Nonetheless, gold's capabilities have attracted interest from companies looking to develop a number of applications, particularly in respiratory protection and in fuel cells6, where trace amounts of carbon monoxide must be removed from the hydrogen that is used as the fuel source. There has also been considerable interest in gold-catalysed chemical synthesis7. For instance, hydrogen peroxide — which is widely used for disinfection and bleaching, and has a global production of around two million tonnes per year7 — is at present manufactured in an indirect process that involves the sequential hydrogenation and oxidation of an anthraquinone (an aromatic organic compound). Hutchings and colleagues have recently developed a gold–palladium alloy that allows hydrogen peroxide to be made directly from hydrogen and oxygen7, 10. Hutchings thinks that this process could have industrial applications, a suggestion Gates agrees with, though he cautions that “issues such as catalyst lifetime and cost would need to be addressed.” Some of the reactions that can be catalysed by gold. Selective oxidation reactions are also of great interest7, particularly the oxidation of alcohols8 and the epoxidation of alkenes (in which a carbon–carbon double bond in a hydrocarbon is converted into a three-membered ring that contains two carbon atoms and an oxygen atom). In 1998, just over a decade after its initial breakthrough, Haruta's team showed that gold nanoparticles supported on titanium dioxide could catalyse the epoxidation of propene when supplied by a mixture of oxygen and hydrogen11. The product of this reaction, propene oxide, is an immensely important commodity chemical and approximately seven million tonnes of it are produced every year12. The development of a heterogeneous route to making propene oxide direct from propene and oxygen is an important goal in catalysis research because at present the industrial production of this molecule involves homogeneous two-stage processes that can lead to undesirable by-products. Haruta, who is now at Tokyo Metropolitan University, and others have steadily increased the efficiency of this epoxidation reaction through the use of improved gold catalysts13. However, the reaction requires both hydrogen and oxygen. “This combination may not be industrially attractive owing to certain safety concerns,” says Haruta. “Without hydrogen, it would be very attractive.” Haruta's group has recently reported encouraging results in this direction14. “At present, catalysts contain only a small fraction of active gold,” Graham Hutchings, Cardiff University. Researchers have also started to explore different types of reactions. “Whereas early studies mostly examined gas-phase reactions,” according to Haruta, “there has now been a dramatic increase in liquid-phase studies.” He links this, in part, to the chemical industry gradually moving away from petroleum chemistry and into biomass chemistry, which relies on biological material derived from plants and other organisms. This shift, Haruta believes, has also lead to hydrogenation reactions becoming more important, something he considers gold catalysts well equipped to handle. “Gold is now widely recognized as one of the best elements for selective oxidation, in the gas and liquid phase,” he says. “But within ten years people will also recognize the applicability of gold for hydrogenation reactions.” Haruta expects industrial applications to follow. The role of nanoscience Further changes, driven by innovations in nanoscience, are also taking place in catalysis. “Of course, heterogeneous catalysis has always been a nanoscience, in that the dimensions of the materials fit the definition,” says Goodman. “However, there have been tremendous advances that have enhanced the characterization of catalysts, both ex situ and in situ, at the molecular level.” Advances in nanoscience and technology have also led to “new methods and technologies for preparing materials with predesigned crystallite sizes and shapes,” adds Avelino Corma of the Universidad Politécnica de Valencia. These developments can be seen in the very latest research, which has begun to explore the chemistry of even smaller gold nanoparticles. For example, Haruta's team has recently studied the epoxidation of propene on gold clusters with diameters of less than 2 nm (ref. 14). Hutchings and colleagues, meanwhile, have used aberration-corrected electron microscopy to show that the high activity of gold for the oxidation of carbon monoxide can be associated with the presence of gold clusters with diameters of just 0.5 nm (ref. 15). Such clusters contain only ten or so gold atoms. “At present, catalysts contain only a small fraction of active gold,” says Hutchings. “We need to be able to control the particle size distributions of gold and gold bimetallics far better than we do, so that we can dial up the active sites we want.” However, the practical concerns that affect all catalysts remain. “Of course the challenge would be stabilizing these very small clusters.” Although translating any of these developments into a viable industrial process will take considerable time, money and effort, gold offers something unique in catalysis. And in the continuing strive for greener, more efficient chemical processes there are numerous opportunities for it to shine. |
回复此楼» 猜你喜欢
中国科大电池方向任晓迪课题组招收2026级博士生-电解液/电池安全性/人工智能方向
已经有21人回复
-
26年秋季博士申请
已经有0人回复
-
分析化学论文润色/翻译怎么收费?
已经有263人回复
-
推荐给英语教学者的一本单词书《金鱼单词讲义：从26个拉丁字母到106万个英语单词》
已经有59人回复
-
推荐给教师的一本单词书《金鱼单词讲义：从26个拉丁字母到106万个英语单词》
已经有32人回复
-
核磁分析软件MestReNova打开文件时报错
已经有0人回复
-
在职博后不能申请博后基金了，那么在职博后意义何在？
已经有2人回复
-
青岛大学化学化工学院分子测量学研究院2026年招收博士研究生
已经有0人回复
-
香港科技大学（广州）诚招电催化方向博士生（2026秋入学）
已经有0人回复
hejin04c
荣誉版主 (著名写手)
小木虫乐乐虫
- ECEPI: 12
- 应助: 2 (幼儿园)
- 贵宾: 0.551
- 金币: 5312.1
- 散金: 266
- 红花: 9
- 沙发: 1
- 帖子: 1441
- 在线: 193.6小时
- 虫号: 694727
- 注册: 2009-01-22
- 性别: MM
- 专业: 电化学分析
- 管辖: 电化学
2楼2010-01-06 08:34:57
打瞌睡的糖
至尊木虫 (文坛精英)
- 应助: 201 (大学生)
- 金币: 12278.2
- 散金: 3629
- 红花: 62
- 沙发: 4909
- 帖子: 31243
- 在线: 2235.4小时
- 虫号: 790774
- 注册: 2009-06-09
- 性别: GG
- 专业: 高分子物理与高分子物理化
3楼2010-01-06 10:21:41
顶  |
4楼2010-01-06 10:43:09
hejin04c
荣誉版主 (著名写手)
小木虫乐乐虫
- ECEPI: 12
- 应助: 2 (幼儿园)
- 贵宾: 0.551
- 金币: 5312.1
- 散金: 266
- 红花: 9
- 沙发: 1
- 帖子: 1441
- 在线: 193.6小时
- 虫号: 694727
- 注册: 2009-01-22
- 性别: MM
- 专业: 电化学分析
- 管辖: 电化学
|
Letter abstract -------------------------------------------------------------------------------- Nature Materials Published online: 20 December 2009 | doi:10.1038/nmat2610 Extreme-angle broadband metamaterial lens Nathan Kundtz1 & David R. Smith1 Top of pageFor centuries, the conventional approach to lens design has been to grind the surfaces of a uniform material in such a manner as to sculpt the paths that rays of light follow as they transit through the interfaces. Refractive lenses formed by this procedure of bending the surfaces can be of extremely high quality, but are nevertheless limited by geometrical and wave aberrations that are inherent to the manner in which light refracts at the interface between two materials. Conceptually, a more natural—but usually less convenient—approach to lens design would be to vary the refractive index throughout an entire volume of space. In this manner, far greater control can be achieved over the ray trajectories. Here, we demonstrate how powerful emerging techniques in the field of transformation optics can be used to harness the flexibility of gradient index materials for imaging applications. In particular we design and experimentally demonstrate a lens that is broadband (more than a full decade bandwidth), has a field-of-view approaching 180° and zero f-number. Measurements on a metamaterial implementation of the lens illustrate the practicality of transformation optics to achieve a new class of optical devices. Top of page -------------------------------------------------------------------------------- |
5楼2010-01-07 08:38:37
|
|
6楼2010-01-07 18:41:26
dyycbj
铜虫 (小有名气)
- 应助: 0 (幼儿园)
- 金币: 193.4
- 散金: 19
- 帖子: 136
- 在线: 66.1小时
- 虫号: 872210
- 注册: 2009-10-14
- 性别: MM
- 专业: 电化学分析
7楼2010-01-07 20:05:48
hejin04c
荣誉版主 (著名写手)
小木虫乐乐虫
- ECEPI: 12
- 应助: 2 (幼儿园)
- 贵宾: 0.551
- 金币: 5312.1
- 散金: 266
- 红花: 9
- 沙发: 1
- 帖子: 1441
- 在线: 193.6小时
- 虫号: 694727
- 注册: 2009-01-22
- 性别: MM
- 专业: 电化学分析
- 管辖: 电化学
8楼2010-01-08 08:34:58
hejin04c
荣誉版主 (著名写手)
小木虫乐乐虫
- ECEPI: 12
- 应助: 2 (幼儿园)
- 贵宾: 0.551
- 金币: 5312.1
- 散金: 266
- 红花: 9
- 沙发: 1
- 帖子: 1441
- 在线: 193.6小时
- 虫号: 694727
- 注册: 2009-01-22
- 性别: MM
- 专业: 电化学分析
- 管辖: 电化学
今日文献一篇
|
Article abstract -------------------------------------------------------------------------------- Nature Chemistry Published online: 20 December 2009 | doi:10.1038/nchem.481 A synthetic small molecule that can walk down a track Max von Delius1, Edzard M. Geertsema1 & David A. Leigh1 -------------------------------------------------------------------------------- AbstractAlthough chemists have made small-molecule rotary motors, to date there have been no reports of small-molecule linear motors. Here we describe the synthesis and operation of a 21-atom two-legged molecular unit that is able to walk up and down a four-foothold molecular track. High processivity is conferred by designing the track-binding interactions of the two feet to be labile under different sets of conditions such that each foot can act as a temporarily fixed pivot for the other. The walker randomly and processively takes zero or one step along the track using a ‘passing-leg’ gait each time the environment is switched between acid and base. Replacing the basic step with a redox-mediated, disulfide-exchange reaction directionally transports the bipedal molecules away from the minimum-energy distribution by a Brownian ratchet mechanism. The ultimate goal of such studies is to produce artificial, linear molecular motors that move directionally along polymeric tracks to transport cargoes and perform tasks in a manner reminiscent of biological motor proteins. Top of page -------------------------------------------------------------------------------- School of Chemistry, University of Edinburgh, The King's Buildings, West Mains Road, Edinburgh EH9 3JJ, UK Correspondence to: David A. Leigh1 e-mail: david.leigh@ed.ac.uk Main navigationJournal content Journal home Advance online publication About AOP Research Highlights Current issue Archive Press releases Journal information Aims and scope About the editors Guide to authors Online submission Guide to referees Contact the journal Pricing Subscribe Help About this site Japanese site NPG services Advertising work@npg Reprints and permissions For librarians NPG resources chemistry@nature The Sceptical Chymist Nature News Nature Nature Biotechnology Nature Chemical Biology Nature Materials Nature Methods Nature Nanotechnology Nature Protocols Nature Reviews Drug Discovery Polymer Journal NPG Asia Materials A-IMBN Research NPG Journals by Subject Area Chemistry Chemistry Drug discovery Biotechnology Materials Methods & Protocols Clinical Practice & Research Cancer Cardiovascular medicine Dentistry Endocrinology Gastroenterology & Hepatology Methods & Protocols Pathology & Pathobiology Urology Earth & Environment Earth sciences Evolution & Ecology Life sciences Biotechnology Cancer Development Drug discovery Evolution & Ecology Genetics Immunology Medical research Methods & Protocols Microbiology Molecular cell biology Neuroscience Pharmacology Systems biology Physical sciences Physics Materials by A - Z Index |
9楼2010-01-08 09:51:00
爱与雨下
荣誉版主 (职业作家)
木虫讲师
- 应助: 10 (幼儿园)
- 贵宾: 3.592
- 金币: 33340.6
- 散金: 21
- 红花: 28
- 沙发: 38
- 帖子: 4644
- 在线: 1456.1小时
- 虫号: 535832
- 注册: 2008-03-29
- 专业: 有机化学
- 管辖: 论文翻译
10楼2010-01-08 13:46:07