改性的金属铝粉末可以与水反应生成氢气。但如何稳定地产生氢气和改性可能不是简单的过程。

21 September 2007

Growing and burning many biofuels may actually raise rather than lower greenhouse gas emissions, a new study led by Nobel prize-winning chemist Paul Crutzen has shown.1  The findings come in the wake of a recent OECD report, which warned nations not to rush headlong into growing energy crops because they cause food shortages and damage biodiversity.

Crutzen and colleagues have calculated that growing some of the most commonly used biofuel crops releases around twice the amount of the potent greenhouse gas nitrous oxide (N2O) than previously thought - wiping out any benefits from not using fossil fuels and, worse, probably contributing to global warming. The work appears in Atmospheric Chemistry and Physics and is currently subject to open review.

'The significance of it is that the supposed benefits of biofuel are even more disputable than had been thought hitherto,' Keith Smith, a co-author on the paper from the University of Edinburgh, told Chemistry World. 'What we are saying is that [growing many biofuels] is probably of no benefit and in fact is actually making the climate issue worse.'


"What we are saying is that growing biofuels is probably of no benefit and in fact is actually making the climate issue worse"
- Keith Smith


Crutzen, famous for his work on nitrogen oxides and the ozone layer, declined to comment before the paper is officially published. But the paper suggests that microbes convert much more of the nitrogen in fertiliser to N2O than previously thought - 3 to 5 per cent or twice the widely accepted figure of 2 per cent used by the International Panel on Climate Change (IPCC).

For rapeseed biodiesel, which accounts for about 80 per cent of the biofuel production in Europe, the relative warming due to N2O emissions is estimated at 1 to 1.7 times larger than the quasi-cooling effect due to saved fossil CO2 emissions. For corn bioethanol, dominant in the US, the figure is 0.9 to 1.5. Only cane sugar bioethanol - with a relative warming of 0.5 to 0.9 - looks like a viable alternative to conventional fuels.

Some previous estimates had suggested that biofuels could cut greenhouse gas emissions by up to 40 per cent.2

Global picture

The IPCC's N2O conversion factor is derived using data from plant experiments. But Crutzen takes a different approach, using atmospheric measurements and ice core data to calculate the total amount of N2O in the atmosphere. He then subtracts the level of N2O in pre-industrial times - before fertilizers were available - to take account of N2O from natural processes such as leguminous plants growing in forests, lightning, and burn offs.

Assuming the rest of the N2O is attributable to newly-fixed nitrogen from fertilizer use, and knowing the amount of fertilizer applied globally, he can calculate thecontribution of fertilizers to N2O levels.

The results may well trigger a rethink by the IPCC, says Smith. 'Should we go along the road of adding up the experimental evidence for each of the processes or are we better off using the global numbers?'

Critical reception

But other experts are critical of Crutzen's approach. Simon Donner, a nitrogen researcher based at Princeton University, US, says the method is elegant but there is little evidence to show the N2O yield from fertilized plants is really as high as 3-5 per cent. Crutzen's basic assumption, that  pre-industrial N2O emissions are the same as natural N2O emissions, is 'probably wrong', says Donner.

One reason he gives is that farmers plant crops in places that have nitrogen rich soils anyway. 'It is possible we are indirectly increasing the "natural" source of N2O by drawing down the soil nitrogen in the world's agricultural regions,' he explains.

Others dispute the values chosen by Crutzen to calculate his budget. Stefan Rauh, an agricultural scientist at the Instituteof Agricultural Economics and Farm Management in Munich, Germany, says some of the rates for converting crops into biofuel should be higher. 'If you use the other factors you get a little net climate cooling,' he said.

Meanwhile, a report prepared by the OECD for a recent Round Table on Sustainable Development questions the benefits of first generation biofuels and concludes that governments should scrap mandatory targets.

Richard Doornbosch, the report's author, says both the report and Crutzen's work highlights the importance of establishing correct full life-cycle assessments for biofuels. 'Without them, government policies can't distinguish between one biofuel and another - risking making problems worse,' said Doornbosch.

Zoe Corbyn


References1 PJ Crutzen et al, Atmos. Chem. Phys. Discuss., 2007, 7, 11191
2 J Hill et al, Proc. Natl. Acad. Sci. USA, 2006, 103, 11206 (DOI: 10.1073/pnas.0604600103)


Source: Chemisry World.

氢能是未来最重要的能源之一，太阳是地球上最重要的能量来源。那么，有没有一种方法能利用太阳能直接产生化学能而不需要电的介入？德国科学家的一项最新研究，开发出了一种新型半导体催化剂，它能够让太阳能直接“劈开”水分子，得到氢气。相关论文即将发表在国际学术期刊《应用化学》（Angewandte Chemie）上。

领导该项研究的是德国马普生物无机化学研究所（Max Planck Institute for Bioinorganic Chemistry）的Martin Demuth，他和同事利用的新型催化剂源自二矽化钛（TiSi2），一种具有特殊光电性能的半导体材料。研究表明，在反应最初阶段，二矽化钛表面的微小氧化物会促使接触反应中心形成，从而直接、高效地将水分解为氢气和氧气。值得注意的是，二矽化钛在反应中所起到的不仅仅是光催化作用，它同时能够可逆存储产生的气体，从而实现氢和氧的完美分离。

Demuth表示，“二矽化钛催化剂分解水的效率比其他利用可见光的半导体系统更高。”此外，尽管存储的气体中有氢气也有氧气，但由于氧气只有在温度高于100摄氏度而且黑暗的条件下才能释放出来，因此研究人员可以方便地利用低温来分离出氢气。

http://www3.interscience.wiley.com/cgi-bin/abstract/116312569/ABSTRACT

Martin Demuth个人主页
http://ewww.mpi-muelheim.mpg.de/bac/mitarbeiter/demuth/demuth_en.php

A Titanium Disilicide Derived Semiconducting Catalyst for Water Splitting under Solar Radiation - Reversible Storage of Oxygen and Hydrogen

Peter Ritterskamp  1, Andriy Kuklya, Dr.1, Marc-André Wüstkamp1, Klaus Kerpen, Dr.1, Claudia Weidenthaler, Dr. 2, Martin Demuth, Prof.

Max-Planck-Institut für Bioanorganische Chemie, 45413 Mülheim an der Ruhr, Germany, Fax: (+49) 208-306-3951 http://www.mpibac.mpg.de 2Max-Planck-Institut für Kohlenforschung, 45470 Mülheim an der Ruhr, Germany

email: Martin Demuth (demuthm@mpi-muelheim.mpg.de)

Correspondence to Martin Demuth, 1Max-Planck-Institut für Bioanorganische Chemie, 45413 Mülheim an der Ruhr, Germany,
Fax: (+49) 208-306-3951
http://www.mpibac.mpg.de

[ 本帖最后由 cc136520 于 2007-9-26 11:23 编辑 ]

这个太牛了

这个反应机理会是什么呢？怎么解释？

原文及附加材料

不错 厉害的东西

能源和环境是人类赖以生存和发展的永恒主题。氢能被誉为21世纪的绿色能源，但是，氢气的保存和运输一直是制约氢经济发展的瓶颈。为此，上海理工大学利用低成本的锌量子点研发了一种便携式制氢系统，它可以安装在交通或运载工具上“在线”为燃料电池提供动力，既可避免氢气的长途运输和长期保存，又可节省建设加氢站的巨大投资。根据初步实验，这种锌量子点与水蒸气的反应温度大约为100°C -150°C，能量消耗很低，使得利用动力设备的余热制氢成为可能。同时，该反应是放热反应，具有进一步节能的潜力。根据估算，该技术的制氢成本只有国内外现有同类技术的10%左右。另一方面，整个生产过程既不产生任何有毒物质，也不产生温室气体，反应产物仅为氢气和氧化锌纳米棒，后者可用于纳米器件（如气敏传感器，薄膜晶体管等）开发和环境保护。根据实验，只需30分钟太阳光照射，这种氧化锌纳米棒对甲基橙的光催化降解率即可达到100%。

这种便携式制氢系统开发成功的关键是锌量子点的干法室温大规模低成本制备。上海理工大学动力学院经过10余年的努力，在国内外率先研制和开发了一种用于纳米结构和纳米材料干法室温大规模低成本制备的滚压振动磨，利用这种设备和方法，制造1公斤尺度在3-5纳米的锌量子点的能耗大约只有8度电。这些量子点是单晶的、透明的、尺度均匀的、随机取向的、等轴的、单分散的、稳定的，从而为工业应用奠定了坚实的基础。

Chemical & Engineering News
October 4, 2007
Partnership aims to develop renewable transportation fuels from biomass
Glenn Hess
ConocoPhillips and Archer Daniels Midland have agreed to collaborate on research aimed at developing biocrude, a nonpetroleum substance derived from agricultural waste and forestry products that can be processed into transportation fuels.

ADM, a major grain processor and the biggest U.S. ethanol producer, will provide biomass from crops, wood, or switchgrass. ConocoPhillips, the nation's third-largest oil company, will convert the materials into biocrude, which will then be refined into gasoline, diesel, and jet fuel.

The companies have each committed $5 million to the initial research on developing biocrude. The project is expected to last five years. Research will be conducted at ADM, ConocoPhillips, and universities.

"ConocoPhillips believes that the development of next-generation biofuels is a critical step in the diversification of our nation's energy sources," says James J. Mulva, CEO of the Houston-based company. "We are hopeful that this collaboration will provide innovative technology toward the large-scale production of biofuels that can be moved efficiently and affordably through existing infrastructure."

"Innovative collaboration like this will identify and bring to market feasible, economic, and sustainable next-generation biofuels," adds ADM's CEO Patricia A. Woertz.

The partnership reflects a growing trend in which companies in the energy industry, often with government support, are actively exploring the development of renewable resources rather than relying solely on fossil fuels.

In April, for example, ConocoPhillips said it would establish an eight-year, $22.5 million research program at Iowa State University to develop technologies to create renewable biofuels (C&EN, April 16, page 24). Other oil companies are funding similar research ventures at other universities.

Silicide compound and sunlight convert water to H2 and O2
Chemical & Engineering News
Mitch Jacoby
In a two-for-one deal that may give the solar energy field a shot in the arm, researchers have discovered a semiconducting silicide that functions effectively as a water-splitting photocatalyst and doubles as a gas separator (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200701626).

Using sunlight to liberate hydrogen from water is an appealing way to generate a clean-burning fuel from a renewable energy source. As a result, scientists have examined a variety of materials over the years in search of a suitable catalyst to accelerate the water-splitting reaction. Several candidates show some level of promise, yet each material suffers from shortcomings that would limit its applications. For example, some catalysts absorb solar radiation inefficiently, exhibit low activity, or are unstable or costly.

Now, a team of researchers at the Max Planck Institutes for Bioinorganic Chemistry and for Coal Research, in Germany, report that titanium disilicide (TiSi2)—an abundant and inexpensive semiconductor not known previously to be a water-splitting catalyst—separates water into hydrogen and oxygen when reactors containing the powdered catalyst are illuminated with simulated sunlight.

"Titanium disilicide has very unusual optoelectronic properties that are ideal for use in solar technology," says research group leader Martin Demuth. Specifically, the material absorbs light over a wide range of the solar spectrum and exhibits a bandgap—an important determinant of semiconductor properties—that varies by nearly 2 eV across that range. Semiconductors typically exhibit a much narrower variation in bandgap.

Another key observation reported by the team, which includes Demuth, Peter Ritterskamp, Andriy Kuklya, and their coworkers, is that hydrogen evolves readily during experiments, but oxygen adsorbs reversibly on the catalyst surface. Raising the temperature above 100 °C rapidly releases the stored oxygen, they say, which provides a convenient way to separate the gases.

On the basis of control experiments, isotope-labeling tests, and other measurements, the researchers propose that exposing commercial TiSi2 to light in the presence of a small amount of oxygen (as found in water that has not been degassed) leads to formation of catalytically active sites. These nanometer-sized domains of oxidized species catalyze the water-splitting and gas-forming reactions, they say.

As news of the findings begins to spread, some scientists are puzzling over the unusual properties reported for TiSi2. At the National Renewable Energy Laboratory, for example, senior research fellow Arthur J. Nozik notes that the "curiously" varying bandgap implies that the material is neither pure nor homogeneous. It is unclear, he says, whether this range represents individual particles with distinct chemical composition or a graded composition for individual particles, which suggests that the mechanism is not well-understood.

Demuth agrees that the behavior is "atypical" but adds that he has founded a start-up company to further study, develop, and possibly commercialize the technology.


SPLIT UP Sunlight and residual oxygen form active domains of oxide species (purple and green regions) on the surface of TiSi2 particles. These species catalyze formation of H2 and O2 from water

[ 本帖最后由 xunhuan008 于 2007-10-5 21:48 编辑 ]