Thursday, April 21, 2011

A chance discovery may revolutionize hydrogen production


Producing hydrogen in a sustainable way is a challenge and production cost is too high. A team led by EPFL Professor Xile Hu has discovered that a molybdenum based catalyst is produced at room temperature, inexpensive and efficient. The results of the research are published online in Chemical Science Thursday the 14th of April. An international patent based on this discovery has just been filled.

Existing in large quantities on Earth, water is composed of hydrogen and . It can be broken down by applying an electrical current; this is the process known as electrolysis. To improve this particularly slow reaction, platinum is generally used as a . However, is a particularly expensive material that has tripled in price over the last decade. Now EPFL scientists have shown that amorphous molybdenum sulphides, found abundantly, are efficient catalysts and hydrogen production cost can be significantly lowered.

Industrial prospects

The new catalysts exhibit many advantageous technical characteristics. They are stable and compatible with acidic, neutral or basic conditions in water. Also, the rate of the hydrogen production is faster than other catalysts of the same price. The discovery opens up some interesting possibilities for industrial applications such as in the area of solar energy storage.

It's only by chance that Daniel Merki, St├ęphane Fierro, Heron Vrubel and Xile Hu made this discovery during an electrochemical experience. "It's a perfect illustration of the famous serendipity principle in fundamental research", as Xile Hu emphasizes: "Thanks to this unexpected result, we've revealed a unique phenomenon", he explains. "But we don't yet know exactly why the catalysts are so efficient."

The next stage is to create a prototype that can help to improve sunlight-driven . But a better understanding of the observed phenomenon is also required in order to optimize the catalysts.

More information: Daniel Merki, St├ęphane Fierro, Heron Vrubel and Xile Hu, "Amorphous Molybdenum Sulfide Films as Catalysts for Electrochemical Hydrogen Production in Water," Chemical Science, 2011.

Provided by Ecole Polytechnique Federale de Lausanne

Scientists finely control methane combustion to get different products

Scientists have discovered a method to control the gas-phase selective catalytic combustion of methane, so finely that if done at room temperature the reaction produces ethylene, while at lower temperatures it yields formaldehyde. The process involves using gold dimer cations as catalysts — that is, positively charged diatomic gold clusters. Being able to catalyze these reactions, at or below room temperature, may lead to significant cost savings in the synthesis of plastics, synthetic fuels and other materials. The research was conducted by scientists at the Georgia Institute of Technology and the University of Ulm. It appears in the April 14, 2011, edition of The Journal of Physical Chemistry C.

"The beauty of this process is that it allows us to selectively control the products of this catalytic system, so that if one wishes to create , and potentially methyl alcohol, one burns by tuning its with oxygen to run at lower temperatures, but if it's ethylene one is after, the reaction can be tuned to run at ," said Uzi Landman, Regents' and Institute Professor of Physics and director of the Center for Computational Materials Science at Georgia Tech.

Reporting last year in the journal Angewandte Chemie International Edition, a team that included theorists Landman and Robert Barnett from Georgia Tech and experimentalists Thorsten Bernhardt and Sandra Lang from the University of Ulm, found that by using gold dimer cations as catalysts, they can convert methane into ethylene at room temperature.

This time around, the team has discovered that, by using the same gas-phase gold dimer cation , methane partially combusts to produce formaldehyde at temperatures below 250 Kelvin or -9 degrees Fahrenheit. What's more, in both the room temperature reaction-producing ethylene, and the formaldehyde generation colder reaction, the gold dimer catalyst is freed at the end of the reaction, thus enabling the catalytic cycle to repeat again and again.

The temperature-tuned catalyzed methane partial combustion process involves activating the methane carbon-to-hydrogen bond to react with molecular oxygen. In the first step of the reaction process, methane and oxygen molecules coadsorb on the gold dimer cation at low temperature. Subsequently, water is released and the remaining oxygen atom binds with the methane molecule to form formaldehyde. If done at higher temperatures, the oxygen molecule comes off the gold catalyst, and the adsorbed methane molecules combine to form through the elimination of hydrogen molecules.

In both the current work, as well as in the earlier one, Bernhardt's team at Ulm conducted experiments using a radio-frequency trap, which allows temperature-controlled measurement of the reaction products under conditions that simulate realistic catalytic reactor environment. Landman's team at Georgia Tech performed first-principles quantum mechanical simulations, which predicted the mechanisms of the catalyzed reactions and allowed a consistent interpretation of the experimental observations.

In future work, the two research groups plan to explore the use of multi-functional alloy cluster catalysts in low temperature-controlled catalytic generation of synthetic fuels and selective partial combustion reactions.

Provided by Georgia Institute of Technology (news : web)

Hot off the press: Nanoscale Gutenberg-style printing

When Gutenberg developed the principles of modern book printing, books became available to the masses. Hoping to bring technology capable of mass production to the nanometer scale, Udo Bach and this team of scientists at Monash University and the Lawrence Berkeley National Laboratory have developed a nanoprinting process modeled on Gutenberg’s printing method. Their goal is the simple, inexpensive production of nanotechnological components for solar cells, biosensors, and other electronic systems. As the researchers report in the journal Angewandte Chemie, their "ink" consists of gold nanoparticles, and the specific bonding between DNA molecules ensures its transfer to the substrate.

Nanopatterns with extremely high resolution are not difficult to produce with today’s technology. However, the methods used so far are analogous those used to produce the hand-written books of the era before Gutenberg; they are too slow and work-intensive for commercial fabrication. “New nanoprinting techniques offer an interesting solution,” says Bach. Along with co-workers, he has developed a process that works with a reusable “printing plate”.

The printing plate is a silicon wafer—like those used for the production of computer chips—that has been coated with a photoresist and covered with a mask. The wafer is then exposed to an electron beam (electron beam lithography). In the areas exposed to the beam, the photoresist is removed, exposing the wafer for etching. The wafer is then coated with gold. When the photoresist layer is removed, the gold only sticks to the etched areas. Polyethylene glycol chains are then bound specifically to the gold through sulfur–hydrogen groups. The chains have positively charged amino groups at their ends. The completed printing plate is then dipped into the “ink”, a solution of gold nanoparticles coated with negatively charged DNA molecules. Electrostatic attraction causes the DNA to stick to the amino groups, binding the gold nanoparticles to the gold-patterned areas of the printing plate.

The “paper” is a silicon wafer coated with a whisper-thin gold film and a layer of DNA. These DNA strands are complementary to those on the gold nanoparticles, with which they pair up to form double strands. This type of bond is stronger than the electrostatic attraction between the DNA and the . When the “paper” is pressed onto the “printing plate” and then removed, the nanoparticles from the ink remain stuck to the “paper” in the desired pattern. The “printing plate” can be cleaned and reused multiple times. Says Bach: “Our results demonstrate that it is possible to produce affordable printed elements based on nanoparticles.”

More information: Udo Bach, Gutenberg-Style Printing of Self-Assembled Nanoparticle Arrays: Electrostatic Nanoparticle Immobilization and DNA-Mediated Transfer, Angewandte Chemie International Edition 2011, 50, No. 19, Permalink to the article: … ie.201006991

Provided by Wiley (news : web)

Putting the squeeze on rare earth metals

 Rare-earth metals are a series of elements that represent one of the final frontiers of chemical exploration. The vigorous reactivity of these substances, however, has made it difficult for researchers to transform them into stable materials with well-defined structures. But when they succeed, the payoff can be enormous—rare-earth compounds have important applications in areas ranging from catalysis to clean energy.

Now, Zhaomin Hou and colleagues from the RIKEN Advanced Science Institute in Wako have discovered a new way to isolate rare-earth metals as hydrogen-infused crystals by using wedge-shaped bis(phosphinophenyl)amido (PNP) ligands to ‘pinch’ them in place1. These ligands squeeze rare-earth yttrium atoms together tighter than any previous material, and can even stabilize highly volatile charged complexes.

Metallic compounds that incorporate multiple hydrogen atoms, or polyhydrides, into their frameworks are useful to chemists because they provide some of the purest understandings of bonding and available. Previously, Hou’s team isolated an yttrium polyhydride containing a hydrogen ligand that simultaneously bonds to four metals2. This compound sparked remarkable chemical curiosity because of its structural novelty.

According to Hou, the trick to producing rare-earth polyhydrides is to surround them with large, cumbersome molecules that easily pack together to form crystals. The distinct structure of PNP ligands—two phosphorus atoms, linked together by a rigid aromatic–amino core that can bind to metals with a pincer-like grip—made this ligand a promising candidate for the researchers’ investigation.

By first substituting extra methyl units onto the aromatic backbone of PNP to increase its bulkiness, and then mixing the ligand with an yttrium alkyl precursor and hydrogen gas, the team synthesized pale yellow crystals of a new yttrium polyhydride complex. X-ray structural analysis revealed that three yttrium atoms, held in place by PNP ‘pincers’, were interlinked by a set of double- and triple-bridged hydrogen ligands (Fig. 1). This intricate network of bonds produced the shortest yttrium–yttrium distance ever recorded—an extraordinary packing density that may be critical for future hydrogen-storage applications.

The researchers found that an ammonium proton could remove a hydride from the complex without disrupting crystallization, yielding the first-ever cationic tri- and di-yttrium polyhydrides. The charged nature of these materials should impart potent chemical activity, attributes which Hou and his team are currently investigating. “Our results clearly demonstrate the vital importance of ligand-tuning in the isolation and characterization of rare earth polyhydrides, and should encourage further explorations in this burgeoning area,” he says.

More information: Cheng, J., et al. Rare-earth polyhydride complexes bearing bis(phosphinophenyl)amido pincer ligands. Angewandte Chemie International Edition 50, 1857–1860 (2011). Article

Hou, Z., et al. Synthesis and reactions of polynuclear polyhydrido rare earth metal complexes containing “(C5Me4SiMe3)LnH2” units: A new frontier in rare earth metal hydride chemistry. European Journal of Inorganic Chemistry 18, 2535–2545 (2007). Article

Provided by RIKEN (news : web)

A safer treatment could be realized for millions suffering from parasite infection

A safer and more effective treatment for 10 million people in developing countries who suffer from infections caused by trypanosome parasites could become a reality thanks to new research from Queen Mary, University of London published today (15 April).

Scientists have uncovered the mechanisms behind a drug used to treat and , infections caused by trypanosome parasites which result in 60,000 deaths each year.

The study, appearing in the , investigated how the drug nifurtimox works to kill off the trypanosome.

Co-author of the study, Dr Shane Wilkinson from Queen Mary's School of Biological and Chemical Sciences, said: "Hopefully our research will lead to the development of anti-parasitic medicines which have fewer side effects than nifurtimox and are more effective.

"What we've found is that an enzyme within the parasites carries out the process nifurtimox needs to be converted to a toxic form. This produces a breakdown product which kills the parasite.

"This mechanism overturns the long-held belief that nifurtimox worked against the parasites by inducing oxidative stress in cells."

Nifurtimox has been used for more than 40 years to treat Chagas disease (also known as American trypanosomiasis) and has recently been recommended for use as part of a nifurtimox-eflornithine for African sleeping sickness (also called human African trypanosomiasis).

Dr Wilkinson and his colleagues Dr Belinda Hall and Mr Christopher Bot from Queen Mary's School of Biological and Chemical Sciences focused their research on the characterisation of the breakdown product from nifurtimox.

"The backbone of nifurtimox contains a chemical group called a nitro linked to a ring structure called a furan," Dr Wilkinson explained.

"When the parasite enzyme discussed in the paper reacts with nifurtimox, it converts the nitro group to a derivative called hydroxylamine. The change effectively acts as a switch causing a redistribution of electrons within the compounds chemical backbone."

"The upshot of this redistribution of electrons causes a specific chemical bond in furan ring to break resulting in formation of a toxic product (called an unsaturated open chain nitrile).

"Understanding how nifurtimox kills trypanosomes may generate new and safer compounds which utilise the bioreductive activity of this parasitic enzyme."

Provided by Queen Mary, University of London (news : web)

Recipe for radioactive compounds aids nuclear waste and fuel storage pools studies

 Easy-to-follow recipes for radioactive compounds like those found in nuclear fuel storage pools, liquid waste containment areas and other contaminated aqueous environments have been developed by researchers at Sandia National Laboratories.

“The need to understand the chemistry of these compounds has never been more urgent, and these recipes facilitate their study,” principal investigator May Nyman said of her group’s success in encouraging significant amounts of relevant compounds to self-assemble.

The trick to the recipes is choosing the right templates. These are atoms or molecules that direct the growth of compounds in much the way islands act as templates for coral reefs.

The synthesized materials are stable, pure and can be studied in solution or as solids, making it easier to investigate their chemistry, transport properties and related phases.

The compounds are bright yellow, soluble peroxides of uranium called uranyl peroxide. These and related compounds may be present in any liquid medium used in the nuclear fuel cycle. They also appear in the environment from natural or human causes.

Made with relatively inexpensive and safe depleted uranium, the recipes may be adapted to include other, more radioactive metals such as neptunium, whose effects are even more important to study, Nyman said.

Cesium — an element of particular concern in its radioactive form — proved to be, chemically, an especially favored template for the compounds to self-assemble.

More information: The research will be featured as the cover article of the May 3 online European Journal of Inorganic Chemistry, to be published in print May 13. … ic.201001355

Provided by Sandia National Laboratories (news : web)

Nobel laureate William Lipscomb dies at 91

A Harvard University professor who won the Nobel chemistry prize in 1976 for work on chemical bonding has died. William Nunn Lipscomb Jr. was 91.

His son, James Lipscomb, said Friday that Lipscomb died Thursday night at a Cambridge, Mass., hospital of and complications from a fall.

Several of his students also have won Nobels. Yale University professor Thomas Steitz, who shared the 2009 chemistry prize, says Lipscomb was an inspiring teacher who encouraged creative thinking.

The Ohio native grew up in Lexington, Ky., and students affectionately referred to him as "Colonel" in reference to his upbringing. He graduated from the University of Kentucky and got a doctorate at the California Institute of Technology under Nobel laureate Linus Pauling.

Lipscomb is survived by his wife and three children.

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