Monday, September 12, 2011

Iron 'veins' are secret of promising new hydrogen storage material

 With a nod to biology, scientists at the National Institute of Standards and Technology (NIST) have a new approach to the problem of safely storing hydrogen in future fuel-cell-powered cars. Their idea: molecular scale "veins" of iron permeating grains of magnesium like a network of capillaries. The iron veins may transform magnesium from a promising candidate for hydrogen storage into a real-world winner.

Hydrogen has been touted as a clean and efficient alternative to gasoline, but it has one big drawback: the lack of a safe, fast way to store it onboard a vehicle. According to NIST materials scientist Leo Bendersky, iron-veined magnesium could overcome this hurdle. The combination of lightweight magnesium laced with iron could rapidly absorb -- and just as importantly, rapidly release -- sufficient quantities of hydrogen so that grains made from the two metals could form the fuel tank for hydrogen-powered vehicles.

"Powder grains made of iron-doped magnesium can get saturated with hydrogen within 60 seconds," says Bendersky, "and they can do so at only 150 degrees Celsius and fairly low pressure, which are key factors for safety in commercial vehicles."

Grains of pure magnesium are reasonably effective at absorbing hydrogen gas, but only at unacceptably high temperatures and pressures can they store enough hydrogen to power a car for a few hundred kilometers -- the minimum distance needed between fill-ups. A practical material would need to hold at least 6 percent of its own weight in hydrogen gas and be able to be charged safely with hydrogen in the same amount of time as required to fill a car with gasoline today.

The NIST team used a new measurement technique they devised that uses infrared light to explore what would happen if the magnesium were evaporated and mixed together with small quantities of other metals to form fine-scale mixtures. The team found that iron formed capillary-like channels within the grains, creating passageways for hydrogen transport within the metal grains that allow hydrogen to be drawn inside extremely fast. According to Bendersky, the magnesium-iron grains could hold up to 7 percent hydrogen by weight.

Bendersky adds that the measurement technique could be valuable more generally, as it can reveal details of how a material absorbs hydrogen more effectively than the more commonly employed technique of X-ray diffraction -- a method that is limited to analyzing a material's averaged properties.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by National Institute of Standards and Technology (NIST).

Journal Reference:

Zhuopeng Tan, Chun Chiu, Edwin J. Heilweil, Leonid A. Bendersky. Thermodynamics, kinetics and microstructural evolution during hydrogenation of iron-doped magnesium thin films. International Journal of Hydrogen Energy, 2011; 36 (16): 9702 DOI: 10.1016/j.ijhydene.2011.04.196

Breakthrough in hydrogen fuel cells: Chemists develop way to safely store, extract hydrogen

A team of USC scientists has developed a robust, efficient method of using hydrogen as a fuel source.

Hydrogen makes a great fuel because of it can easily be converted to electricity in a fuel cell and because it is carbon free. The downside of hydrogen is that, because it is a gas, it can only be stored in high pressure or cryogenic tanks.

In a vehicle with a tank full of hydrogen, "if you got into a wreck, you'd have a problem," said Travis Williams, assistant professor of chemistry at the USC Dornsife College.

A possible solution is to store hydrogen in a safe chemical form. Earlier this year, Williams and his team figured out a way to release hydrogen from an innocuous chemical material -- a nitrogen-boron complex, ammonia borane -- that can be stored as a stable solid.

Now the team has developed a catalyst system that releases enough hydrogen from its storage in ammonia borane to make it usable as a fuel source. Moreover, the system is air-stable and re-usable, unlike other systems for hydrogen storage on boron and metal hydrides.

The research was published this month in the Journal of the American Chemical Society.

"Ours is the first game in town for reusable, air stabile ammonia borane dehydrogenation," Williams said, adding that the USC Stevens Institute is in the process of patenting the system.

The system is sufficiently lightweight and efficient to have potential fuel applications ranging from motor-driven cycles to small aircraft, he said.

The research was funded by the Hydrocarbon Research Foundation and the National Science Foundation.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by University of Southern California. The original article was written by Robert Perkins.

Journal Reference:

Brian L. Conley, Denver Guess, Travis J. Williams. A Robust, Air-Stable, Reusable Ruthenium Catalyst for Dehydrogenation of Ammonia Borane. Journal of the American Chemical Society, 2011; 110818113439060 DOI: 10.1021/ja2058154


What's really in that luscious chocolate aroma?

The mouth-watering aroma of roasted cocoa beans -- key ingredient for chocolate -- emerges from substances that individually smell like potato chips, cooked meat, peaches, raw beef fat, cooked cabbage, human sweat, earth, cucumber, honey and an improbable palate of other distinctly un-cocoa-like aromas.

That's among the discoveries emerging from an effort to identify the essential aroma and taste ingredients in the world's favorite treat, described in Denver at the 242nd National Meeting & Exposition of the American Chemical Society (ACS). The research, which chronicles flavor substances from processing of cocoa beans to melting in the mouth, could lead to a new genre of "designer chocolates" with never-before-experienced tastes and aromas, according to Peter Schieberle, Ph.D.

"To develop better chocolate, you need to know the chemistry behind the aroma and taste substances in cocoa and other ingredients," said Schieberle. A pioneer in revealing those secrets, Schieberle received the 2011 ACS Award for the Advancement of Application of Agricultural and Food Chemistry at the meeting. "That understanding must begin with the flavor substances in the raw cocoa bean, extend through all the processing steps and continue as the consumer eats the chocolate.

"When you put chocolate in your mouth, a chemical reaction happens," explained Schieberle. "Some people just bite and swallow chocolate. If you do that, the reaction doesn't have time to happen, and you lose a lot of flavor."

Chocolate is made from cacao (or cocoa) beans, the seeds of cacao trees. Raw cocoa beans have an intense, bitter taste and must be processed to bring out their characteristic flavor. Processing starts with fermentation, in which the moist seeds sit for days in baskets covered with banana leaves while yeasts and bacteria grow on the beans and alter their nature. The beans are dried in the sun and then roasted. Much of the chocolate used in baking, ice cream and hot cocoa undergoes "Dutch processing," which gives it a milder taste. Worldwide, about 3 million tons of cocoa are produced each year.

Cocoa production developed over the years by trial and error, not by scientific analysis, so the substances that give chocolate its subtle flavors were largely unknown, said Schieberle. He is a professor at the Institute for Food Chemistry at the Technical University of Munich, Germany. Over the past 20 years, his team has uncovered many secrets of chocolate's allure.

The distinctive chocolate flavor evolves throughout its production. Odorless, tasteless "precursors" form during fermentation, and these precursors react during roasting to form taste and aroma compounds. The flavors of chocolate and other foods come not just from taste buds in the mouth, Schieberle noted. Odor receptors in the nose play an important role in the perception of aroma. Schieberle and colleagues identified various substances present in cocoa for aromas that bind to human odor receptors in the nose. They mimicked the overall chocolate flavor in so-called "recombinates" containing those ingredients, and taste testers couldn't tell the difference when they sampled some of those concoctions. Individually, those substances had aromas of potato chips, peaches, cooked meat and other un-chocolatey foods.

"To make a very good cocoa aroma, you need only 25 of the nearly 600 volatile compounds present in the beans," said Schieberle. "We call this type of large-scale sensory study 'sensomics.'" Sensomics involves compiling a profile of the key chemical players responsible for giving specific foods their distinctive taste and aroma.

Because no individual compound was identified bearing the typical aroma of cocoa, the researchers had to pick apart individual aromas and put them back together for taste testers to experience. This is a crucial step toward determining how aroma substances work together to stimulate human odor and taste receptors to finally generate the overall perception of chocolate in the brain.

Some of Schieberle's research also uncovered a way to improve the taste of chocolate. The group found that by adding a little bit of sugar to the cocoa before Dutch processing, the chocolate becomes even milder and more velvety due to the formation of previously unknown taste components.

Schieberle's data could help manufacturers control and improve the flavor of cocoa products by assessing these key components in their mixtures.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by American Chemical Society, via EurekAlert!, a service of AAAS.

New salts for chemical 'soups'

 Organozinc reagents are an important class of organometallic compounds with a wide range of applications. LMU chemists have developed a novel route for the synthesis of so-called organozinc pivalates in a stable powdered form. They promise to be extremely useful in many industrial contexts.

In order to meet future demands for new pharmaceuticals, innovative materials and agricultural pesticides, the chemical industry is dependent on the ongoing development of effective methods for the synthesis of complex organic compounds. Because they are so versatile, organometallic molecules are of special significance in this context. Among these, reagents containing zinc atoms have certain advantages over the corresponding organolithium or -magnesium compounds, as they are compatible with a broader array of functional groups.

LMU chemists led by Professor Paul Knochel have now developed a simple "one-pot" method for the economical synthesis of organozinc pivalates. Up until now, such functionalized organozinc compounds were only available in liquid form, and were difficult to transport and store due to their susceptibility to degradation upon contact with air or moisture.

The new synthetic route permits their formation as salt-stabilized solids, which can easily be recovered in powder form. "In this form, the reagents can be stored in an argon atmosphere for months without loss of activity," says Knochel. "They can even be exposed to air for short periods without risk of degradation or ignition."

One of the most prominent applications for organozinc reagents is their use for the so-called Negishi cross-coupling, a type of reaction that provides a simple means of linking carbon atoms together in a virtually unlimited variety of ways, and earned its discoverer a share of the Nobel Prize for Chemistry in 2010. "The new class of organozinc pivalates makes it possible to employ different solvents in the Negishi cross-coupling reaction and greatly extends the spectrum of coupling partners it can be applied to," says Sebastian Bernhardt, who is the lead author on the new study. "The new reagents contain magnesium salts, which also facilitate the addition of organozinc pivalates to carbonyl groups."

This opens the way to their use for a whole series of applications relevant to the industrial manufacture of fine chemicals. The new scheme for synthesis of these compounds is the subject of an international patent application.

The research is reported in Angewandte Chemie International Edition, early view (Aug. 24, 2011).

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Ludwig-Maximilians-Universit√§t M√ľnchen.

Journal Reference:

Sebastian Bernhardt, Georg Manolikakes, Thomas Kunz and Paul Knochel. Preparation of Solid Salt-Stabilized Functionalized Organozinc Compounds and their Application to Cross-Coupling and Carbonyl Addition Reactions. Angewandte Chemie International Edition, 2011 DOI: 10.1002/anie.201104291