Saturday, October 8, 2011

Positioning and pinching slow proton movement in catalyst

Twisting and pinching slow a catalyst's ability to generate energy from hydrogen, according to scientists at Pacific Northwest National Laboratory's Center for Molecular Electrocatalysis. In converting hydrogen to electricity, the catalyst uses claw-like extensions, called ligands, to get needed items in place. However, the ligands opening and closing during the reaction can't be speeded up, making it the rate-limiting step; the ligands' tendency to grasp the protons a bit too tightly can also slow the reaction.

Why It Matters: Reducing our nation's reliance on relies on creating technologies to quickly and efficiently convert the power generated at and other sources into a use-any-time fuel, such as .  Scientists are striving to design affordable, abundant catalysts that turn energy into hydrogen and then release the energy when desired. This study, which appears in the Journal of the American Chemical Society, answers important questions about how the chemical energy in the hydrogen would be converted into electrical energy.

The team examined a nickel-centered with two , six-sided molecular bits that extend off the edge of the catalyst and resemble crab claws. The specific catalyst is [Ni(PCy2NBn2H)2]2+ (PCy2NBn2 = 1,5-dibenzyl-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane).

The catalyst's ligands snag a hydrogen molecule and move it to nickel at the heart of the catalyst. The nickel cracks the molecular hydrogen into 2 electrons and 2 . The electrons remain at the center and are then free to do work, just like the electrons generated by fossil fuel combustion. The ligand picks up the protons using a pendant amine, a small string of atoms containing nitrogen that dangle off the ligand.

During this process, the ligand twists between two different conformations, known as "boat" and "chair." Changing between boat and chair is the rate-limiting step in the reaction, meaning that the reaction can only go as fast as this change occurs. This proved to be an unexpected result for the team.

But, there were other surprises to be found in the data as well. When the ligand picks up the protons it uses the same pendant amine that was involved in taking the hydrogen to the center.

"Intuitively, I would have expected the molecules to completely scramble the protons," said Dr. Wendy Shaw, recipient of the U.S. Department of Energy's Early Career Award and physical chemist on this study. "That the protons moved on the same ligand every time is really interesting and could have implications for future catalysts."

Further, the team found that the pendant amine isn't always ready to give up the protons. Under certain conditions, the molecule holds on tightly to the protons, pinching them. The amines can pinch the protons so hard that they can't move.

In this study, the researchers used a complementary experimental and theoretical approach. The experimental scientists determined the conformation of the catalyst and the rates of reaction using nuclear magnetic resonance spectroscopy experiments in PNNL's Physical Sciences Laboratory. The theorists described the proton movement using complex calculations, including density functional theory and molecular dynamics simulations. The theoreticians used supercomputers at two user facilities. The team used resources at EMSL, Environmental Molecular Sciences Laboratory, and NERSC, the National Energy Research Scientific Computing Center.

"This paper is an example of what a research team can do when they are working closely together," said Dr. Morris Bullock, Director of the Center for Molecular Electrocatalysis at PNNL. "Together the experimentalists and theorists really answer the question of how the protons move."

The experimentalists and theorists, together in the Center for Molecular Electrocatalysis, are using this research as they tackle two new challenges in proton movement. First, they are conducting a more detailed examination of proton pinching. Second, the team is studying how pendant amines take the next step, moving the proton from the edge of the molecule to the environment beyond. This relay hand-off is critical for fuel cells and other alternative energy technologies.

"What we found has really helped us think about how to design new catalysts," said Shaw.

More information: O'Hagan M, WJ Shaw, S Raugei, S Chen, JY Yang, UJ Kilgore, DL DuBois, and R Bullock. 2011. "Moving Protons with Pendant Amines: Proton Mobility in a Nickel Catalyst for Oxidation of Hydrogen." Journal of the American Chemical Society. Article ASAP.

Provided by Pacific Northwest National Laboratory (news : web)

Research demonstrates method that allows inexpensive carbon materials to store hydrogen at room temperature

Hydrogen has long been considered a promising alternative to fossil fuels for powering cars, trucks and even homes. But one major obstacle has been finding lightweight, robust and inexpensive ways of storing the gas, whose atoms are so tiny they can easily escape from many kinds of containers.

New research by a team from MIT and several other institutions analyzes the performance of a class of materials considered a promising candidate for such storage: activated carbon that incorporates a , so can bond directly to the surface of and then be released when needed.

Such a could avoid the cost and weight associated with conventional : Current approaches either liquefy the gas, requiring energy-intensive systems and heavy to maintain a temperature of minus 423 degrees Fahrenheit; or store it under high pressure, requiring powerful pumps and robust tanks to withstand 5,000 to 10,000 pounds per square inch (psi) of pressure. Bonding the to a highly porous, sponge-like material such as a or activated carbon makes it possible to use ambient pressure and in storage tanks that could be lighter, cheaper and safer.

The tricky part of designing such systems is finding a storage medium that bonds the hydrogen atoms tightly enough so they don’t leak away, but not so tightly that they can’t be released when needed. “You have to be able to pump the gas in [at room temperature], and release it when you need it to burn,” explains MIT's Sow-Hsin Chen, senior author of a paper describing the new method.

Such a storage system could be key to making hydrogen-powered cars practical and economically viable, and has been a key goal of the U.S. Department of Energy (DoE). The hydrogen fuel could be made by splitting water; fuel cells would then “burn” the fuel with no emissions at all except water vapor.

Activated carbon has been proposed as a possible storage medium that could work by bonding dissociated hydrogen atoms, but previously there was no good way of analyzing the material’s behavior and optimizing its storage capability. Now, such a method has been demonstrated by a team led by Chen, MIT professor emeritus in the Department of Nuclear Science and Engineering; former student Yun Liu SM ’03, PhD ’05, now at the National Institute of Standards and Technology and the University of Delaware; and researchers at Taiwan’s Institute of Nuclear Energy Research (including lead author Cheng-Si Tsao, who was a visiting scientist at MIT for a year working with Chen), National Tsinghua University in Taiwan and Pennsylvania State University. Their findings were reported in a paper published online in the Journal of Physical Chemistry Letters in August, and scheduled to appear in a forthcoming print issue.

The team analyzed the activated carbon’s storage of hydrogen using a technique called inelastic neutron scattering, which they say is uniquely capable of determining whether the hydrogen in the sample exists as individual atoms or H2 molecules. This approach can also assess the gas’s interaction with the storage material.

Using this method, they were able to provide convincing evidence, for the first time, that hydrogen moves into the material as a result of a phenomenon called the spillover effect, in which atoms — thanks to the presence of platinum particles as a catalyst — split off from their molecules and diffuse through the carbon, where they bond to its surface. Other researchers had suspected the spillover effect was involved, but had been unable to demonstrate that this was the case. “Although this concept had been proposed, there was a lot of debate about it in the community,” Liu says.

The new analysis method should make it possible to fine-tune the properties of the activated carbon material to increase its storage capacity, Chen says. The key is to find the optimum sizes and concentrations for the particles of platinum and carbon, he adds. Ultimately, the researchers also hope to identify a catalyst more abundant and less expensive than platinum.

This storage system, once tuned to achieve the desired capacity, should be capable of storing hydrogen under moderate pressure (possibly around 500 psi), then releasing the gas on demand simply by releasing the pressure, Chen says. “When you break the hydrogen molecules down to atoms” using the spillover effect, “it binds with the material with much less binding energy, so you can pump it out easily,” he says.

Provided by Massachusetts Institute of Technology (news : web)

Scientists reveal how organisms avoid carbon monoxide poisoning

Scientists have discovered how living organisms – including humans – avoid poisoning from carbon monoxide generated by natural cell processes.

Carbon monoxide is a toxic gas that can prove fatal at high concentrations; the gas is most commonly associated with faulty domestic heating systems and car fumes, and is often referred to as 'the silent killer'.

But carbon monoxide – chemical symbol CO – is also produced within our bodies through the normal activity of cells. Scientists have long wondered how organisms manage to control this internal carbon monoxide production so that it does no harm.

University of Manchester researchers, working with colleagues at the University of Liverpool and Eastern Oregon University, have now identified the mechanism whereby cells protect themselves from the toxic effects of the gas at these lower concentrations.

Carbon monoxide molecules should be able to readily bind with protein molecules found in blood cells, known as haemproteins. When they do, for instance during high concentration exposure from inhaling, they impair normal cellular functions, such as oxygen transportation, cell signaling and energy conversion. It is this that causes the fatal effects of carbon monoxide poisoning.

The haemproteins provide an ideal 'fit' for the CO molecules, like a hand fitting a glove, so the natural production of the gas, even at low concentrations, should in theory bind to the haemproteins and poison the organism, except it doesn't.

"Toxic carbon monoxide is generated naturally by chemical metabolic reactions in cells but we have shown how organisms avoid poisoning by these low concentrations of 'natural' carbon monoxide," said Professor Nigel Scrutton, who is based in the Manchester Interdisciplinary Biocentre within the Faculty of Life Sciences.

"Our work identifies a mechanism by which haemproteins are protected from carbon monoxide poisoning at low, physiological concentrations of the gas. Working with a simple, bacterial haemprotein, we were able to show that when the haemprotein 'senses' the toxic gas is being produced within the cell, it changes its structure through a burst of energy and the carbon monoxide molecule struggles to bind with it at these low concentrations.

"This mechanism of linking the CO binding process to a highly unfavourable energetic change in the haemprotein's structure provides an elegant means by which organisms avoid being poisoned by carbon monoxide derived from natural metabolic processes. Similar mechanisms of coupling the energetic structural change with gas release may have broad implications for the functioning of a wide variety of haemprotein systems. For example, haemproteins bind other gas molecules, including oxygen and nitric oxide. Binding of these gases to haemproteins is important in the natural functions of the cell."

Co-author Dr Derren Heyes, also based in the Manchester Interdisciplinary Biocentre, added: "We were surprised to discover that haemproteins could have a simple mechanism involving unfavourable energetic changes in structure to prevent carbon monoxide binding. Without this structural change would bind to the haemoprotein almost a million times more tightly, which would prevent the natural cellular function of the haemprotein."

The scientists say the work has potential for the use of haem-based sensors for gas sensing in a wide range of biotechnological applications. For example, such sensors could be used to monitor gas concentrations in industrial manufacturing processes or biomedical gas sensors, where accurate control of concentration is critical.

The study, headed by Professor Samar Hasnain, from the University of Liverpool's Institute of Integrative Biology, is published in Proceedings of the National Academy of Science.

More information: A copy of the paper, 'Carbon monoxide poisoning is prevented by the energy costs of conformational changes in gas-binding haemproteins,' is available on request.

Provided by University of Manchester (news : web)

Solar rays could replace petroleum fuels, research shows

Alternative fuel sources for cars may have a glowing future as a Kansas State University graduate student is working to replace petroleum fuels with ones made from sunlight.

Yen-Ting Kuo, a doctoral candidate in chemistry, Taiwan, has spent several years in K-State's chemistry program working to create that better use sunlight in chemical reaction processes to generate energy.

"People tend to think of chemistry as test-tube experiments and not really creating practical things. That's just not true," Kuo said. "A big focus now is on 'green chemistry.' This means wanting to have the same quality of life that we have right now, but using chemistry to replace some things with materials that are more eco-friendly, such as biodegradable products or clean fuel."

As a way to advance the clean fuel research, Kuo is making and studying metal-oxide catalysts that react with light. These catalysts, called photocatalysts, cause a chemical reaction when triggered by sunlight, but are not destroyed during the reaction. Photocatalysts are crucial to producing new fuels, like solar gasoline, which use hydrogen.

To make solar gasoline, sunlight is channeled into a tank of that contains photocatalysts. The sunlight triggers the photocatalysts to react with the water. This reaction causes the water to split into hydrogen and oxygen. When the hydrogen is combined with it forms a synthetic gas -- called syngas -- that is the basic building block in fossil fuel and can be used to power cars.

In recent years solar gasoline has been getting more mileage as more international laboratories attempt to improve and perfect the process. But developing a photocatalyst that efficiently uses sunlight to create a chemical reaction and produce hydrogen is proving difficult for researchers. It also is needed for production to reach commercial levels. Kuo is working to solve that problem by creating and analyzing new photocatalysts in the lab.

To make a photocatalyst, Kuo mixes various elements in powdered form, and then cooks them at temperatures between 700 degrees Celsius and 850 degrees Celsius.

Once the material is made, its structure is studied with a transmission electron microscope and ultraviolet spectrums. Doing this allows Kuo to look at ways to structurally improve the photocatalyst and its performance.

In addition to improving the material's photocatalytic properties -- which will intensify reaction with the sunlight -- Kuo focuses on increasing the material's surface area. An increased surface area means bigger and better reactions, and a material with a high and with high photocatalytic properties could mean a bright future for solar gasoline and other alternative fuels.

Engineering a that efficiently splits water into hydrogen and oxygen could also be a boon to fuel cell technology, Kuo said. Fuel cells operate by essentially reversing the chemical reaction that's used to split water. Hydrogen is converted into electrical power, and water is given off as a byproduct.

"Even though the mature technology of fuel cells is in the near future, the source of hydrogen is still a question since most of the hydrogen sources now are from petroleum," Kuo said. "Therefore, water splitting using photocatalysts is one of the solutions providing a new pathway to obtain ."

Kuo came to K-State after reading work published from his adviser, Ken Klabunde. Klabunde, a university distinguished professor of chemistry, is an expert in turning chemistry into new environmentally-friendly materials. He's created inorganic materials and nanotechnology that filter water and air; control odor, bacteria and viruses; and detoxify hazardous chemical spills.

Kuo will defend his dissertation, "Novel photocatalytic water splitting with the N-doped In2O3/TiO2 D10-D0 configuration composite oxide semiconductors," in mid-September. He then will begin a postdoctoral position at the University of Michigan, one of the few universities in the U.S. to study solar gasoline.

Provided by Kansas State University (news : web)

Iowa State chemists help astronauts make sure their drinking water is clean

Bob Lipert held up a syringe, attached a plastic cartridge and demonstrated how chemistry developed at Iowa State University is helping astronauts and cosmonauts make sure they have safe drinking water at the International Space Station.

Each cartridge contains a thin, one-centimeter disk that's loaded with , said Lipert, an associate scientist with Iowa State's Institute for Physical Research and Technology and an associate of the U.S. Department of Energy's Ames Laboratory. Run a 10-milliliter water sample through a disk and it will change color in the presence of , which uses to inhibit the growth of microorganisms in the stored at the space station. The disk will turn from white to yellow and, as it's exposed to higher concentrations of iodine, it will turn to orange and finally to a rust color.

A – a diffuse reflectance spectrometer – can read the disk's color changes and precisely measure the concentration of molecular iodine, or I2. The whole process is called colorimetric solid phase extraction.

Starting in late September, Lipert said astronauts at the space station will use new developments and procedures that convert all forms of iodine in the water samples to molecular iodine. That will give astronauts a more precise reading of total iodine in their drinking water. Lipert said they'll know in real time whether there's too much, too little or just enough iodine in the water.

Disks loaded with different chemistry can also measure and record concentrations of silver, which the Russian Federal Space Agency uses as a biocide in its water supply at the space station. As silver concentrations increase, disks turn from yellow to purple.

Before Iowa State chemists helped develop the new tests, the only way to test the space station's drinking water was to send samples back to earth.

"We figured out the chemistry and put it into a form that can be used in space," Lipert said. "We also took lab techniques and simplified them as much as possible. And we developed procedures that can be used in the absence of gravity."

The result is a quick, accurate test that doesn't use up much drinking water or much astronaut time.

"What's neat about what we came up with is that all the chemistry we need to do can be accomplished in about one minute per sample using a little, 1-centimeter cartridge," Lipert said.

It took some work to develop the test's chemistry and procedures. The NASA-sponsored project began more than a decade ago under the direction of Marc Porter, a former Iowa State professor of chemistry and chemical and biological engineering who is now a USTAR Professor at the University of Utah in Salt Lake City. Lipert has worked on the project since 2000.

Other Iowa State researchers who have worked on the project include Jim Fritz, Distinguished Professor Emeritus of Liberal Arts and Sciences; former post-doctoral researchers Matteo Arena and Neil Dias; and former graduate students April Hill, Daniel Gazda, John Nordling, Lisa Ponton and Cherry Shih. Lorraine Siperko, a research scientist at the University of Utah, has also worked on the project.

The university researchers have also collaborated with the Wyle Integrated Science and Engineering Group, a NASA subcontractor that helped develop and certify the water-testing hardware that has been deployed on the space station.

After a series of successful space tests in 2009 and '10, the researchers' water-testing equipment is now certified operational hardware and is part of the space station's environmental monitoring toolbox.

Lipert said the testing technology can also be a useful tool in many earthbound applications, including forensics tests for drugs, environmental tests for heavy metals and water quality tests for pesticides or herbicides.

"This is a very flexible platform," he said. "You just have to work out the chemistry for each substance you're analyzing."

Provided by Iowa State University (news : web)