From BNL: “Studying Argon Gas Trapped in Two-Dimensional Array of Tiny ‘Cages'”

Brookhaven Lab

July 17, 2017
Ariana Tantillo
atantillo@bnl.gov
(631) 344-2347

Peter Genzer
genzer@bnl.gov
(631) 344-3174

Understanding how individual atoms enter and exit the nanoporous frameworks could help scientists design new materials for gas separation and nuclear waste remediation.

(Left to right) Anibal Boscoboinik, Jian-Qiang Zhong, Dario Stacchiola, Nusnin Akter, Taejin Kim, Deyu Lu, and Mengen Wang at Brookhaven Lab’s Center for Functional Nanomaterials (CFN). The team of scientists (including John Kestell and Alejandro Boscoboinik) carried out experiments at CFN, at Brookhaven’s National Synchrotron Light Source I and II, and in the Lab’s Chemistry Division to study the trapping of individual argon gas atoms (blue prop in Stacchiola’s hand) in two-dimensional (2D) nanoporous frameworks like the one Boscoboinik and Zhong are holding. They had been using these 2D frameworks as analogues to study catalysis in 3D porous materials called zeolites (structural model on the table), which speed up many important reactions such as the conversion of nitrogen-oxide emissions into nitrogen.

Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory had just finished an experiment with a two-dimensional (2D) structure they synthesized for catalysis research when, to their surprise, they discovered that atoms of argon gas had gotten trapped inside the structure’s nanosized pores. Argon and other noble gases have previously been trapped in three-dimensional (3D) porous materials, but immobilizing them on surfaces had only been achieved by either cooling the gases to very low temperatures to condense them, or by accelerating gas ions to implant them directly into materials.

“We are the first team to trap a noble gas in a 2D porous structure at room temperature,” said Anibal Boscoboinik, a materials scientist at Brookhaven Lab’s Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility where part of the research was conducted.

This achievement, reported in a paper published today in Nature Communications, will enable scientists to use traditional surface-science tools—such as x-ray photoelectron and infrared reflection absorption spectroscopy—to perform detailed studies of single gas atoms in confinement. The knowledge gained from such research could inform the design, selection, and improvement of adsorbent materials and membranes for capturing gases such as radioactive krypton and xenon generated by nuclear power plants.

The team of scientists from Brookhaven Lab, Stony Brook University, and the National University of San Luis in Argentina synthesized 2D aluminosilicate (composed of aluminum, silicon, and oxygen) films on top of a ruthenium metal surface. The scientists created this 2D model catalyst material to study the chemical processes happening in the industrially used 3D catalyst (called a zeolite), which has a cage-like structure with open pores and channels the size of small molecules. Because the catalytically active surface is enclosed within these cavities, it is difficult to probe with traditional surface-science tools. The 2D analogue material has the same chemical composition and active site as the 3D porous zeolite but its active site is exposed on a flat surface, which is easier to access with such tools.

An artistic rendering of an argon (Ar) atom trapped in a nanocage that has a silicon (Si)-oxygen (O) framework.

To confirm that the argon atoms were trapped in these “nanocages,” the scientists exposed the 2D material to argon gas and measured the kinetic energy and number of electrons ejected from the surface after striking it with an x-ray beam. They performed these studies at the former National Synchrotron Light Source I (NSLS-I) and its successor facility, NSLS-II (both DOE Office of Science User Facilities at Brookhaven), with an instrument developed and operated by the CFN.

BNL NSLS

BNL NSLS-II

BNL NSLS II

Because the binding energies of core electrons are unique to each chemical element, the resulting spectra reveal the presence and concentration of elements on the surface. In a separate experiment conducted at the CFN, they grazed a beam of infrared light over the surface while introducing argon gas. When atoms absorb light of a specific wavelength, they undergo changes in their vibrational motions that are specific to that element’s molecular structure and chemical bonds.

To get a better understanding of how the framework itself contributes to caging, the scientists investigated the trapping mechanism with silicate films, which are similar in structure to the aluminosilicates but contain no aluminum. In this case, they discovered that not all of the argon gets trapped in the cages—a small amount goes to the interface between the framework and ruthenium surface. This interface is too compressed in the aluminosilicate films for argon to squeeze in.

After studying adsorption, the scientists examined the reverse process of desorption by incrementally increasing the temperature until the argon atoms completely released from the surface at 350 degrees Fahrenheit. They corroborated their experimental spectra with theoretical calculations of the amount of energy associated with argon entering and leaving the cages.

In another infrared spectroscopy experiment conducted in Brookhaven’s Chemistry Division, they explored how the presence of argon in the cages affects the passage of carbon monoxide molecules through the framework. They found that argon restricts the number of molecules that adsorb onto the ruthenium surface.

“In addition to trapping small atoms, the cages could be used as molecular sieves for filtering carbon monoxide and other small molecules, such as hydrogen and oxygen,” said first author Jian-Qiang Zhong, a CFN research associate.

While their main goal going forward will be to continue investigating zeolite catalytic processes on the 2D material, the scientists are interested in learning the impact of different pore sizes on the materials’ ability to trap and filter gas molecules.

“As we seek to better understand the material, interesting and unexpected findings keep coming up,” said Boscoboinik. “The ability to use surface-science methods to understand how a single atom of gas behaves when it is confined in a very small space opens up lots of interesting questions for researchers to answer.”

This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility at Lawrence Berkeley National Laboratory, and was supported by Brookhaven’s Laboratory Directed Research and Development program and the National Scientific and Technical Research Council (CONICET) of Argentina.

NERSC Cray XC40 Cori II supercomputer

LBL NERSC Cray XC30 Edison supercomputer

The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.

NERSC PDSF

PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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From ANL: “A catalytic balancing act “

News from Argonne National Laboratory

Argonne scientists and their collaborators have used a new and counterintuitive approach to balance three important factors — activity, stability and conductivity — in a new catalyst designed for splitting water. (Image by Argonne National Laboratory.)

Balance forms the foundation for a happy life or a healthy diet. For scientists working to design new catalysts to create renewable energy, balancing different materials and their properties is equally important. (Catalysts help accelerate chemical reactions.)

In a new study Nature Communications, researchers from the U.S. Department of Energy’s (DOE) Argonne National Laboratory, Johns Hopkins University, Drexel University and several universities in South Korea used a new and counterintuitive approach to create a better catalyst that supports one of the reactions involved in splitting water into hydrogen and oxygen. Scientists plan to use the generated hydrogen as a clean fuel.

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“Finding a material that works well for energy conversion or storage is like creating a happy marriage.” – Nenad Markovic, Argonne materials scientist and study author.
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By first creating an alloy of two of the densest naturally occurring elements and then removing one, the scientists reshaped the remaining material’s structure so that it better balanced three factors important for chemical reactions: activity, stability and conductivity.

“Finding a material that works well for energy conversion or storage is like creating a happy marriage,” said Nenad Markovic, an Argonne materials scientist and author of the study. “In our case, we found that a dynamic partnership between two different materials helped us integrate competing concerns.”

Scientists searching for new catalysts have scoured the periodic table to find the right elements or combinations of elements to maximize a catalyst’s activity in water-splitting reactions, as well as the durability of the active sites on its surface. Finding materials that are both stable and active, however, has been a challenge.

“More active catalysts tend to be less stable,” Markovic said. “Those that seem to work twice as well usually work only half as long. It is becoming obvious that designing active catalysts is not enough — we need to have not only active, but also stable, materials.”

For the new catalyst, Markovic and his colleagues turned to iridium, a metal most commonly associated with meteorites. As a thin film, iridium is catalytically active, but as it reacts over time with an electrolyte environment, iridium atoms become oxidized. During this process, some of them leave the catalyst’s surface through corrosion, increasingly impairing its performance.

The research team worked to prevent the oxidation by reorganizing the iridium’s structure. To help stabilize and activate iridium, they alloyed it with its neighbor on the periodic table, osmium.

Unlike iridium, osmium is neither catalytically active nor stable, but it did offer a key benefit. After alloying the osmium and iridium together, the researchers then de-alloyed the two metals, leaving behind only a reconfigured structure of three-dimensional iridium nanopores.

“Without the osmium, the iridium would never achieve this state,” Markovic said. “We needed to introduce and then remove the osmium to get a form of iridium that was both active and stable.”

Markovic said each nanopore’s enhanced catalytic stability is due to the small volume of electrolyte within a pore becoming quickly saturated with iridium ions so that surface atoms stop dissolving, in much the same way that it is easier to saturate a teacup of water with sugar than a 10-gallon jug.

While the nanopore’s structure addressed the need for a stable, active catalyst, it was another facet of the iridium’s reconfiguration that helped boost the material’s electron conductivity. Under operational conditions, the porous catalyst actually forms a unique shell of less-conductive iridium oxide around its highly conductive iridium metal interior. This way, electrons can move easily through most of the catalyst to reach the surface, where the water molecule waits on electrons to initiate the water-splitting reaction.

“Essentially, we’re trying to find a way to send electrons through on the ‘expressway,’ rather than making them take the side roads,” Markovic said. “This core-shell configuration [of the nanoporous material] allows us to do that.”

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition
Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science

From BNL: “New Efficient, Low-Temperature Catalyst for Converting Water and CO to Hydrogen Gas and CO2”

Brookhaven Lab

June 22, 2017
Karen McNulty Walsh
kmcnulty@bnl.gov
(631) 344-8350

Peter Genzer
genzer@bnl.gov
(631) 344-3174

Low-temperature “water gas shift” reaction produces high levels of pure hydrogen for potential applications, including fuel cells.

Brookhaven Lab chemists Ping Liu and José Rodriguez helped to characterize structural and mechanistic details of a new low-temperature catalyst for producing high-purity hydrogen gas from water and carbon monoxide. No image credit.

Scientists have developed a new low-temperature catalyst for producing high-purity hydrogen gas while simultaneously using up carbon monoxide (CO). The discovery—described in a paper set to publish online in the journal Science on Thursday, June 22, 2017—could improve the performance of fuel cells that run on hydrogen fuel but can be poisoned by CO.

“This catalyst produces a purer form of hydrogen to feed into the fuel cell,” said José Rodriguez, a chemist at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory. Rodriguez and colleagues in Brookhaven’s Chemistry Division—Ping Liu and Wenqian Xu—were among the team of scientists who helped to characterize the structural and mechanistic details of the catalyst, which was synthesized and tested by collaborators at Peking University in an effort led by Chemistry Professor Ding Ma.

Because the catalyst operates at low temperature and low pressure to convert water (H2O) and carbon monoxide (CO) to hydrogen gas (H2) and carbon dioxide (CO2), it could also lower the cost of running this so-called “water gas shift” reaction.

“With low temperature and pressure, the energy consumption will be lower and the experimental setup will be less expensive and easier to use in small settings, like fuel cells for cars,” Rodriguez said.

The gold-carbide connection

The catalyst consists of clusters of gold nanoparticles layered on a molybdenum-carbide substrate. This chemical combination is quite different from the oxide-based catalysts used to power the water gas shift reaction in large-scale industrial hydrogen production facilities.

“Carbides are more chemically reactive than oxides,” said Rodriguez, “and the gold-carbide interface has good properties for the water gas shift reaction; it interacts better with water than pure metals.”

Wenqian Xu and José Rodriguez of Brookhaven Lab and Siyu Yao, then a student at Peking University but now a postdoctoral research fellow at Brookhaven, conducted operando x-ray diffraction studies of the gold-molybdenum-carbide catalyst over a range of temperatures (423 Kelvin to 623K) at the National Synchrotron Light Source (NSLS) at Brookhaven Lab. The study revealed that at temperatures above 500K, molybdenum-carbide transforms to molybdenum oxide, with a reduction in catalytic activity. No image credit

“The group at Peking University discovered a new synthetic method, and that was a real breakthrough,” Rodriguez said. “They found a way to get a specific phase—or configuration of the atoms—that is highly active for this reaction.”

Brookhaven scientists played a key role in deciphering the reasons for the high catalytic activity of this configuration. Rodriguez, Wenqian Xu, and Siyu Yao (then a student at Peking University but now a postdoctoral research fellow at Brookhaven) conducted structural studies using x-ray diffraction at the National Synchrotron Light Source (NSLS) while the catalyst was operating under industrial or technical conditions.

BNL NSLS

These operando experiments revealed crucial details about how the structure changed under different operating conditions, including at different temperatures.

With those structural details in hand, Zhijun Zuo, a visiting professor at Brookhaven from Taiyuan University of Technology, China, and Brookhaven chemist Ping Liu helped to develop models and a theoretical framework to explain why the catalyst works the way it does, using computational resources at Brookhaven’s Center for Functional Nanomaterials (CFN).

“We modeled different interfaces of gold and molybdenum carbide and studied the reaction mechanism to identify exactly where the reactions take place—the active sites where atoms are binding, and how bonds are breaking and reforming,” she said.

Additional studies at Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory, and two synchrotron research facilities in China added to the scientists’ understanding.

“This is a multipart complex reaction,” said Liu, but she noted one essential factor: “The interaction between the gold and the carbide substrate is very important. Gold usually bonds things very weakly. With this synthesis method we get stronger adherence of gold to molybdenum carbide in a controlled way.”

That configuration stabilizes the key intermediate that forms as the reaction proceeds, and the stability of that intermediate determines the rate of hydrogen production, she said.

The Brookhaven team will continue to study this and other carbide catalysts with new capabilities at the National Synchrotron Light Source II (NSLS-II), a new facility that opened at Brookhaven Lab in 2014, replacing NSLS and producing x-rays that are 10,000 times brighter.

BNL NSLS-II

With these brighter x-rays, the scientists hope to capture more details of the chemistry in action, including details of the intermediates that form throughout the reaction process to validate the theoretical predictions made in this study.

The work at Brookhaven Lab was funded by the U.S. DOE Office of Science.

Additional funders for the overall research project include: the National Basic Research Program of China, the Chinese Academy of Sciences, National Natural Science Foundation of China, Fundamental Research Funds for the Central Universities of China, and the U.S. National Science Foundation.

NSLS, NSLS-II, CFN, CNMS, and ALS are all DOE Office of Science User Facilities.

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

From SLAC: “How a Single Chemical Bond Balances Cells Between Life and Death”

SLAC Lab

June 22, 2017
Amanda Solliday

An optical laser (green) excites the iron-containing active site of the protein cytochrome c, and then an X-ray laser (white) probes the iron a few femtoseconds to picoseconds later. The critical iron-sulfur bond is broken as the optical laser heats the protein, and rebinds as the system cools. (Greg Stewart/SLAC National Accelerator Laboratory)

Slight changes in the machinery of a cell determine whether it lives or begins a natural process known as programmed cell death. In many forms of life—from bacteria to humans—a single chemical bond in a protein called cytochrome c can make this call. As long as the bond is intact, the protein transfers electrons needed to produce energy through respiration. When the bond breaks, the protein switches gear and triggers the breakdown of mitochondria, the structures that power the cell’s activities.

For the first time, scientists have measured exactly how much energy cytochrome c puts into maintaining that bond in a state where it’s strong enough to endure, but easy enough to break when the cell’s life span is ending.

They used intense X-rays from two facilities, the Linac Coherent Light Source (LCLS) X-ray free-electron laser and the Stanford Synchrotron Radiation Lightsource (SSRL) at the Department of Energy’s SLAC National Accelerator Laboratory.

SLAC/LCLS

SLAC/SSRL

The collaboration, led by Edward Solomon, professor of chemistry at Stanford University and of photon science at SLAC, published their results today in Science.

“This is a very general yet extremely important process in biochemistry, and with an X-ray laser we now have insight into how this regulation works,” says Roberto Alonso-Mori, LCLS staff scientist and a co-author of the study. “These are processes that are going on a million-fold in our bodies and everywhere there is life.”

The study marks the first time that anyone has been able to experimentally quantify how the rigid structure of the cytochrome c molecule supports this crucial bond between iron and sulfur atoms in what’s known as an entatic state, where the protein maintains a bond that is just strong enough to perform both of its jobs, says Michael Mara, lead author of the study and a former postdoctoral researcher at Stanford University, now at University of California, Berkeley.

“This was important because we had shown the bond is weak and shouldn’t be present at room temperature in the absence of the protein constraints,” says Solomon. “But the protein is able to contribute energy to keep this bond intact for electron transfer. In this LCLS experiment, we determined exactly how much energy the rest of the protein contributes to maintaining the bond: about 4 kcal/mol that is derived from an adjacent hydrogen bond network.”

“We were able to show how nature tunes this system to change the properties on a fundamental level and perform two very different functions,” Mara says. “The energy contribution by cytochrome c is really at a sweet spot. It makes me wonder what sort of similar effects you might see in other protein systems, and it makes us realize that there is exciting new science on the horizon.”

Ultrafast Changes

Cytochrome c is present in a wide range of life forms and contributes to both cellular respiration and programmed cell death, the pathway to the natural end of a cell’s life cycle. How exactly the state of the bond relates to these two functions had not yet been demonstrated or quantified.

Scientists knew from earlier studies that a particular iron-sulfur bond is key. When iron in the protein binds to sulfur contained in one of the protein’s amino-acid building blocks, cytochrome c participates in electron transfer. By transferring electrons, the protein helps generate energy needed for biological processes that maintain life.

But when cytochrome c encounters cardiolipin, a lipid present in the membrane of the cell’s mitochondria, the iron-sulfur bond breaks, and the protein becomes an enzyme that creates holes in the mitochondria’s outer membrane – the first step in programmed cell death.

These changes occur incredibly fast, in less than 20 picoseconds, so the experiment required ultrafast pulses of X-rays generated by LCLS to take snapshots of the process.

“We photoexcited the iron atoms in the protein’s active site—which contains an iron-rich compound known as heme—with an ultrafast laser before probing it with the LCLS X-ray pulses at different time delays,” says Alonso-Mori.

Each 50-femtosecond laser pulse heated the heme by a couple of hundred degrees. X-ray pulses from LCLS took images of what happened as the heat traveled from the iron to other parts of the protein. After 100 femtoseconds, the iron-sulfur bond would break, only to form again once the sample cooled. Watching this process allowed the scientists to measure energy fluctuations in real time and better understand how this critical bond forms and breaks.

“The entatic state concept is really interesting, but you have to come up with creative ways to demonstrate and quantify it,” says Ryan Hadt, a former Stanford University doctoral student on an Enrico Fermi Fellowship at Argonne National Laboratory who together with his advisor, Professor Solomon, came up with the idea for the experiment and co-wrote the initial proposal around the time LCLS first came online in 2009.

“Our research group was excited about this new instrument and wanted to use it to do a definitive experiment,” Hadt adds.

A Question Raised by Earlier Work

This experiment builds on an earlier study [JACS] conducted at SSRL that found that the iron-sulfur bond was quite weak, says Thomas Kroll, staff scientist at SSRL and lead author of this prior study.

In the latest study, spectroscopy at SSRL also built the framework for the LCLS pump-probe experiment. It allowed the scientists to compare what the molecule originally looked like to how it changed when the temperature rose.

“It’s important to understand how these proteins actually work,” Kroll says. “Because if you don’t understand how they work, how can we create better medicines in an informed and controlled way?”

Knowledge of cytochrome c’s function is also valuable to the fields of bioenergy and environmental science, since it is a critically important protein in bacteria and plants.

The DOE Office of Science and the National Institute of General Medical Sciences of the National Institutes of Health supported this research. The Structural Molecular Biology program at SSRL is funded by DOE Office of Science and the National Institutes of Health, National Institute of General Medical Sciences. LCLS and SSRL are DOE Office of Science User Facilities.

See the full article here .

Please help promote STEM in your local schools.

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SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

From BNL: “Chemists ID Catalytic ‘Key’ for Converting CO2 to Methanol”

Brookhaven Lab

March 23, 2017
Karen McNulty Walsh,
(631) 344-8350
kmcnulty@bnl.gov

Peter Genzer
(631) 344-3174
genzer@bnl.gov

Results will guide design of improved catalysts for transforming pollutant to useful chemicals.

Jingguang Chen and Jose Rodriguez (standing) discuss the catalytic mechanism with Ping Liu and Shyam Kattel (seated).

Capturing carbon dioxide (CO2) and converting it to useful chemicals such as methanol could reduce both pollution and our dependence on petroleum products. So scientists are intensely interested in the catalysts that facilitate such chemical conversions. Like molecular dealmakers, catalysts bring the reacting chemicals together in a way that makes it easier for them to break and rearrange their chemical bonds. Understanding details of these molecular interactions could point to strategies to improve the catalysts for more energy-efficient reactions.

With that goal in mind, chemists from the U.S. Department of Energy’s Brookhaven National Laboratory and their collaborators just released results from experiments and computational modeling studies that definitively identify the “active site” of a catalyst commonly used for making methanol from CO2. The results, published in the journal Science, resolve a longstanding debate about exactly which catalytic components take part in the chemical reactions—and should be the focus of efforts to boost performance.

“This catalyst—made of copper, zinc oxide, and aluminum oxide—is used in industry, but it’s not very efficient or selective,” said Brookhaven chemist Ping Liu, the study’s lead author, who also holds an adjunct position at nearby Stony Brook University (SBU). “We want to improve it, and get it to operate at lower temperatures and lower pressures, which would save energy,” she said.

But prior to this study, different groups of scientists had proposed two different active sites for the catalyst—a portion of the system with just copper and zinc atoms, or a portion with copper zinc oxide.

“We wanted to know which part of the molecular structure binds and breaks and makes bonds to convert reactants to product—and how it does that,” said co-author Jose Rodriguez, another Brookhaven chemist associated with SBU.

To find out, Rodriguez performed a series of laboratory experiments using well-defined model catalysts, including one made of zinc nanoparticles supported on a copper surface, and another with zinc oxide nanoparticles on copper. To tell the two apart, he used an energetic x-ray beam to zap the samples, and measured the properties of electrons emitted. These electronic “signatures” contain information about the oxidation state of the atoms the electrons came from—whether zinc or zinc oxide.

Brookhaven chemist Ping Liu

Meanwhile Liu, Jingguang Chen of Brookhaven Lab and Columbia University, and Shyam Kattel, the first author of the paper and a postdoctoral fellow co-advised by Liu and Chen, used computational resources at Brookhaven’s Center for Functional Nanomaterials (CFN) and the National Energy Research Scientific Computing Center (NERSC)—two DOE Office of Science User Facilities—to model how these two types of catalysts would engage in the CO2-to-methanol transformations. These theoretical studies use calculations that take into account the basic principles of breaking and making chemical bonds, including the energy required, the electronic states of the atoms, and the reaction conditions, allowing scientists to derive the reaction rates and determine which catalyst will give the best rate of conversion.

“We found that copper zinc oxide should give the best results, and that copper zinc is not even stable under reaction conditions,” said Liu. “In fact, it reacts with oxygen and transforms to copper zinc oxide.”

Those predictions matched what Rodriguez observed in the laboratory. “We found that all the sites participating in these reactions were copper zinc oxide,” he said.

But don’t forget the copper.

“In our simulations, all the reaction intermediates—the chemicals that form on the pathway from CO2 to methanol—bind at both the copper and zinc oxide,” Kattel said. “So there’s a synergy between the copper and zinc oxide that accelerates the chemical transformation. You need both the copper and the zinc oxide.”

Ping Liu and Shyam Kattel with the x-ray source used in this study.

Optimizing the copper/zinc oxide interface will become the driving principal for designing a new catalyst, the scientists say.

“This work clearly demonstrates the synergy from combining theoretical and experimental efforts for studying catalytic systems of industrial importance,” said Chen. “We will continue to utilize the same combined approaches in future studies.”

For example, said Rodriguez, “We’ll try different configurations of the atoms at the copper/zinc oxide interface to see how that affects the reaction rate. Also, we’ll be going from studying the model system to systems that would be more practical for use by industry.”

An essential tool for this next step will be Brookhaven’s National Synchrotron Light Source II (NSLS-II), another Office of Science User Facility. NSLS-II produces extremely bright beams of x-rays—about 10,000 times brighter than the broad-beam laboratory x-ray source used in this study. Those intense x-ray beams will allow the scientists to take high-resolution snapshots that reveal both structural and chemical information about the catalyst, the reactants, and the chemical intermediates that form as the reaction occurs.

Brookhaven scientists identified how a zinc/copper (Zn/Cu) catalyst transforms carbon dioxide (two red and one grey balls) and hydrogen (two white balls) to methanol (one grey, one red, and four white balls), a potential fuel. Under reaction conditions, Zn/Cu transforms to ZnO/Cu, where the interface between the ZnO and Cu provides the active sites that allow the formation of methanol.

“And we’ll continue to expand the theory,” said Liu. “The theory points to the mechanistic details. We want to modify interactions at the copper/zinc oxide interface to see how that affects the activity and efficiency of the catalyst, and we’ll need the theory to move forward with that as well.”

An additional co-author, Pedro Ramírez of Universidad Central de Venezuela, made important contributions to this study by helping to test the activity of the copper zinc and copper zinc oxide catalysts.

This research was supported by the DOE Office of Science.

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

From Duke via phys.org: “Light-driven reaction converts carbon dioxide into fuel”

Duke University

phys.org

February 23, 2017

Duke University researchers have engineered rhodium nanoparticles (blue) that can harness the energy in ultraviolet light and use it to catalyze the conversion of carbon dioxide to methane, a key building block for many types of fuels. Credit: Chad Scales

Duke University researchers have developed tiny nanoparticles that help convert carbon dioxide into methane using only ultraviolet light as an energy source.

Having found a catalyst that can do this important chemistry using ultraviolet light, the team now hopes to develop a version that would run on natural sunlight, a potential boon to alternative energy.

Chemists have long sought an efficient, light-driven catalyst to power this reaction, which could help reduce the growing levels of carbon dioxide in our atmosphere by converting it into methane, a key building block for many types of fuels.

Not only are the rhodium nanoparticles made more efficient when illuminated by light, they have the advantage of strongly favoring the formation of methane rather than an equal mix of methane and undesirable side-products like carbon monoxide. This strong “selectivity” of the light-driven catalysis may also extend to other important chemical reactions, the researchers say.

“The fact that you can use light to influence a specific reaction pathway is very exciting,” said Jie Liu, the George B. Geller professor of chemistry at Duke University. “This discovery will really advance the understanding of catalysis.”

The paper appears online Feb. 23 in Nature Communications.

Despite being one of the rarest elements on Earth, rhodium plays a surprisingly important role in our everyday lives. Small amounts of the silvery grey metal are used to speed up or “catalyze” a number of key industrial processes, including those that make drugs, detergents and nitrogen fertilizer, and they even play a major role breaking down toxic pollutants in the catalytic converters of our cars.

Rhodium accelerates these reactions with an added boost of energy, which usually comes in the form of heat because it is easily produced and absorbed. However, high temperatures also cause problems, like shortened catalyst lifetimes and the unwanted synthesis of undesired products.

Rhodium nanocubes were observed under a transmission electron microscope. Credit: Xiao Zhang

In the past two decades, scientists have explored new and useful ways that light can be used to add energy to bits of metal shrunk down to the nanoscale, a field called plasmonics.

“Effectively, plasmonic metal nanoparticles act like little antennas that absorb visible or ultraviolet light very efficiently and can do a number of things like generate strong electric fields,” said Henry Everitt, an adjunct professor of physics at Duke and senior research scientist at the Army’s Aviation and Missile RD&E Center at Redstone Arsenal, AL. “For the last few years there has been a recognition that this property might be applied to catalysis.”

Xiao Zhang, a graduate student in Jie Liu’s lab, synthesized rhodium nanocubes that were the optimal size for absorbing near-ultraviolet light. He then placed small amounts of the charcoal-colored nanoparticles into a reaction chamber and passed mixtures of carbon dioxide and hydrogen through the powdery material.

When Zhang heated the nanoparticles to 300 degrees Celsius, the reaction generated an equal mix of methane and carbon monoxide, a poisonous gas. When he turned off the heat and instead illuminated them with a high-powered ultraviolet LED lamp, Zhang was not only surprised to find that carbon dioxide and hydrogen reacted at room temperature, but that the reaction almost exclusively produced methane.

“We discovered that when we shine light on rhodium nanostructures, we can force the chemical reaction to go in one direction more than another,” Everitt said. “So we get to choose how the reaction goes with light in a way that we can’t do with heat.”

This selectivity—the ability to control the chemical reaction so that it generates the desired product with little or no side-products—is an important factor in determining the cost and feasibility of industrial-scale reactions, Zhang says.

“If the reaction has only 50 percent selectivity, then the cost will be double what it would be if the selectively is nearly 100 percent,” Zhang said. “And if the selectivity is very high, you can also save time and energy by not having to purify the product.”

Now the team plans to test whether their light-powered technique might drive other reactions that are currently catalyzed with heated rhodium metal. By tweaking the size of the rhodium nanoparticles, they also hope to develop a version of the catalyst that is powered by sunlight, creating a solar-powered reaction that could be integrated into renewable energy systems.

“Our discovery of the unique way light can efficiently, selectively influence catalysis came as a result of an on-going collaboration between experimentalists and theorists,” Liu said. “Professor Weitao Yang’s group in the Duke chemistry department provided critical theoretical insights that helped us understand what was happening. This sort of analysis can be applied to many important chemical reactions, and we have only just begun to explore this exciting new approach to catalysis.”

Read more at: https://phys.org/news/2017-02-light-driven-reaction-carbon-dioxide-fuel.html#jCp

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Younger than most other prestigious U.S. research universities, Duke University consistently ranks among the very best. Duke’s graduate and professional schools — in business, divinity, engineering, the environment, law, medicine, nursing and public policy — are among the leaders in their fields. Duke’s home campus is situated on nearly 9,000 acres in Durham, N.C, a city of more than 200,000 people. Duke also is active internationally through the Duke-NUS Graduate Medical School in Singapore, Duke Kunshan University in China and numerous research and education programs across the globe. More than 75 percent of Duke students pursue service-learning opportunities in Durham and around the world through DukeEngage and other programs that advance the university’s mission of “knowledge in service to society.”

From Princeton: “New chemistry makes strong bonds weak”

Princeton University

July 28 2015
Tien Nguyen

Researchers at Princeton have developed a new chemical reaction that breaks the strongest bond in a molecule instead of the weakest, completely reversing the norm for reactions in which bonds are evenly split to form reactive intermediates.

Catalytic alkene carboamination enabled by oxidative proton-coupled electron transfer

Published on July 13 in the Journal of the American Chemical Society, the non-conventional reaction is a proof of concept that will allow chemists to access compounds that are normally off-limits to this pathway. The team used a two-component catalyst system that works in tandem to selectively activate the strongest bond in the molecule, a nitrogen-hydrogen (N-H) bond, through a process known as proton-coupled electron transfer (PCET).

“This PCET chemistry was really interesting to us. In particular, the idea that you can use catalysts to modulate an intrinsic property of a molecule allows you to access chemical space that you couldn’t otherwise,” said Robert Knowles, an assistant professor of chemistry who led the research.

Using PCET as a way to break strong bonds is seen in many essential biological systems, including photosynthesis and respiration, he said. Though this phenomenon is known in biological and inorganic chemistry settings, it hasn’t been widely applied to making new molecules—something Knowles hopes to change.

Given the unexplored state of PCET catalysis, Knowles decided to turn to theory instead of the trial and error approach usually taken by synthetic chemists in the initial stages of reaction development. Using a simple mathematical formula, the researchers calculated, for any pair of catalysts, the pair’s combined “effective bond strength,” which is the strength of the strongest bond they could break. Because both molecules independently contribute to this value, the research team had a high degree of flexibility in designing the catalyst system.

When they tested the catalyst pairs in the lab, the researchers observed a striking correlation between the “effective bond strength” and the reaction efficiency. While effective bond strengths that were lower or higher than the target N-H bond strength gave low reaction yields, the researchers found that matching the strengths promoted the reaction in very high yield.

“To see this formula actually working was really inspiring,” said Gilbert Choi, a graduate student in the Knowles lab and lead author on the work. Once he identified a successful catalyst system, he explored the scope of the reaction and its mechanism.

Proposed catalytic cycle

The researchers think that the reaction starts with one of the catalysts, a compound called dibutylphosphate, tugging on a hydrogen atom, which lengthens and weakens the N-H bond. At the same time, the other catalyst, known as a light-activated iridium complex, targets the weakened bond and plucks off one electron from the two-electron bond, slicing it down the middle.

Once the bond is split, the reactive nitrogen intermediate goes on to form a new carbon-nitrogen bond, giving rise to structurally complex products. This finding builds on work the Knowles lab published earlier this year also in the Journal of the American Chemical Society on a similar reaction that used a more sensitive catalyst system.

Their research has laid a solid foundation for PCET catalysis as a platform for developing new reactions. “My sincere view is that ideas are a lot more valuable than reactions,” Knowles said. “I’m optimistic that people can use these ideas and do things that we hadn’t even considered.”

See the full article here.

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About Princeton: Overview

Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

From SLAC: “Scientists Get First Glimpse of a Chemical Bond Being Born”

SLAC Lab

February 12, 2015

Scientists have used an X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory to get the first glimpse of the transition state where two atoms begin to form a weak bond on the way to becoming a molecule.

This illustration shows atoms forming a tentative bond, a moment captured for the first time in experiments with an X-ray laser at SLAC National Accelerator Laboratory. The reactants are a carbon monoxide molecule, left, made of a carbon atom (black) and an oxygen atom (red), and a single atom of oxygen, just to the right of it. They are attached to the surface of a ruthenium catalyst, which holds them close to each other so they can react more easily. When hit with an optical laser pulse, the reactants vibrate and bump into each other, and the carbon atom forms a transitional bond with the lone oxygen, center. The resulting carbon dioxide molecule detaches and floats away, upper right. The Linac Coherent Light Source (LCLS) X-ray laser probed the reaction as it proceeded and allowed the movie to be created. (SLAC National Accelerator Laboratory)

This fundamental advance, reported Feb. 12 in Science Express and long thought impossible, will have a profound impact on the understanding of how chemical reactions take place and on efforts to design reactions that generate energy, create new products and fertilize crops more efficiently.

“This is the very core of all chemistry. It’s what we consider a Holy Grail, because it controls chemical reactivity,” said Anders Nilsson, a professor at the SLAC/Stanford SUNCAT Center for Interface Science and Catalysis and at Stockholm University who led the research. “But because so few molecules inhabit this transition state at any given moment, no one thought we’d ever be able to see it.”

Anders Nilsson, a professor at SLAC and at Stockholm University, explains how scientists used an X-ray laser to watch atoms form a tentative bond, and why that’s important.

The experiments took place at SLAC’s Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility. Its brilliant, strobe-like X-ray laser pulses are short enough to illuminate atoms and molecules and fast enough to watch chemical reactions unfold in a way never possible before.

Researchers used LCLS to study the same reaction that neutralizes carbon monoxide (CO) from car exhaust in a catalytic converter. The reaction takes place on the surface of a catalyst, which grabs CO and oxygen atoms and holds them next to each other so they pair up more easily to form carbon dioxide.

In the SLAC experiments, researchers attached CO and oxygen atoms to the surface of a ruthenium catalyst and got reactions going with a pulse from an optical laser. The pulse heated the catalyst to 2,000 kelvins – more than 3,000 degrees Fahrenheit – and set the attached chemicals vibrating, greatly increasing the chance that they would knock into each other and connect.

The team was able to observe this process with X-ray laser pulses from LCLS, which detected changes in the arrangement of the atoms’ electrons – subtle signs of bond formation – that occurred in mere femtoseconds, or quadrillionths of a second.

“First the oxygen atoms get activated, and a little later the carbon monoxide gets activated,” Nilsson said. “They start to vibrate, move around a little bit. Then, after about a trillionth of a second, they start to collide and form these transition states.”

‘Rolling Marbles Uphill’

The researchers were surprised to see so many of the reactants enter the transition state – and equally surprised to discover that only a small fraction of them go on to form stable carbon dioxide. The rest break apart again.

“It’s as if you are rolling marbles up a hill, and most of the marbles that make it to the top roll back down again,” Nilsson said. “What we are seeing is that many attempts are made, but very few reactions continue to the final product. We have a lot to do to understand in detail what we have seen here.”

Theory played a key role in the experiments, allowing the team to predict what would happen and get a good idea of what to look for. “This is a super-interesting avenue for theoretical chemists. It’s going to open up a completely new field,” said report co-author Frank Abild-Pedersen of SLAC and SUNCAT.

A team led by Associate Professor Henrik Öström at Stockholm University did initial studies of how to trigger the reactions with the optical laser. Theoretical spectra were computed under the leadership of Stockholm Professor Lars G.M. Pettersson, a longtime collaborator with Nilsson.

Preliminary experiments at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), another DOE Office of Science User Facility, also proved crucial. Led by SSRL’s Hirohito Ogasawara and SUNCAT’s Jerry LaRue, they measured the characteristics of the chemical reactants with an intense X-ray beam so researchers would be sure to identify everything correctly at the LCLS, where beam time is much more scarce. “Without SSRL this would not have worked,” Nilsson said.

The team is already starting to measure transition states in other catalytic reactions that generate chemicals important to industry.

“This is extremely important, as it provides insight into the scientific basis for rules that allow us to design new catalysts,” said SUNCAT Director and co-author Jens Nørskov.

Researchers from LCLS, Helmholtz-Zentrum Berlin for Materials and Energy, University of Hamburg, Center for Free Electron Laser Science, University of Potsdam, Fritz-Haber Institute of the Max Planck Society, DESY and University of Liverpool also contributed to the research. The research was funded by the DOE Office of Science, the Swedish National Research Council, the Knut and Alice Wallenberg Foundation, the Volkswagen Foundation and the German Research Foundation (DFG) Center for Ultrafast Imaging.

See the full article here.

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SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

From Berkeley Lab: “…Black Nanoparticles Could Play Key Role in Clean Energy Photocatalysis”

Berkeley Lab

“A unique atomic-scale engineering technique for turning low-efficiency photocatalytic “white” nanoparticles of titanium dioxide into high-efficiency “black” nanoparticles could be the key to clean energy technologies based on hydrogen.

Samuel Mao, a scientist who holds joint appointments with Berkeley Lab’s Environmental Energy Technologies Division and the University of California at Berkeley, leads the development of a technique for engineering disorder into the nanocrystalline structure of the semiconductor titanium dioxide. This turns the naturally white crystals black in color, a sign that the crystals are now able to absorb infrared as well as visible and ultraviolet light. The expanded absorption spectrum substantially improves the efficiency with which black titanium dioxide can use sunlight to split water molecules for the production of hydrogen.

Berkeley Lab’s Samuel Mao used disorder engineering to transform titanium nanocrystals into highly efficient solar hydrogen photocatalysts, a transformation marked by turning the crystals from white to black. (Photo by Roy Kaltschmidt)

‘We have demonstrated that black titanium dioxide nanoparticles are capable of generating hydrogen through solar-driven photocatalytic reactions with a record-high efficiency,’ Mao said in a talk at the American Chemical Society (ACS)’s national meeting in New Orleans.

‘The synthesis of black titanium dioxide nanoparticles was based on a hydrogenation process in which white titanium dioxide nanocrystals were subjected to high pressure hydrogen gas,’ said Mao. ‘The unique disordered structure creates a photocatalyst that is both durable and efficient, and gives titanium dioxide, one of the most-studied of all oxide materials, a renewed potential.’”

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From Brookhaven Lab: “New Catalyst for Safe, Reversible Hydrogen Storage”

Room-temperature reaction takes place in water; can switch from hydrogen storage to release by changing pH

Karen McNulty Walsh
March 18, 2012

“Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and collaborators have developed a new catalyst that reversibly converts hydrogen gas and carbon dioxide to a liquid under very mild conditions. The work — described in a paper published online March 18, 2012, in Nature Chemistry — could lead to efficient ways to safely store and transport hydrogen for use as an alternative fuel.

This diagram shows the new catalyst in its protonated and deprotonated states as it reversibly converts hydrogen and CO2 gas to and from liquid formate or formic acid at ambient temperature and pressure. The gases can thereby be stored and transported as a liquid, and used later in carbon-neutral energy applications, simply by adjusting the pH. NO image credit.

Interested? See the full article here.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.