Tag Archives: platinum

When an atom more or less makes a big difference

As scientists continue exploring the nanoscale, it seems that finding the number of atoms in your particle makes a difference is no longer so surprising. From a Jan. 28, 2016 news item on ScienceDaily,

Combining experimental investigations and theoretical simulations, researchers have explained why platinum nanoclusters of a specific size range facilitate the hydrogenation reaction used to produce ethane from ethylene. The research offers new insights into the role of cluster shapes in catalyzing reactions at the nanoscale, and could help materials scientists optimize nanocatalysts for a broad class of other reactions.

A Jan. 28, 2016 Georgia Institute of Technology (Georgia Tech) news release (*also on EurekAlert*), which originated the news item, expands on the theme,

At the macro-scale, the conversion of ethylene has long been considered among the reactions insensitive to the structure of the catalyst used. However, by examining reactions catalyzed by platinum clusters containing between 9 and 15 atoms, researchers in Germany and the United States found that at the nanoscale, that’s no longer true. The shape of nanoscale clusters, they found, can dramatically affect reaction efficiency.

While the study investigated only platinum nanoclusters and the ethylene reaction, the fundamental principles may apply to other catalysts and reactions, demonstrating how materials at the very smallest size scales can provide different properties than the same material in bulk quantities. …

“We have re-examined the validity of a very fundamental concept on a very fundamental reaction,” said Uzi Landman, a Regents’ Professor and F.E. Callaway Chair in the School of Physics at the Georgia Institute of Technology. “We found that in the ultra-small catalyst range, on the order of a nanometer in size, old concepts don’t hold. New types of reactivity can occur because of changes in one or two atoms of a cluster at the nanoscale.”

The widely-used conversion process actually involves two separate reactions: (1) dissociation of H2 molecules into single hydrogen atoms, and (2) their addition to the ethylene, which involves conversion of a double bond into a single bond. In addition to producing ethane, the reaction can also take an alternative route that leads to the production of ethylidyne, which poisons the catalyst and prevents further reaction.

The project began with Professor Ueli Heiz and researchers in his group at the Technical University of Munich experimentally examining reaction rates for clusters containing 9, 10, 11, 12 or 13 platinum atoms that had been placed atop a magnesium oxide substrate. The 9-atom nanoclusters failed to produce a significant reaction, while larger clusters catalyzed the ethylene hydrogenation reaction with increasingly better efficiency. The best reaction occurred with 13-atom clusters.

Bokwon Yoon, a research scientist in Georgia Tech’s Center for Computational Materials Science, and Landman, the center’s director, then used large-scale first-principles quantum mechanical simulations to understand how the size of the clusters – and their shape – affected the reactivity. Using their simulations, they discovered that the 9-atom cluster resembled a symmetrical “hut,” while the larger clusters had bulges that served to concentrate electrical charges from the substrate.

“That one atom changes the whole activity of the catalyst,” Landman said. “We found that the extra atom operates like a lightning rod. The distribution of the excess charge from the substrate helps facilitate the reaction. Platinum 9 has a compact shape that doesn’t facilitate the reaction, but adding just one atom changes everything.”

Here’s an illustration featuring the difference between a 9 atom cluster and a 10 atom cluster,

A single atom makes a difference in the catalytic properties of platinum nanoclusters. Shown are platinum 9 (top) and platinum 10 (bottom). (Credit: Uzi Landman, Georgia Tech)

A single atom makes a difference in the catalytic properties of platinum nanoclusters. Shown are platinum 9 (top) and platinum 10 (bottom). (Credit: Uzi Landman, Georgia Tech)

The news release explains why the larger clusters function as catalysts,

Nanoclusters with 13 atoms provided the maximum reactivity because the additional atoms shift the structure in a phenomena Landman calls “fluxionality.” This structural adjustment has also been noted in earlier work of these two research groups, in studies of clusters of gold [emphasis mine] which are used in other catalytic reactions.

“Dynamic fluxionality is the ability of the cluster to distort its structure to accommodate the reactants to actually enhance reactivity,” he explained. “Only very small aggregates of metal can show such behavior, which mimics a biochemical enzyme.”

The simulations showed that catalyst poisoning also varies with cluster size – and temperature. The 10-atom clusters can be poisoned at room temperature, while the 13-atom clusters are poisoned only at higher temperatures, helping to account for their improved reactivity.

“Small really is different,” said Landman. “Once you get into this size regime, the old rules of structure sensitivity and structure insensitivity must be assessed for their continued validity. It’s not a question anymore of surface-to-volume ratio because everything is on the surface in these very small clusters.”

While the project examined only one reaction and one type of catalyst, the principles governing nanoscale catalysis – and the importance of re-examining traditional expectations – likely apply to a broad range of reactions catalyzed by nanoclusters at the smallest size scale. Such nanocatalysts are becoming more attractive as a means of conserving supplies of costly platinum.

“It’s a much richer world at the nanoscale than at the macroscopic scale,” added Landman. “These are very important messages for materials scientists and chemists who wish to design catalysts for new purposes, because the capabilities can be very different.”

Along with the experimental surface characterization and reactivity measurements, the first-principles theoretical simulations provide a unique practical means for examining these structural and electronic issues because the clusters are too small to be seen with sufficient resolution using most electron microscopy techniques or traditional crystallography.

“We have looked at how the number of atoms dictates the geometrical structure of the cluster catalysts on the surface and how this geometrical structure is associated with electronic properties that bring about chemical bonding characteristics that enhance the reactions,” Landman added.

I highlighted the news release’s reference to gold nanoclusters as I have noted the number issue in two April 14, 2015 postings, neither of which featured Georgia Tech, Gold atoms: sometimes they’re a metal and sometimes they’re a molecule and Nature’s patterns reflected in gold nanoparticles.

Here’s a link to and a citation for the ‘platinum catalyst’ paper,

Structure sensitivity in the nonscalable regime explored via catalysed ethylene hydrogenation on supported platinum nanoclusters by Andrew S. Crampton, Marian D. Rötzer, Claron J. Ridge, Florian F. Schweinberger, Ueli Heiz, Bokwon Yoon, & Uzi Landman.  Nature Communications 7, Article number: 10389  doi:10.1038/ncomms10389 Published 28 January 2016

This paper is open access.

*’also on EurekAlert’ added Jan. 29, 2016.

Hybrid bacterial genes and virus shell combined to create ‘nano reactor’ for hydrogen biofuel

Turning water into fuel may seem like an almost biblical project (e.g., Jesus turning water to wine in the New Testament) but scientists at Indiana University are hopeful they are halfway to their goal. From a Jan. 4, 2016 news item on ScienceDaily,

Scientists at Indiana University have created a highly efficient biomaterial that catalyzes the formation of hydrogen — one half of the “holy grail” of splitting H2O to make hydrogen and oxygen for fueling cheap and efficient cars that run on water.

A Jan. 4, 2016 Indiana University (IU) news release (also on EurekAlert*), which originated the news item, explains further (Note: Links have been removed),

A modified enzyme that gains strength from being protected within the protein shell — or “capsid” — of a bacterial virus, this new material is 150 times more efficient than the unaltered form of the enzyme.

“Essentially, we’ve taken a virus’s ability to self-assemble myriad genetic building blocks and incorporated a very fragile and sensitive enzyme with the remarkable property of taking in protons and spitting out hydrogen gas,” said Trevor Douglas, the Earl Blough Professor of Chemistry in the IU Bloomington College of Arts and Sciences’ Department of Chemistry, who led the study. “The end result is a virus-like particle that behaves the same as a highly sophisticated material that catalyzes the production of hydrogen.”

The genetic material used to create the enzyme, hydrogenase, is produced by two genes from the common bacteria Escherichia coli, inserted inside the protective capsid using methods previously developed by these IU scientists. The genes, hyaA and hyaB, are two genes in E. coli that encode key subunits of the hydrogenase enzyme. The capsid comes from the bacterial virus known as bacteriophage P22.

The resulting biomaterial, called “P22-Hyd,” is not only more efficient than the unaltered enzyme but also is produced through a simple fermentation process at room temperature.

The material is potentially far less expensive and more environmentally friendly to produce than other materials currently used to create fuel cells. The costly and rare metal platinum, for example, is commonly used to catalyze hydrogen as fuel in products such as high-end concept cars.

“This material is comparable to platinum, except it’s truly renewable,” Douglas said. “You don’t need to mine it; you can create it at room temperature on a massive scale using fermentation technology; it’s biodegradable. It’s a very green process to make a very high-end sustainable material.”

In addition, P22-Hyd both breaks the chemical bonds of water to create hydrogen and also works in reverse to recombine hydrogen and oxygen to generate power. “The reaction runs both ways — it can be used either as a hydrogen production catalyst or as a fuel cell catalyst,” Douglas said.

The form of hydrogenase is one of three occurring in nature: di-iron (FeFe)-, iron-only (Fe-only)- and nitrogen-iron (NiFe)-hydrogenase. The third form was selected for the new material due to its ability to easily integrate into biomaterials and tolerate exposure to oxygen.

NiFe-hydrogenase also gains significantly greater resistance upon encapsulation to breakdown from chemicals in the environment, and it retains the ability to catalyze at room temperature. Unaltered NiFe-hydrogenase, by contrast, is highly susceptible to destruction from chemicals in the environment and breaks down at temperatures above room temperature — both of which make the unprotected enzyme a poor choice for use in manufacturing and commercial products such as cars.

These sensitivities are “some of the key reasons enzymes haven’t previously lived up to their promise in technology,” Douglas said. Another is their difficulty to produce.

“No one’s ever had a way to create a large enough amount of this hydrogenase despite its incredible potential for biofuel production. But now we’ve got a method to stabilize and produce high quantities of the material — and enormous increases in efficiency,” he said.

The development is highly significant according to Seung-Wuk Lee, professor of bioengineering at the University of California-Berkeley, who was not a part of the study.

“Douglas’ group has been leading protein- or virus-based nanomaterial development for the last two decades. This is a new pioneering work to produce green and clean fuels to tackle the real-world energy problem that we face today and make an immediate impact in our life in the near future,” said Lee, whose work has been cited in a U.S. Congressional report on the use of viruses in manufacturing.

Beyond the new study, Douglas and his colleagues continue to craft P22-Hyd into an ideal ingredient for hydrogen power by investigating ways to activate a catalytic reaction with sunlight, as opposed to introducing elections using laboratory methods.

“Incorporating this material into a solar-powered system is the next step,” Douglas said.

Here’s a link to and a citation for the paper,

Self-assembling biomolecular catalysts for hydrogen production by Paul C. Jordan, Dustin P. Patterson, Kendall N. Saboda, Ethan J. Edwards, Heini M. Miettinen, Gautam Basu, Megan C. Thielges, & Trevor Douglas. Nature Chemistry (2015) doi:10.1038/nchem.2416 Published online 21 December 2015

This paper is behind a paywall.

*(also on EurekAlert) added on Jan. 5, 2016 at 1550 PST.

Nanoscale snowman and Season’s Greetings

It’s being described as a ‘jeweled nano-snowman’ but platinum and titanium aren’t my idea of jewels. Still, it’s a cheerful, seasonal greeting.

Courtesy of the University of Birmingham Nanoscale Physics Research Laboratory

Courtesy of the University of Birmingham Nanoscale Physics Research Laboratory

A December 22, 2015 news item on Nanowerk tells more of the story,

Would a jewel-encrusted snowman make the perfect Christmas present? At only 5 nanometres in size, the price might be lower than you think. And it’s functional too, catalysing the splitting of water to make green hydrogen for fuel cells.

A December 22, 2015 University of Birmingham Nanoscale Physics Research Laboratory (NPRL) press release, which originated the news item, provides more detail,

The nanoparticle, as imaged with an aberration-corrected scanning transmission electron microscope, features eyes, nose and mouth of precious-metal platinum clusters embedded in a titanium dioxide face. Each platinum cluster typically contains 30 platinum atoms; within the whole nanoparticle there are approximately 1,680 titanium atoms and 180 platinum atoms. The nano-snowman formed spontaneously from a self-assembled platinum-titanium nanoparticle which was oxidised in air, drawing the titanium atoms out to the surface. The self-assembly occurred in a gas phase, cluster beam condensation source, before size-selection with a mass spectrometer and deposition onto a carbon surface for oxidation and then imaging. The mass of the snowman is 120,000 atomic mass units. Compared with a more conventional pure platinum catalyst particle, the inclusion of the titanium atoms offers two potential benefits: dilution of how much precious platinum is needed to perform the catalysis, and protection of the platinum cores against sintering (i.e. aggregation of the nanoparticles). The shell is porous enough to allow hydrogen through and the particles are functional in the hydrogen evolution reaction. The research was performed at the Nanoscale Physics Research Lab by Caroline Blackmore and Ross Griffin. …

The scientists did a little bit of work adding colour (most of these images are gray on gray), as well as, the holly and berry frame.

Joyeux Noël et Bonne Année or Season’s Greetings!

Combining gold and palladium for catalytic and plasmonic octopods

Hopefully I did not the change meaning when I made the title for this piece more succinct. In any event, this research comes from the always prolific Rice University in Texas, US (from a Nov. 30, 2015 news item on Nanotechnology Now),

Catalysts are substances that speed up chemical reactions and are essential to many industries, including petroleum, food processing and pharmaceuticals. Common catalysts include palladium and platinum, both found in cars’ catalytic converters. Plasmons are waves of electrons that oscillate in particles, usually metallic, when excited by light. Plasmonic metals like gold and silver can be used as sensors in biological applications and for chemical detection, among others.

Plasmonic materials are not the best catalysts, and catalysts are typically very poor for plasmonics. But combining them in the right way shows promise for industrial and scientific applications, said Emilie Ringe, a Rice assistant professor of materials science and nanoengineering and of chemistry who led the study that appears in Scientific Reports.

“Plasmonic particles are magnets for light,” said Ringe, who worked on the project with colleagues in the U.S., the United Kingdom and Germany. “They couple with light and create big electric fields that can drive chemical processes. By combining these electric fields with a catalytic surface, we could further push chemical reactions. That’s why we’re studying how palladium and gold can be incorporated together.”

The researchers created eight-armed specks of gold and coated them with a gold-palladium alloy. The octopods proved to be efficient catalysts and sensors.

A Nov. 30, 2015 Rice University news release (also on EurekAlert), which originated the news item, expands on the theme,

“If you simply mix gold and palladium, you may end up with a bad plasmonic material and a pretty bad catalyst, because palladium does not attract light like gold does,” Ringe said. “But our particles have gold cores with palladium at the tips, so they retain their plasmonic properties and the surfaces are catalytic.”

Just as important, Ringe said, the team established characterization techniques that will allow scientists to tune application-specific alloys that report on their catalytic activity in real time.

The researchers analyzed octopods with a variety of instruments, including Rice’s new Titan Themis microscope, one of the most powerful electron microscopes in the nation. “We confirmed that even though we put palladium on a particle, it’s still capable of doing everything that a similar gold shape would do. That’s really a big deal,” she said.

“If you shine a light on these nanoparticles, it creates strong electric fields. Those fields enhance the catalysis, but they also report on the catalysis and the molecules present at the surface of the particles,” Ringe said.

The researchers used electron energy loss spectroscopy, cathodoluminescence and energy dispersive X-ray spectroscopy to make 3-D maps of the electric fields produced by exciting the plasmons. They found that strong fields were produced at the palladium-rich tips, where plasmons were the least likely to be excited.

Ringe expects further research will produce multifunctional nanoparticles in a variety of shapes that can be greatly refined for applications. Her own Rice lab is working on a metal catalyst to turn inert petroleum derivatives into backbone molecules for novel drugs.

Here’s a link to and a citation for the paper,

Resonances of nanoparticles with poor plasmonic metal tips by Emilie Ringe, Christopher J. DeSantis, Sean M. Collins, Martial Duchamp, Rafal E. Dunin-Borkowski, Sara E. Skrabalak, & Paul A. Midgley.  Scientific Reports 5, Article number: 17431 (2015)  doi:10.1038/srep17431 Published online: 30 November 2015

This is an open access paper,

Green tech with single atom platinum catalyst?

There’s something mind boggling to me about the notion of a single atom catalyst. Luckily, an Oct. 5, 2015 news item on Nanowerk describes the research (Note: A link has been removed),

A new generation of platinum-copper catalysts that require very low concentrations of platinum in the form of individual atoms to cleanly and cheaply perform important chemical reactions is reported today by Tufts University researchers in the journal Nature Communications (“Selective hydrogenation of butadiene on platinum copper alloys at the single atom limit”).

An Oct. 9, 2015 Tufts University news release on EurekAlert, which originated the news item, describes the nature of the problem the researchers were trying to resolve and their solution,

Platinum is used as a catalyst in fuel cells, in automobile converters and in the chemical industry because of its remarkable ability to facilitate a wide range of chemical reactions. However, its future potential uses are significantly limited by scarcity and cost, as well as the fact that platinum readily binds with carbon monoxide, which “poisons” the desired reactions, for example in polymer electrolyte membrane (PEM) fuel cells, which are the leading contenders for small-scale and mobile power generation not based on batteries or combustion engines.

The Tufts researchers discovered that dispersing individual, isolated platinum atoms in much less costly copper surfaces can create a highly effective and cost-efficient catalyst for the selective hydrogenation of 1,3 butadiene, a chemical produced by steam cracking of naphtha or by catalytic cracking of gas oil. Butadiene is an impurity in propene streams that must be removed from the stream through hydrogenation in order to facilitate downstream polymer production. The current industrial catalyst for butadiene hydrogenation uses palladium and silver.

Like Sugar in Coffee

Copper, while a relatively cheap metal, is not nearly as catalytically powerful as platinum, noted Professor of Chemistry Charles Sykes, Ph.D., one of the senior authors on the paper. “We wanted to find a way to improve its performance.”

The researchers first conducted surface science experiments to study precisely how platinum and copper metals mix. “We were excited to find that the platinum metal dissolved in copper, just like sugar in hot coffee, all the way down to single atoms. We call such materials single atom alloys,” said Sykes.

The Tufts chemists used a specialized low temperature scanning tunneling microscope to visualize the single platinum atoms and their interaction with hydrogen. “We found that even at temperatures as low as minus 300 degrees F these platinum atoms were capable of splitting hydrogen molecules into atoms, indicating that the platinum atoms would be very good at activating hydrogen for a chemical reaction,” Sykes said.

With that knowledge, Sykes and his fellow chemists turned to long-time Tufts collaborator Maria Flytzani-Stephanopoulos, Ph.D., the Robert and Marcy Haber Endowed Professor in Energy Sustainability at the School of Engineering, to determine which hydrogenation reaction would be most significant for industrial applications. The answer, she said, was butadiene.

The model catalyst performed effectively for that reaction in vacuum conditions in the laboratory, so Flytzani-Stephanopoulos’s team took the study to the next level. They synthesized small quantities of realistic catalysts, such as platinum-copper single atom alloy nanoparticles supported on an alumina substrate, and then tested them under industrial pressure and temperatures.

“To our delight, these catalysts worked very well and their performance was steady for many days,” said Flytzani-Stephanopoulos. “While we had previously shown that palladium would do related reactions in a closed reactor system, this work with platinum is our first demonstration of operation in a flow reactor at industrially relevant conditions. We believe this approach is also applicable to other precious metals if added as minority components in copper.”

Further, the researchers found that the reaction actually became less efficient when they used more platinum, because clusters of platinum atoms have inferior selectivity compared with individual atoms. “In this case, less is more,” said Flytzani-Stephanopoulos, “which is a very good thing.”

Environmental Benefits

Because platinum is at the center of many clean energy and green chemicals production technologies, such as fuel cells, catalytic converters, and value-added chemicals from bio-renewable feedstocks, the new, less expensive platinum-copper catalysts could facilitate broader adoption of such environmentally friendly devices and processes, she added.

The news release goes on to describe this cross-disciplinary partnership,

The work is the latest fruit from a long cross-disciplinary partnership between Sykes and Flytzani-Stephanopoulos.

“Maria and I met more than seven years ago and talked regularly about how to combine our fairly different fields of research into an effective collaboration across the schools of Arts and Sciences and Engineering,” said Sykes. “I had a state-of-the-art microscope that could see and manipulate atoms and molecules, and I wanted to use its unique capabilities to gain insight into industrially important chemical reactions. In the early 2000s, Maria’s group had pioneered the single-atom approach for metals anchored on oxide supports as the exclusive active sites for the water-gas shift reaction to upgrade hydrogen streams for fuel cell use. Catalyst design know-how already existed in her lab. In retrospect, it seems obvious that combining forces would be a ‘natural’ development. Together we embarked on a new direction involving single atom alloys as catalysts for selective hydrogenation reactions. Our microscope was uniquely suited for characterizing the atomic composition of surfaces. We got funding from the National Science Foundation, U.S. Department of Energy and the Tufts Collaborates initiative to pursue this new area of research.”

Sykes and Flytzani-Stephanopoulos have used this approach to design a variety of single atom alloy catalysts that have, in the last two years, sparked international interest.

“Traditionally catalyst development happens by trial and error and screening many materials,” said Flytzani-Stephanopoulos. “In this study we took a fundamental approach to understanding the atomic scale structure and properties of single atom alloy surfaces and then applied this knowledge to develop a working catalyst. Armed with this knowledge, we are now ready to compare the stability of these single atom alloy catalysts to single atom catalysts supported on various oxide or carbon surfaces. This may give us very useful criteria for industrial catalyst design.”

Here’s a link to and a citation for the paper,

Selective hydrogenation of 1,3-butadiene on platinum–copper alloys at the single-atom limit by Felicia R. Lucci, Jilei Liu, Matthew D. Marcinkowski, Ming Yang, Lawrence F. Allard, Maria Flytzani-Stephanopoulos, & E. Charles H. Sykes. Nature Communications 6, Article number: 8550 doi:10.1038/ncomms9550 Published 09 October 2015

This is an open access paper.

Graphene gains metallic powers after laser-burning

Rice University (Texas, US) researchers have developed a technique for embedding metallic nanoparticles in graphene with the hope of one day replacing platinum catalysts in fuel cells. From an August 20, 2015 news item on ScienceDaily,

Laser-induced graphene, created by the Rice lab of chemist James Tour last year, is a flexible film with a surface of porous graphene made by exposing a common plastic known as polyimide to a commercial laser-scribing beam. The researchers have now found a way to enhance the product with reactive metals.

An August 20, 2015 Rice University news release (also on EurekAlert), which originated the news item, provides further description,

With the discovery, the material that the researchers call “metal oxide-laser induced graphene” (MO-LIG) becomes a new candidate to replace expensive metals like platinum in catalytic fuel-cell applications in which oxygen and hydrogen are converted to water and electricity.

“The wonderful thing about this process is that we can use commercial polymers, with simple inexpensive metal salts added,” Tour said. “We then subject them to the commercial laser scriber, which generates metal nanoparticles embedded in graphene. So much of the chemistry is done by the laser, which generates graphene in the open air at room temperature.

“These composites, which have less than 1 percent metal, respond as ‘super catalysts’ for fuel-cell applications. Other methods to do this take far more steps and require expensive metals and expensive carbon precursors.”

Initially, the researchers made laser-induced graphene with commercially available polyimide sheets. Later, they infused liquid polyimide with boron to produce laser-induced graphene with a greatly increased capacity to store an electrical charge, which made it an effective supercapacitor.

For the latest iteration, they mixed the liquid and one of three concentrations containing cobalt, iron or molybdenum metal salts. After condensing each mixture into a film, they treated it with an infrared laser and then heated it in argon gas for half an hour at 750 degrees Celsius.

That process produced robust MO-LIGs with metallic, 10-nanometer particles spread evenly through the graphene. Tests showed their ability to catalyze oxygen reduction, an essential chemical reaction in fuel cells. Further doping of the material with sulfur allowed for hydrogen evolution, another catalytic process that converts water into hydrogen, Tour said.

“Remarkably, simple treatment of the graphene-molybdenum oxides with sulfur, which converted the metal oxides to metal sulfides, afforded a hydrogen evolution reaction catalyst, underscoring the broad utility of this approach,” he said.

Here’s a link to and a citation for the paper,

In situ Formation of Metal Oxide Nanocrystals Embedded in Laser-Induced Graphene by Ruquan Ye, Zhiwei Peng, Tuo Wang, Yunong Xu, Jibo Zhang, Yilun Li, Lizanne G. Nilewski, Jian Lin, and James M. Tour. ACS Nano, Just Accepted Manuscript DOI: 10.1021/acsnano.5b04138 Publication Date (Web): August 18, 2015
Copyright © 2015 American Chemical Society

This paper is open access provided you have an ACS ID, which is a free registration. ACS is the American Chemical Society.

Platinum catalysts and their shortcomings

The problem boils down to the fact that platinum isn’t cheap and so US Dept. of Energy research laboratories are looking for alternatives to or ways of making more efficient use of platinum according to a June 16, 2015 news item on Nanowerk,

Visions of dazzling engagement rings may pop to mind when platinum is mentioned, but a significant share of the nearly half a million pounds of the rare metalExternal link [sic] mined each year ends up in vehicle emission systems and chemical manufacturing plants. The silvery white metal speeds up or enhances reactions, a role scientists call serving as a catalyst, and platinum is fast and efficient performing this function.

Because of its outstanding performance as a catalyst, platinum plays a major role in fuel cells. Inside a fuel cell, tiny platinum particles break apart hydrogen fuel to create electricity. Leftover protons are combined with oxygen ions to create pure water.

Fuel cells could let scientists turn wind into fuel. Right now, electricity generated by wind turbines is not stored. If that energy could be converted into hydrogen to power fuel cells, it would turn a sporadic source into a continuous one.

The problem is the platinum – a scarce and costly metal. Scientists funded by the U.S. Department of Energy’s Office of Science are seeing if something more readily available, such as iron or nickel, could catalyze the reaction.

But, earth-abundant metals cannot simply be used in place of platinum and other rare metals. Each metal works differently at the atomic level. It takes basic research to understand the interactions and use that knowledge to create the right catalysts.

A June 15, 2015 US Department of Energy Office of Science news release, which originated the news item, describes various efforts,

At the Center for Molecular Electrocatalysis, an Energy Frontier Research Center, scientists are gaining new understanding of catalysts based on common metals and how they move protons, the positively charged, oft-ignored counterpart to the electron.

Center Director Morris Bullock and his colleagues showed that protons’ ability to move through the catalyst greatly influences the catalyst’s speed and efficiency. Protons move via relays — clusters of atoms that convey protons to or from the active site of catalysts, where the reaction of interest occurs. The constitution, placement, and number of relays can let a reaction zip along or grind to a halt. Bullock and his colleagues are creating “design guidelines” for building relays.

Further, the team is expanding the guidelines to examine proton movement related to the solutions and surfaces where the catalyst resides. For example, matching the proton-donating abilityExternal link [sic] of a nickel-based catalyst to that of the surrounding liquid, much like matching your clothing choice with the event you’re attending, eases protons’ travels. The benefit? Speed. A coordinated catalyst pumped out 96,000 hydrogen molecules a second — compared to just 27,000 molecules a second without the adjustment.

This and other research at the Energy Frontier Research Center is funded by the DOE Office of Science’s Office of Basic Energy Sciences. The Center is led by Pacific Northwest National Laboratory.

At two other labs, research shows how changing the catalyst’s superstructure, which contains the proton relays and wraps around the active site, can also increase the speed of the reaction. Led by Argonne National Lab’s Vojislav Stamenkovic and Berkeley Lab’s Peidong Yang, researchers created hollow platinum and nickel nanoparticles, a thousand times smaller in diameter than a human hair. The 12-sided particles split oxygen molecules into charged oxygen ions, a reaction that’s needed in fuel cells. The new catalyst is far more active and uses far less platinum than conventional platinum-carbon catalysts.

Building the catalysts begins with tiny structures made of platinum and nickel held in solution. Oxygen from the air dissolves into the liquid and selectively etches away some of the nickel atoms. The result is a hollow framework with a highly active platinum skin over the surface. The open design of the catalyst allows the oxygen to easily access the platinum. The new catalyst has a 36-fold increase in activity compared to traditional platinum–carbon catalysts. Further, the new hollow structure continues to work far longer in operating fuel cells than traditional catalysts.

I think we’re entering the ‘slow’ season newswise so there are likely to be more of these ’roundup’ pieces being circulated in the online nanosciencesphere and, consequently, here. too.

Eco-friendly nitrogen-doped graphene nanoplatelets from South Korea

South Korean researchers from Ulsan National Institute of Science and Technology (UNIST) have devised a new technique to fix nitrogen to graphene, from the July 24, 2013 news item on Azonano,

A simple, low-cost and eco-friendly method of creating nitrogen-doped graphene nanoplatelets (NGnPs), which could be used in dye-sensitized solar cells and fuel cells, is published in Scientific Reports today.

The work, carried out at Ulsan National Institute of Science and Technology (UNIST) in South Korea, could be a step towards replacing conventional platinum (Pt)-based catalysts for energy conversion.

The UNIST July 23, 2013 news release by Eunhee Song, which originated the news item, provides some context for why the technique is exciting interest,

The search for economically viable alternatives to fossil fuels has attracted attention among energy communities because of increasing energy prices and climate change. Solar cells and fuel cells are to be promising alternatives, but Pt-based (platinum-based) electrodes are expensive and susceptible to environmental damage.

Nitrogen fixation is where nitrogen (N2) in the atmosphere is converted into ammonia (NH3). Fixation processes free up nitrogen atoms from their diatomic form to be used in other ways, but nitrogen does not easily react with other chemicals to form new compounds.

The most common method of industrial nitrogen fixation is the Harber-Bosch process, which requires extremely harsh conditions, 200 atm of pressure and 400 °C of temperature.

The UNIST team previously reported that dry ball-milling can efficiently produce chemically modified graphene particles in large quantities*. This research, in Scientific Reports, presents another innovation to improve the materials. Along the way, the research team discovered a novel nitrogen fixation process.

They focus on modifications with nitrogen, developing a technique with direct nitrogen fixation, carbon-nitrogen bond formation, at the broken edges of graphite frameworks using ball-milling graphite in the presence of nitrogen gas.

In my search for this latest paper I found an earlier piece of work based on a wet-chemical reaction and published in the Journal of the American Chemical Society,

Nitrogen-Doped Graphene Nanoplatelets from Simple Solution Edge-Functionalization for n-Type Field-Effect Transistors by Dong Wook Chang, Eun Kwang Lee, Eun Yeob Park, Hojeong Yu, Hyun-Jung Choi, In-Yup Jeon, Gyung-Joo Sohn, Dongbin Shin, Noejung Park, Joon Hak Oh, Liming Dai, and Jong-Beom Baek. J. Am. Chem. Soc., 2013, 135 (24), pp 8981–8988 DOI: 10.1021/ja402555n Publication Date (Web): May 27, 2013
Copyright © 2013 American Chemical Society

That paper is behind a paywall while this latest work featuring a ‘dry’ technique is open access,

Direct nitrogen fixation at the edges of graphene nanoplatelets as efficient electrocatalysts for energy conversion by In-Yup Jeon, Hyun-Jung Choi, Myung Jong Ju, In Taek Choi, Kimin Lim, Jaejung Ko, Hwan Kyu Kim, Jae Cheon Kim, Jae-Joon Lee, Dongbin Shin, Sun-Min Jung, Jeong-Min Seo, Min-Jung Kim, Noejung Park, Liming Dai, & Jong-Beom Baek. Scientific Reports 3, Article number: 2260 doi:10.1038/srep02260 Published 23 July 2013

This team has been quite prolific recently. I last mentioned them in a June 7, 2013 posting highlighting another iteration of this ‘dry’ technique.

Canadian and Japanese researchers create new technique for using iron nanoparticles in greener hydrogenation process

McGill University’s Audrey Moores and her team’s latest green chemistry work with researchers at RIKEN (The Institute of Physical and Chemical Research, Wako, Japan) and the Institute for Molecular Science (Okazaki, Japan) is featured in a June 27, 2013 news item on Nanowerk,

Researchers from McGill University, RIKEN (The Institute of Physical and Chemical Research, Wako, Japan) and the Institute for Molecular Science (Okazaki, Japan) have discovered a way to make the widely used chemical process of hydrogenation more environmentally friendly – and less expensive.

Hydrogenation is a chemical process used in a wide range of industrial applications, from food products, such as margarine, to petrochemicals and pharmaceuticals. The process typically involves the use of heavy metals, such as palladium or platinum, to catalyze the chemical reaction. While these metals are very efficient catalysts, they are also non-renewable, costly, and subject to sharp price fluctuations on international markets.

Because these metals are also toxic, even in small quantities, they also raise environmental and safety concerns. Pharmaceutical companies, for example, must use expensive purification methods to limit residual levels of these elements in pharmaceutical products. Iron, by contrast, is both naturally abundant and far less toxic than heavy metals.

Previous work by other researchers has shown that iron nanoparticles — tiny pieces of metallic iron — can be used to activate the hydrogenation reaction. Iron, however, has a well-known drawback: it rusts in the presence of oxygen or water. When rusted, iron nanoparticles stop acting as hydrogenation catalysts. This problem, which occurs with so much as trace quantities of water, has prevented iron nanoparticles from being used in industry.

The June 27, 2013 McGill University news release on EurekAlert, which originated the news item, provides details about the new technique,

The key to this new method is to produce the particles directly inside a polymer matrix, composed of amphiphilic polymers based on polystyrene and polyethylene glycol. The polymer acts as a wrapping film that protects the iron surface from rusting in the presence of water, while allowing the reactants to reach the water and react.

This innovation enabled the researchers to use iron nanoparticles as catalyst in a flow system, raising the possibility that iron could be used to replace platinum-series metals for hydrogenation under industrial conditions.

“Our research is now focused on achieving a better understanding of how the polymers are protecting the surface of the iron from water, while at the same time allowing the iron to interact with the substrate,” says Audrey Moores, an assistant professor of chemistry at McGill and co-corresponding author of the paper.

“The approach we have developed through this collaboration could lead to more sustainable industrial processes,” says Prof. Uozumi [Prof. Yasuhiro Uozumi of Riken]. “This technique provides a system in which the reaction can happen over and over with the same small amount of a catalytic material, and it enables it to take place in almost pure water — the green solvent par excellence.”

I last wrote about greener chemistry and iron nanoparticles in a March 28, 2012 posting concerning some work at the University of Toronto while the last time McGill, green chemistry, and Audrey Moores were mentioned here was in a Jan. 10, 2011 posting concerning ‘nanomagnetics.

For those who are interested in this latest work from McGill, here’s a link to and a citation for the published paper,

Highly efficient iron(0) nanoparticle-catalyzed hydrogenation in water in flow by Reuben Hudson, Go Hamasaka, Takao Osako, Yoichi M. A. Yamada, Chao-Jun Li, Yasuhiro Uozumi, and Audrey Moores.
Green Chem., 2013, Advance Article DOI: 10.1039/C3GC40789F

First published online 27 Jun 2013

This paper is behind a paywall.

Phyto-mining and environmental remediation flower in the United Kingdom

Researchers on a £3 million research programme called “Cleaning Land for Wealth” (CL4W) are confident they’ll be able to use flowers and plants to clean soil of poisonous materials (environmental remediation) and to recover platinum (phyto-mining). From the Nov. 21, 2012 news item on Nanowerk,

A consortium of researchers led by WMG (Warwick Manufacturing Group) at the University of Warwick are to embark on a £3 million research programme called “Cleaning Land for Wealth” (CL4W), that will use a common class of flower to restore poisoned soils while at the same time producing perfectly sized and shaped nano sized platinum and arsenic nanoparticles for use in catalytic convertors, cancer treatments and a range of other applications.

The Nov. 20, 2012 University of Warwick news release, which originated the news item, describes both how CL4W came together and how it produced an unintended project benefit,

A “Sandpit” exercise organised by the Engineering and Physical Sciences Research Council (EPSRC) allowed researchers from WMG (Warwick Manufacturing group) at the University of Warwick, Newcastle University, The University of Birmingham, Cranfield University and the University of Edinburgh to come together and share technologies and skills to come up with an innovative multidisciplinary research project that could help solve major technological and environmental challenges.

The researchers pooled their knowledge of how to use plants and bacteria to soak up particular elements and chemicals and how to subsequently harvest, process and collect that material. They have devised an approach to demonstrate the feasibility in which they are confident that they can use common classes of flower and plants (such as Alyssum), to remove poisonous chemicals such as arsenic and platinum from polluted land and water courses potentially allowing that land to be reclaimed and reused.

That in itself would be a significant achievement, but as the sandpit progressed the researchers found that jointly they had the knowledge to achieve much more than just cleaning up the land.

As lead researcher on the project Professor Kerry Kirwan from WMG at the University of Warwick explained:

“The processes we are developing will not only remove poisons such as arsenic and platinum from contaminated land and water courses, we are also confident that we can develop suitable biology and biorefining processes (or biofactories as we are calling them) that can tailor the shapes and sizes of the metallic nanoparticles they will make. This would give manufacturers of catalytic convertors, developers of cancer treatments and other applicable technologies exactly the right shape, size and functionality they need without subsequent refinement. We are also expecting to recover other high value materials such as fine chemicals, pharmaceuticals, anti-oxidants etc. from the crops during the same biorefining process.”

I last mentioned phyto-mining in my Sept. 26, 2012 post with regard to an international project being led by researchers at the University of York (UK).  The biorefining processes (biofactories) mentioned by Kirwan takes the idea of recovering platinum, etc. one step beyond phyto-mining recovery.

Here’s a picture of the flower (Alyssum) mentioned in the news release,

Alyssum montanum photographed by myself in 1988, Unterfranken, Germany [http://en.wikipedia.org/wiki/Alyssum]

From the Wikipedia essay (Note: I have removed links],

Alyssum is a genus of about 100–170 species of flowering plants in the family Brassicaceae, native to Europe, Asia, and northern Africa, with the highest species diversity in the Mediterranean region. The genus comprises annual and perennial herbaceous plants or (rarely) small shrubs, growing to 10–100 cm tall, with oblong-oval leaves and yellow or white flowers (pink to purple in a few species).