Dec 13, 2013 Sponge
Catalysts – substances that enable or speed up the rates of chemical reactions without themselves being chemically changed – are used to initiate virtually every industrial manufacturing process that involves chemistry. Metallic catalysts are the workhorses with platinum being one of the best.
In industry catalysts typically operate under pressures ranging from millitorr to atmospheres, and at temperatures ranging from room to hundreds of degrees Celsius. However, surface science experiments have traditionally been performed under high vacuum conditions and low temperatures.
Now a study led by Gabor Somorjai and Miquel Salmeron of Berkeley Lab’s Materials Sciences Division shows that under high pressure, comparable to the pressures at which many industrial technologies operate, nanoparticle clusters of platinum potentially can out-perform the single crystals of platinum now used in fuel cells and catalytic converters. A new path to researching better catalyst design is now opened up.
At about $2,000 an ounce, platinum is much more expensive than gold. The high cost of the raw material presents major challenges for the future wide scale use of platinum in fuel cells. This is a matter of intense concern as fuel cells offer a huge gain in efficiency.
Somorjai, one of the world’s foremost experts on surface chemistry and catalysis explains, “We’ve discovered that the presence of carbon monoxide molecules can reversibly alter the catalytic surfaces of platinum single crystals, supposedly the most thermodynamically stable configuration for a platinum catalyst. This indicates that under high-pressure conditions, single crystals of platinum are not as stable as nanoclusters, which actually become more stabilized as carbon monoxide molecules are co-adsorbed together with platinum atoms.”
Salmeron, a leading authority on surface imaging and developer of the in situ imaging and spectroscopic techniques used in this study and also the director of Berkeley Lab’s Materials Sciences Division expounds with, “Our results also demonstrate that the limitations of traditional surface science techniques can be overcome with the use of techniques that operate under realistic conditions.”
They’re jumping from experimental theory into real world conditions in the lab.
For the study, single crystal platinum surfaces were examined under high-pressure. The surfaces were structured as a series of flat terraces about six atoms wide separated by atomic steps. Such structural features are common in metal catalysts and are considered to be the active sites where catalytic reactions occur. Single crystals are used as models for these features.
The pair of scientists coated the platinum surfaces with carbon monoxide gas, a reactant involved in many important industrial catalytic processes, including the Fischer-Tropsch process for making liquid hydrocarbons, the oxidation process in automobile catalytic converters, and the degradation of platinum electrodes in hydrogen fuel cells.
As carbon monoxide coverage of the platinum crystal surfaces approached 100-percent, the terraces began to widen – the result of increasing lateral repulsion between the individual molecules. When the surface pressure reached one torr, the terraces fractured into nanometer-sized clusters. The terraces were re-formed upon removal of the carbon monoxide gas.
Somorjai said, “Our observations of the large-scale surface restructuring of stepped platinum highlights the strong connection between coverage of reactant molecules and the atomic structure of the catalyst surface. The ability to observe catalytic surfaces at the atomic and molecular levels under actual reaction conditions is the only way such a phenomenon could be detected. Such conditions will likely inhibit any surface restructuring process that requires the overcoming of even moderate activation barriers.”
Salmeron takes us to the next step, “The unanswered question today is what are the geometry and location of the catalyst atoms when the surfaces are covered with dense layers of molecules, as occurs during a chemical reaction.”
There’s the gold, er platinum moment – getting to the surface structures that make optimal use of the expensive active catalyst and the coming experiments that can guide engineers to better designs.
Somorjai and Salmeron have collaborated many years on the development of instrumentation and techniques that enable them to do catalysis studies under realistic conditions. They now have at their disposal unique high-pressure scanning tunneling microscopes (STM) and an ambient pressure x-ray photoelectron spectroscopy (AP-XPS) beamline operating at the Berkeley Lab’s Advanced Light Source, a premier source of synchrotron radiation for scientific research.
“With these two resources, we can image the atomic structure and identify the chemical state of catalyst atoms and adsorbed reactant molecules under industrial-type pressures and temperatures,” Salmeron says.
Perhaps lots more people in the field need these instruments. The STM images revealed the formation of nanoclusters on the platinum crystal surfaces, and the AP-XPS spectra revealed a change in carbon monoxide electron binding energies.
The team then collaborated with Lin-Wang Wang, a theorist in Berkeley Lab’s Computational Sciences Division, explained the change in structure as the result of the relaxation of the strong repulsion between carbon monoxide molecules that arises from their very high density on the surface when in equilibrium with elevated pressures of the gas.
Looking forward Somorjai said, “In the future, the use of these stable platinum nanoclusters as fuel cell catalysts may help to boost performance and reduce costs.” The next step for the Berkley research team will be to determine whether other adsorbed reactants, such as oxygen or hydrogen, also result in the creation of nanoclusters in platinum. They also want to know if nanoclusters can be induced in other metal catalysts as well, such as palladium, silver, copper, rhodium, iron and cobalt. We want to know as well.
Somorjai gets to the point with, “If this nanoclustering is a general phenomenon, it will have major consequences for the type of structures that catalysts must have under high-pressure, high-temperature catalytic reaction conditions.”
The paper is in Science titled “Break-Up of Stepped Platinum Catalyst Surfaces by High CO Coverage.” It’s a good read professionally done and the supporting materials (pdf) simply very pretty to see. This is very welcome research result. Perhaps more researchers can follow on now with more ideas. That platinum cost matter needs cracked.
The original is here: New Energy and Fuel
Purdue University researchers have genetically engineered a super yeast using genes from a fungus to re-engineer a yeast’s genetic code. The improved a strain of yeast can produce more biofuel from cellulosic plant material by fermenting all five types of the plant’s sugars.
Nancy Ho, a research professor of chemical engineering at Purdue explains, “Natural yeast can ferment three sugars: galactose, manose and glucose. The original yeast (Professor Ho developed) added xylose to that, and now the fifth, arabinose, has been added.” Adding the fungus genes allowed the yeast to create necessary enzymes to get through those steps. That about covers the sugars obtainable. It’s serious news for any ethanol production.
Thus the sugars found in plant material biomass such as corn stalks, straw, switchgrass and other crop residues could be used as ethanol fuel sources. The fungus genes should increase the amount of ethanol that can be produced from cellulosic material. Arabinose makes up about 10 percent of the sugars contained in those plants. That’s part one.
The resulting yeast, if it can be produced for use in economically viable commercial quantities, may have an important impact on ethanol production. Just what a complete commercial process would entail isn’t discussed, but having new sources of biomass material outside of the corn and sugar cane crops may serve to promote more effort in ethanol powered fuel cells. Oxidizing or burning ethanol by combustions still leaves the big majority of available energy unused. More is good, cheaper is better, but abundance at low cost should incite more effort in the fuel cell area.
Part two is the Purdue group has been able to develop strains that are more resistant to acetic acid. Acetic acid, the main ingredient in vinegar, is natural to plants and released with sugars before the fermentation process during ethanol production. Acetic acid gets into yeast cells and slows the fermentation process, adding to the cost of ethanol production.
Nathan Mosier, an associate professor of agricultural and biological engineering at Purdue explains, “It inhibits the microorganism. It doesn’t produce as much biofuel, and it produces it more slowly. If it slows down too much, it’s not a good industrial process.”
The group accomplished the choice of genetic change by compared the genes in the more resistant strains to others to determine which genes made the yeast more resistant to acetic acid. By improving the expression of those genes, they increased the yeast’s resistance.
The group is reporting achieving about 72.5% yield from five-sugar mixtures containing glucose, galactose, mannose, xylose, and arabinose in the published fungus gene insertion paper. This co-fermentation of five-sugar mixture is important and crucial for application in industrial economical ethanol production using lignocellulosic biomass as the feedstock.
Research assistant professor of agricultural and biological engineering Miroslav Sedlak said, “This gave the yeast a new tool set. This gives the yeast the tools it needs to get arabinose into the chain.”
Having the acetic acid genetics in hand might be the most immediately useful segment of the group’s work. When the results of the paper on the acetic acid are integrated better yeasts could result further increasing the efficiency of biological production methods for biofuels.
This is good work. It will get serious attention form the ethanol community as cost cutting and efficiency is key to the industry’s growth and survival in a volatile supply and price situation. Ethanol is getting more attention across the world than national media shows, and ethanol fuel cells could be available soon as well.
While it doesn’t go to the costs of the preprocessing needed to release the sugars, all available sugars going to ethanol increases the economic output thus allowing more costs to preprocessing. The effort in preprocessing isn’t over by any means, but this is progress and when factored in to production cost analysis, industrial facility development will come quicker. Perhaps marginal farming potential and subsistence farming might get a boosted sooner than later.
The original post is created by: New Energy and Fuel
Steven Brown, staff microbiologist in the Biosciences Division at the Department of Energy’s Oak Ridge National Laboratory and one of the inventors of the improved Z. mobilis strain explains, “Microbes have been breaking down plant material to access sugars for millennia, so plants have evolved to have very sophisticated cell structures that make accessing these sugars difficult.”
As the science stands in production now, biomass materials like corn stover, switchgrass and miscanthus must undergo a series of pretreatments to loosen the cellular structure enough to extract the sugar from the cellulose. Brown said these treatments add new challenges because, although they are necessary, they create a range of chemicals known as inhibitors that stall or stop microorganisms like Z. mobilis from performing the fermentation.
Brown said, “There are two ways to combat recalcitrance, or the difficulty created by the inhibitors. One way is to remove the inhibitors, but this method is very expensive and would not help biofuels become cost-competitive with gasoline. The second way is what we do, which is to develop microorganisms that are more tolerant of the inhibitors.”
The Oak Ridge team has for the first time identified a key Z. mobilis gene and shown the strain’s improved efficiency and its potential use for more cost-effective biofuel production. The non-mutated strain of Z. mobilis cannot grow in the presence of one of the predominant inhibitors, acetate. However, when gene nhaA is over-expressed by inserting a slice of DNA containing the gene into the non-mutated strain, the bacterium can withstand acetate in its environment. An open access paper on their work was published online 19 May in the Proceedings of the National Academy of Sciences. (Abstract link)
Round two! Brown and lead author Shihui Yang did not stop with Z. mobilis but looked at related genes in other microorganisms and found that the method translates in different organisms. Yang said, “We took this gene and integrated it into a strain of yeast, and the improvements carried over into the yeast.”
Brown suggests this method of processing biomass for ethanol has the potential to become a “tool kit” – a combination of mutant genes that reduce the impact of specific inhibitors. The tool kit could expand quickly, too, as scientists now have more advanced DNA sequencing technology available to identify and resequence genes. More broadly, the researchers say, their study shows that the application of biology systems tools holds promise for rational industrial microbial strain development. The combination of classical and biology systems tools used in their work is a paradigm for accelerated industrial strain improvement and combines benefits of few distinguishable types of propositional assumptions with detailed, rapid, mechanistic studies. They believe they have a kind of lab test method coming up.
The Oak Ridge microbiologists are currently sequencing other microorganisms used in biofuels production that could also be advantageous if genetically altered to resist different types of inhibitors.
Brown said, “The DNA sequencer we used was unavailable as recently as five years ago, and it has unprecedented sequencing capabilities. It is 4,000 times more powerful than the machine that finished sequencing the human genome almost a decade ago.”
Yang looks further out, “By looking at the behavioral response to the genetic changes in this bacteria, Zymomonas, we can then look forward to improving other bacteria.”
It’s a good start. Acetate is a major problem in conditioning cellulose. Should the Oak Ridge team spread out the gene search perhaps the other inhibitors will fall as well.
Ethanol – the fuel many complain vociferously about – may be coming to a threshold of process development that could open up more plants as sources for production. The use of cane sugar and corn in Brazil and the U.S. drive many to outrage over the idea of competition between foods and fuels. While the issue is pointless, ethanol as a light alcohol has great potential as a fuel cell fuel, a gasoline additive and with other alcohols in gasoline substitutes. The complaints are little but food for the foolish.
When researchers at the US Department of Energy’s Oak Ridge National Laboratory have identified a key gene that can yield more cost-competitive cellulosic ethanol the complaint matters will change course, probably to land use choices. But the idea, a much wider source of plants to produce cellulose would bring more marginal land into productivity where farming is now a low net income proposition.
Source: New Energy and Fuel
Platinum – the joy of a jewelry designer – the bane of a catalyst user, and in the current economy its the most expensive element on earth. Platinum is the cost problem for fuel cells. Developing alternatives are treasure hunts of the highest caliber.
Chemists at Brown University have demonstrated that a nanoparticle with a palladium core and an iron-platinum shell outperforms commercially available pure-platinum catalysts and lasts longer. A writer could be tempted to repeat, bold or add emphasis. If the Brown team’s work can be replicated and can show a commercial path they have the first treasure. The race to the ‘Platinum Replacement Prize’ is on.
The team’s leaders Shouheng Sun, professor of chemistry at Brown and co-author of the paper and Brown graduate student and co-author Vismadeb Mazumder’s findings are now reported in the Journal of the American Chemical Society.
The precious metal platinum has two major downsides: It is very expensive, and it breaks down over time in fuel-cell reactions.
The Brown University chemists report a promising advance with the new study. The team built a unique palladium core and an iron-platinum shell nanoparticle that uses far less platinum yet performs more efficiently and lasts longer than commercially available pure-platinum catalysts at the cathode end of fuel-cell reactions.
The research team created a five-nanometer palladium (Pd) core and enclosed it within a shell consisting of iron and platinum (FePt). The trick, Mazumder said, was in molding a shell that would retain its shape and require the smallest amount of platinum to pull off an efficient reaction. The team created the iron-platinum shell by decomposing iron pentacarbonyl Fe(CO)5 and reducing platinum acetylacetonate Pt(acac)2, a technique Professor Sun first reported in a 2000 Science paper. The result is a shell that uses only 30 percent as much platinum, although the researchers say they expect they will be able to make thinner shells and use even less platinum.
Mazumder said in accrediting Sun’s earlier work, “If we don’t use iron pentacarbonyl, then the platinum doesn’t form on the (palladium) core.”
The test results, Ready? The team demonstrated for the first time that they could consistently produce the unique core-shell structures. In the laboratory performance tests the palladium/iron-platinum nanoparticles generated 12 times more current than commercially available pure-platinum catalysts at the same catalyst weight. The output also remained consistent over 10,000 cycles, at least ten times longer than commercially available platinum models that begin to deteriorate after 1,000 cycles. That’s a “Wow!” moment.
The team created iron-platinum shells that varied in width from one to three nanometers. In lab tests, the group found the one-nanometer shells performed best.
Mazumber says, “This is a very good demonstration that catalysts with a core and a shell can be made readily in half-gram quantities in the lab, they’re active, and they last. The next step is to scale them up for commercial use, and we are confident we’ll be able to do that.”
Mazumder and Sun are studying why the palladium core increases the catalytic abilities of the iron platinum shell, although they think it has something to do with the transfer of electrons between the core and shell metals. To that end, they are trying to use a chemically more active metal than palladium as the core to confirm the transfer of electrons in the core-shell arrangement and its importance to the catalyst’s function.
The team leaders are hinting that this, a stunning of a result as it is, has room for more research and innovation.
The rest of the team and coauthors includes Miaofang Chi and Karren More at the Oak Ridge National Laboratory. The U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy funded the research as part of its Fuel Cell Technologies Program.
The issue in a fuel cell is the chemistry known as oxygen reduction reaction takes place at the fuel cell’s cathode, creating water as its only waste. Sun explains the cathode is also where up to 40 percent of a fuel cell’s efficiency is lost, so “this is a crucial step in making fuel cells a more competitive technology with internal combustion engines and batteries.”
For those of us with a deep-seated intuition that fuel cells are a critical segment of fuel to energy conversion power units for the future, the Brown University research team’s paper is the most important news in months. At lower cost with useful cycles measured up to 10,000 times with 12 times the current flow – this writer is . . . just thrilled.
Congratulations to Professor Sun, Mazumber, Chi and More. To use an overworked word, but applies here, it’s a breakthrough.
Here is the original: New Energy and Fuel