Electrochemical dissolution of platinum in an ionic liquid

Recycling platinum is a difficult, complicated process. The first step is the dissolution of the used platinum. Because platinum is a very special precious metal, this isn’t so easy. The solvents used for this are usually highly corrosive aqua regia, a mixture of nitric and hydrochloric acids, or a highly oxidizing mixture of sulfuric acid and hydrogen peroxide known as piranha. There are also electrochemical recycling processes, but these mostly require highly toxic electrolytes or corrosive media, or they release toxic gases. They also suffer from insufficient current densities and passivation of the electrodes.

Huang and Chen have now developed a novel process that avoids all of these disadvantages. In this procedure, platinum is electrochemically dissolved in a mixture of zinc chloride and a special ionic liquid. An ionic liquid is an organic salt that is in a melted state at temperatures below 100 °C. Ionic liquids are considered environmentally friendly solvents because they have very low vapor pressures and are very thermally stable, so they do not release any toxic substances. They also have high ionic conductivity, which makes them very useful in electrochemical applications.

The used platinum is introduced in the form of an electrode, a voltage is applied, and the surrounding ionic liquid heated to about 100 °C. The platinum then dissolves surprisingly fast. The dissolved platinum can then be removed on a carrier electrode, either as the pure metal or as a zinc alloy, without prior treatment of the solution. The scientists are optimistic that this process can also be adapted for other precious metals.

Says Huang: “We are doing our best to solve the problem about the effective use of precious metals. The recycling of precious metals is a possible strategy. Even now, we do not think we have found the best process. We will continuously modify the process in order to extend its applications or look for a much better one”.

More information: Angewandte Chemie International Edition, DOI: 10.1002/anie.201107997

Provided by Wiley

Clearing a potential road block to bisabolane: Key enzyme structure identified

The JBEI research team, led by bioengineers Paul Adams and Jay Keasling, solved the protein crystal structure of an enzyme in the Grand fir (Abies grandis) that synthesizes bisabolene, the immediate terpene precursor to bisabolane. The performance of this enzyme – the Abies grandis ?-bisabolene synthase (AgBIS) – when engineered into microbes, has resulted in a bottleneck that hampers the conversion by the microbes of simple sugars into bisabolene.

“Our high resolution structure of AgBIS should make it possible to design changes in the enzyme that will enable microbes to make bisabolene faster,” says Adams, a leading authority on x-ray crystallography. “It should also enable us to engineer out inhibition effects that slow throughput, and perhaps also  engineer the enzyme to produce other kinds of fuels similar to bisabolane.”

Adams, who heads JBEI’s Technologies Division, is the corresponding author of a paper describing this work in the Cell Press journal Structure. The paper is titled “Structure of a Three-Domain Sesquiterpene Synthase: A Prospective Target for Advanced Biofuels Production.” Co-authoring it with Adams and Keasling were Ryan McAndrew, Pamela Peralta-Yahya, Andy DeGiovanni, Jose Pereira and Masood Hadi.

JBEI is one of three DOE Bioenergy Research Centers established by DOE’s Office of Science to advance the technology for the commercial production of advanced biofuels. It is a multi-institutional partnership led by the Lawrence Berkeley National Laboratory (Berkeley Lab) and headquartered in Emeryville, CA.

This past fall, JBEI researchers identified bisabolane as a potential new advanced biofuel that could replace D2 diesel, today’s standard fuel for diesel engines, with a clean, green, renewable alternative that’s produced in the United States. Using the tools of synthetic biology, the researchers engineered strains of bacteria and yeast to produce bisabolene from simple sugars, which was then hydrogenated into bisabolane. While showing much promise, the yields of bisabolene have to be improved for microbial-based production of bisabolane fuel to be commercially viable.

“The inefficient terpene synthase enzyme is one of the bottlenecks in the metabolic pathway used by the engineered microbes,” says Peralta-Yahya, a lead member of the earlier JBEI team as well as the current team. “Knowing the AgBIS crystal structure will guide us in engineering it for improved catalytic efficiency and stability, which should bring our bisabolene yields closer to economic competitiveness.”

Peralta-Yahya and her colleagues determined that the AgBIS enzyme consists of three helical domains, the first three-domain structure ever found in a synthase of sesquiterpenes – terpene compounds that contain 15 carbon atoms. The discovery of this unique structure holds importance on several fronts, as co-lead author of the Structure paper McAndrew explains.

“That we found the structure of AgBIS to be more similar to diterpene (two carbon terpene compounds) synthases not only provides us with insight into the function of these less well characterized enzymes, it also provides us with clues to the evolutionary heritage as the archetypal three-domain terpenoid synthases became two-domain sesquiterpene synthases in plants.

Furthering our knowledge of the structures and functions of terpenoid synthases may prove to have abundant practical applications aside from advanced biofuels because these enzymes produce a wide variety of specialized chemicals.”

Solving the three-dimensional crystal structure of AgBIS was made possible by the protein crystallography capabilities of Berkeley Lab’s Advanced Light Source (ALS), a DOE Office of Science national user facility for synchrotron radiation, and the first of the world’s third generation light sources. For this work, the JBEI team used three of the five protein crystallography beamlines operated by the Berkeley Center for Structural Biology (BCSB) – beamlines 8.2.1, 8.2.2, and 5.0.3.

“We needed to use multiple beamlines because we collected data on several crystals – the protein by itself, and the protein with different inhibitors/cofactors,” says Adams, who headed the  BCSB from 2004 to 2011. “Also, the approach we used to solve the AgBIS structure required high flux tunable x-rays such as those provided at 8.2.1 and 8.2.2, which are superbend beamlines.”

Provided by Lawrence Berkeley National Laboratory (news : web)

SRNL research paves way for portable power systems

SRNL has demonstrated a practical path to portable power systems based on alane and similar high capacity hydrogen storage materials that provide the sought-after high specific energy, which means the amount of energy per weight. Their accomplishments to date include developing a lower-cost method of producing alane, developing a method to dramatically increase the amount of hydrogen it releases, and demonstrating a working system powering a 150 W fuel cell. Portable power equipment manufacturers are looking for systems that can provide specific energies greater than 1000 watt-hours per kilogram (Wh/kg); that's more than 2 to 3 times the capacity of the best primary lithium batteries today. "Higher specific energy means more energy per weight," said SRNL's Dr. Ted Motyka. "The goal is to provide sufficient energy to a system that is light enough to be carried by a soldier or used in unmanned aircraft and other applications where weight is a factor."

Hydrogen, at 33,000 Wh/kg, has the highest specific energy of any fuel, so it is a natural candidate to fuel such high-capacity systems. The challenge, however, has been developing a material for storing hydrogen with both the high capacity and the low weight needed for portable systems.

SRNL has been working for years on developing several light-weight, high capacity solid-state hydrogen storage materials for automotive applications. While most of these materials do not meet all the various requirements needed for automotive applications, many may be viable for small portable power systems.

One of the most promising materials is aluminum hydride, (AlH3) or alane. Alane, while not a new material, has only in the last few years been considered as a hydrogen storage material for fuel cell applications. SRNL researchers are among only a handful of researchers, worldwide, currently working with alane and beginning to unwrap its material and engineering properties.

Dr. Motyka, Dr. Ragaiy Zidan and Dr. Kit Heung, all of SRNL, led a team to characterize and optimize alane as a hydrogen storage material, develop a small hydrogen storage vessel containing alane, and demonstrate hydrogen release at delivery rates suitable for powering small commercial fuel cells. The results of that work are attracting interest from several commercial companies working in the area of portable power systems.

Alane is one of the classes of materials known as chemical hydrogen storage materials. Like metal hydrides, chemical hydrogen storage materials provide a solid-state storage medium for hydrogen. Unlike metal hydrides, however, chemical hydrogen storage materials, like alane, do not readily reabsorb hydrogen, so once their hydrogen is released the material must be chemically reprocessed to restore its hydrogen. An advantage of alane is its very high hydrogen capacities; it can store twice as much hydrogen, in the same volume, as liquid hydrogen, and can do so at the very high gravimetric capacity of 10 wt%. Alane also exhibits very favorable discharge conditions, making it one of the ideal chemical hydrogen storage materials.

Among the biggest challenges the team addressed were the limited amount of readily available commercial alane, and its high cost to produce – which could be significant impediments to widespread use. As part of this project, they initially developed a bench-scale system to produce the quantities of alane needed for experimental and optimization studies. This work led to the development of a new and potentially lower cost process for producing alane. "Our process overcomes some of the handicaps of traditional methods for producing alane," says Dr. Zidan. "This novel method minimizes the use of solvents, and is able to produce pure, halide-free alane."

Work led by Dr. Zidan also resulted in a process to increase the amount of hydrogen that can be extracted from alane. This two-step process was found to double the amount of hydrogen that can be liberated from alane using a traditional one-step process.

A major part of this project was to evaluate alane systems for compatibility with small fuel cell applications. Preliminary results on a proof-of-concept vessel containing approximately 22 grams of alane showed that the system could scale nicely to meet the required hydrogen release rate for a small 100-watt fuel cell system. Based on those results a larger system containing 240 grams of alane was designed, fabricated and tested with a 150 watt commercial fuel cell. The results show that the system was able to operate the fuel cell at near full power for over three hours and at reduced power for several more hours.

Provided by Savannah River National Laboratory

Longer-lasting chemical catalysts

Attaching metal catalysts to an insoluble polymer support, which is recoverable at the end of a reaction by simple filtration, is far from a new idea. Traditionally, chemists attached their metal catalyst to an insoluble polymer resin. However, the metal invariably leached out of the polymer over time so the catalysts were still slowly lost.

Yamada and his colleagues’ approach, in contrast, integrated the metal into the polymer matrix, which trapped it much more effectively. The researchers achieved this level of integration by starting with a soluble polymer precursor instead of an insoluble resin. This material contains imidazole units, a chemical structure known to bind strongly to metals such as palladium (Fig. 1). An insoluble composite material formed only after the researchers added palladium to the mixture because it causes the imidazole units to self-assemble around atoms of the metal—a process that they call ’molecular convolution’.

Scanning electron microscopy revealed that the resulting polymer–palladium globules ranged from 100 to 1,000 nanometers in diameter, which aggregated into a highly porous structure reminiscent of a tiny bathroom sponge. “This sponge-like insoluble material can easily capture substrates and reactants from the solution, which readily react with metal species embedded in the sponge,” says Yamada.

The researchers showed that the catalyst is highly active as well as reusable; it is the most active catalyst yet reported for a carbon–carbon bond-forming reaction known as an allylic arylation. They also reused the catalyst multiple times with no apparent loss of activity, and detected no leaching of palladium from the polymer into the reaction mixture.

Yamada and colleagues are now developing a range of composite catalysts incorporating different metals that can catalyze many other kinds of reactions. “These extremely highly active and reusable catalysts will provide a safe and highly efficient chemical process, which we hope will be adopted for industrial chemical process,” Yamada says.

More information: Sarkar, S.M., et al. A highly active and reusable self-assembled poly(imidazole/palladium) catalyst: allylic arylation/alkenylation. Angewandte Chemie International Edition 50, 9437–9441 (2011) DOI: 10.1002/anie.201103799

Provided by RIKEN (news : web)