In a lab in Princeton University’s ultra-sleek chemistry building, researchers toil in a modern-day hunt for an elusive power: alchemy.
Throughout the centuries, alchemists tried in vain to transform common metals like iron and lead into precious ones like gold or platinum. Today, Paul Chirik, a professor of chemistry at Princeton, has managed a new twist on the timeworn pursuit. Chirik, 39, has learned how to make iron function like platinum, in chemical reactions that are crucial to manufacturing scores of basic materials. While he can’t, sadly, transmute a lump of iron ore into a pile of valuable jewelry, his version of alchemy is far more practical, and the implications are wide-ranging.
The process could herald a new era of flexible manufacturing technologies, while enabling companies to steer clear of scarce elements as prices rise or obtaining them becomes environmentally or geopolitically risky. “No chemist would think lithium was in short supply,” Chirik said, “but what happens if you put a lithium battery in every car? This is why chemistry needs to be ahead of the curve. We need to have adaptable solutions.”
Despite the cost and relative scarcity of precious metals like iridium, platinum, and rhodium, we rely on them to manufacture products from denim to beer, pharmaceuticals to fuel cells. The elements are used as catalysts, substances that kick off or enable chemical reactions.
Chirik’s work involves dissolved catalysts, which are mixed into the end product. The molecules of the catalyst dissipate during the reaction. For instance, a solution containing platinum is used to make silicone emulsifiers, compounds that in turn feed products like makeup, cookware and glue. Tiny amounts of the expensive metal are scattered in all these things; your jeans, for instance, contain unrecoverable particles of platinum.
“We’re not about to run out of platinum,” said Matthew Hartings, a chemist at American University in Washington, “but this process spends that platinum in a non-sustainable way.”
Chirik’s chemistry essentially wraps an iron molecule in another, organic molecule called a ligand. The ligand alters the number of electrons available to form bonds. It also serves as a scaffold, giving the molecule shape. “Geometry is really important in chemistry,” Hartings said. Chirik’s “ligands help the iron to be in the right geometry to help these reactions along.”
In addition to iron, Chirik’s lab also works with cobalt, which sits beside iron on the periodic table. Using cobalt, Chirik said, the scientists have generated “a whole new reaction that no one has ever seen before.” It produces new types of plastics using very inexpensive starting materials.
But the price of cobalt has shot up since the lab first began its research, thanks to the element’s use in the flat batteries that power gadgets like iPads and iPhones. “The iPad has completely changed the price of cobalt,” Chirik said, “so something that once was garbage is now valuable.”
While the rising cost may undermine the economic incentive to use Chirik’s cobalt-fueled materials, it seems to perfectly underscore his basic point about the need for flexibility.
“There’s a broad appeal and logic to focusing on more abundant elements in designing catalysts,” said Roderick Eggert, a professor of economics and business at the Colorado School of Mines.
A vast majority of the chemicals we manufacture and then use to make other products require catalysts. And a lot of catalysts use so-called noble metals like platinum, palladium, and rhodium, which are expensive. A pound of platinum costs about $22,000. A pound of iron, meanwhile, costs about fifty cents.
As an undergraduate chemistry major, Chirik worked on reactions that used iridium as a catalyst. A pound of iridium costs about $16,000. Chirik’s boss kept the iridium-based compound locked in a desk drawer. “You had to walk from his office to the lab holding it with two hands, and not talk to anyone,” Chirik recalled. The experience left him with the seed of an idea, he said. “Why can’t we do this with something cheaper?”
On a spring afternoon at the Princeton lab, a graduate student toiled away at a glovebox, a vacuum chamber that prevents the iron from rusting. Rust is a potential downside of using iron in manufacturing, and controlling it could prove challenging and expensive. “We’re not talking about making a dish of spaghetti at home,” Chirik said, referring to the volume of chemicals involved when doing reactions on an industrial scale. It remains to be seen, he said, whether concerns about the use of an “air sensitive” substance outweigh concerns about the costs and environmental impact of precious metals.
There have been other hurdles. Chirik showed two small dishes of silicone flakes, used to make glue for envelopes. One he made using iron, the other platinum. They were indistinguishable. Getting them that way, however, was no easy task; it’s taken nearly a decade of work. “One of the reasons most of us got involved in this type of chemistry is that compounds that have metals in them turn really cool colors and it’s fun to watch,” Chirik said. “But if you’re making something that’s going to go in a consumer product, the glue on an envelope, the bottom of a shoe, an ingredient in shampoo, you really don’t want it to be black.”
Chevron and Momentive, a silicone manufacturer, are financing Chirik’s work. Merck is also a partner in the research. (Many drugmaking processes rely on rhodium or palladium.) One product in development is a fuel-efficient tire that employs a new, cleaner process, with no byproducts, by using iron instead of platinum.
Dr. Hartings, of American University, believes that using abundant materials where possible could free up the scarcer materials for applications that truly require them. “There’s less of an argument to do crazy mining when you’ve got something else that works just as well,” he said.
Researchers in Chirik’s lab are also hunting for ways to use catalysts to convert nitrogen from the air into forms used in various products, from fertilizer to carpet fiber. The current method, the Haber-Bosch process, is so energy-intensive it accounts for 1 percent of all global energy use.
Sustainability often focuses on “recycling cans and better gas mileage,” Chirik said. While important, those efforts are only part of the picture. There’s also the way products are made. “When you buy jeans, some weird element on the periodic table was used to make them,” Chirik said. “Or you think you’re doing something good by buying a Prius, but it’s got all this neodymium in it that comes out of a pit mine in Mongolia. If you can transition to a completely earth-abundant world,” he said, “you can have a huge impact.”
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