Researchers at Washington State University, Pacific Northwest National Laboratory, and the University of New Mexico have created a catalyst capable of reducing pollutants at the lower temperatures expected in advanced engines. Their work presents a new way to create a more powerful catalyst while using smaller amounts of platinum — the most expensive component of emission-control catalysts.
Tech Briefs: How do the standard catalysts in catalytic converters work, and how do yours differ?
Dr. Abhaya Datye: Standard catalysts used in cars involve nanometer-size particles of precious metals like platinum. These have a high surface area because the smaller you go, the more surface you have. Since the volume of any particle varies as the cube of its diameter, and the surface area varies as the square of the diameter, the ratio of surface to volume is inversely proportional to the diameter. As I make the diameter smaller, there is more surface for a given volume. At 1 nanometer, most of the atoms of that precious metal will be at the surface — very few are buried inside. That's important because the reaction only happens at the surface. Any platinum present inside the surface never sees the gas, so it doesn't work as a catalyst.
However, under realistic conditions, at high temperatures, a 1-nanometer particle can grow to 40 nanometers by the end of the life of a car. This is why you have to have your car inspected periodically to make sure the catalyst is still working. Auto manufacturers add more metal to make sure they will always meet the exhaust emissions standards over the lifetime of the car.
We set out to find how we could make the particle smaller, and in the limit, get to a single isolated atom. We discovered that by heating the platinum and supporting it on cerium oxide, you trap the platinum in the form of single atoms, but it was not in the form of nanoparticles, and the catalyst wasn't very active. We later found that treating the catalyst in steam preserves the isolated atoms of platinum and makes the catalyst very active.
Tech Briefs: What are the next steps?
Dr. Datye: To continue to try to get rid of all of the components of exhaust. We can get to the carbon monoxide and hydrocarbons, but nitrogen oxide is more difficult. We need to make better catalysts to treat all of the exhaust components, while conserving the metals like platinum and palladium that are necessary to make this happen.
For the last 15 or 20 years, I have been studying how to make catalysts stop losing activity by studying the mechanisms that make it happen. I'm excited that now we have the means to reverse the growth in size of the platinum particles. Although a 20-nanometer particle is very small, only 5% of the atoms being active means you've wasted 95% of the platinum because it's in the interior. I'm very happy that this research has enabled us to come up with simple, facile methods to make every atom active.
Tech Briefs: How long before this becomes commercialized?
Dr. Datye: We share all of this with our partners — with General Motors, for example. Naturally, we work under more idealized conditions and we leave it up to them to make these materials. I have a program in which we partner with General Motors, so whatever we make, we take to their labs and they put it through the paces, check it out, tell us how it works, and what we have to do to make it better.