Cars use catalytic converters to remove carbon monoxide, hydrocarbons, and other harmful chemicals from exhaust emissions, and they’ve done a good job over the years in cleaning up exhaust fumes. But those converters rely on costly metals such as palladium to do the job, and they quickly lose their effectiveness. Replacing the converters is an option, but they are one of the costliest components on a car at about $1,000 apiece.
Fortunately, Matteo Carnegello, a professor at Stanford University, and his team have come up with a way to reduce the cost of converters and extend their operational life.
Catalytic converters are costly in part because they contain up to five grams of palladium at $50/gram, which is more than the price of gold. But the palladium and other metals are the catalysts needed to maintain and accelerate the chemical reactions that clean the exhaust. In theory, catalysts can be used over and over. In practice, however, catalysts’ performance go down over time. To compensate, auto engineers use more of these expensive metals, adding to the cost.
Ideally, catalysts should have the greatest surface areas possible to promote the greatest number of chemical reactions. So, manufacturers typically spread a layer of small particles over the surface of new catalytic converters. Past research has shown that these metal atoms move, forming larger and larger particles with less surface area, and thus becoming less effective. This clumping process is called sintering.
To counteract sintering, manufacturers use enough catalytic metal that the converter will meet emissions standards for 10 to 15 years, roughly the lifespan of the car.
Carnegello discovered that sintering isn’t the only cause of catalyst deactivation. In fact, this new deactivation mechanism turns out to be quite the opposite of sintering. Under some circumstances, instead of particles sintering, they decompose into smaller particles and eventually become inactive single atoms.
Carnegello wants to carefully control the size and spacing of catalytic particles so they will neither sinter into large clumps nor decompose into single atoms. Previously, many people in the catalysis community thought that to make particles stable, you had to keep them as far apart as possible to prevent them from moving. The Stanford researchers provided a scientific basis for maintaining catalytic converters’ pollution reduction while using less precious metal. If automotive engineers confirm and implement these findings, it should lower the cost of converters without harming their performance.
Andrew Myers is a communication specialist at Stanford University.
