Modern cars rely on catalytic converters to remove carbon monoxide, hydrocarbons and other harmful chemicals from exhaust emissions.
Modern cars rely on catalytic converters to remove carbon monoxide, hydrocarbons and other harmful chemicals from exhaust emissions.
To do so they rely on costly metals that have special chemical properties that diminish in effectiveness over time. Assistant professor Matteo Cargnello and doctoral candidate Emmett Goodman recently led a team that has proposed a new way to reduce the cost and extend the lifespan of these materials, solving a problem that has vexed automotive engineers for years. In the process, Cargnello and colleagues have done something remarkable: made a breakthrough in a mature field where change comes slowly, if at all.
What about catalytic converters needs to be improved?
A new catalytic converter can cost $1,000 or more, making it among the most expensive individual parts on any car. They are costly because they use expensive metals such as palladium to promote the chemical reactions that cleanse the exhaust. Palladium costs about $50 a gram — more than gold — and each catalytic converter contains about 5 grams of it. Metals like palladium are catalysts — a special class of materials that speed up chemical reactions but don’t chemically change themselves. In theory, catalysts can be used over and over, indefinitely. In practice, however, the performance of catalysts degrades over time. To compensate, we are forced to use more of these expensive metals up front, adding to the cost. Our goal is to better understand the causes of this degradation and how to counteract it.
Why do catalysts go bad?
Ideally, catalysts should be designed to have the greatest surface area possible to promote the greatest number of chemical reactions. So, manufacturers typically spread many small particles over the surface of a new catalytic converter. From past research we know that, over time, the metal atoms begin to move, forming larger and larger particles that offer less surface area, and thus become less effective. We call this clumping process “sintering.” To counteract sintering, manufacturers use excessive amounts of metal so that the converter will meet emissions standards for the 10- or 15-year lifespan of a car. Our team has discovered that sintering isn’t the only cause of deactivation. In fact, this new deactivation mechanism turns out to be quite the opposite of sintering. Under some circumstances, instead of particles getting larger, they decompose into smaller particles and eventually become single atoms that are essentially inactive. This is a new understanding we believe no one has presented before, and it prompted us to look for an entirely new way to maximize the lifespan and performance of the metals in catalytic converters.
Read more at Stanford University
Image by kuanish Sarsenov from Pixabay
