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Catalytic Converter Material Could
Make For Cleaner, Cheaper Cars

Imagine a fuel-efficient, clean-burning diesel engine that costs $1,000 to $5,000 less than those built today. That's the possibility raised by research published this week in the journal Science, from chemical engineers at GM who've found a way to substitute a cheap mineral for wedding-ring-quality metals in catalytic converters.

The GM chemists found a way to use a mineral called perovskite, doped with strontium, in place of the expensive precious metals. It's something of a holy grail in the industry, which many groups have been working on for the past 15 years. While the GM scientists were focusing on diesel engines, their technology should also work in gasoline engines.

"It's an order of magnitude cheaper," says Chang Hwan Kim, a chemical engineer at GM's technology center in Warren, Mich. and the senior author on the paper.

"It's a really significant step forward," says Charles Peden, a chemist and director of the Institute for Interfacial Catalysis at the Pacific Northwest National Laboratory in Richland, Wash. "The high cost of platinum is really causing problems for these new emissions control technologies."

Getting cars today to be both fuel efficient and low-emission is a difficult trade-off.

To make a car fuel efficient, you want to get a mix of air and fuel that burns as much of the fuel as possible. But to put out few pollutants, the current catalyst technology requires that not all the fuel is burned. "The catalytic converter doesn't work if it doesn't have enough unburnt fuel," says Peden.

The catalytic converter changes the smog-creating chemicals nitrogen oxide and nitrogen dioxide put out by the engine into harmless nitrogen.

To cut down on smog car companies began adding catalytic converters to their products in the 1970s. Those catalytic converters used precious metals such as platinum, palladium and rhodium as catalysts, to speed up the conversion of the nitrogen oxide and nitrogen dioxide into plain nitrogen. It's this technology that's decreased air pollution from cars tremendously over the past 15 years. But it's also raised their price.

Newer catalytic converters require less unburnt fuel to work, but in order to do so they require a lot more platinum or other precious metals. And with prices going up, that's been a huge headache for auto manufacturers.

"There are still a few things we have to work on to develop this as a commercial product, but we were very excited," says Kim.

March 29, 2010

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