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This 1970 Oldsmobile Delta 88, owned by ES&E President Steve Davey, employs one of the first air pollution control systems designed to reduce emissions. Emission systems on today's cars are far more complex and effective. |
UK chemists have developed a new catalytic converter for vehicle exhausts that will reduce air pollution from car exhausts more effectively than today's catalysts and at lower cost. The converter, made at Dundee University in Scotland, contains a new patented design of catalyst using palladium rather than platinum and rhodium as in the current generation of devices.
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This 1970 Oldsmobile Delta 88, owned by ES&E President Steve Davey, employs one of the first air pollution control systems designed to reduce emissions. Emission systems on today's cars are far more complex and effective. |
The new catalyst is both cheaper and more efficient than those in road vehicles today and is more suitable for use with the "lean-burn" engines that will be increasingly used in the next century to protect the atmosphere. The United States has taken the initiative in enforcing the fitting of catalytic converters in road vehicles. Western Europe, including the UK, is now following the US example, brought about by growing concern about the harmful effects of gases in car exhausts.
As Jim Cairns, Professor of Electronic and Mechanical Engineering at Dundee University explains: "If an engine were absolutely 100 percent efficient, it would produce only carbon dioxide and water vapour in its exhaust. "But in practice, all engines produce varying amounts of carbon monoxide, unburnt hydrocarbons, and oxides of nitrogen. And all these gases are potential health hazards and cause undesirable pollution."
The catalytic converters increasingly fitted in car exhausts convert these harmful gases to harmless carbon dioxide and water. Carbon dioxide in the atmosphere contributes to global warming but it is generally agreed that the contribution to this made by vehicles is a much less serious problem than the health hazards of carbon monoxide and unburnt hydrocarbons.
The catalysts used in exhausts today are cylinders filled with porous ceramic material similar to a honeycomb or a sponge and with an enormous internal surface area. The linings of the pores in the honey-comb are sprinkled with particles of the precious metals platinum, rhodium, palladium or iridium. The platinum catalyses reactions that oxidize the carbon monoxide and unburnt hydrocarbons to carbon dioxide, while the iridium breaks down the oxides of nitrogen. But Jim Cairn's new catalyst, he explains, does it all with just one ingredient.
"Our catalyst is different because it contains just one precious metal, palladium, with another non-precious metal, zinc. We've shown that this combination can remove all the exhaust gas pollutants, including the oxides of nitrogen," he said. "One advantage of palladium is that it is less expensive than platinum or rhodium."
The new catalyst is mounted on a ceramic honeycomb, like existing catalysts. The difference lies in some clever chemistry that has been used to attach the palladium and zinc catalyst material to a framework made of zirconia (zirconium oxide). This is what allows palladium alone to remove all the pollutants in the exhaust gases.
The similarity of the basic design to that of existing catalytic converters means that it will be quite easy for vehicle manufacturers to switch to producing the new catalyst. At least one of these is already showing strong interest.
The new catalyst still has to prove that it can go on working for 100,000 miles (160,000 km), the lifetime that is now being required for catalytic converters.