Catalytic converters have used precious metals for years to remove harmful emissions from car and truck exhausts. Platinum and palladium are the most popular, but the recent addition of gold to catalytic converters used on diesel-powered vehicles opens up a new use for the metal. These gold-added converters are coming into widespread use in Europe, where engines have to meet the world's most stringent emission requirements. When the technology was introduced in 2008, gold was cheaper than platinum or palladium, making those catalytic converters at the time cheaper than those using other precious metals. For the moment, this is no longer the case.