Catalytic converters are in car exhausts and convert toxic carbon monoxide into much less harmful carbon dioxide, as well as removing other pollutants. On a petrol car, they are the metal box you see just before the exhaust. Unfortunately, current catalytic converters don't work effectively at lower temperatures, usually only starting to work well when heated to about 200°C, once the vehicle has been running for a few minutes. This is what's known as the cold start problem and why the US Department of Energy have set a target to remove 90% of harmful emissions from exhausts below 150°C. A... Like this podcast? Please help us by supporting the Naked Scientists