Animation of the inside of a catalytic converter attached to a car's engine, showing how it converts harmful polluting gases into relatively harmless ones. The converter sits near the engine and in the path of the hot exhaust gases. It consists of a honeycomb structure made of a ceramic, which provides a large surface area. The inside surface is lined with the catalyst, which is a combination of rhodium (Rh) and platinum (Pt) metals. On the rhodium, nitrogen oxides (nitric oxide, NO, shown here) are reduced to nitrogen and oxygen. On the platinum, carbon monoxide (CO) reacts with oxygen to form carbon dioxide. These gases are then emitted in the exhaust.