This paper introduces the three-way emission control technology and the principle of auto exhaust catalytic converter. The main composition of the three-way-catalyst is also reviewed.

The petrol composition influent emission of the engine markedly. It is especially important to control petrol composition particularly after three way conversion catalyst were installed in modern car.

Authors propose that the partial or whole replacement of noble metals by rare earth elements is an important direction in the future developments of emission control three way catalysts.