The catalytic converter, also known as pollution control, is the muffler-like device used in the exhaust system. An active substance called catalyst causes a chemical reaction that turns exhaust emissions into harmless substances. The early catalytic converters contained a platinum-coated ceramic or aluminum-oxide pellet coated with platinum. These convert hydrocarbon and carbon monoxide into water vapor and carbon dioxide. But this converter needs extra oxygen to properly perform since oxygen is pumped into the exhaust system by an air aspirator valve. On the other hand, new converters are a two-in-one design. The front section is called a three-way catalyst because it controls hydrocarbon, carbon monoxide, and nitric oxide by turning them into water, carbon dioxide, and nitrogen. The rear section is an oxidation catalyst that further reduces hydrocarbon and carbon monoxide.