Catalytic Converter: Description and Operation

Three-Way Catalyst:

THREE-WAY CATALYST

This catalytic converter decreases HC, CO, and NOx emissions. The catalytic converter combines hydrocarbons (HC) and carbon monoxide (CO) with oxygen to form water (H2O) and carbon dioxide (CO2). The three-way catalytic converter contains rhodium which reduces or separates oxides of nitrogen (NOx) into nitrogen and oxygen. This action provides better exhaust emission control than is obtainable by using only exhaust gas recirculation, an oxidation catalyst or engine modifications. The three-way catalyst allows richer air/fuel mixtures, more spark advance and less exhaust gas recirculation. All these improve both driveability and fuel economy.

Effective catalytic control of all three pollutants is possible when the correct level of CO is obtained, and excess oxygen is reduced. Therefore, it is necessary to maintain precise control of the air/fuel mixture entering the engine, keeping it very close to the stoichiometric point (chemically correct for theoretical complete combustion).