What is the Three-Way Catalytic Converter?

Three-way catalytic converters effectively reduce carbon monoxide, hydrocarbons and oxides of nitrogen by oxidation and reduction into non-polluting CO2, H2O and N2.

These reactions take place most efficiently when operating within a narrow band of air-to-fuel ratios near stoichiometry; to do this effectively requires a closed-loop fuel injection system with oxygen sensors.

What is a catalytic converter?

Catalytic converters use precious metal catalysts to reduce harmful emissions from automobiles. They convert hydrocarbons, carbon monoxide and nitrogen oxides into non-hazardous gases such as water vapor, carbon dioxide and nitrogen oxides for emission-free operation.

Catalytic converters utilize a ceramic block coated with platinum, rhodium and palladium that provides high surface area for gasses to pass over, enabling both reduction and oxidation reactions to occur simultaneously.

Three-way catalytic converters have been widely utilized on gasoline engines since 1981, helping reduce carbon monoxide, oxides of nitrogen and unburnt hydrocarbon emissions by oxidation to produce CO2, water vapor and nitrogen emissions. For maximum effectiveness this process should occur when running slightly above stoichiometric (14.6-24.8 parts air to one part fuel) while being equipped with an oxygen sensor that monitors and adjusts the air-fuel ratio.

Catalytic converters used on diesel and lean-burn gasohol engines utilize similar processes in order to oxidize any nitrogen oxide emissions produced.

How does a catalytic converter work?

A catalytic converter is a metal box with an intake pipe for exhaust gases to enter and an output pipe for them to exit. Exhaust gases pass through this catalytic converter where they undergo both oxidation and reduction reactions – the latter scrubping away nitrogen oxide molecules to produce nitrogen and oxygen while the former converts carbon monoxide and unburnt hydrocarbons into water vapor and carbon dioxide.

Normal operation of the three-way catalyst operates within a narrow band of air/fuel ratios close to stoichiometry; however, under certain conditions an engine may operate lean of its ideal operating conditions and thus cause its three-way catalyst to reduce NOx emissions but fail to effectively lower CO and HC levels.

In order to overcome this problem, modern cars contain three-way catalytic converters with special redox catalysts made up of platinum and rhodium for reduction and oxidation reactions, respectively. To optimize reaction rates further, this type of three-way converter comes equipped with honeycomb-shaped ceramic substrates to maximize reaction rates – effectively purifying their exhaust gases.

What are the benefits of a catalytic converter?

Your engine produces three harmful emissions after combustion: carbon monoxide (CO), hydrocarbons and nitrogen oxides. A three way catalytic converter reduces these emissions through oxidation-reduction reactions.

Precious metals like platinum, rhodium and palladium form part of a catalyst system designed to assist chemical reactions occurring in exhaust streams and convert CO, HC and NOx emissions into less harmful molecules such as water or carbon dioxide.

To operate effectively, catalysts must be operated within a specific air-to-fuel ratio range; otherwise, their reaction efficiency quickly deteriorates and performance becomes impaired. Therefore, your car must feature a computerized closed-loop fuel injection system with oxygen sensors known as lambda sensors for proper functioning.

Three-way catalytic converters can reduce CO, HC and NOx emissions by more than 99% if the air-to-fuel ratio is precisely managed. For maximum conversion of these pollutants to fuel (approx. 14.60-14.8 parts air to one part fuel), however, an engine must run slightly above its stoichiometric point (14.6 to 14.8 parts of air per part of fuel).

What are the disadvantages of a catalytic converter?

The three-way catalytic converter converts harmful emissions like CO (carbon monoxide), hydrocarbons and nitrogen oxides to less harmful carbon dioxide and oxygen emissions – an invaluable asset of your engine’s exhaust system that reduces pollutants by as much as 90%.

A three-way catalytic converter utilizes a catalyst made up of platinum, rhodium and palladium as its catalyst. These precious metals serve as catalysts in redox reactions to reduce emissions while simultaneously acting as noble metal storage fuels to prevent its oxidation under high temperature conditions.

Catalytic converters work best when engines operate slightly above stoichiometry (14.6 to 14.8 parts air to one part gasoline). A lambda sensor located just in front of the catalytic converter determines this ratio using oxygen signals sent from it directly to either the carburetor or fuel injection system, where they adjust accordingly in order to keep an appropriate air-fuel ratio. A failure in either of these sensors may result in lean fuel conditions which damage catalytic converters.