Understanding Two Way Catalytic Converters
A two way catalytic converter (also called an oxidation catalyst) performs two of the three catalytic reactions: it oxidizes carbon monoxide to carbon dioxide (CO → CO₂) and oxidizes unburned hydrocarbons to carbon dioxide and water (HC → CO₂ + H₂O). Unlike three way converters, two way cats cannot reduce nitrogen oxides (NOx), which limited their effectiveness as emissions standards tightened.
Historical Context
Two way catalytic converters were the first type widely adopted by the auto industry, appearing in vehicles starting in 1975 when the EPA mandated catalytic converters for all new cars. They remained the standard through 1980 until stricter NOx regulations led to the adoption of three way converters beginning in 1981. During their era, two way cats significantly reduced CO and HC emissions but left NOx pollution largely unaddressed.
Modern Uses
While rare in modern passenger vehicles, two way catalytic converters are still used in some applications: diesel engines (where different NOx reduction methods are employed), small engines (lawnmowers, generators, construction equipment), lean-burn gasoline engines, and some industrial exhaust treatment systems. They remain relevant where NOx reduction is handled by other means or not required by regulations.
Related Guides
Read more about high flow catalytic converter. Read more about mini catalytic converter. Read more about universal catalytic converter. See bad catalytic converter symptoms.
Frequently Asked Questions
Learn about two way catalytic converters: how they differ from three way cats, where they're still used, and historical significance in emissions control.
Prices vary from $50 for basic universal models to $600+ for premium direct-fit converters. CARB-compliant variants cost more.
EPA-compliant catalytic converters are legal at the federal level. CARB-compliant converters are legal in all states including California.