Three-Way Conversion (TWC) Catalysts
NOx emission standards created real design problems:
NOx reduction is most effective in the absence of O2
CO and HC abatement generally requires O2
To avoid a reducing reactor and an oxidizing reactor in series, effluent oxidations and reductions must be conducted in the same space.
Available reducing agents (CO, H2 and hydrocarbons) must react with available oxidizing agents (O2 and NO).
Fuel mixtures must be controlled to stay within a narrow TWC catalyst operating window