TWC Construction

Two different types of Three-Way Catalytic Converters have been used on fuel injected Toyota vehicles. Some early EFI vehicles used a pelletized TWC that was constructed of catalyst coated pellets tightly packed in a sealed shell, while later model vehicles are equipped with a monolith type TWC that uses a honeycomb shaped catalyst element. While both types operate similarly, the monolith design creates less exhaust backpressure, while providing ample surface area to efficiently convert feed gases.

The Three-Way Catalyst, which is responsible for performing the actual feed gas conversion, is created by coating the internal converter substrate with the following key materials:

• Platinum/Palladium; Oxidizing catalysts for HC and CO

• Rhodium; Reducing catalyst for NOx

• Cerium; Promotes oxygen storage to improve oxidation efficiency The diagram below shows the chemical reaction that takes place inside the converter.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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