ICE-22 — The Catalytic Converter

ASSUMPTION — This lesson covers catalyst chemistry conceptually; specific precious-metal loadings are not given.

In this lesson you will learn:

• How the three-way catalyst works
• The lambda window
• The GPF’s role

1. Three-Way Catalyst (TWC)

The TWC reduces three pollutants simultaneously: CO, HC and NOx.

FACT — Two processes work together: oxidation (CO and HC → CO2 and H2O) and reduction (NOx → N2 and O2). Both require a near-stoichiometric mixture (λ ≈ 1).

2. The Lambda Window

FACT — The TWC efficiently reduces all three pollutants only within a narrow λ range (the lambda window). Hence gasoline engines continuously control stoichiometry via the lambda sensor (ICE-26).

3. GPF (Gasoline Particulate Filter)

Direct-injection (GDI) engines can produce particulates, so a GPF is used.

FACT — The GPF traps gasoline particulate (PN) emissions — the gasoline counterpart of the diesel DPF. It has become common as GDI spread.

4. Trade-offs

INTERPRETATION — The catalyst is inefficient until it reaches its “light-off” temperature, so cold-start emission control is hard (ICE-39). Catalyst position and warm-up strategy manage this trade-off.

5. Summary

• TWC reduces CO/HC/NOx simultaneously.
• Requires the λ ≈ 1 window.
• GPF controls GDI particulates.
• Cold start reduces catalyst efficiency.

6. Sources

• Bosch, Emissions Control Technology
• Bosch, Gasoline-Engine Management

Next Lesson

• ICE-23 — The Diesel Particulate Filter (DPF).