Intermediate Topic 499 of 1102 Kinetics & Equilibrium
Catalytic Converters
Platinum group metals convert CO, NOx and hydrocarbons in exhaust into CO2, N2 and water.
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In-depth explanation of Catalytic Converters
Catalytic converters in automobile exhaust systems use platinum group metals, mainly platinum, palladium and rhodium, dispersed on a ceramic honeycomb support. They convert carbon monoxide to carbon dioxide, unburned hydrocarbons to carbon dioxide and water, and nitrogen oxides to nitrogen, reducing exhaust pollutants by more than 90 percent under proper operating conditions. The catalyst must be hot and the air to fuel ratio must be controlled, since the converter works best near stoichiometric conditions. Lead and sulfur compounds in fuel poison the catalyst by blocking active sites, which is why unleaded fuel is required.
Going deeper: Catalytic Converters
Key ideas: Three-way converter reactions: oxidation of CO and hydrocarbons, and reduction of NOx, all by Pt, Pd and Rh on a washcoat of alumina with ceria that stores oxygen. Operation requires an exhaust temperature above the light-off value of about 250 to 300 degrees C, so most pollution is emitted in the first minutes. An oxygen sensor holds the air to fuel mixture near 14.7 to 1 by mass.
Common mistakes and connections: Students think that the converter eliminates CO2, which it actually produces. Another mistake is claiming a catalyst is used up by the exhaust or that it works equally well when cold. Leaded fuel and sulfur poison the surface. Diesel engines run lean, so special NOx reduction with urea is needed. Ties to heterogeneous catalysis and catalyst poisons.
Visualization of Catalytic Converters
A warm three-way converter removes roughly 90 percent or more of each pollutant using Pt, Pd and Rh on a ceramic honeycomb (typical values). The interactive lesson shows this as a live animation or chart.
Worked example and use case
Over rhodium the reaction 2CO + 2NO -> 2CO2 + N2 removes two harmful gases in one step.
Frequently asked questions about Catalytic Converters
What is Catalytic Converters?
Platinum group metals convert CO, NOx and hydrocarbons in exhaust into CO2, N2 and water.
Is Catalytic Converters a beginner, intermediate or advanced topic?
Catalytic Converters is a intermediate topic in Kinetics & Equilibrium. It builds on the vocabulary of beginner topics in this area.
What should I learn before Catalytic Converters?
Study these earlier topics in Kinetics & Equilibrium first: Flash Photolysis, Clock Reactions, Rate vs Time Graphs.
What comes after Catalytic Converters?
The next topics in Kinetics & Equilibrium are Inhibitors and Poisons and Surface Catalysis Steps.
Can I practise Catalytic Converters with quizzes?
Yes. The interactive lesson includes a self-check question on Catalytic Converters, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Where Catalytic Converters fits in Kinetics & Equilibrium
Catalytic Converters is topic 80 of 91 in Kinetics & Equilibrium.