Why two or more substrates may be needed in one catalytic converter？

• To reduce different types of emissions. Catalytic converters use different precious metals to catalyze different chemical reactions. For example, rhodium is used to reduce nitrogen oxide (NOx) emissions, while platinum and palladium are used to oxidize unburned hydrocarbons (HC) and carbon monoxide (CO) emissions. By using two or more substrates coated with different precious metals, a catalytic converter can effectively reduce all three types of emissions.

• To improve efficiency. Using multiple substrates with different catalyst compositions can improve the overall efficiency of a catalytic converter. This is because the different catalysts can work together to promote different reactions under different conditions.

• To increase durability. Catalytic converters are exposed to high temperatures and harsh chemicals in the exhaust gas. This can cause the catalyst to degrade over time. By using multiple substrates, the catalyst can be distributed more evenly, which can help to extend the life of the catalytic converter.

For example

• Three-way catalytic converters: These converters are used in most modern gasoline-powered vehicles. They have two substrates, one coated with rhodium and the other coated with platinum and palladium. The first substrate reduces NOx emissions, while the second substrate oxidizes HC and CO emissions.