So what exactly is a catalytic converter? Sure, they play a role in smog control. But beyond that, what are they? What do they do? Where are they located? They’re actually an essential component in your exhaust system, removing harmful contaminates before they make their way into the air. Here’s everything you always wanted to know about catalytic converters, and perhaps a bit more.
A catalytic converter reduces the amount of pollution produced by an engine by filtering it through a system not much unlike a Brita filter in simplified terms. Hot exhaust gases containing carbon monoxide, oxides of nitrogen and hydrocarbons make their way through the exhaust pipe and are filtered through a coating of precious metals found on the converter's substrate. With a honeycomb-patterned catalyst (pictured below), the substrate is a network of small ceramic passageways that weaken the polluting chemicals and convert them into a more environmentally-friendly byproduct of combustion. At the same time, it maximizes the surface area your exhaust flows over to further reduce restrictions.
Exhaust Passes Through Catalyst Substrate
In doing so, a stock catalytic converter creates considerable engine backpressure due to the constrictive effects placed on engine exhaust gases as they pass through. To achieve the ultimate in unbridled performance, one can consider upgrading to performance-grade catalytic converters. These typically consist of a different density cell count, and are sometimes larger in diameter for increased exhaust flow.
Three-Way Catalytic Converters
Most modern cars are equipped with three-way catalytic converters. This refers to the three regulated emissions it helps to reduce: carbon monoxide (CO), hydrocarbons or volatile organic compounds (VOCs), and nitrogen oxides (NO and NO2, together called NOx).
In the catalytic converter, there are two different types of catalysts at work: a reduction catalyst and an oxidation catalyst. Both types feature a ceramic structure coated with a metal catalyst, usually platinum, rhodium or palladium. The structure is intended to expose the widest possible surface area to the exhaust stream while minimizing the amount of catalyst required for the process to take place effectively, due to the high costs of the materials. In fact, some of the newest converters are incorporating gold mixed with the more traditional catalysts. It’s cheaper and some suggest it may even increase the reduction of pollutants by up to 40 percent.
Where On The Vehicle Are They Located?
Converters are located in-line as part of your exhaust system. If you simply follow the exhaust from your cylinder head downward, you'll eventually see a larger section of the exhaust pipe where the diameter expands. This section contains the cell catalyst and is often found right next to your secondary oxygen sensor. The secondary oxygen sensor is designed to read the mixture after the catalyst to determine if it's working properly. If you've ever suffered a P0420 engine code, chances are it's the secondary oxygen sensor that's reporting the catalyst is below its efficiency threshold, and time to be replaced.
Emissions Testing Tip: Catalytic converters are most efficient once warmed up, which is why you should always let your car run for a few minutes before taking it in for an emissions test. The higher the temperature, the more effective the catalyst is.