How Catalytic Converters Work

Since the early 1970s there have been millions and millions of vehicles on the road. Because of this fact, the Government sought out to do something about the increasing pollution that was being thrust into the atmosphere every single day. In 1975 one of the biggest advances in pollution control came out and it was dubbed the catalytic converter.

1When you look at the name in a scientific way you can see exactly what the catalytic converter does. In chemistry terms a catalyst is a substance that can make a chemical reaction occur without being directly affected itself. This means that a catalyst can participate in the reactions without being a byproduct of the reactions.

In a catalytic converter there are actually two types of completely different catalysts that are working. One is a reduction catalyst and the other is referred to as an oxidation catalyst. These catalysts consist of ceramic materials that are coated with extremely expensive materials such as platinum, palladium, rhodium, and even gold. The idea is to expose as much of the catalyst surface area to the exhaust stream. As the exhaust passed through the catalytic converter the harmful emissions are turned (or converted) into a less harmful emission.

Most of today’s vehicles are equipped with a three way catalytic converter, which refers to the three different emissions that it helps to lessen. The three stages are:

  1. Reaction Catalyst: This is the first stage of a three stage catalytic converter. In this stage rhodium or platinum will be used to help with the reduction of NO or NO2 emissions. When molecules comprised of NO or NO2 contact this first catalyst the result is the nitrogen atom being taken out and held onto freeing less harmful emissions including O and O2. The nitrogen atom will then bond with other nitrogen atoms that also get stuck and form a less harmful N2.
  2. Oxidation Catalyst: This is the second stage of the three stage catalytic converter. This stage reduces the unburned hydrocarbons and C02 by oxidizing them over the catalyst that is typically palladium, platinum, or gold. This will in turn aid the reaction of the C0 with the oxygen that is left in the exhaust gas.
  3. Control System: In this third stage of a three stage catalytic converter the fuel injection system is controlled with information derived from an oxygen sensor that will be located closer to the engine than that of the catalytic converter. The oxygen sensor will tell the computer of the vehicle how much oxygen is left in the exhaust so that the computer can then increase or decrease the oxygen but adjusting the air to fuel ratio. This allows the engine to run as close to its stoichiometric point as possible which allows for peak performance of the vehicle.

When you put it all together you have a catalytic system that reduces the pollutants that are let out into the atmosphere by as much as 40 percent.

The one drawback to a catalytic converter is that it works best when it is at a hot temperature. When you first start your car and are running your exhaust through the catalytic converter there is almost no change in the emissions. One way that automobile manufacturers have combated this is by putting the catalytic converters closer to the engine so that the gasses are hotter when they reach it. However, this can shorten the life of the catalytic converter if put too close and anyone who has had a catalytic converter go bad knows how this can be an extremely unwelcomed outcome.

New developments continue to take place with the making of catalytic converters but for the most part they do a great job in reducing emissions as is. While the next generation may prove to be even more effective, the current catalytic converters that are on vehicles today are still much better for the environment then the vehicles of yesteryear that had no emissions help whatsoever.

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