There are millions of cars on the road in the United States, and each one is a source of air pollution. Especially in large cities, the amount of pollution that all the cars produce together can create big problems.
To solve those problems, cities, states and the federal government create clean-air laws that restrict the amount of pollution that cars can produce. Over the years, automakers have made many refinements to car engines and fuel systems to keep up with these laws.
One of these changes came about in 1975 with an interesting device called a catalytic converter. The job of the catalytic converter is to convert harmful pollutants into less harmful emissions before they ever leave the car's exhaust system.
How Catalytic Converters Reduce Pollution
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In chemistry, a catalyst is a substance that causes or accelerates a chemical reaction without itself being affected. Catalysts participate in the reactions, but are neither reactants nor products of the reaction they catalyze.In the human body, enzymes are naturally occurring catalysts responsible for many essential biochemical reactions
In the catalytic converter, there are two different types of catalyst at work, a reduction catalyst and an oxidation catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium.The idea is to create a structure that exposes the maximum surface area of catalyst to the exhaust stream, while also minimizing the amount of catalyst required, as the materials are extremely expensive. Some of the newest converters have even started to use gold mixed with the more traditional catalysts.Gold is cheaper than the other materials and could increase oxidation, the chemical reaction that reduces pollutants, by up to 40 percent.
Causes of Catalytic Converter Failure
There are two ways a converter can fail:
It can become clogged.
It can become poisoned.
There really is no "inspection port" for the consumer or mechanic to see an actual clog in a converter. Often, the only way to tell if a catalytic converter is malfunctioning (plugged) is to remove it and check the change in engine performance, or you can perform a back pressure test.
A catalytic converter relies on receiving the proper mix of exhaust gases at the proper temperature. Any additives or malfunctions that cause the mixture or the temperature of the exhaust gases to change reduce the effectiveness and life of the catalytic converter. Leaded gasoline and the over-use of certain fuel additives can shorten the life of a catalytic converter.
A catalytic converter can also fail because of:
Bad exhaust valves on the engine
Fouled plugs causing unburned fuel to overheat the converter
Misfires, or most engine related problems
Sometimes you can tell that a converter is clogged because you don't go any faster when you push the gas pedal. Also, there usually is a noticeable drop in gas mileage associated with a clogged catalytic converter. A partially clogged converter often acts like an engine governor, limiting the actual RPMs to a fast idle. A totally clogged converter causes the engine to quit after a few minutes because of all the increased exhaust back pressure.