Catalytic converter and its working

catalytic converter

Pollutant gases are made of harmful molecules, but those molecules are made from relatively harmless atoms. So if we could find a way of splitting up the molecules after they leave a car's engine and before they get pumped out into the air, we could crack the problem of pollution. That's the job that a catalytic converter does.

IMAGE: A catalytic Converter

These gadgets are much simpler than they sound. A catalyst is simply a chemical that makes a chemical reaction go faster without itself changing in the process. It's a bit like an athletics coach who stands by the side of the track and shouts at the runners to go faster. The coach doesn't run anywhere; he just stands there, waves his arms about, and makes the runners speed up. In a catalytic converter, the catalyst's job is to speed up the removal of pollution. The catalyst is made from platinum or a similar, platinum-like metal such as palladium or rhodium.

A catalytic converter is a large metal box, bolted to the underside of your car, that has two pipes coming out of it. One of them (the converter's "input") is connected to the engine and brings in hot, polluted fumes from the engine's cylinders (where the fuel burns and produces power). The second pipe (the converter's "output") is connected to the tailpipe (exhaust). As the gases from the engine fumes blow over the catalyst, chemical reactions take place on its surface, breaking apart the pollutant gases and converting them into other gases that are safe enough to blow harmlessly out into the air.

One very important thing to note about catalytic converters is that they require you to use unleaded fuel, because the lead in conventional fuel "poisons" the catalyst and prevents it from taking up the pollutants in exhaust gases.

Inside the converter

Inside the converter, the gases flow through a dense honeycomb structure made from a ceramic and coated with the catalysts. The honeycomb structure means the gases touch a bigger area of catalyst at once, so they are converted more quickly and efficiently.

Typically, there are two different catalysts in a catalytic converter:

• One of them tackles nitrogen oxide pollution using a chemical reaction called reduction .This breaks up nitrogen oxides into nitrogen and oxygen gases.
• The other catalyst works by an opposite chemical process called oxidation  and turns carbon monoxide into carbon dioxide. Another oxidation reaction turns unburned hydrocarbons in the exhaust into carbon dioxide and water.

In effect, three different chemical reactions are going on at the same time. That's why we talk about three-way catalytic converters. (Some, less-effective converters carry out only the second two (oxidation) reactions, so they're called two-way catalytic converters.) After the catalyst has done it's job, what emerges from the exhaust is mostly nitrogen, oxygen, carbon dioxide, and water (in the form of steam).

One final note: We generally think of carbon dioxide as a safe gas, because it's not toxic. Nevertheless, it isn't entirely harmless, because we now know it's the major cause of global warming and climate change.