How Catalytic Converters Work
Back in the pre-emissions regulation days, cars and trucks pumped out a lot of air pollution. Since it was particularly severe in some areas of the country, individual states started mandating maximum allowable emissions levels within their territories. The first to do so was the state of California in 1968; others soon jumped in. By the early '70s, the federal government stepped in and started phasing-in even more restrictive emissions standards for the entire country. According to our sources at Zeigler of Downers Grove, a local Dodge, Chrysler, Jeep, Ram dealer in Downers Grove, IL , to meet these new standards, the automotive engineers at Chrysler and other companies developed a plethora of engine add-ons. These were all designed to cut down on Carbon Monoxides (CO), Nitrous Oxides (NO2), Hydrocarbons (HCx) and other pollutants.
In the meantime, the government emission standards continued to get more and more stringent as the years rolled on. In the mid-1970s, in order to meet the latest federal emission standards, most of the auto manufacturers started to add catalytic convertors to their cars. Catalytic converters are devices that sit in the middle of an engine's exhaust flow and via a chemical reaction, clean up a car's exhaust gases. These devices have evolved through the years but they have been so successful that most cars use them today.
How an internal combustion engine creates pollutants
Internal combustion engines mix air and gasoline and burn them in combustion chambers. If the two are burned in a precise ratio of 14.7 to 1 (air to gasoline), very few pollutants would be emitted. As matter of fact, just water and carbon dioxide would be produced. However, this 14.7 to 1 ratio is almost impossible to maintain over the entire range of speeds and temperatures that engines operate at. The result is that carbon monoxide, nitrous oxide and volatile hydrocarbons are generated and leave through the exhaust. And just for added measure, sunlight converts some of these compounds to form ozone and even more nitrous oxides.
Catalytic convertors appear
Catalytic convertors are muffler-like devices that are installed in exhaust pipes to chemically change leftover engine emissions into less-destructive compounds. They do so by means of a reduction catalyst. The surface area on the inside of the catalytic converter is coated with a catalyst, usually platinum or rhodium. When the exhaust gas contacts the catalyst, the catalyst grabs a nitrogen atom out of nitrous oxide molecules and frees the oxygen atom. This reaction only works at high temperatures (700-800 degrees), so catalytic converters tend to run very hot. This is why you usually will see a heat shield mounted above and under a car's convertors.
Two types exist
The first catalytic convertors were "two-way" devices that performed two primary chemical reactions. The primary one was to convert carbon monoxide (CO) into carbon dioxide (CO2). The second reaction was to further burn off any remaining hydrocarbons (unburned gas) and converting it into CO2 and water.
In the early 1980s, engineers developed a "three-way" catalytic convertor. These devices performed the two chemical transformations we discussed above plus it converted nitrous oxides (NO2) into harmless Oxygen (O2) and nitrogen (N2). Note that three way convertors are superior to the early two-way ones but they create a tiny amount of unwanted compounds such as hydrogen sulfide and ammonia. This is why some three-way convertors can be somewhat odoriferous.
Catalytic convertors have proven to be reliable, effective devices to reduce atmospheric pollutants but one indirect effect should be noted. Two of the most common metals in catalytic convertors are palladium and platinum. Unfortunately, a significant amount of these metals are mined near Norilsk, Russia and the effects of this mining process has made Norilsk one of the most polluted places in the world.