Group+3

The job of the catalytic converter is to convert harmful pollutants into less harmful emissions before they ever leave the car's­ exhaust system ([]) In order to reduce emissions, modern car engines carefully control the amount of fuel they burn. They try to keep the air-to-fuel ratio very close to the **stoichiometric ** point, which is the ideal ratio of air to fuel. ( [] ) Sometimes the mixture can be **lean ** (an air-to-fuel ratio higher than 14.7), and other times the mixture can be **rich ** (an air-to-fuel ratio lower than 14.7).

The main emissions of a car engine are:  · **Nitrogen gas ** (N2) - Air is 78-percent nitrogen gas, and most of this passes right through the car engine.  · **Carbon dioxide ** (CO2) - This is one product of combustion. The carbon in the fuel bonds with the oxygen in the air.  · **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;">Water vapor **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;"> (H2O) - This is another product of combustion. The hydrogen in the fuel bonds with the oxygen in the air. <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%; margin: 0in 0in 10pt;">mostly benign <span style="background: white; color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: normal; margin: 0in 0in 3.75pt;">Catalytic converters are designed to reduce all three: <span style="background: white; line-height: normal; margin: 0in 0in 0pt; tabstops: list .5in; text-indent: -0.25in;"> · **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;">Carbon monoxide **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;"> (CO) is a poisonous gas that is colorless and odorless. <span style="background: white; line-height: normal; margin: 0in 0in 0pt; tabstops: list .5in; text-indent: -0.25in;"> · **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;">Hydrocarbons **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;"> or **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;">volatile organic compounds **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;"> (VOCs) are a major component of smog produced mostly from evaporated, unburned .fuel. <span style="background: white; line-height: normal; margin: 0in 0in 0pt; tabstops: list .5in; text-indent: -0.25in;"> · **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;">Nitrogen oxides **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;"> (NO and NO2, together called NOx) are a contributor to smog and acid rain, which also causes irritation to human mucus membranes.

<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">In chemistry, a **<span style="font-family: 'Arial','sans-serif';">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. ( <span style="font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">[] <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">) <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%; margin: 0in 0in 10pt;">In the catalytic converter, there are two different types of catalyst at work, a **<span style="font-family: 'Arial','sans-serif';">reduction catalyst ** and an **<span style="font-family: 'Arial','sans-serif';">oxidation catalyst **. <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%; margin: 0in 0in 10pt;">Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">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 ( <span style="font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">[] <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">) <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;">Most modern cars are equipped with **<span style="font-family: 'Arial','sans-serif';">three-way catalytic converters **. This refers to the three regulated emissions it helps to reduce. ( <span style="font-family: 'Arial','sans-serif'; font-size: 9pt;">[] <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;">) **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;">reduction catalyst **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;"> is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen <span style="font-family: 'Arial','sans-serif'; font-size: 9pt;">[|atom] <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;"> out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2. For example: **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;">2NO => N2 + O2 **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;"> or **<span style="font-family: 'Arial','sans-serif';">2NO2 => N2 + 2O2 ** **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;">oxidation catalyst **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;"> is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. For example: **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt;">2CO + O2 => 2CO2 **

<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%; margin: 0in 0in 10pt;">two main types of structures used in catalytic converters -- **<span style="font-family: 'Arial','sans-serif';">honeycomb ** and **<span style="font-family: 'Arial','sans-serif';">ceramic beads **. Most cars today use a honeycomb structure. <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">third stage of conversion is a **<span style="font-family: 'Arial','sans-serif';">control system ** that monitors the exhaust stream, and uses this information to control the <span style="font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">[|fuel injection system] <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">. There is an <span style="font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">[|oxygen sensor] <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;"> mounted upstream of the catalytic converter, meaning it is closer to the engine than the converter. This sensor tells the engine computer how much oxygen is in the exhaust. The engine computer can increase or decrease the amount of oxygen in the exhaust by adjusting the air-to-fuel ratio. This control scheme allows the engine computer to make sure that the engine is running at close to the stoichiometric point, and also to make sure that there is enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and CO. ( <span style="font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">[] <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">) <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%; margin: 0in 0in 10pt;">only works at a fairly high temperature. When you start your car cold, the catalytic converter does almost nothing to reduce the pollution in your exhaust **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">Preheating **<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;"> the catalytic converter is a good way to reduce emissions - use electric resistance heaters <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;">Catalytic converters in [|**diesel engines**]<span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%;"> do not work as well in reducing NOx. One reason is that diesel engines run cooler than standard engines <span style="color: #333333; font-family: 'Arial','sans-serif'; font-size: 9pt; line-height: 115%; margin: 0in 0in 10pt;">inject a **<span style="font-family: 'Arial','sans-serif';">urea ** solution in the exhaust pipe, before it gets to the converter, to evaporate and mix with the exhaust and create a chemical reaction that will reduce NOx. Urea, also known as **<span style="font-family: 'Arial','sans-serif';">carbamide **, is an organic compound made of carbon, nitrogen, oxygen and hydrogen. It's found in the urine of mammals and amphibians. Urea reacts with NOx to produce nitrogen and water vapor, disposing more than 90 percent of the nitrogen oxides in exhaust gases

HISTORY [] Catalytic converters were developed and adopted for [|automobile] use because of rising concerns over smog and other harmful [|car] emissions. Eugene Houdry (1892-1962) was a French engineer who designed the first catalytic converter. developed the first catalytic converter in 1953, but the application was not useful because the lead in United States gasoline destroyed the catalyst in the converter Houdry died in 1962. He never saw how his invention would come to change the world. put on hold until lead started to be discontinued as a fuel additive use of lead was not officially banned in passenger cars until 1996 by an amendment to the Clean Air Act leaded gasoline began being phased out in 1975 when federal law required all new vehicles to be equipped with catalytic converters. team of engineers, led by Carl D. Keith, re-tooled Eugene Houdrys catalytic converter for specific automobile use. re-tooled converter was called a three-way catalytic converter and it was more efficient in screening automobile emissions.

Theft Because catalytic converters use precious metals (usually platinum, rhodium and palladium) to filter emissions, theft has become a major problem. Thieves steal the converters from wrecking yards, car dealerships and personal vehicles. Catalytic converters can fetch anywhere from $75 to $150, depending on where they are sold. The rising cost of precious metals in the past decade has increased the theft of converters.