How does catalytic converter reduce pollution

Emissions regulations have been progressively tightened to the extent that just one car sold in the s would have produced as many harmful exhaust emissions as one hundred of today's automobiles equipped with catalytic converters. As the number of cars throughout the world increases, further cuts in pollution per vehicle are needed to keep improving air quality.

Many governments in the fast growing emerging markets of Brazil, India, and China — the BRIC countries —, are putting legislation in place to catch up with the standards already implemented in the US, Europe and Japan. 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 with an interesting device called a catalytic converter. Catalytic converters are amazingly simple devices, so it is incredible to see how big an impact they have. In this article, you will learn which pollutants are produced by an engine and how a catalytic converter deals with each of these pollutants to help reduce vehicle emissions.

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. Theoretically, at this ratio, all of the fuel will be burned using all of the oxygen in the air. For gasoline , the stoichiometric ratio is about The fuel mixture actually varies from the ideal ratio quite a bit during driving.

Sometimes the mixture can be lean an air-to-fuel ratio higher than These emissions are mostly benign, although carbon dioxide emissions are believed to contribute to global warming. Because the combustion process is never perfect, some smaller amounts of more harmful emissions are also produced in car engines.

Catalytic converters are designed to reduce all three:. Gallon for gallon, new lawn mower engines contribute 93 times more smog-forming emissions than new cars. It's no wonder that the EPA and the state regulators of California are trying hard to get golf ball-sized catalytic converters into lawn mower and other small engines. However, just like in the s, the lawmakers are being met with a powerful lobby.

Four smaller lawn mower engine manufacturers have refuted this charge. California democrats and the EPA think it has more to do with the bottom line. Pending regulations proposed in California could reduce emissions by the equivalent of , cars per day [source: Barringer ]. 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 [source: Chemicool ]. In the catalytic converter, there are two different types of catalyst at work, a reduction catalyst and an oxidation catalyst.

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.

Most modern cars are equipped with three-way catalytic converters. This refers to the three regulated emissions it helps to reduce. 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 atom 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:. The oxidation catalyst is the second stage of the catalytic converter. Without the redox process to filter and convert the nitrogen oxides, carbon monoxides, and hydrocarbons, the air quality especially in large cities becomes harmful to the human being. Nitrogen oxides: These compounds are of the same family as nitrogen dioxide, nitric acid, nitrous oxide, nitrates, and nitric oxide. When NO x is released into the air, it reacts, stimulated by sunlight, with organic compounds in the air; the result is smog.

Smog is a pollutant and has adverse effects on children's lungs. NO x reacting with sulfur dioxide produces acid rain, which is highly destructive to everything it lands on. Acid rain corrodes cars, plants, buildings, national monuments and pollutes lakes and streams to an acidity unsuitable for fish. NO x can also bind with ozone to create biological mutations such as smog , and reduce the transmission of light.

Carbon monoxide: This is a harmful variant of a naturally occurring gas, CO 2. Odorless and colorless, this gas does not have many useful functions in everyday processes.

Hydrocarbons: Inhaling hydrocarbons from gasoline, household cleaners, propellants, kerosene and other fuels can be fatal to children. Further complications include central nervous system impairments and cardiovascular problems.

The catalytic converter is a sensitive device with precious metals coating the inside. Without these metals, the redox reactions cannot occur. There are several substances and chemicals that inhibit the catalytic converter.

These contaminants prevent the catalytic converter from functioning properly. However, this process could be reversed by running the engine at a high temperature to increase the hot exhaust flow through the converter, melting or liquefying some of the contaminants and removing them from the exhaust pipe. This process does not work if the metal is coated with lead, because lead has a high boiling point.

If the lead poisoning is severe enough, the whole converter is rendered useless and must be replaced. Recall that thermodynamics predicts whether or not a reaction or process is spontaneous under certain conditions, but not the rate of the process. The redox reactions below occur slowly without a catalyst; even if the processes are thermodynamically favorable, they cannot occur without proper energy.

A catalyst aids in the thermodynamic process by lowering the activation energy; the catalyst itself does not produce a product, but it does affect the amount and the speed at which the products are formed. Due to the precious metals in the coating of the inner ceramic structure, many catalytic converters have been targeted for theft.

The converter is the most easily-accessible component because it lies on the outside and under the car. A thief could easily slide under the car, saw the connecting tubes on each end, and leave with the catalytic converter.

Although the catalytic converter has helped reduce toxic emissions from car engines, it also has detrimental environmental effects.