Catalytic converters contain catalysts — chemicals which speed up the process of chemical reactions, which themselves do not change during this process.
Catalysts break down the harmful exhaust gases coming from the engine by separating the atoms which make up these molecules. There are typically two different catalysts inside of a common three-way catalytic converter — one which tackles nitrogen oxide by removing oxygen through a process called reduction, and the other which turns carbon monoxide into carbon dioxide by adding oxygen, called oxidation. 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.
Exhaust emissions from the engine will travel through the coated honeycomb structures and react with the compounds.
There are two different catalyst stages that emissions will travel through: a reduction catalyst and an oxidation catalyst. During the first catalyst stage the reduction catalyst , nitrogen oxides react with a platinum and rhodium coated honeycomb structure. When these harmful nitrogen oxides react with the catalysts platinum and rhodium , the catalysts remove the nitrogen molecule, hold onto it, and release the oxygen molecules. Then, the nitrogen molecules left over will join with other nitrogen molecules and exit through the exhaust system.
During this stage, harmful nitrogen oxide gases are converted into harmless oxygen and nitrogen gases. During the second catalyst stage the oxidation catalyst , carbon monoxide and hydrocarbons are oxidized. This means that oxygen molecules will react with the carbon monoxide and hydrocarbon molecules. Diesel cars typically have special catalytic converters to cope with the specific emissions from compression ignition diesel engines. These Diesel Oxidation Catalyst units are routinely paired with additional exhaust treatment technologies such as exhaust gas recirculation, Diesel Particulate Filters to trap soot and Selective Catalytic Reduction which uses injections of AdBlue urea solution to remove NOx.
Reports suggest that the growth could be attributed to supply chain issues which have made it harder for dealers to secure replacement catalytic converters through official channels, creating a black market. Historically, however, the greatest driver of thefts has been the overseas markets for the precious metals inside the units. Catalytic converters stolen in the UK are often illegally transported abroad and the metals recycled. While thefts of catalytic converters are still rare, there are some simple steps you can take to protect your vehicle Catalytic converters have been around since the 19th century when metal cylinders containing filters coated in platinum, Iridium and palladium were fitted to early French motor cars in an attempt to clean up the smoke coming out of their exhausts.
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