Catalytic Converter has the main function of reducing exhaust emissions. The Catalytic Converter, which is located in the car exhaust, will ensure the emission of exhaust gasses to be much cleaner. The Catalytic Converter has a honeycomb shape and is made of platinum or palladium attached to a ceramic block. The exhaust gas that touches the metal catalyst undergoes a chemical reaction and results in the loss of pollutants such as hydrocarbons HC.
In return, the exhaust gas becomes cleaner and no longer contains harmful pollutants. The platinum or palladium metal used as a catalyst will not change its nature in the presence of this chemical reaction but will experience a decrease in its ability.
These catalysts are quite expensive since they are made of platinum and palladium. However, in most modern cars available today, the Catalytic Converter is placed in the oxygen sensor housing in the exhaust area near the engine block so that it is more difficult to steal.
As a precaution against catalytic convertor theft, you can first of all be more careful when parking your car. We recommend that you park your car in a closed garage to avoid any burglars. You can also install additional fasteners and bolts to increase the safety of this component.
Eugene Houdry, the inventor of the catalytic converter, likely never imagined his creation as a target for criminal conspiracies. Houdry had invented catalytic cracking in the s, a process that produced more and higher-octane gasoline from crude oil and one that gave the Allied military effort a vital edge during World War II.
In the early s Houdry turned his attention to the toxic automobile emissions choking Los Angeles and other cities. Both the black smog and the stink of car exhaust worried him. An article from the June issue of Popular Science colorfully describes this process:. So Houdry throws in a cat [catalyst], and—wham! Oxygen from the air leaps with a snarl at the smelly stuff. While the cats glow with the heat of the fight, oxygen rips the hydrocarbons apart. The hydrogen joins some of the oxygen to form water H 2 O.
And the widowed carbon is swallowed by other oxygen, burning into harmless carbon dioxide CO 2. Deadly carbon mon oxide CO gets the business, too. Attacked by oxygen, it also burns to CO 2. So Houdry shifted to building systems for indoor forklifts and industrial chimneys instead. No more than grams of these precious metals are used in a single converter.
The converter uses simple oxidation and reduction reactions to convert the unwanted fumes. Recall that oxidation is the loss of electrons and that reduction is the gaining of electrons. The precious metals mentioned earlier promote the transfer of electrons and, in turn, the conversion of toxic fumes. The last section of the converter controls the fuel-injection system.
There are two types of "systems" running in a catalytic converter, "lean" and "rich. On the contrary, when the system is running "rich," there is more fuel than needed, and the reactions favor the reduction of nitrogen oxides into elemental nitrogen and oxygen at the expense of the two oxidation reactions. Note: converters can store "extra" oxygen in the exhaust stream for later use. This storage usually occurs when the system is running lean; the gas is released when there is not enough oxygen in the exhaust stream.
The released oxygen compensates for the lack of oxygen derived from NO x reduction, or when there is hard acceleration and the air-to-fuel ratio system becomes rich faster than the catalytic converter can adapt to it. 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.
The diesel exhaust composition poses a whole new set of challenges to the chemist and engineer, compared to conventional gasoline powered vehicles.
As the combustion occurs in an excess of air lean , all the emissions control processes must also operate under oxidising conditions. The rising popularity of diesel vehicles has also brought with it new legislation. This deals with the same pollutants found in a gasoline exhaust, but now also includes PM, which is a major concern.
This is typically composed of hydrocarbons and sulfur oxides adsorbed onto solid carbonaceous matter. As was the case for gasoline vehicles, emissions control catalysis for diesel is not new. The simplest device to incorporate on a diesel vehicle is a diesel oxidation catalyst, which is based on a supported platinum or palladium catalyst.
This uses the excess air from the engine to oxidise carbon monoxide and hydrocarbons to carbon dioxide and water. The first such devices were fitted to fork lift trucks in the s, 2 but are now to be found on most diesel powered road vehicles.
Removing the carbon monoxide and hydrocarbons from a diesel exhaust presents a number of challenges, chiefly converting these pollutants often at the low temperature encountered in a diesel exhaust.
However, it is the NO x and PM that pose the greatest concerns, both from the point of view of ease of removal and their deleterious impact on human health.
It is in the implementation of devices to remove these pollutants where all the major new developments have been made. For NO x control two solutions have been proposed. The first is known as selective catalytic reduction SCR , in which a reductant, usually a urea solution, is sprayed into the exhaust to provide the conditions necessary for NO x reduction.
The urea vapourises and decomposes to ammonia, which then reacts with the NO x over the SCR catalyst, typically supported vanadium oxide V 2 O 5 , or iron or copper supported on zeolite, which is coated onto a monolith as for the TWC.
In some situations, such as in cold countries during the winter this temperature is difficult to obtain. If the stoichiometry of can be achieved, the SCR reaction will occur at a lower temperature, though in reality only a small temperature advantage is possible as urea decomposition starts to become rate limiting below ?
Alternatively, using a catalyst that is extruded from the catalyst material, rather than coated onto an inert support structure can also enhance the reaction. These catalyst materials have only become available to the automotive industry in the past few years. One of the main problems with SCR is the challenge of injecting the correct amount of urea for the reaction, so that no ammonia exits at the tailpipe. The pungent odour of ammonia in the air is definitely not welcome. A catalyst can be fitted to convert any ammonia breaking through as insurance.
It is also necessary to ensure the compliance of the vehicle operator, who now must purchase urea solution solely for environmental purposes. It is likely to dominate for small diesel vehicles, such as passenger cars, at least in the near term, as it is a more cost effective solution for these vehicles than SCR. In a NO x trap, a NO x storage component, usually an alkali or alkaline earth metal oxide, eg barium oxide, is added to the platinum and rhodium catalyst. Under normal lean diesel conditions this stores NO x as nitrate, but every seconds or so the nitrate regenerates by running the engine with more fuel for a few seconds, so that some carbon monoxide and hydrocarbon can reduce the nitrate to harmless nitrogen.
Fig 2 The lean NOx trap running under a lean conditions b period regeneration rich conditions. This requires complex engine design and operation, and also results in a fuel being used for exhaust clean up rather than motive power, so some of the advantage of using a diesel engine is lost. The technology also relies on very low sulfur fuel, as sulfur can be stored as sulfate on the storage material.
As this is very stable, there is a loss of catalyst performance necessitating a periodic high temperature desulfation step. This removes the sulfur once a certain level has been accumulated, thus regenerating the catalyst.
This comprises a diesel oxidation catalyst to remove carbon monoxide and hydrocarbons, and also to oxidise some of the NO to NO 2.
It has already been shown that this can be beneficial for the SCR catalyst, and this is also the case here.
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