When was the catalytic converter introduced

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. This is known as passive regeneration and is a continuous process.

Typically constructed from cordierite, silicon carbide SiC , or aluminium titanate Al 2 TiO 5 , these devices capture the PM in their porous wall structure as the gas is forced through the wall from the inlet channel to outlet channel fig 3.

Thousands of researchers were put to work by catalyst companies and car manufacturers. Automobile catalytic converters were soon adapted to nullify three types of gases nitrogen oxides, hydrocarbons, and carbon monoxide ; these next-generation devices were dubbed three-way converters.

The honeycomb structure inside the metal casing vastly increased the surface area of the catalyst that came into contact with the fumes. Leaded gasoline—for older cars—and unleaded gasoline were sold side by side until amendments to the Clean Air Act made the sale and use of all leaded gasoline in cars illegal beginning in Thanks to the work of Houdry and his successors, virtually every fuel-burning car sold in the United States has a catalytic converter.

Unfortunately, their rising cost makes every car a potential target for thieves. Some companies now sell special devices to protect catalytic converters. It is one of the greatest technical successes of chemical work, ever. Later Hegedus went on to direct research at W. Grace and Arkema.

Cohen, a professor of chemistry at the University of California, Berkeley, and director of the Berkeley Atmospheric Sciences Center, remarking on the role of catalytic converters in improving air quality. In the midth century, colleagues-turned-rivals Maria Telkes and Hoyt Hottel engineered new ways of heating American homes. Because of the precious metals coating catalytic converters, and a recent skyrocketing of the price of these metals, they have increasingly become the target of theft as they are worth hundreds of pounds and are easy to access.

Although catalytic converters solve one problem, researchers have suggested they are also responsible for higher environmental levels of platinum group metals in the atmosphere, soil, surface water and even Antarctic ice, as a result of nano- and micro-particles of the coatings that are emitted in exhaust fumes.

Use the button to select a material and get started. This website places cookies on your computer to improve your experience. By continuing to browse the site, you are agreeing to our use of cookies. 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.