How does catalytic converter reduce air pollution

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. 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. There are two main types of structures used in catalytic converters -- honeycomb and ceramic beads.

Most cars today use a honeycomb structure. In the next section, we'll look at the third stage of the conversion process and how you can get the most from your catalytic converter. The third stage of conversion is a control system that monitors the exhaust stream, and uses this information to control the fuel injection system. There is an oxygen sensor 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.

The catalytic converter does a great job at reducing the pollution, but it can still be improved substantially. One of its biggest shortcomings is that it 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. One simple solution to this problem is to move the catalytic converter closer to the engine. This means that hotter exhaust gases reach the converter and it heats up faster, but this may also reduce the life of the converter by exposing it to extremely high temperatures.

Most carmakers position the converter under the front passenger seat, far enough from the engine to keep the temperature down to levels that will not harm it. Preheating the catalytic converter is a good way to reduce emissions.

The easiest way to preheat the converter is to use electric resistance heaters. Unfortunately, the volt electrical systems on most cars don't provide enough energy or power to heat the catalytic converter fast enough. Most people would not wait several minutes for the catalytic converter to heat up before starting their car.

Hybrid cars that have big, high-voltage battery packs can provide enough power to heat up the catalytic converter very quickly. Vapour rises into the carbon canister, which then returns the petrol to the tank, hence avoiding a loss due to evaporation. Lean burn engines are more fuel-efficient than other engines and produce less NOx and CO, but they do emit higher levels of hydrocarbons. At the present time they are still under development and have not yet been able to meet EU emission standards, especially at high speeds.

This involves returning exhaust air to the fuel inlet, which results in a reduction in peak engine temperatures and emissions of NOx gasses from petrol vehicles. Levels of CO and HC are also reduced. Smaller, lighter cars use less fuel and hence produce less pollution. Technological development using lighter materials for construction may therefore reduce emissions. The above technologies all provide a reduction in emissions from vehicles.

Electric transport is an alternative development that could lead to a large reduction in pollution at ground level, if it became more wide spread. Electric transport produces no emissions at the point of use, although pollution is emitted during the production of electricity. The amount of pollution created is lower than that from individual vehicles, and the emissions occur away from city centres where the public live and work.

Electric vehicles also produce less noise pollution than diesel and petrol vehicles. The main drawback for electric vehicles is the need to recharge batteries.

The maximum range of these vehicles is currently around 50 - miles. However, they can reach maximum speeds of 60 - 90 miles per hour and have good acceleration. 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. 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.