INTRODUCTION

There are millions of cars on the road that are potential sources of air pollution. In a major effort to reduce vehicle emissions, carmakers have developed an interesting device called a catalytic converter, which treats the exhaust before it leaves the car and removes a lot of the pollution.

In order to reduce emissions, modern cars have been designed to carefully control the amount of fuel they burn. The goal is to keep the air-to-fuel ratio very close to the "stoichiometric" point, which is the calculated 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 petrol, the stoichiometric ratio is about 14.7 to 1, meaning that for each pound of fuel, 14.7 pounds of air will be burned. 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 14.7); and other times the mixture can be "rich" (an air-to-fuel ratio lower than 14.7).]

Most modern cars are equipped with three-way catalytic converters. "Three-way" refers to the three regulated emissions it helps to reduce - carbon monoxide, unburnt hydrocarbons and nitrogen oxide molecules. The converter uses two different types of catalysts, a reduction catalyst and an oxidization catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. The idea is to create a structure that exposes the maximum surface area of the catalyst to the exhaust stream, while also minimising the amount of catalyst required (they are very expensive).
There are three main types of structures used in catalytic converters - ceramic honeycomb, metal plate and ceramic beads (now almost obsolete) - the Scorpio like most cars today use a ceramic honeycomb structure.

CATALYTIC CONVERTER: WHAT IS IT?

A long time ago, probably around 1975 somebody determined that a vast majority of our air pollution was coming from our automobiles. That makes sense. If there have millions and millions of automobiles all over the world letting out harmful exhaust into the air it only stands to reason that cars are one of the major culprits when it comes to air pollution.
So someone decided to do something about it. They made it mandatory for every automobile to have a catalytic converter installed to help curve air pollution. What exactly is this device? A catalytic converter helps to stop harmful elements from a car's exhaust from being propelled into the air. It does this by actually converting these harmful elements into less harmful elements from they are released into the atmosphere by way of a car's exhaust.
However, in the chemistry side, we can also say that catalytic converter is a vehicle emissions control device that converts toxic pollutants in exhaust gas to less toxic pollutants by catalyzing a redox reaction (oxidation or reduction). Catalytic converters are used in internal combustion engines fueled by either petrol (gasoline) or diesel—including lean burn engines.
These “two-way” converters combined carbon monoxide (CO) with unburned hydrocarbons (HC) to produce carbon dioxide (CO2) and water (H2O). In 1981, two-way catalytic converters were rendered obsolete by “three-way” converters that also reduce oxides of nitrogen (NOx); however, two-way converters are still used for lean burn engines.
Although catalytic converters are most commonly applied to exhaust systems in automobiles, they are also used on electrical generators, forklifts, mining equipment, trucks, buses, locomotives, motorcycles, and airplanes. They are also used on some wood stoves to control emissions. This is usually in response to government regulation, either through direct environmental regulation or through health and safety regulations.

THE USES OF CATALYTIC CONVERTER

Cars pollute the air, and clean-air laws have made catalytic converters a legal requirement because they convert harmful pollutants from an engine's exhaust into cleaner emissions. The devices work thanks to chemistry and the notion of a catalyst - - something that causes or speeds up a chemical reaction without itself being changed. The chemical reaction strips the exhaust of some of its polluting potency. Catalytic converters contain two types of catalyst: reduction and oxidation. They consist of a metal catalyst coating - - usually palladium, platinum and/or rhodium - - on a ceramic form built to expose the maximum surface area to the exhaust stream.
The first stage of catalytic conversion, the reduction catalyst, uses a catalyst made of platinum and rhodium to diminish nitrogen oxide emissions. When a nitrogen oxide molecule touches the catalyst, the catalyst tears the nitrogen atom from the molecule and traps it, thereby freeing the oxygen. The second stage of catalytic conversion is the oxidation catalyst, which reduces unburned hydrocarbons and carbon monoxide by oxidizing or burning them with a catalyst composed of palladium and platinum. The final stage of catalytic conversion uses a control system to monitor the exhaust stream and regulate the fuel injection system. An oxygen sensor detects the oxygen level in the exhaust and transmits this data to the engine's computer. The computer then regulates the amount of oxygen in the exhaust by adjusting the air-to-fuel ratio, ensuring that the engine is running at close to the ratio that pollutes the least.
Although catalytic converters are great pollution reducers, there is always room for improvement. One flaw is that they require a relatively high temperature: When your car is cold, the efficacy of the catalytic converter is almost nil. One solution is to place the converter closer to the engine, where hot gases can heat it up quicker, but this may shorten the converter's lifespan. Another solution is to preheat the catalytic converter so it can start doing its job sooner. The drawback here is the electrical systems in most cars can't provide enough power to heat the converter fast enough; most people won't want to wait for the converter to warm up before they can start their cars.
In gasoline engines, catalytic converters are reliable and efficient at reducing pollution. They convert an estimated 90% of the hydrocarbons, carbon monoxide, and nitrogen oxides produced into less harmful compounds.

However, catalytic converters are less efficient when used with diesel engines, which run colder than gasoline engines. Catalytic converters work best at higher temperatures. Diesel engines also produce particles such as soot. But adding a particulate filter to the catalysts in the catalytic converter can reduce emissions of ultra-fine particles by up to 99%.

HOW CATALYTIC CONVERTER WORKS

For an automobile’s internal combustion engine to operate, a controlled combustion reaction needs to occur inside the vehicle’s engine. But this reaction also produces harmful burnt gases that contribute significantly to air pollution. And good air quality is very important for an individual’s overall health.

In order to reduce air pollution, modern automobiles are equipped with a device called a catalytic converter that reduces emissions of three harmful compounds found in car exhaust:

1. carbon monoxide (a poisonous gas) 2. nitrogen oxides (a cause of smog and acid rain) 3. hydrocarbons (a cause of smog)

These are converted into less harmful compounds before leaving the car’s exhaust system. This is accomplished using a catalyst, which gives the device its name.
The catalyst used in a catalytic converter is a combination of platinum (Pt), palladium (Pd), and rhodium (Rh). These metals coat a ceramic honeycomb (or ceramic beads) contained within a metal casing that is attached to the exhaust pipe. The catalytic converter’s honeycomb structure provides the maximum surface area on which reactions can take place while using the least amount of catalyst.

A reduction and oxidation reaction occurs inside the device. Carbon monoxide (CO) in converted to carbon dioxide (CO2). Nitrogen oxides (NOx) are broken down into nitrogen gas (N2) and oxygen gas (O2). And hydrocarbons (HC) are converted into carbon dioxide (CO2) and water (H2O).

First of all, the catalytic converter uses a reduction catalyst composed of platinum and rhodium to reduce the nitrous oxides. As the nitrous oxide molecules (NO and NO2) pass through the device, the catalyst removes the nitrogen atom, allowing the free oxygen to form oxygen gas (O2). The nitrogen atom that is attached to the catalyst reacts with other attached nitrogen atoms to form nitrogen gas (N2). * Reduction Reaction 1: 2NO => N2 + O2 * Reduction Reaction 2: 2NO2 => N2 + 2O2

In the second stage of the reaction, an oxidative catalyst of platinum and palladium decreases emissions of carbon monoxide (CO) and unburned hydrocarbons (HC). * Oxidation Reaction 1: 2CO + O2 => 2CO2 * Oxidation Reaction 2: H4C2 + 3O2 => 2CO2 + 2H2O

TYPES OF CATALYTIC CONVERTER
A three-way catalytic converter has three simultaneous functions: 1. Reduction of nitrogen oxides into elemental nitrogen and oxygen: 2NO => N2 + O2 2. Oxidation of carbon monoxide to carbon dioxide : 2CO + O2 => 2CO2 3. Oxidation of hydrocarbons into carbon dioxide and water: H4C2 + 3O2 => 2CO2 + 2H2O
There are two types of "systems" running in a catalytic converter, "lean" and "rich." When the system is running "lean," there is more oxygen than required, and the reactions therefore favor the oxidation of carbon monoxide and hydrocarbons (at the expense of the reduction of nitrogen oxides). 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). With a constant imbalance of the reactions, the system never achieves 100% efficiency.
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 NOx 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. In addition, the release of the stored oxygen stimulates the the oxidation processes of CO and CxH4x .
Dangers of pollutants
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 NOx 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. NOx 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. NOx can also bind with ozone to create biological mutations (such as smog), and reduce the transmission of light.

Catalytic inhibition and destruction
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. 1. Lead: Most vehicles run on unleaded gasoline, in which all the lead has been removed from the fuel. However, if lead is added to the fuel and is burned, it leaves a residue that coats the catalytic metals (Pt, Rh, Pd, and Au) and prevents contact with the exhaust fumes, which is necessary in performing the necessary redox reactions. 2. Manganese and silicon: Manganese is primarily found in the organometallic compound MMT (methylcyclopentadienyl manganese tricarbonyl). MMT is a compound used in in the 1990's to increase fuel's octane rating (a higher octane rating indicates that the gas is less likely to combust, causing the engine to explode. This is important since higher performing engines have a high compression ratio, which would need a higher octane gas to complement the amount of compression in the engine), and has now been banned from commercial sale due to the EPA's regulations. Silicon can leak from the combustion chamber into the exhaust stream from the coolant inside the engine.
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.

THE LIMITATION AND DRAWBACK OF THE USES OF CATALYTIC CONVERTER
From an environmental standpoint, there are two great disadvantages to catalytic converters. The first and most obvious in terms of air pollution is that they convert harmful contaminants to less harmful ones. This does not mean that their byproducts are harmless; they are simply less harmful in regards to certain parameters. Catalytic converters can be used to oxidize the toxin carbon monoxide or hydrocarbons to form the less immediately dangerous compound of carbon dioxide, which is formed with both types of pollutants, and water, which is only in the case of hydrocarbons. They may also be used to convert the smog inducing compounds of nitric oxides into the greenhouse gas of nitrous oxide. Thus, catalytic converters transform a local air pollutant, a contaminant that mainly damages the area near its point of emission, to locally benign greenhouse gases which are global pollutants. The end product of these greenhouse gases has always been an expected result of the use of catalytic converters and until recently, it was not considered a problem. However, now that the dangers of greenhouse gases in regards to climate change have started to be understood, the aggregated benefit of catalytic converters is being brought into question (Wald).

The second great issue with using catalytic reactions to decontaminate air in terms of an overall environmental standpoint is that the extraction process of the precious metals needed in these reactions is very destructive. To reach ores containing platinum, companies used mechanized drills and explosives to create holes in mountains.
The generated waste rock can cause mine tailings and contaminate the local ecosystem. Mine tailings contaminate watersheds as erosion brings toxic sediments like lead or arsenic from the waste into rivers and streams. Some companies, like the Stillwater Mining Company, the only platinum and palladium mining company in the United States, backfill their emptied mine shafts with waste rock and sand to limit mine tailings (Mined). This process does not completely eliminate mine tailings, sources of contamination of watersheds, but it does help protect the tailings erosion which is the primary cause of the dispersion of their toxins (Arizona).
However, the vast majority of platinum mining occurs in South Africa where environmental regulations are more lax than in the United States and so this positive technique is likely not widely used resulting in higher levels of environmental poisoning from these tailings.
The disadvantages, however, are that they are very expensive to get/replace. Also, because carbon dioxide is a product of the reaction that takes place inside catalytic converters, widespread use of catalytic converters has also contributed to increased atmosphere levels of carbon dioxide. 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. Depending on the type and amount of precious metals inside, a catalytic converter can be easily sold for $200 apiece.

CONCLUSION

The report has been done to determine what and how a catalytic converter works and these have all been discussed in the contents above. Not only has its importance been highlighted, but also its effects and other converter-related problems have been elaborated.
To sum up, its invention has been a great help to many and continue to do so to reduce the amount of poisonous gases in the atmosphere and thus creating a better world for the organisms on earth.
Islamically, studies have found a correlation between the converter and Islamic point of view as mentioned below, taken from the Holy Quran.

Mischief has appeared on land and sea because of (the meed) that the hands of men have earned, that (Allah) may give them a taste of some of their deeds : in order that they may turn back (from Evil)
[30:41] Ar Ruum

“But seek, with the (wealth) which Allah has bestowed on thee, the Home of the Hereafter, nor forget thy portion in this world : but do thou good, as Allah has been good to thee, and seek not (occasion for) mischief in the land : for Allah loves not those who do mischief.
[28:77] Al Qasas

And, finally, not to forget this beautiful hadeeth below:

Mu’adh (may Allah be pleased with him) reported that the Prophet warned, “Beware of the three acts that cause you to be cursed : relieving yourselves in shaded places (that people utilize), in walkway or in watering place.” (Ranked sound, Hassan, by Al-Albani)