What is Catalytic Converter and detail explanation l Catalyst Applications l How Catalytic Converters Work l Limitation of Catalytic Converter l Conclusion l

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Introduction

The pollutants have undesirable effect on air the quality environment and human health that tips in the stringent norms of pollutant the emission. Numbers of the different technologies like Upgrading in engine design fuel pre-treatment use of the alternative fuels fuel flavors exhaust treatment or superior tuning of the combustion process etc. are they being pain taking to the reduce emission levels of the engine. Out of the many technologies available for automobile exhaust emission control a catalytic converter is found to the best option to control HC, CO and the NOx emissions from petrol driven vehicles while diesel particulate filter and the diesel oxidation catalyst or oxidation catalysts converter have so far been the most potential option to the control particulates emissions from diesel driven the vehicle. A catalytic converter is the placed inside tailpipe through which the deadly exhaust gases containing HC, CO, NOx are the emitted. The function of catalytic convertor is to the convert these gases into CO2, H2O, N2 and the O2 and currently it is the necessary for all automobiles pursuing on the roads.

Position of Catalytic Converter in Car

Limitation of Catalytic Converter

In the severe situations experienced in the exhaust stream with temperatures up to the 1000 °C the metal in the catalyst is disposed to deactivation by the sintering, leading to a decrease in surface area and the hence catalytic activity. The conventional means to meet constriction the legislative emissions control goals is simply to increase the amount of PGM in the auto catalyst. The requirement to guarantee catalyst performance over the distinctive vehicle lifetime of the 80,000 km also means that excess metal must be added since the performance of the catalyst drops off over the time. In addition rising PGM request and the costs are inducements towards attaining lower metal loadings and the higher activity.

The compounds of the PGM are generally considered highly toxic while the Pd and Rh are carcinogenic in the nature. Due to the fact that PGM are created due to the scrape of an automotive catalyst wash the coat. That is why the road traffic is responsible for the metallic and organic pollutant emissions which contaminate the environment.

Reaction in the Catalytic Converter

2CO + O2 = 2CO2                                                              
Oxidation the HC + O2 = CO2 + H2O                                    
Reduction the Three way 2CO + 2NO = 2CO2 +N2              
HC + NO = CO2 + H2O + N2+2H2                                 
2NO = 2H2O + N2
Water Gas the Shift CO + H2O = CO2 + H2                          
Steam Reforming the HC + H2O = CO2 + H2                       

Removing Catalytic Converter

Some the early converter designs created a great deal of restriction to the flow of exhaust which the negatively affected vehicle performance drivability and the fuel economy because they were used with the carburetors incapable of precise fuel air mixture control and they could overheat and set fire to the flammable materials under the car. Removing the modern catalytic converter in new condition will be the only slightly increase vehicle performance without retuning but their removal or the gutting continues.

The exhaust section where the converter was may be replaced with a welded-in section of the straight pipe or a flanged section of the test pipe legal for off-road use that can then be replaced with the similarly fitted converter- choked section for legal on-road use or the emissions testing. In many other jurisdictions including US, it is illegal to the remove or disable a catalytic converter for any reason other than it’s the immediate replacement vehicles without functioning catalytic converters generally fail emission the inspections.

The aftermarket supplies high-flow converters for the vehicles with upgraded engines or those owners who prefer an exhaust system with the larger-than-stock capacity. Catalytic converters have proven to be the reliable and effective in reducing noxious the emissions. However they may have some the adverse environmental impacts in the use.

Catalyst Applications

1.Two-way Converter

The Two-way catalytic converter is widely used on diesel engines to the reduce hydrocarbon and the carbon monoxide emissions and they were also used on spark ignition gasoline engines in the USA market automobiles through 1981 when the two-way converter’s inability to the control NOx led to its supersession by three-way the converters. A two-way the catalytic converter has two simultaneous the tasks.

Oxidation of the carbon monoxide to carbon the dioxide:
   2CO + O2 → 2CO2
• Oxidation of the un-burnt and partially-burnt hydrocarbons to carbon dioxide and the water:
   CxH2x+2 + 3x+1/2 O2 → xCO2 + x+1 H2O a combustion the reaction

2.Three-way Converter

The Since 1981 three-way catalytic converters have been used in the vehicle emission control systems in North America and the many other countries on road going the vehicles. A three-way the catalytic converter has three simultaneous the tasks.

Oxidation of the carbon monoxide to carbon the dioxide:
   2CO + O2 → 2CO2
• Oxidation of the un-burnt hydrocarbons (HC) to carbon dioxide and the water:
   CxH2x+2 + 3x+1/2 O2 → xCO2 + x+1 H2O
• Reduction of the nitrogen oxides to nitrogen and the oxygen:
  2NOx → xO2 + N2

Diesel Oxidation Catalyst (DOC)

For the compression-ignition diesel engines the commonly used catalytic converter is the diesel oxidation catalyst (DOC). In the most applications a diesel oxidation catalyst consists of the stainless steel canister that contains a honeycomb structure called a substrate or the catalyst support. There are no moving parts just large amounts of the interior surface area. The interior surfaces are coated with the precious metals such as platinum or palladium as the oxidation catalytic material. It is the called an oxidation catalyst because the device converts exhaust gas pollutants into harmless gases by means of the chemical oxidation.

 In the case of diesel engine exhaust the catalyst oxidizes CO, HC, and the liquid hydrocarbons adsorbed on carbon the particles. In the field of mobile source emission control the liquid hydrocarbons adsorbed on the carbon particles in engine exhaust are referred to as the soluble organic fraction (SOF) the soluble part of particulate matter in the exhaust. Diesel oxidation catalysts are the efficient at converting the soluble organic fraction of the diesel particulate matter into carbon dioxide and water typically can be the achieve 25% to 40% over all the  particulate reduction by simply burning the soluble organic fraction (SOF) component of the particulate matter.

Diesel Oxidation Catalyst

How Catalytic Converters Work

There are millions of cars on the road in United States and each one is the potentially a source of air the pollution. Especially in the large cities amount of pollution that all the cars produce together can create big the problems. To the solve those problems cities states and the federal government create clean-air laws and the many laws have been enacted that restrict the amount of pollution that cars can be the produce. To the keep up with these laws automakers have made many refinements to car engines and the fuel systems.

To help reduce the emissions further they have developed an the interesting device called a catalytic converter which treats the exhaust before it leaves the car and removes a lot of the pollution. In this article you will be the learn which pollutants are produced by an engine and why and the how a catalytic converter deals with each of the pollutants. Catalytic converters are the amazingly simple devices so it is incredible to the see how big an impact they have.

Working Principles of Three-Way Catalytic Converters

Internal combustion engines use the exhaust stroke to expel the spent gases, via exhaust system where the harmful emissions are then passed through a muffler-type looking device which is the catalytic converter. Components of the spent gases consist of unburned hydrocarbons, NO, and the CO. As mentioned above the main purpose of catalytic converter is to reduce the original harmful emissions to the most acceptable levels by the means of catalyst controlled chemical the reactions. Therefore there are needs to be the most careful attention to the engine design before venting out gas into the air.

  1. Oxidation of the unburned hydrocarbons where oxygen gas is present in the exhaust gas has its bonds broken and the oxygen atom reacts with the unburned hydrocarbons to the produce CO2 and water vapors as the final products. An example would be the oxidation of benzene Equation 1:
    2C6 H6(g) + 15O2(g) → 12CO2(g) + 2H2O(l)
  2. Oxidation of the unburned hydrocarbons where oxygen gas is present in the exhaust gas has its bonds broken and the oxygen atom reacts with the unburned hydrocarbons to the produce CO2 and water vapors as the final products. An example would be the oxidation of benzene Equation 1:
    2C6 H6(g) + 15O2(g) → 12CO2(g) + 2H2O(l)
  3. Reduction of the N2O to give stable nitrogen and oxygen gas Equation 3. Since this is a reduction reaction rhodium is the used instead. Since it is a rare type of noble metal rhodium is usually alloyed with platinum or the palladium.
    2NOX (g) → XO2(g) + N2(g) (3)
Automobile catalytic converter

How Catalytic Converters Reduce Pollution

Most modern cars are the equipped with three-way catalytic the converters. Three-way refers to the three regulated emissions it helps to the reduce carbon monoxide VOCs and the NOx molecules. The converter uses two different types of the catalysts, a reduction catalyst and the oxidation catalyst. Both types consist of the ceramic structure coated with a metal catalyst usually platinum rhodium and or the palladium. The idea is to create the structure that exposes maximum surface area of the catalyst to exhaust stream while also minimizing the amount of catalyst required they are very the expensive.

1.The Reduction Catalyst

The reduction catalyst is the first stage of catalytic converter. It uses platinum and the rhodium to help reduce the NOx emissions. When an NO or the NO2 molecule contacts catalyst the catalyst rips nitrogen atom out of the molecule and holds on to it freeing the oxygen in form of O2. The nitrogen atoms bond with the other nitrogen atoms that are also stuck to the catalyst forming N2. For the example:
2NO N2 + O2

2.The Oxidization Catalyst

The oxidation catalyst is second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by the burning oxidizing them over a platinum and the palladium catalyst. This catalyst aids reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. For example:
2CO + O2 2CO2

3.The Control System

The third stage is a control system that monitors the exhaust stream and uses this is information to control the fuel injection system. There is and the oxygen sensor mounted upstream of the catalytic converter meaning it is closer to the engine than converter is. This is sensor tells the engine computer how much oxygen is in the exhaust. The engine computer can increase or decrease the amount of oxygen in 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 the make sure that there is enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and the CO.

4.Other Ways to Reduce Pollution

The catalytic converter does a great job at reducing the pollution but it can still be improved the substantially. One of its biggest shortcomings is that it only works at the fairly high temperature. When you start your car cold the catalytic converter does almost nothing to reduce the pollution in you’re the exhaust. One simple solution to the problem is to move 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 converter by exposing it to extremely high the temperatures. Most carmakers position the converter under the front passenger seat far the enough from engine to keep the temperature down to levels that will not the harm it.

Conclusion

With almost all the current investigation on catalytic converters it is possible to the predict a day where automobiles are no longer identified to pollute and harm the environment. Today’s automobiles are the meeting emission standards that need to the reduce of up to 99 percent for CO, Unburned Hydrocarbons and NOx compared to the unrestrained levels of automobiles sold in the 1960s.

Categories: Mechanical

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