In today’s world, the population of vehicle is increasing day by day and by product of their exhaust are NOx, CO which are two major pollutants which causes several respiratory disease. So, it become necessary to vanish this by product by providing pre exhaust or after exhaust treatment. Number of alternative technologies like improvement in engine design, fuel pretreatment, fuel additives, exhaust treatment of better turning of the combustion process are been considered to reduce the emission level of the engine.
This review paper discusses automotive exhaust emission and its impact on environment and controlling the emission of harmful gases with the use of catalyst such as platinum (noble gas) and sum more additive like cobalt oxide etc, history of catalytic, use of catalytic, process use up to now, limitation of catalytic and achievement of catalytic.
Keywords – catalyst, oxidation and reduction process, exhaust emissions, nobel metal, gas metal, analyzer.
Vehicle population is projected to grow close to 1300 million by the year 2030. Due to incomplete combustion in the engine, there are a number of incomplete combustion products CO, HC, NOx, particulate matters etc. The pollutants have undesirable effect on air quality, environment and human health that tips in stringent norms of pollutant emission. As the technology keep on evolving and emerging, it carries along undesirable effects apart from its broad application and use. One of the main contributors is said to be the emission of harmful gases produced by vehicle exhaust lines. The number of vehicles miles travels per year continues to increase as a result of higher demand and needs. Consequently, an increase in the number led to the increase of the content of pollutants in air. Most vehicular transportation relies on combustion of gasoline, diesel and jet fuels with large amount of emission of carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx) and particulates matter (PM) are especially concern. HC and CO occur because the combustion efficiency is less than 100%. The NOx is formed during the very high temperatures (>1500 0C) of the combustion process resulting in thermal fixation of the nitrogen in the air which forms NOx. Typical exhaust gas composition at the normal engine operating conditions are: carbon monoxide (CO, 0.5 vol.%), unburned hydrocarbons (HC, 350 vppm),nitrogen oxides (NOx, 900 vppm) hydrogen (H2, 0.17 vol.%), water (H2O, 10 vol.%), carbon dioxide (CO2, 10 vol.%), oxygen (O2, 0.5 vol.%). Carbon monoxide is a noted poison that has an affinity for hemoglobin in the blood 210 times greater than the oxygen affinity prolonged exposure to levels above 9 ppm can lead to reduce mental acuity for some individuals. HC and NOx lead to photochemical smog in presences of sunlight give secondary pollutant ozone, nitro dioxide & peroxyacyl nitrate which cause also global environmental problems.
A catalytic converter is placed inside the tailpipe through which deadly exhaust gases containing HC, CO, NOx are emitted. The function of the catalytic convertor is to convert these gases into CO2, H2O, N2 and O2 and currently, it is necessary for all automobiles pursuing on roads. As primary measures many different possibilities and technical methods of reducing exhaust gas emission are used e.g. combustion of lean air fuel mixture, multistage injection fuel, exhaust gas recirculation, fuel gas after burning, loading of additional water into cylinder volume.
NOx gas coming out from the commercial vehicle should be vanished. Now a days catalytic converter are used. The catalytic converter was invented by Eugene Houdry, a French mechanical engineer and expert in catalytic oil refining who lived in the U.S. around 1950. When the results of early studies of smog in Los Angeles were published, Houdry became concerned about the role of smoke stack exhaust and automobile exhaust in air pollution and founded a company, Oxy-Catalyst. Houdry first developed catalytic converters for smoke stacks called cats for short. Then he developed catalytic converters for warehouse fork lifts that used low grade non-leaded gasoline. Then in the mid 1950s he began research to develop catalytic converters for gasoline engines used on cars.
Widespread adoption of catalytic converters didn’t occur until more stringent emission control regulations forced the removal of the anti-knock agent, tetraethyllead, from most gasoline, because lead was a ‘catalyst poison’ and would inactivate the converter by forming a coating on the catalyst’s surface, effectively disabling it. Catalytic converters were further developed by a series of engineers including John J. Mooney and Carl D. Keith at the Engelhard Corporation, creating the first production catalytic converter in 1973.Dr. William C. Pfefferle developed a catalytic combustor for gas turbines in the early 1970s, allowing combustion without significant formation of nitrogen oxides and carbon monoxide.
Fig.2.1. catalytic convertor
A catalytic converter (CC) is placed inside the tailpipe through which deadly exhaust gases containing unburnt fuel, CO, NOx are emitted. The function of the catalytic convertor is to convert these gases into CO2, water, N2 and O2 and currently, it is compulsory for all automobiles plying on roads in US and Japan to have catalytic converters as they use unleaded petrol. In India the government has made catalytic converters mandatory for registration of new cars. A washcoat is a carrier for the catalytic materials and is used to disperse the materials over a large surface area. Aluminum oxide, titanium dioxide, silicon dioxide, or a mixture of silica and alumina can be used. The catalytic materials are suspended in the washcoat prior to applying to the core. Washcoat materials are selected to form a rough, irregular surface, which greatly increases the surface area compared to the smooth surface of the bare substrate. This in turn maximizes the catalytically active surface available to react with the engine exhaust. The coat must retain its surface area and prevent sintering of the catalytic metal particles even at high temperatures (1000 °C).
Fig.3.1. diagram of catalytic convertor
4.TYPES OF CATALYTIC CONVERTOR
4.1- The Oxidization Catalytic Converter
An oxidation catalyst is an expedient placed on the tailpipe of a car. The oxidation catalyst is the second stage of the catalytic converter. It decreases the unburned hydrocarbons and carbon monoxide by burning 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.
HC + O2 = CO2 + H2O
2CO + O2 = CO2
4.2- The Reduction Catalytic Convertor
A reduction catalyst to control NOx can be used as a distinct system in addition to the oxidation catalytic converter. The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to decrease the nitrogen oxide emissions. When such molecules come in contact with 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.
2NO = N2+ O2
4.3- The Three Way Catalytic Converter (TWCs)
TWCs have the benefit of performing the oxidation of carbon monoxide (CO), hydrocarbons (HC) and the reduction of nitrogen oxides (NOx) simultaneously. Noble metals are usually used as the active phase in TWCs. Pd catalysts are especially attractive since Pd is by far the inexpensive noble metal in the market and has well selectivity and activity for hydrocarbons. Rhodium the other vital constituent of three-way catalysts is broadly recognized as the most efficient catalyst for promoting the reduction of NO to N2. The TWCs performance in the emission control can be affected by operating the catalyst at elevated temperatures greater than 600°C.
The major reactions are the oxidation of CO and HC and the reduction of NOx. Also, water gas shift and steam reforming reaction occur. Intermediate products such as N2O and NO2 are also originated. The NOx storing concept is based on combination of a storage component into the three-way catalyst (TWCs) to store NOx during lean conditions for a time period of minutes.
2CO + O2 = 2CO2
Oxidation HC + O2 = CO2 + H2O
Reduction/ Three way 2CO + 2NO = 2CO2 +N2
HC + NO = CO2 + H2O + N2+2H2
2NO = 2H2O + N2
Water Gas Shift CO + H2O = CO2 + H2
Steam Reforming HC + H2O = CO2 + H2
These include oxides of base metals e.g. copper, chromium, nickel, cobalt etc. and the noble metals platinum (Pt), palladium (Pd) and rhodium (Rh). Base metal oxides although found to be effective at higher temperature but they sinter and deactivate when subjected to high-end exhaust gas temperature of conventional SI (Spark-Ignition) engine operation. Also, their conversion efficiency is severely inhibited by Sulphur dioxide resulting from Sulphur in fuel. The base metal catalysts are required in a relatively large volume and consequently due to high thermal inertia they took longer to heat up to operating temperature. Therefore, in practice only the noble metals are used as they have high specific activity high resistance to thermal degradation, Superior cold start performance and low deactivation caused by fuel Sulphur.
Some early converter designs greatly restricted the flow of exhaust, which negatively affected vehicle performance, drivability, and fuel economy. Because they were used with carburetors incapable of precise fuel-air mixture control, they could overheat and set fire to flammable materials under the car.
Removing a modern catalytic converter in new condition will not increase vehicle performance without retuning, but their removal or “gutting” continues. In such cases, the converter may be replaced by a welded-in section of ordinary pipe or a flanged “test pipe” ostensibly meant to check if the converter is clogged by comparing how the engine runs with versus without the converter, which facilitates reinstallation of the converter in order to pass an emission test.
Vehicles without functioning catalytic converters generally fail emission inspections. The automotive aftermarket supplies high-flow converters for vehicles with upgraded engines, or whose owners prefer an exhaust system with larger-than-stock capacity.
- Environmental, ecological and concern result in increasingly stringent emissions regulations of pollutant emission from vehicle engines.
- Among all the types of technologies developed so far, use of catalytic converters is the best way to control auto exhaust emission.
- The economical reasons, limited resources of platinum group metal and some operating limitations of platinum group metal based catalytic converters have motivated the investigation of catalyst material.
- This type of Catalytic converters have also been developed for use on trucks, buses and motorcycles as well as on construction equipment lawn and garden equipment marine engines and other non-road engines. Catalytic converters are also used to reduce emissions from alternative fuel vehicles powered by natural gas, methanol, ethanol and propane. To date more than 500 million vehicles equipped with catalytic converters have been sold worldwide. In 2005, 100 percent of new cars sold in the U.S. were equipped with a catalytic converter, and worldwide over 90 percent of new cars sold had a of metal monolith type.
CO Carbon monoxide
NOx Nitrogen oxides
PM Particulates matter
TWC Three way catalytic convertor
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- Review paper on Catalytic Converter for Automotive Exhaust Emission, Julie M Pardiwala, Femina Patel, Sanjay Patel
- EMISSION TESTING OF CATALYTIC CONVERTER USING ZIRCONIUM OXIDE (ZrO) AND COBALT OXIDE (CoO) AS CATALYST, RAJAT KUMAR1, SUPREET SINGH2 & MANPREET KAUR3 1,2Department of Automobile Engineering, Chandigarh University, Mohali, India 3Department of Mechanical Engineering, BBSBEC Fatehgarh Sahib, India.
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