Career Point University

Presented by:- Sourabh GuptaBRANCH-MECHANICALUID-K11180SUBMITTED TO-AMARDEEP KUMAR

INTRODUCTION

There are four possible cases of atmospheric pollution from the automobile. Without emission control, a carburettor and fuel tank emit fuel vapour. The crankcase emits blow by gases and fuel vapour, and the tailpipe emits exhaust gases that contain pollutants. The pollutants are hydrocarbons (HC), carbon monoxide (CO), and nitrogen gases (NOx).These air pollutants are harmful to plants and animals, including human being. The need to control engine emissions was recognized as early as 1909. Due to the more stringent rules and emission standards, automotive manufacturers begun to develop a treatment device for exhaust gases known as catalytic convertor for their vehicle models.

CATALYTIC CONVERTERThe catalyst convertor converts the harmful pollutants in the exhaust gases into harmless gases. It is located in the exhaust system and all exhaust gas must flow through it. The catalyst is a material in catalyst converter that causes a chemical change without being a part of the chemical reaction. The result in exhaust gas leaving the catalyst converter contains less HC, CO, NOx .

TYPES OF CATALYTIC CONVERTER

1. The oxidization catalytic converter :-The oxidation catalyst is the second stage of catalyst converter. It reduces the unburned hydrocarbon and carbon monoxide by burning (oxidizing) them over a platinum palladium catalyst.

HC + O₂ → CO₂ + H₂O 2CO + O₂ → 2CO₂

2. The reduction catalytic converter :-The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to reduce nitrogen oxide emissions.

2NO → N2 + O2

3. The three-way catalytic converter (TWC):-TWCs have the advantages of performing the oxidation of CO, HC and the reduction of nitrogen oxides (NOx) simultaneously. Noble metals used as the active phase in TWCs. Pd are generally used. The major reactions are the oxidation of CO and HC and reduction of NOx. Also, water gas shift and steam reforming reaction occur.

  2CO + O2 → 2CO2Oxidation HC + O2 → CO2 + H2O Reduction/three-ways 2CO + 2NO → 2CO2 + N2 HC + NO → CO2 + H2O + N2

Water gas shifting CO + H2O → CO2 + H2

Steam reforming HC + H2O → CO2 + H2

Component of catalytic converter:-a) Catalyst:-

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.

b) Substrate or support:- i) Pellets :- The first catalytic converters of passenger cars in early 1970s used a bed of spherical ceramic pellets. These are also known as packed bed catalytic converter. The spherical pellets made of γ-alumina (γ – Al2O3). The material of pellets is selected to have a high mechanical strength against crush and abrasion.

ii) Monolith:-In our daily practice a monolith is a ceramic block consisting of a large number of small straight and parallel channels. A special mixture of clay binders and additives is pushed through a sophisticated dye to create the monolith structure.

iii) Washcoat: - A thin layer of inorganic oxides known as wash coat is applied to the cells in monolith structure to increase effective surface area for dispersion of active catalyst that increase its contact with the reacting gases.

iv) Air to fuel ratio :- Conversion efficiency of NO, CO and HC as a function of the air - fuel in a three way catalytic converter. There is a narrow range of air - fuel ratio near stoichiometry in which high conversion efficiencies for all three pollutants are achieved.

EFFECT OF COLD START EMISSION ON THE EFFICIENCY OF CATALYTIC CONVERTER :-While a catalytic converter is running under the ideal operating conditions, it is very successful at purifying exhaust: collecting and eliminating 97% of toxins including hydrocarbons, nitrogen oxides, and carbon monoxide. But the issue of cold-start emissions is that automobiles do not always meet these conditions. An obvious solution to prevent cold-start emissions would be to make the engine hotter, as fast as possible.

LIMITATION:-

1) In the exhaust stream with temperatures up to 1000 °C the metal in the catalyst is prone to deactivation by sintering, leading to a reduction in surface area and hence catalytic activity.

2) Platinum used as catalyst have high cost and also vaporized at high temperature.

3)Palladium also used as catalyst with the platinum having less ability of absorption and desorption of oxygen.

4)Three – way catalytic converter CO2, which is also harmful for the environment.

MODIFICATION IN CATALYTIC CONVERTER:- 1) Replacement of Platinum and Palladium:- Due to high cost we can use another material as catalyst in catalytic converter We can use Perovskite Oxide(CaTiO3) due to low costs, high thermal stability, better redox properties.

2) Development of four – way catalytic converter:- In this converter we use high alunimium content Zeolite which absorb all the CO2 produced in three – way catalytic converter.

APPLICATION OF CATALYTIC CONVERTER :-

1) A catalytic converter is a device used to reduce the toxicity of emissions from an internal combustion engine.

2) Catalytic converters are most commonly used in motor vehicle exhaust systems.

3) Catalytic converters are also used on generator sets, forklifts , mining equipment, trucks , buses, trains, and other engine-equipped machines

4) A catalytic converter provides an environment for a chemical reaction wherein toxic combustion by-products are converted to less-toxic substances.

CONCLUSION

Three-way catalyst with stoichiometric engine control systems remain the state of art method for simultaneously controlling hydrocarbon, CO and NOx emissions from vehicle. Due to high cost of platinum and operating limitation platinum based catalytic converter motivates the investigators of alternative catalyst material, which have low coast and provide high efficiency. catalytic converter is best option for reducing the pollutant. It is essential for investigation and modification in catalytic to increase the efficiency of catalytic converter.

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