A REVIEW PAPER ON

Presented by:-

Rajendra Kumar Gupta (Sr. Lect. ME)

Bhanu Prakash Aggarwal (3rd Yr. ME)

Abhishek Kumar Soni (3rd Yr. ME)

CONTENTS

:-

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 CONVERTER

The catalyst convertor converts theharmful pollutants in the exhaustgases into harmless gases. It islocated in the exhaust system and allexhaust gas must flow through it. Thecatalyst is a material in catalystconverter that causes a chemicalchange without being a part of thechemical reaction. The result inexhaust gas leaving the catalystconverter 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 → 2CO2

Oxidation 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 highmechanical 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 aspossible.

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.

REFERENCES

1) P. Pundir, Engine emissions pollutant Formation and Advances in Control Technology, Narosa Publishing house, New Delhi, Chapter 1, pp. 1-10.

2) auto.howstuffworks.com/catalytic-converter.htm

3)www.wikipedia.com

4) http://www.easterncatalytic.com/education/tech-tips/catalyst-basics-platinum-

palladium-and-rhodium-%E2%80%93-key-ingredients-that-make-converters-

tick/

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