Combustible engines releases so many harmful pollutants and with the use of catalytic converters this harmful pollutants are reduced to less harmful ones.

1. CATALYTIC C CONVERTERS
Objectives
1. What is catalytic converters
2. Uses of catalytic converters
3. Construction of catalytic converters
4. Types of catalytic converters

2. CATALYTIC CONVERTERS
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).
Are used with internal combustion engines fueled by either petrol(gasoline)
or diesel—including 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 and motorcycles.

3. CATALYTIC CONVERTERS
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.

4. CONSTRUCTION OF CATALYTIC CONVERTERS
• They consist of many of components but we will only look at the
important three.
• The catalyst core or Substrate: For automotive catalytic converters,
the core is usually a ceramic monolith with a honeycomb structure.
• Metallic foil monoliths made of FeCrAl are used in some applications.
• Either material is designed to provide a high surface area to support
the catalyst washcoat, and therefore is often called a “catalyst support”.
• The cordierite ceramic substrate used in most catalytic converters was
invented by Rodney Bagley, Irwin Lachman and Ronald Lewis at
Corning Glass, for which they were inducted into the National Inventors
Hall of Fame in 2002.

5. CONSTRUCTION OF CATALYTIC CONVERTERS
• The washcoat: is a carrier for the catalytic materials and is used to
disperse the materials over a high surface area.
• Aluminum oxide, titanium dioxide, silicon dioxide, or a mixture of silica and
alumina can be used.
• 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).

6. CONSTRUCTION OF CATALYTIC CONVERTERS
• The catalyst: is most often a precious metal.
• Platinum is the most active catalyst and is widely used, but is
not suitable for all applications.
• Rhodium is used as a reduction catalyst, palladium is used as
an oxidation catalyst, and platinum is used both for reduction
and oxidation.

7. CONSTRUCTION OF CATALYTIC CONVERTERS

8. TYPES OF CATALYTIC CONVERTERS
TWO-WAY CATALYTIC
CONVERTERS
• Also known as an oxidation
catalytic converter has two
simultaneous tasks.
• Oxidation of carbon monoxide to carbon dioxide: 2CO +
O2 → 2CO2.
• Oxidation of hydrocarbons (unburnt and partially burnt
fuel) to carbon dioxide and water: CxH2x+2 + [(3x+1)/2]
O2 → xCO2 + (x+1) H2O (a combustion reaction).
TWO-WAY CATALYTIC
CONVERTERS
• Widely used on diesel engines to reduce hydro carbon
and carbon monoxide emissions.
• Also used on American and Canadian market
automobiles until 1981.
• Disadvantage: inability to
control oxides of Nitrogen.

9. TYPES OF CATALYTIC CONVERTERS
THREE-WAY CATALYTIC
CONVERTERS
• also known as oxidation and
reduction catalytic converters to
which the reduction and
oxidation catalysts are typically
contained in a common housing.
• It has three simultaneous
tasks:
THREE-WAY CATALYTIC
CONVERTERS
• Reduction of nitrogen oxides to nitrogen
and oxygen: 2NOx→ xO2 + N2
• Oxidation of carbon monoxide to carbon
dioxide: 2CO + O2 → 2CO2
• Oxidation of unburnt hydrocarbons (HC) to
carbon dioxide and water: CxH2x+2 +
[(3x+1)/2] O2 → xCO2 + (x+1) H2O.

10. CATALYTIC CONVERTERS
By: PaulusN. Nakashole
B.Sc Environmental Science
5th Sem
09/20/2015
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