Catalytic converters

1
Catalytic converters

• A catalytic converter is a device used to reduce
  the toxicity of emissions from an internal
  combustion engine.
• First widely introduced on production automobiles
  in the US market for the 1975 model year to
  comply with tightening regulations on auto
  exhaust, catalytic converters are still most
  commonly used in motor vehicle exhaust systems

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2
Catalytic converters

• There are two types of catalytic converter 3
  way and 2 way
• Three-way catalytic converters
• A three-way catalytic converter has three tasks
• 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
• 2CxHy (2xy/2)O2 ? 2xCO2 yH2O
• These three reactions occur most efficiently when
  the engine is running slightly above the
  stoichiometric point. This is between 14.8 and
  14.9 parts air to 1 part fuel, by weight, for
  gasoline (the ratio for LPG, natural gas and
  ethanol fuels is slightly different, requiring
  modified fuel system settings when using those
  fuels)

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3
Catalytic converters

• Two-way catalytic converters
• A two-way catalytic converter has two tasks
• Oxidation of carbon monoxide to carbon dioxide
• 2CO O2 ? 2CO2
• Oxidation of unburnt hydrocarbons (unburnt and
  partially-burnt fuel) to carbon dioxide and
  water
• 2CxHy (2xy/2)O2 ? 2xCO2 yH2O
• This type of catalytic converter is widely used
  on diesel engines to reduce hydrocarbon and
  carbon monoxide emissions. They were also used on
  spark ignition (gasoline) engines in USA market
  automobiles up until 1981, when they were
  replaced by three-way converters due to
  regulatory changes requiring reductions on NOx
  emissions.

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4
Catalytic converters

• The catalytic converter consists of several
  components
• The core, or substrate. In modern catalytic
  converters, this is most often a ceramic
  honeycomb, however stainless steel foil
  honeycombs are also used. The purpose of the core
  is to "support the catalyst. The ceramic
  substrate was invented by Rodney Bagley, Irwin
  Lachman and Ronald Lewis at Corning Glass.
• The washcoat. In an effort to make converters
  more efficient, a washcoat is utilized, most
  often a mixture of silica and alumina. The
  washcoat, when added to the core, forms a rough,
  irregular surface which has a far greater surface
  area than the flat core surface and therefore
  more places for active precious metal sites. The
  catalyst is added to the washcoat (in suspension)
  before application to the core.
• The catalyst itself is most often a precious
  metal. Platinum is the most active catalyst and
  is widely used. However, it is not suitable for
  all applications because of unwanted additional
  reactions and/or cost. Palladium and rhodium are
  two other precious metals that are used. Platinum
  and rhodium are used as a reduction catalyst,
  while platinum and palladium are used as an
  oxidization catalyst. Cerium, iron, manganese and
  nickel are also used, though each has its own
  limitations. Nickel is not legal for use in the
  European Union (due to reaction with carbon
  monoxide). While copper can be used, its use is
  illegal in North America due to the formation of
  dioxin.

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5
Catalytic converters

• Construction of catalytic converter

Alumina or Silica coating Of honeycomb with
catalyst Particles
Ceramic or Stainless Steel Honeycomb (lower
Pressure drop)
Clean exhaust
Engine exhaust
Catalytic converter
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6
Catalytic converters

• Future improvements to catalytic converter

Particulate solids removal
Higher activity catalysts
Nano-particle coatings
Clean exhaust
Engine exhaust
Catalytic converter
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7
Catalytic converters

• In the future Catalytic converters will be
• - smaller
• - lighter
• - more efficient
• - capable of nano particle removal
• - required until hydrogen fuel becomes widely
  available.
• See Taymark Engineering for more information on
  future
• improvements

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