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

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 + (2x+y/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)

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 + (2x+y/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.

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.

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

Catalytic converters Future improvements to catalytic converter Engine exhaust Catalytic converter Clean exhaust Particulate solids removal Higher activity catalysts Nano-particle coatings

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