Monolithic catalyst supports are

extruded Extrusion is a process used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex c ...

structures that are the core of many

catalytic converter A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usuall ...

s,Williams, J.; ''Monolithic structures, materials, properties and uses''; Catalysis Today, 69 (2001) 3-9 most

diesel particulate filter A diesel particulate filter (DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine.Tom Nash (May 2003) "Diesels: The Smoke is clearing", ''Motor '' Vol.199 No. 5, p. 54, Hearst Business Publ ...

s, and some catalytic reactors. Most catalytic converters are used for

vehicle emissions control Vehicle emissions control is the study of reducing the emissions produced by motor vehicles, especially internal combustion engines. Types of emissions Emissions of many air pollutants have been shown to have variety of negative effects on publi ...

. Stationary catalytic converters can reduce

air pollution Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different type ...

from

fossil fuel power station A fossil fuel power station is a thermal power station which burns a fossil fuel, such as coal or natural gas, to produce electricity. Fossil fuel power stations have machinery to convert the heat energy of combustion into mechanical energy, ...

Properties

Monoliths for automotive catalytic converters are made of a

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelai ...

that contains a large proportion of synthetic

cordierite Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: to . A high-tempera ...

, 2MgO•2Al₂O₃•5SiO₂, which has a low

coefficient of thermal expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic ...

. Each monolith contains thousands of parallel channels or holes, which are defined by many thin walls, in a

honeycomb structure Honeycomb structures are natural or man-made structures that have the geometry of a honeycomb to allow the minimization of the amount of used material to reach minimal weight and minimal material cost. The geometry of honeycomb structures can ...

. The channels can be square,

hexagon In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A ''regular hexagon'' h ...

al, round, or other shapes. The hole density may be from 30 to 200 per cm², and the separating walls can be 0.05 to 0.3 mm. The many small holes have a much larger

surface area The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of ...

than one large hole. High surface area facilitates catalytic reaction or filtration. The open spaces in the cross-sectional area are 72 to 87% of the frontal area, so resistance to the flow of gases through the holes is low, which minimizes energy consumed forcing gases through the structure. The monolith is a

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

that supports a

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

. After the monolith is complete, a washcoat is applied that deposits oxides and catalyst(s) (most commonly

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...

palladium Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself nam ...

, and/or

rhodium Rhodium is a chemical element with the symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring ...

) on the walls of the holes. Alternative structures include corrugated metal and a

packed bed In chemical processing, a packed bed is a hollow tube, pipe, or other vessel that is filled with a packing material. The packing can be randomly filled with small objects like Raschig rings or else it can be a specifically designed structure ...

of coated pellets or other shapes.

Uses

Diesel particulate filter A diesel particulate filter (DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine.Tom Nash (May 2003) "Diesels: The Smoke is clearing", ''Motor '' Vol.199 No. 5, p. 54, Hearst Business Publ ...

s (DPF) *Catalytic incineration *

Catalyst support In chemistry, a catalyst support is the material, usually a solid with a high surface area, to which a catalyst is affixed. The activity of heterogeneous catalysts is mainly promoted by atoms present at the accessible surface of the material. Cons ...

for chemical processes *

Vehicle emissions control Vehicle emissions control is the study of reducing the emissions produced by motor vehicles, especially internal combustion engines. Types of emissions Emissions of many air pollutants have been shown to have variety of negative effects on publi ...

References

Catalysis {{Catalysis-stub