Substrates and catalytic coatings
The technology of the substrates on which the active catalyst is supported has seen great progress. In 1974, ceramic substrates had a density of 200 cells per square inch (cpsi) of cross section (31 cells/cm2) and a wall thickness of 0.012 inch or 12 mil (0.305 mm). By the end of the 1970s, the cell density had increased from 300 to 400 cpsi and wall thickness had been reduced by 50% to 6 mil. Now 400, 600 and 900 and even 1200 cpsi substrates are available and wall thickness can be reduced to 2 mil – almost 0.03 mm.
The substrates on which the active catalyst is supported can be ceramic or metallic, with each offering particular advantages for specific applications and positions in the exhaust system. The development of strong ultra-thin wall substrates with cell densities of up to 1200 cells per square inch (186 cells/square cm) has been a major factor in the increasing efficiency of catalysts.
As explained on the landing page, emission control systems need to be brought to operating temperature as quickly as possible. Thin walls reduce the substrate mass and hence the time to reach these temperatures.
Coatings systems have been developed which allow the maximum efficiency with optimum use of the precious metals platinum (Pt), palladium (Pd) and rhodium (Rh). The nanotechnology used in catalytic coatings involves stabilised crystallites, washcoat materials that maintain high surface area at temperatures around 1000°C, improved oxygen storage components and novel coating processes to optimise the distribution of the coatings. All play a part in the high efficiencies of catalysts.
Precious metals used in emission control catalysts can be recycled, and recycling rates are increasing, further contributing to the affordability of future vehicles.
In this case, active compounds are extruded simultaneously with the catalyst structure and are therefore fully integrated, this catalyst is an alternative to the coated substrate. Today, this technology can be used for Selective Catalytic Reduction (SCR) catalysts.