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The stringent emissions legislation has necessitated advances in the catalytic converter system comprising the substrate, washcoat technology, catalyst formulation and packaging design. These advances are focused on reducing light-off emissions at lower temperature or shorter time, increasing FTP efficiency, reducing back pressure and meeting the mechanical and thermal durability requirements over 100,000 vehicle miles. This paper reviews the role of cordierite ceramic substrate and how its design can help meet the stringent emissions legislation. In particular, it compares the effect of cell geometry and size on performance parameters like geometric surface area, open frontal area, hydraulic diameter, thermal mass, heat transfer factor, mechanical integrity factor and thermal integrity factor - all of which have a bearing on emissions, back pressure and durability. The properties of advanced cell configurations like hexagon are compared with those of standard square cell.

The stringent emissions regulations, notably for cold start, have led to design modifications in each of the converter components, notably the catalyst support. With the faster light–off requirement, the catalyst support must have a lower thermal mass so as to reach the 50% conversion temperature as quickly as possible. Simultaneously, for higher warmed–up efficiency, the catalyst support must offer higher geometric surface area. Similarly, for improved fuel economy and for preserving engine power, the catalyst support must exert lower back pressure. Indeed, these three performance requirements might be met by certain thin wall ceramic substrates, including 400/4.5 and 600/4.3, which have 22% lower thermal mass, 25% higher geometric surface area and 8% larger open frontal area than the standard 400/6.5 substrate. Testing by automakers and international laboratories on engine dynamometers has verified the above advantages of thin wall substrates.