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With stricter emissions standards, low back pressure requirements, and 100,000 mile durability specifications, ceramic catalysts have undergone significant developments over the past few years. The thrust in the ceramics area has centered on thin-wall structures to minimize back pressure and on high cell density for rapid light-off in close-coupled applications. The thin-wall structures are extruded from low expansion cordierite ceramic with adequate strength and thermal shock resistance equivalent to those of standard cordierite substrate. Examples of thin-wall substrate include 350XT which is extruded from a very low expansion dense cordierite ceramic, and 400/4 and 600/4 cell structures extruded from a low expansion modified cordierite ceramic. This paper will focus on the high fatigue resistance, excellent conversion efficiency, and low back pressure of 350 XT substrates with advanced washcoat system.

The preconverter is an essential element of exhaust gas treatment to help meet the tighter emission standards of TLEV and LEV levels. Its design must be chosen so as to meet the simultaneous requirements of compactness, faster light-off, low back pressure, high temperature durability and low cost. This paper presents design options for a ceramic substrate and durable package which lead to an optimum and cost-effective preconverter system. Preliminary data for high temperature physical durability of selected converter systems are presented. Performance parameters for light-off activity and back pressure are also computed and compared with those of standard substrates used in underbody application. Laboratory tests comprising of axial push-out test, high temperature vibration test, exhaust gas simulation test and the engine dynamometer test demonstrate the viability of ceramic preconverters for automotive application.

New test methods were developed to characterize the high temperature durability of intumescent mats that are used to mount ceramic catalyst supports in stainless steel cans. The key attribute of these tests is the use of an electric resistance heating method to maintain a temperature gradient through the thickness of the mat when a cyclic or constant shear stress is applied to the mat interface. These tests are simple to perform and do not require expensive equipment or highly skilled operators. Using these new test methods, the durability of ceramic preconverters mounted with 4070 gm/m2 intumescent mat was studied. The results of these tests indicate that a preconverter package with 4070 gm/m2 intumescent mat can perform satisfactorily in the close-coupled application where temperatures exceed 900°C. The mat performance can be quantified in terms of applied stress and test temperature by utilizing the experimental methods described in the present study.

Thin wall ceramic catalysts offer improved performance by way of faster light-off, lower back pressure and higher FTP efficiency than standard ceramic catalysts. These advantages are attributed to their lower thermal mass, larger open frontal area and higher geometric surface area. This paper will focus on their physical durability, notably their thermal shock resistance. The critical physical properties which influence thermal shock resistance - namely modulus of rupture, elastic modulus and coefficient of thermal expansion - will be examined over a wide range of operating temperatures for both standard (400/6.5) and thin wall catalyst supports (600/4.3 and 400/4.5) with stable high temperature washcoat systems. These data help evaluate the thermal shock capability of each system via computation of thermal shock parameter. The validity of such computations is tested against the thermal shock data from oven test.