1998-02-23

Fatigue and Performance Data for Advanced Thin Wall Ceramic Catalysts 980670

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 fatigue data at 200°C and 400°C show that the 350 XT catalyst is considerably superior to the standard three-way-catalyst employing 400/6.5 substrate. The fatigue constant for 350 XT catalyst ranges from 35 at 200°C to 45 at 400°C which implies that the advanced 350 XT catalyst can sustain 20 to 40% higher stress than the standard 400/6.5 catalyst over the 100,000 mile durability requirement. The advanced catalyst technology contains a high temperature stabilized alumina and ceria washcoat system which, following aging equivalent to 100,000 miles, yields FTP efficiencies which meet Tier 1 emission standards. The paper will conclude with the back pressure data which are superior to those for the standard 400/6.5 catalyst system due to thinner walls and larger hydraulic diameter.

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