Substrates Washcoat Technologies

Catalysis and Automotive Pollution Control III Studies in Surface Science and Catalysis, Vol. 96 1995 Elsevier Science B.V. All rights reserved. 

The successful performance of cordierite ceramic converter system over the past 19 years in a myriad of applications - automotive, light duty vehicles and trucks - has amply demonstrated its suitability as emissions treatment device [5]. Furthermore, new developments in the area of ceramic converter systems have helped extend their applicability to small engines, both two-stroke, used in motorcycles [6-8]. In addition to design flexibility, the ceramic converter offers higher offers higher use temperature, improved heath retention and lower system cost. 

The preconverter system must meet the following requirements  

From automakers point of view, a preconverter package designed and assembled in the above manner is readily implemented in the exhaust system. It also shortens the developmental cycle and reduces engineering costs—a most desirable combination for meeting legal and commercial requirements. 

They are readily computed for a given cell geometry and are very useful for preliminary design. They have a direct impact on physical properties and converter performance. For example, the substrate strength O3 is proportional to the product of MIF and wall strength 5,, i.e. 

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Table 3 describes the 12 different converters built for tliis study. All of the converters had a catalyst volume of 1.8 liters and used 400 cpsi ceramic substrates with a frontal area of 88 cm2. Each converter was built with two catalyst bricks having an equal volume of 0.9L. This experiment varied both the Pd front brick technology and loading and the Pt/Rh rear brick catalyst technology and loading. The Pd and the Std Pt/Rh washcoat technologies are the same ones described in the first experiment. The "HT" Pt/Rh washcoat... 

For the preparation of the three-way catalysts several procedures were used, which are summarized in Table 1. The reference catalyst samples were prepared by coating monolithic ceramic substrates with a cell density of 400 cpsi and a wall thickness of 6.5 mil. After drying and calcination of the coated monoliths, they were impregnated Avith the precious metals, precious metal loadings and precious metal ratios of choice. This method will be referred to as preparation method A. The novel catalyst technologies were prepared by placing the precious metals directly onto the washcoat. To do so, several methods were used. Preparation method C was used to apply the precious metals on all the washcoat components. The methods B and D were used to apply the precious metals selectively on one or more of the washcoat components. Details of the catalysts are given in Table 2. 

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