Supports for automobile exhaust catalysts are of two general types: alumina pellets (spheres and extrudates) and ceramic monoliths coated with a thin alumina washcoat (Figure 14). The reasons for choosing alumina supports for the noble metals include high surface area, attrition resistance, stable structure under typical exhaust conditions, favorable pore structure, and adequate supply . Both support types have perceived advantages and disadvantages which have influenced their selection for use by automobile manufacturers . Factors considered include converter size and cost, catalyst performance and durability on a particular vehicle, availability of support material from suppliers, and ease of replacement. In this section the recent literature on both support types will be reviewed.
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