How do ceramic catalyst supports help reduce automobile emissions?

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advanced structural ceramics Figure 1: Resistance to cracking in transformation-toughened zirconia. In a ceramic composed of tetragonal zirconia dispersed in a zirconia matrix, the stress field advancing ahead of a propagating crack transforms the small tetragonal particles to larger monoclinic particles. The larger particles exert a crack-closing force in the process zone behind the crack tip, effectively resisting propagation of the crack.

Ceramic catalyst supports are essential components in catalytic converters, which reduce harmful automotive emissions like nitrogen oxides, carbon monoxide, and unburned hydrocarbons.1

These supports facilitate emission control by providing a high-surface-area substrate for platinum-group metals or base-metal catalysts. Because these precious metals are expensive, they are deposited onto the ceramic as finely divided particles to maximize their reactive surface area.1

The supports are engineered into two primary structures to optimize efficiency:
* Pellets: Porous beads, often made of alumina, that provide immense internal pore surface area.1
* Honeycomb Monoliths: Extruded structures, commonly made of cordierite due to its low thermal expansion, which feature numerous longitudinal pores. These are coated with a wash of alumina to support the catalyst particles.1

By engineering these microstructures, manufacturers achieve the large surface areas necessary for effective catalytic conversion while minimizing pressure drops in the exhaust system.1