Which catalyst is NOT typically found in a three-way catalytic converter?

Three-way catalytic converters play a vital role in reducing harmful emissions from gasoline engines by facilitating chemical reactions that convert carbon monoxide, unburned hydrocarbons, and nitrogen oxides into less harmful substances. The catalysts typically used in these converters are precious metals known for their ability to endure high temperatures and to promote significant chemical reactions.

Platinum, palladium, and rhodium are the three primary catalysts found in three-way catalytic converters. Platinum is particularly effective at oxidizing carbon monoxide and hydrocarbons, while palladium serves a similar purpose. Rhodium is essential for reducing nitrogen oxides, making it critical for the converter's overall efficiency in reducing emissions.

In contrast, milladium is not a recognized or used catalyst in automotive catalytic converters, including three-way converters. Therefore, the correct answer identifies milladium as the catalyst that is not typically found in such devices, highlighting its absence from the standard composition utilized for emission control in gasoline engines. Understanding the specific roles and utilization of these catalysts can aid in recognizing how conventional catalytic converters function to mitigate harmful exhaust emissions.