Which metals are typically used in a TWC?

The correct choice identifies platinum and palladium as the metals typically used in a three-way catalyst (TWC). These precious metals serve critical roles in the catalytic process that reduces harmful emissions in internal combustion engines.

In a TWC, platinum and palladium facilitate the chemical reactions necessary to convert toxic gases such as carbon monoxide, unburned hydrocarbons, and nitrogen oxides into less harmful substances like carbon dioxide and nitrogen. Their high catalytic activity and ability to withstand extreme conditions make them well-suited for this application.

Other metals listed, such as iron and nickel, aren't used in TWCs due to their lower effectiveness in catalyzing the necessary reactions for emissions reduction. Similarly, copper and aluminum, along with gold and silver, do not possess the required catalytic properties for effective use in a TWC. Thus, the choice of platinum and palladium is not only based on their efficiency but also on their ability to operate within the harsh environments typical of exhaust systems, making them the preferred choice in this area of emission control technology.