The six Platinum Group Metals (i.e., platinum, palladium, rhodium, iridium, ruthenium and osmium) are chemically very similar and are used for many applications.
An autocatalyst is a cylinder or elliptical cross section made from ceramic or metal formed into a fine honeycomb and coated with a solution of chemicals and a combination of platinum, rhodium and/or palladium. It is mounted inside a stainless steel canister (the whole assembly is called a catalytic converter) and installed in a vehicle's exhaust line where it converts pollutants from the combustion of fuel into harmless gases.