In the Haber process for manufacturing ammonia, the catalyst used is

Explanation

Iron with small amounts of potassium and aluminium oxide as promoters is used because it is effective and cheap enough for a process operating on this scale. Vanadium pentoxide is the catalyst of the Contact process for sulphuric acid and nickel is used in the hydrogenation of oils, both of which appear here as familiar but wrong answers. The gases are recycled repeatedly since a single pass converts only about fifteen per cent.