The precious metal used as a catalyst in the Ostwald process is platinum.
In the first stage, ammonia is oxidized by oxygen over a platinum catalyst to form nitric oxide and water. The nitric oxide is then oxidized to nitrogen dioxide, which is absorbed in water to produce nitric acid. Platinum provides a surface that speeds the reaction without being consumed in the overall chemical equation.
Industrial catalyst gauze is commonly platinum alloyed with about 10% rhodium. Rhodium strengthens the gauze and can improve nitric oxide yield, helping it tolerate an intensely hot, corrosive, and exothermic environment. The catalyst operates at roughly 900°C, with pressure sometimes reaching about 8 atmospheres.
The process is named for German chemist Wilhelm Ostwald, who developed it around the turn of the 20th century. It became economically important because it supplied nitric acid for fertilizers and explosives without relying on natural nitrate deposits. A frequent mix-up is to answer rhodium: rhodium is an important alloying partner, but platinum is the principal catalytic metal named in the standard answer.