 The most common use of platinum is as a catalyst in chemical reactions , often as platinum black . It has been employed as a catalyst since the early 19th century , when platinum powder was used to catalyze the ignition of hydrogen . Its most important application is in automobiles as a catalytic converter , which allows the complete combustion of low concentrations of unburned hydrocarbons from the exhaust into carbon dioxide and water vapor . Platinum is also used in the petroleum industry as a catalyst in a number of separate processes , but especially in catalytic reforming of straight @-@ run naphthas into higher @-@ octane gasoline that becomes rich in aromatic compounds . PtO2 , also known as Adams ' catalyst , is used as a hydrogenation catalyst , specifically for vegetable oils . Platinum also strongly catalyzes the decomposition of hydrogen peroxide into water and oxygen and it is used in fuel cells as a catalyst for the reduction of oxygen . 
