Why is a vanadium oxide catalyst used in the contact process?

In the contact process, a vanadium oxide catalyst—typically pellets of porous siliceous material impregnated with vanadium pentoxide ($V_2{O}_5$) and a potassium compound—is used to facilitate the oxidation of sulfur dioxide into sulfur trioxide.12

This reaction is a critical step in the modern industrial production of sulfuric acid. The catalyst functions at moderately high temperatures, allowing the sulfur dioxide and oxygen to unite efficiently to form the sulfur trioxide required for the subsequent production of the acid.12