Vanadium (V) oxide (V2O5) is used as a catalyst for the oxidation of sulfur dioxide to sulfur trioxide. It is able to catalyze this reaction because it releases oxygen (O2) when heated up. The reaction is shown below.
V2O5 --> 2VO2 + (1/2)O2
This release of oxygen allows V2O5 to act as a catalyst for numerous oxidation reactions. This release of oxygen is a reversible process, and the VO2 produced will eventually reabsorb O2 and revert back to V2O5. This makes the vanadium catalytic. The production of SO3 is important commercially since it is used to make sulfuric acid on industrial scale.