Vanadium trioxide is the chemical compound V₂O₃. It is prepared by reduction of V₂O₅ with hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 or carbon monoxide

Carbon monoxide

Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

.It is a basic oxide dissolving in acids to give reducing vanadium(III) solutions. V₂O₃ has the corundum structure. It is antiferromagnetic with a critical temperature of 160 K. At this temperature there is an abrupt change in conductivity from metallic to insulating.

On exposure to air it is gradually converted into indigo-blue crystals of V₂O₄. Vanadium trioxide is generally used as a catalyst when making ethanol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 from ethylene

Ethylene

Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

.

In nature it occurs only rarely, as the mineral karelianite.