MarsvanKrevelenModell

The Mars-van Krevelen mechanism, or Mars–van Krevelen mechanism, is a widely used model to describe oxidation reactions on metal oxide catalysts. It proposes that lattice oxygen from the oxide participates directly in the oxidation of an adsorbed substrate, forming reduced oxide with oxygen vacancies, which are subsequently replenished by molecular oxygen from the gas phase.

In the mechanism, a substrate (such as a hydrocarbon, CO, or alcohol) abstracts an oxygen from the oxide lattice, producing the oxidized product and leaving an oxygen vacancy in the oxide lattice. The oxide is reoxidized by O2, entering back onto the lattice, thereby restoring the lattice oxygen and completing the redox cycle. The rate can be limited by either the oxidation step or the vacancy replenishment step, depending on conditions such as temperature and gas composition.

The mechanism was proposed by C. Mars and H. van Krevelen in 1954 and has since been used to explain oxidation catalysis on a wide range of metal oxides, including ceria (CeO2), vanadia (V2O5), manganese oxides (MnOx), and iron oxides (FeOx). It is particularly relevant for oxidation reactions where lattice oxygen mobility and oxygen storage capacity influence activity and selectivity, as well as for catalysts used in automotive emissions control and selective oxidation processes.

Limitations and extensions: Not all oxidation reactions on oxide surfaces follow Mars–van Krevelen; some proceed via surface-adsorbed species or dual- mechanism pathways. Modern interpretations often combine redox steps with Langmuir-Hinshelwood steps and defect-chemistry concepts.