Mechanism and activity of CO oxidation on (001) and (110) surfaces of spinel Co3O4, NiCo2O4 and NiFe2O4: A DFT + U study

•Spinel Co3O4, NiCo2O4 and NiFe2O4 are highly active oxidation catalysts.•CO oxidation proceeds through the Mars–Van Krevelen mechanism on all these materials.•Surface reoxidation is the rate limiting step of the CO oxidation reaction (COOR) on (001) surfaces.•CO2 formation is rate limiting on Co3O4(110).•Water adsorption can inhibit reoxidation and thus block the COOR.