A Carbon monoxide oxidation device (1), for oxidizing carbon monoxide contained in a hydrogen rich reformat gas (B), wherein the oxidation device (1) comprises a housing (2), wherein the housing (2) incorporates an oxidation catalyst (8), which is adapted to oxidize the carbon monoxide of the reformat gas (B) by means of an oxidizing agent (A) to carbon dioxide, comprises upstream of the catalyst (8) at least one gas inlet (4) for providing a gas stream (B; C) of at least said reformat gas (B) into the housing (2), comprises downstream of the catalyst (8) a gas outlet (6) for exiting treated gas from the housing (2), and incorporates a gas stream perturbation device (10) which is arranged upstream of the catalyst (8) and which is adapted to provide a perturbation in the gas stream, wherein the gas stream perturbation device (10) is designed as at least one propeller-shaped plate (14) with a plate portion (15) having a surface facing the gas stream and at least one blade (16) which is connected to the plate portion (15) and has a leading edge (20) and an effluent edge (22), wherein a surface defined between leading edge (20) and effluent edge (22) is inclined in relation to the surface of the plate portion (15) with a predetermined blade inclination angle (a), thereby defining at least one opening (24) in the plate.