An oxidizer assembly provided with a housing having a plurality of inlets each for receiving a different gas and a plurality of outlets each corresponding to a different one of the inlets and outputting gas resulting from the gas received from its corresponding inlet. A catalyst assembly able to support gas flow therethrough is disposed within the housing and includes a catalyst able to oxidize carbon monoxide gas and to be regenerated. The catalyst assembly is further adapted to be movable such that successive parts of the assembly are able to be brought repeatedly in communication with a first inlet and its corresponding first outlet and then a second inlet and its corresponding second outlet of the housing. In the preferred form of the invention, the catalyst assembly is additionally adapted so that each section is brought in communication with a third inlet and its corresponding third outlet after being in communication with the second inlet and its corresponding second outlet and prior to being brought back into communication with the first inlet and its corresponding outlet.