Carbon monoxide removal reactor, fuel reforming system and method of removing carbon monoxide

The present invention relates to a carbon monoxide removal reactor including a casing having a catalyst accommodating portion accommodating a carbon monoxide removal catalyst for removing carbon monoxide present in a mixture gas containing hydrogen and the carbon monoxide and a mixture gas communicating passage for introducing the mixture gas to the catalyst accommodating portion and discharging the mixture gas therefrom; wherein inner wall faces of portions or entireties of said catalyst accommodating portion and said mixture gas communicating passage upstream thereof are formed of a non-iron material. The invention further relates to a fuel reforming system and to a filter.