Apparatus and methods for the production of a secure supply of breathable air are important under conditions where threats from chemical and biological weapons may be present. A method and a multi-stage CATOX system for producing a purified air flow from ambient air which may have nitrogen containing toxicants is provided. The multi-stage CATOX system has a first stage and second stage, at least one of the first or the second stage has a first catalytic heat exchanger with a cold side supporting a first catalyst and a hot side configured to transfer heat therefrom to the first catalyst.