Abstract: 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 catalytic oxidation (CATOX) system may include of at least two primary elements: (1) a catalyst to destroy toxic chemicals by oxidation, and (2) a post treatment filter (PTF, also known as a post treatment adsorbent (PTA)) to remove acidic gases that may be produced by reaction over the catalyst and also remove acidic gases that can not be oxidized. Biological materials may be destroyed by sterilization at the CATOX normal operating temperatures. The catalyst and the post treatment filter may be operated in a two-stage manner, each operating at an independent temperature.