Haber process is a continuous process of ammonia synthesis. Catalyst will be always in environment of hydrogen:nitrogen~(3:1) composition. Since hydrogen composition will always keep catalyst in reduced form. Even if the process is stopped due to some unwanted reasons, catalyst will not oxidise for the reason that its a closed system and runs at high pressures. Just one precaution is to be taken that is not to ingress atmospheric air or compressed air by any means.