Our experimental results proof the theoretical concept of polymeric reactors for thermocatalytic reactions up to 220°C under elevated pressure for methanation as typical example. The successful proof is based on the fact that the used Ru/TiO2 can be activated and is stable within the temperature limits of the polymer. Our results successfully demonstrate a significant and stable production rate of methane under a wide range of process conditions with sufficient capacity for in-situ propellant production on Mars.