MeH was decompd. to H and C over a nanocryst. Fe 17 nm catalyst (grains 1.2 to 1.5 mm) in a thermobalance at 500-700 degrees C for 100 min. The catalyst was prepd. by fusion of magnetite with small amts. of At, Ca and K oxides with following H redn. Formation of C deposit or Fe,C on the catalyst surface was obsd. The carburized catalyst was annealed in air to remove C as CO. The catalyst mass increased with the increasing temp. The addn. of K2O to the catalyst resulted in a decreasing the catalyst activity The activation energy of the Fe,C formation was 158 kJ/moL The presence of H in the reaction mixt. resulted in a decreasing the catalyst carburization rate. The activation energy of Fe,C hydrogenation and C deposition was 135 and 150 kJ/mol, resp.