2528.     ---------------.  [OLMER, F.]  [Reduction of Iron Oxides in the Presence of Foreign Substances.]  Rev. mét., vol. 38, 1941, pp. 129-134; Chem. Abs., vol. 36, 1942, p. 6931.

        Reduction of Fe compounds was studied by photographically recording pressure drop of a constant volume of a reducing gas, after adsorption of H₂O and CO₂ formed during the reaction.  The powdered sample was reduced in a fused SiO₂ chamber in a resistance furnace, regulated by an auxiliary nichrome-wound furnace.  Reduction of Fe₂O₃ with H₂ begins around 325° and continues until pure Fe is formed, without intermediate formation of FeO.  For an oxide simply dried at 300°, reduction begins at 240°; for an oxide that has been calcined at 1,300°, at least 400° is required.  In the first case, Fe₃O₄ is formed at 300°; in the second, no Fe₃O₄ is formed.  The decomposition of CO in the presence of different Fe compounds was studied to determine catalytic reactions, if any.  No decomposition takes place with CO lower than 45%.  For greater CO concentrations than 55%, catalysis is very pronounced.  Fe₂O₃, Fe₃O₄, and cementite have no catalytic effect on the decomposition of CO.  No FeO is produced by CO reduction.  Catalysis of CO decomposition with about 20 metals and oxides was studied.  Cu, Pb, Zn, and Sn oxides are reduced quantitatively; oxides of W and Mo only partly even at 1,000°; Al₂O₃ and Cr₂O₃ are unaffected.  Only oxides of Fe, Co, and Ni show a pronounced drop in gas pressure and a heavy C deposit; only these are decomposition catalysts.  Experiments were conducted to show the relation between catalytic properties and magnetism of metals.  The catalytic effect is believed to be connected with surface absorption, which depends on the radius of curvature of catalyst particles.  The velocity of catalysis by Fe increases up to 580°.  It appears that the reduced Fe is in a state of very fine division, and, at 580° these particles agglomerate; this increases the radius of curvature.  Dilution of the powdered Fe with an inert substance prevents agglomeration and preserves catalytic activity independently of temperature.