2297.     MITTASCH, A., KUSS, E., AND EMERT, O.  [Thermal Decomposition of Complex Iron Cyanides in Connection With the Ammonia Synthesis.]  Ztschr. anorg. Chem., vol. 170, 1928, pp. 193-212; Chem. Abs., vol. 22, 1928, p. 2441.

        Complex Fe cyanides as such are not NH₃ catalysts, but the products of their decomposition and reduction are, (NH₄)₄Fe(CN)₆ and KAlFe(CN)₆ are decomposed at high temperature in a N₂-H₂ mixture with intermediate formation of a substance corresponding in composition to Fe(CN)₂.  The purely thermal decomposition of Fe(CN)₂ gives Fe, C, Fe₃C, Fe nitride and N₂, probably with the intermediate formation of FeC₂.  In N₂+H₂, Fe(CN)₂ reacts as follows:  At 230°, the C and the N in the CN groups are reduced at the same rate, and the completed reaction yields Fe.  At 400° the rates of reduction differ and there is obtained, probably through the intermediate formation of FeC₂, a mixture of Fe, Fe₃C, C, and probably the 2 latter in varieties easily reduced by the N₂-H₂ mixture.  These varieties are changed by prolonged heating above 400°, although the Fe₃C can still be reduced.  Fe must always be formed first; Fe₃C could not be prepared under any conditions without the formation of Fe, while it is possible to control the conditions so as to obtain only Fe.  The NH₃ contact catalysts prepared from complex Fe cyanides must always contain Fe and are composed chiefly or exclusively of products of reduction.  These are activated by the N₂-H₂ mixture and constitute then a catalyst.  Fe₃C in finely divided form is readily reduced by H₂ to a compact form, at least superficially, so that the catalytic action of Fe₃C as such has never been observed.