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.