3748.     WYCKOFF, R. W. G. R., AND CRITTENDEN, E. D.  X-Ray Examination of Some Ammonia Catalysts.  Jour. Am. Chem. Soc., vol. 47, 1925, pp. 2866-2876; Chem. Abs., vol. 20, 1926, p. 526.

        The effect of promoters in activated catalysts is studied by means of X-rays to show that certain additions produce their activating effects by favoring the formation of numerous active points and by stabilizing these specifically active metal particles.  X-ray photographs, prepared in the usual way for powder photographs, were obtained (1) from various fused Fe oxides having compositions near to Fe3O4 and others richer in ferrous Fe than Fe3O4, (2) from artificial magnetites containing various amounts of Al2O3 and K2Al2O4 as promoters, and (3) from the Fe catalysts obtained by reducing these fused oxides.  One function of the promoters of Al2O3 and K2Al2O4 in reduced Fe oxide catalysts for the synthesis of NH3 is suggested.  The length of the edge of the unit cube of magnetite was found to be Ao=8.370.010 . U.  In magnetites containing an excess of FeO this substance occurs as a separate phase.  This phase disappears when the equivalent amount of the promoter, Al2O3, is added.  The composition of the oxide is thus adjusted toward Fe3O4 with the formation of FeAl2O4, which is apparently in solid solution in the magnetite.  The value of Ao for magnetite containing K2Al2O4 differs so little from Ao for pure Fe3O4 that it is impossible to decide whether or not there is solid solution of one in the other.  Ao is for a-iron obtained by the reduction of Fe3O4 is 2.8590.004 . U.  The size of the unit cell of Fe in the reduced material containing the promoters differs from that of pure Fe by less than 0.1%.  The presence of the composite promoters, K and Al oxides, in the reduced catalysts has been found to maintain a large surface of Fe by preventing the rapid growth of the Fe crystals.