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 A_o=8.37±0.010 Å. 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 A_o for magnetite containing K₂Al₂O₄ differs so little from A_o for pure Fe₃O₄ that it is impossible to decide whether or not there is solid solution of one in the other.  A_o is for a-iron obtained by the reduction of Fe₃O₄ is 2.859±0.004 Å. 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.