822.    EMMETT, P. H., AND BRUNAUER, S.  The Poisoning Action of Water Vapor at High Pressure on Iron Synthetic Ammonia Catalysts.  Jour. Am. Chem. Soc., vol. 52, 1930, pp. 2682-2693; Chem. Abs., vol. 24, 1930, p. 4693.

      Poisoning of synthetic NH₃ catalysts by water vapor was studied at 450° at pressures as high as 100 atm. and at various partial pressures of H₂O vapor between 0.08 and 0.64%.  

The amount of O retained by the catalyst is 

proportional to  ________     √P_H2O : P_H2

 Very active catalysts are capable of retaining more O than less active catalysts.  The poisoning of both doubly and singly promoted catalysts by water vapor is almost entirely reversible, although a slight permanent injury to the catalyst results.  A probable mechanism of NH₃ synthesis consists in the reduction by H₂ of surface Fe₄N formed by the reaction of N₂ with surface Fe atoms having average free energies sufficiently in excess of those of normal Fe atoms.