3368.     TEMKIN, M., AND PYZHEV, V. [Kinetics of the Synthesis of Ammonia on Promoted Iron Catalysts.]  Jour. Phys. Chem. (U.S.S.R.), vol. 13, 1939, pp. 851-867; Chem. Abs., vol. 34, 1940, p. 6512.

        From experimental data on the synthesis and decomposition of NH₃ technical Fe catalysts promoted by Al₂O₃ and K₂O at 400°-450° and 1 atm. pressure and H₂:N₂ ratios of 0.5 up to 8.5, the rate constants are k=1.04X10³ at 400° and 7.78 at 450°.  The rate of formation of NH₃ is given by v=k₁P_N2 (P³_H2/P²_HN3)a with a=0.5.  The determining factor in the forward process is the rate of activated adsorption on the N₂-free surface.  For the reverse process, the rate of NH₃ desorption is the rate-determining factor.  For the complete process, the equation

dP_NH3/dt=k₁(P_N2P^1.5_H2/P_NH3)-k₂(P_NH3/P^1.5_H2)

holds both for the experimental data of Temkin and Pyzhev and for those of other authors.  The apparent energy of activation for NH₃ formation is ~14 cal. and for decomposition ~40 cal. per mol.