Abstract
It is shown that the mechanism proposed by Temkin and Pyzhev for ammonia synthesis does not correspond to the experimental data on the properties of the catalyst surface and the stages of the process. A three-stage mechanism is discussed: 1) N2+ Z = ZN2; 2) 2ZN + 3H2 = 2NH3 + 2Z; 3) 2ZN2 + Z\(\vec \equiv \) 2ZN (2 and 3 are equilibria, 3 being displaced to the right, 1 is the limiting stage), based on simple Langmuir concepts, which leads to a kinetic equation which agrees with the data of Winter on the kinetics of NH3 decomposition and the data of Benton on the retardation of the NH3 synthesis reaction by the product. An equation is derived for dissociative adsorption on a uniform surface involving the adsorption of each adatom at two adsorption sites; the equation corresponds to the same dependence of θ on P as the logarithmic adsorption isotherm.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
Literature cited
E. Winter, “The catalytic decomposition of ammonia on iron,” [in German], Z. Phys. Chem. B,13, No. 6, 401–424 (1931).
A. F. Benton, “Kinetics of catalyzed gas reactions in flow systems,” Ind. Eng. Chem.,19, No. 4, 494–497 (1927).
M. I. Temkin and V. P. Pyzhev, “Kinetics of ammonia synthesis over a promoted iron catalyst,” Zh. Fiz. Khim.,13, No. 7, 851–867 (1939).
G. M. Shvab, Catalysis from the Point of View of Chemical Kinetics [in Russian], ONTI; Gos. Khim.-Tekhnol. Izd., Leningrad (1934).
E. Chornet and R. W. Coughlin, “Chemisorption of hydrogen on iron,” J. Catal.,21, No. 2, 246–265 (1972).
F. I. Brocker and G. Wedler, “Calorimetric studies of the chemisorption and desorption of hydrogen on nickel films under ultrahigh vacuum conditions,” Disc. Faraday Soc.,41, 87–94 (1966).
S. V. Artamonov and G. D. Zakumbaeva, “Heat of adsorption of hydrogen on platinum black,” in: Seventh All-Union Conference on Calorimetry, Chernogolovka, 1977 [in Russian], Chernogolovka (1977), pp. 288–292.
Yu. D. Pankrat'ev, E. M. Malyshev, Yu. A. Ryndin, et al., “Catalysts obtained by the interaction of organometallic compounds with the support surface. Calorimetric study of the adsorption of hydrogen and oxygen on Pt/SiO2, W/SiO2, and (W + Pt)/SiO2 catalysts,” Kinet. Katal.,19, No. 6, 1543–1548 (1978).
D. Brennan, D. O. Hayward, and B. M. W. Trapnell, “The Calorimetric determination of the heat of adsorption of oxygen on evaporated metal films,” Proc. R. Soc. A,256, No. 1, 81–105 (1960).
V. E. Ostrovskii, “The heat of chemisorption of oxygen on cobalt and the effect of inert gases on the rate of chemisorption,” Zh. Fiz. Khim.,62, No. 3, 674–678 (1988).
V. E. Ostrovskii, “A study of the adsorption of oxygen and hydrogen on copper by adsorption calorimetry,” Dokl. Akad. Nauk SSSR,172, No. 4, 892–894 (1967).
V. E. Ostrovskii and E. A. Medvedkova, “A Calorimetric and adsorption study of the interaction of oxygen, hydrogen, and water with the surface of a silver catalyst,” Kinet. Katal.,20, No. 4, 966–972 (1979).
V. E. Ostrovskii and E. G. Igranova, “Calorimetric study of the heats of chemisorption of nitrogen on an ammonia synthesis catalyst,” ibid.,19, No. 3, 681–684 (1978).
M. Grunze and P. A. Dowben, “Thermodynamic measurements for N2 adsorption on Ni(100),” Surf. Sci.,141, No. 2, 455–472 (1984).
M. Ehsasi and K. Christmann, “The interaction of hydrogen with rhodium (110) surface,” ibid.,194, No. 1, 172–198 (1988).
E. G. Igranova, V. E. Ostrovskii, and M. I. Temkin, “A Calorimetric study of the products from the incomplete hydriding of nitrogen adsorbed on an iron catalyst, in connection with the mechanism of ammonia synthesis,” Kinet. Katal.,17, No. 5, 1257–1262 (1976).
F. Bozso, G. Ertl, M. Grunze, and M. Weiss, “Interaction of nitrogen with iron surfaces. 1. Fe(100) and Fe(111),” J. Catal.,49, No. 1, 18–41 (1977).
F. Bozso, G. Ertl, and M. Weiss, “Interaction of nitrogen with iron surfaces. 2. Fe(110),” ibid.,50, No. 2, 519–529 (1977).
I. Langmuir, “The adsorption of gases on plane surfaces of glass, mica, and platinum,” J. Am. Chem. Soc.,40, No. 7, 1361–1403 (1918).
M. I. Temkin, “The reactivity and mutual effect of adsorbed atoms and radicals,” in: Problems in Chemical Kinetics, Catalysis, and Reactivity [in Russian], Izd. Akad. Nauk SSSR, Moscow (1955), pp. 484–495.
V. K. Fedyanin, “The problem of the heat of adsorption taking account of the interactions between molecules. The remote action effect,” Kinet. Katal.,12, No. 5, 1353–1355 (1971).
P. H. Emmett and S. Brunauer, “The adsorption of nitrogen by iron synthetic ammonia catalysts,” J. Am. Chem. Soc.,56, No. 1, 35–41 (1934).
S. Brunauer, K. S. Love, and R. G. Keenan, “Adsorption of nitrogen and the mechanism of ammonia decomposition over iron catalysts,” ibid.,64, No. 4, 751–758 (1942).
B. M. W. Trapnell, Chemisorption [Russian translation], Izd. Inostr. Lit., Moscow (1958).
E. G. Igranova and V. E. Ostrovskii, “Calorimetric study of the sorption of hydrogen on an iron catalyst for ammonia synthesis,” Dokl. Akad. Nauk SSSR,221, No. 6, 1351–1354 (1975).
J. J. F. Scholten, P. Zwietering, J. A. Konvalinka, and J. H. de Boer, “Chemisorption of nitrogen on iron catalysts in connection with ammonia synthesis,” Trans. Faraday Soc.,55, No. 12, 2166–2179 (1955).
J. K. Roberts and A. R. Miller, “The application of statistical methods to immobile adsorbed films,” Proc. Cambr. Phil. Soc.,35, No. 2, 293–297 (1939).
V. E. Ostrovskii and M. I. Temkin, “The use of statistical methods for calculating the rates of adsorption on homogeneous surfaces,” Kinet. Katal.,10, No. 1, 118–123 (1969).
V. E. Ostrovskii and M. I. Temkin, “Some problems in the theory of adsorption on homogeneous surfaces,” ibid.,12, No. 4, 1070–1072 (1971).
A. E. Romanushkina, S. L. Kiperman, and M. I. Temkin, “Equilibrium in the reaction of hydrogen with nitrogen adsorbed on iron,” Zh. Fiz. Khim.,27, No. 8, 1181–1194 (1953).
V. Frankenburger, “The current state in the theory of the catalytic synthesis of ammonia,” Usp. Khim.,2, No. 6, 720–759 (1933).
P. Stoltze and J. K. Nörskov, “An interpretation of the high-pressure kinetics of ammonia synthesis based on a microscopic model,” J. Catal.,110, No. 1, 1–10 (1988).
A. Ozaki, F. R. S. Taylor, and M. Boudart, “Kinetics and mechanism of the ammonia synthesis,” Proc. R. Soc. A,258, No. 1, 47–62 (1960).
N. P. Samchenko and G. I. Golodets, “The reasons for the variation in the power function and the rate constant in the Temkin equation for the ammonia synthesis reaction,” Kinet. Katal.,27, No. 2, 378–382 (1986).
Author information
Authors and Affiliations
Additional information
Published for purposes of discussion.
Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 213–221, March–April, 1989.
Rights and permissions
About this article
Cite this article
Ostrovskii, V.E. Mechanism of ammonia synthesis over iron catalysts in the equilibrium region. Theor Exp Chem 25, 193–201 (1989). https://doi.org/10.1007/BF01135010
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF01135010