Pyzhev

The Temkin-Pyzhev equation deseribes the net rate of synthesis over promoted iron eatalyst as ... 

Develop the rate equation of Temkin Pyzhev for the rate of the reaction, N2 (A) + 3H2(B) > 2NH3(C), on these assumptions ... 

The Temkin and Pyzhev rate expression (Annable, 1952) is used, given by... 

As an example, the Temkin-Pyzhev rate expression for ammonia synthesis reproduces the experimentally observed kinetics quite well. However, this rate expression was originally derived from a proposed mechanism which had both the wrong key intermediates and the wrong rate-limiting step. 

This result has been explained by means of a complex theory due to Temkin and Pyzhev 23), but it can be explained equally well and more simply by the methods just described. The fraction of the surface covered by nitrogen atoms will be... 

This agrees with the experimentally found equation for n = 0.5. These rate laws were formerly derived on the assumption of surface heterogeneity according to the scheme first put forward by Temkin and Pyzhev (39) for the ammonia synthesis. As shown by one of us (40) the assumption of heterogeneity is unnecessary for the derivation of the rate expression even in that case. 

It is almost surprising that in spite of this a simple kinetic equation has been formulated which gives a good approximation to experimental data under widely different conditions of temperature, pressure, gas composition, and space velocity and for different types of catalysts. An equation has been suggested by Temkin and Pyzhev (62,63) and the simple form in which it was originally presented is given in Equation (1)... 

Temkin and Pyzhev take as their starting point a paper by Winter (64). Winter studied the decomposition of ammonia with excess hydrogen over an iron catalyst and found the expression (5)... 

Winter s treatment leading from (6) to (5) is not correct, as pointed out by Temkin and Pyzhev one of its consequences would be an activation energy for the decomposition amounting to approximately 100,000 cal. 

Following Temkin and Pyzhev, the empirical equation (1) when combined with the assumption of equilibrium according to (6) leads to a logarithmic adsorption isotherm for nitrogen... 

Temkin and Pyzhev also checked Equation (1), using a = 0.5 on the experimental data published by Larson and Tour (68), which cover a range of pressures up to 100 atm., and later Emmett and Kummer (66)... 

As previously discussed, the theory by Temkin and Pyzhev predicts that at low conversions, the ammonia percentages in the reacted gas vary inversely proportional to the square root of space velocities. At higher conversions the decrease in conversion percentages with increase in space velocity is still less, as is clearly seen from Table IV showing conversion percentage, efficiency, z2 (S.V.), and S.T.Y. as functions of S.V. at 450° and 330 atm. 

M. Temkin and V. Pyzhev, Acta Physicochim. U.R.S.S., 12, 327 (1940), have used what is equivalent to a complex Langmuir isotherm to explain the very complex kinetics of NHs decomposition on Fe surfaces. A theoretical discussion of nonuniform surfaces is given by G. D. Halsey, J. Chem. Phys., 17, 758 (1949). 

Pronounced TJomkin. Named after M.I. Temkin. Zhur. Fiz. Khim. 4 (1933) 573 and M.I. Temkin and W.M. Pyzhev, Acta Physicochim USSR 12 (1940) 327. 

It all started in 1938 when Temkin first applied transition state theory to heterogeneous catalysis. Soon after, he published with V. Pyzhev one of the most frequently cited papers in catalytic ammonia synthesis. Since both Mikhail Temkin and Paul Emmett had a profound influence on the theory and practice of this famous reaction, it seems proper to quote here Emmett s assessment of the 1939-1940 paper of Temkin and Pyazhev. ... 

Numerous studies of the kinetics of ammonia synthesis and decomposition have been made. With a few exceptions, work has tended to show that the slow step in the synthesis of ammonia is the chemisorption of nitrogen and the slow step for the decomposition is the desorption of nitrogen. Furthermore, it turns out that the decomposition and synthesis of ammonia usually involve in the rate expression a term where y/x is close to 1.5. In 1940, Temkin and Pyzhev derived an equation consistent with both of these observations [M. I. Temkin and V. Pyzhev, Acta Physiochim. U.R.S.S. 12, 327 (1940)]. It has formed the basis for most of the kinetic treatments of ammonia synthesis and decomposition in recent years. 

Like the kinetic concepts of Christiansen and Horiuti, those of Temkin were far ahead of their common acceptance by the catalytic community. Even today, more than 50 years after the Temkin-Pyzhev paper, the idea of virtual fiigacity is not well understood by the majority of workers in catalytic kinetics. It is safe to predict that many of the other ideas of Temkin, like that of average stoichiometric number or reaction routes, will influence younger catalytic ki-neticists who now have access to powerful computers. 

In the studies, specially purified clay minerals, mainly from Ukrainian deposits, were used montmorillonite (Pyzhev), hydromica and palygorskite (Cherkassy), kaolinite (Glukhov), vermiculite (Kovdor, Russia). The diatomite supports from Armenia and the Czech Republic (produced by Lachema), and macroporous silica (made in the experimental plant for production of adsorbents for petrochemical industry, Nizhnii Novgorod, Russia) were employed. 

Temkin and Pyzhev 49) successfully derived a kinetic expression for the ammonia s3mthesis assuming that the chemisorption of nitrogen is... 

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