Temkin contributions

All his life, Temkin contributed to science in many areas, such as diffusion of heavy water into ordinary water, fugacity of gas mixtures, theory of mixtures of molten salts, and mass transfer in chemical engineering. But he left his indelible mark in the fundamentals of catalytic kinetics, on a par with C. J. Christiansen and J. Horiuti. 

The general subject of enumerating reaction mechanisms has been considered previously in reviews that have appeared in this series over the past 30 years [see the reviews by Christiansen (2), Horiuti and Nakamura (4), and Temkin (5)]. Each of these successive contributions presented developments based on concepts developed earlier, as does the present treatment. Studies conducted by those authors are of special interest here since the subject matter is largely in the field of heterogeneous catalysis. 

Jackson has proposed a simple lattice model for the interface, in which the points of an infinite lattice are identified as solidlike or liquidlike. A single interfacial plane (containing both types of atoms) is taken to separate the solid from the liquid. The problem with this model (and with its multilayer generalization by Temkin in Woodruff S) is that it gives a large negative entropic contribution to a so that for small values of the ratio AH/k T characteristic of most metals a becomes negative.We thus do not consider these models further here. 

The adsorption of either ions or neutral molecules on the electrode surface depends on qn, i.e., on the apphed electric potential. Correspondingly, the electric field at the electrochemical interface is an additional free-energy contribution that either favors or restricts the adsorption of species on the electrode from the ionic conducting phase. A variety of adsorption isotherms has been proposed to account for the behavior of different electrochemical systems. Among them are the Langmuir, Frumkin, and Temkin isotherms [2]. Frumkin and Temkin isotherms, at variance with the Langmuir one, include effects such as adsorbate—adsorbate or adsorbate—surface interactions. 

Chierche et al. [110] were first to study copper underpotential deposition on poly crystalline palladium. They assigned different copper voltammetric peaks to the contributions of the different low Miller index crystallographic planes of palladium. They also proposed that copper underpotential deposition obeys a Temkin-type isotherm with a saturation charge density of 420 pC cm 2. The electrochemical response on polyfaceted palladium is observed in Figure 9.6. 

The treatment below originated from M.Temkin, who in the late 1930s developed the theory of adsorption and kinetics on real (nonuniform) surfaces and proposed a special model of nonuniformity. Contributions by Zeldovich and Roginskii to this field in the same years were also essential. 

The analysis is straightforward in cases where adsorbate interaction effects do not play a role. This is the case either under Langmuirian adsorption conditions or in the saturation limit, 6>o 1. The former is an unrealistic assumption, since it is known that Temkin conditions prevail, illustrated in the seminal work of Sepa et al. (1981). Under the latter assumption, one can proceed to determine values of the effective transfer coefficient in the Butler-Volmer equation. Each quasi-equilibrium step, represented by a factor K in vqrr, contributes an amount of ( — to... 

In 1918, together with Lev Yakovlevich Karpov (1879-1921), Bakh had founded the Central Chemical Laboratory of the Supreme Council of the National Economy in Moscow. He became the first Director of this laboratory and, after Karpov s untimely death in 1921, it was renamed the L. Ya. Karpov Physicochemical Institute. For many years, this was the largest (and only) center for physical chemistry in the USSR. Despite the chaotic circumstances of its birth, it soon developed into one of the world s leading scientific centers, making important contributions to various fields of physical chemistry (electrochemistry and corrosion, theory of catalysis, chemistry of polymers, etc.). Famous scientists who worked in the Institute included A. N. Frumkin, Ya. K. Syrkin, N. M. Zhavoronkov, V. A. Kargin, I. V. Petryanov-Sokolov, S. S. Medvedev, K. A. Kocheshkov, Ya. M. Kolotyrkin, Kh. S. Bagdasar yan, G. K. Boreskov, and M. I. Temkin. 

Of the adsorption isotherms discussed above, the Langmuir equation is important because of its theoretical and conceptual contribution to the studies of adsorption and the kinetics of surface reactions. The Freundlich isotherm has found a wide use in correlating experimental data the Temkin isotherm is obeyed by certain systems [62-64], but it is expected to apply only in the intermediate range of coverage due to the simplifying assumptions made in its derivation. 

Let us now compare the preexponential factors for an ordinary discharge and a barrierless discharge. For an ordinary discharge, it is impossible to completely overcome the difficulties associated with the determination of the entropy of an activated complex, and the contribution from AS°, the entropy of an individual electrode process, since the value of this quantity cannot be determined by purely thermodynamic methods. Temkin[10] proposed an approximate method for estimating these quantities. He proceeded from the fact established by Frumkin and Jofa[104] that the hydrogen overpotential is independent of the activity coefficient for H30 ions. In the absolute rate theory, this experimental result can be described as a relation between the activity coefficients of the activated complex and hydrogen ions ... 

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