Temkin identity

Early work on the kinetics of the steam reforming of methane [59] was based on the assumption that the methane adsorption was ratedetermining, in agreement with the general assumption of a first-order dependence on methane concentration. Later work by Khomenko et al. [271] avoided the discussion of a rate-determining step instead, the researchers inserted the quasi steady-state approximation in terms of the Temkin identity [75], and the following rate expression was obtained for the temperature range of 470-700°C ... 

The constants of equations 6.16 and 6.17 are identical, on the basis of the principle of equal reactivity of cocondensing functional groups. Adopting Temkin s model for fused salts, and thus assuming that molar fractions represent activities over the appropriate matrix, we obtain... 

For some conditions, the inclusion of other pools in the model may be important, and this can be carried out in a straightforward manner using the numerical methods discussed previously (107). The overall rates and the forward and backward rales are related by the identities formulated by Temkin (105, 109). One can hope to represent the kinetics over a wide range by such an elementary-step model. This way of treating the experimental data seems clearer and more powerful than linking the analysis to a parameter such as the response time obtained from certain isotopic experiments. 

Here, b = 1 for linear chains and b = 3 for branched chains. According to what is known as the Temkin law, the activity, Mto, is identical to the ion mole fraction for bivalent cations. The concentration of these ions can be determined by mass spectroscopy after capping the silicate anions with trimethyl silyl free radicals. According to these measurements, Co and Ni form linear polymers, but Sn Fe Mn Pb and Ca form branched polymers (see also Figure 32-2). 

In order to deduce fundamental information on intrinsic catalyst performance it is important to reduce the influence of the chosen reactor set-up on catalyst performance to a minimum. The first reactor requirement is ideal isothermal operation conditions. The second requirement is continuously operated ideal plug flow without axial hackmixing, this being identical to a series of infinitesimally small, continuously stirred tank reactors each fulfilling the stationary concentration requirement The realization of such an optimum reactor concept is not trivial, and in 1969 Temkin and Kul kova developed a concept in which actual-size catalyst bodies could be tested under ideal conditions. Catalyst spheres and inert cylinders are alternately placed in a tube with a diameter slightly bigger than the catalyst spheres. Inert cylinders and catalyst spheres are fixed by three wires. Excellent heat transport... 

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