Zero coverage theory

Table 10.4 lists the rate parameters for the elementary steps of the CO + NO reaction in the limit of zero coverage. Parameters such as those listed in Tab. 10.4 form the highly desirable input for modeling overall reaction mechanisms. In addition, elementary rate parameters can be compared to calculations on the basis of the theories outlined in Chapters 3 and 6. In this way the kinetic parameters of elementary reaction steps provide, through spectroscopy and computational chemistry, a link between the intramolecular properties of adsorbed reactants and their reactivity Statistical thermodynamics furnishes the theoretical framework to describe how equilibrium constants and reaction rate constants depend on the partition functions of vibration and rotation. Thus, spectroscopy studies of adsorbed reactants and intermediates provide the input for computing equilibrium constants, while calculations on the transition states of reaction pathways, starting from structurally, electronically and vibrationally well-characterized ground states, enable the prediction of kinetic parameters. 

Prior to a discussion of adsorption kinetic rate laws and mechanistic theories, we review the very large amount of data that has been gathered in recent years. We consider first the values reported in the literature for the sticking probabilities at zero coverage, s0, for a variety of gas—metal systems secondly, the variations of s0 with gas temperature, Tg, and surface temperature, Ts and thirdly, the dependence of s on surface coverage. 

Derderian and Steele [57] have combined the virial analysis with the development proposed by Steele for the gas-solid potential energy. Results for " He and He isotopes have been compared with theories and experimental results. Parameters for the L-J 12-6 (see Table 8) and the gas-sohd interaction were obtained. The study also includes the calculation of the isosteric heat at 15 K extrapolated to zero coverage and the calculation of the nonconfiginational entropy per adsorbed particle. A notable conclusion is that the solid, at these temperatines, is not perturbed by the adsorbate. 

Two cases may arise. If the intermediate species is a surface species, i.e., strongly adsorbed and at a negligible concentration in solution, the change is limited practically to the surface concentration only, which can vary from surface coverage zero to unity. Hence, the maximum amount of the intermediate that can be formed or removed will be of the order of 10 molcm . However, when the intermediate has a finite stability in solution, as is the case with copper, the steady state can in theory be reached only after the concentration has been appropriately adjusted throughout the bulk of the solution. Hence, the amount of charge for charging the pseudocapacitance... 

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