Abstract
For a complex catalytic reaction with a single-route linear mechanism, a new, kinetico-thermodynamic form of the steady-state reaction rate is obtained, and we show how its symmetries in terms of the kinetic and thermodynamic parameters allow better discerning their influence on the result. Its reciprocal is equal to the sum of n terms (n is the number of complex reaction steps), each of which is the product of a kinetic factor multiplied by a thermodynamic factor. The kinetic factor is the reciprocal apparent kinetic coefficient of the i-th step. The thermodynamic factor is a function of the apparent equilibrium constants of the i-th equilibrium subsystem, which includes the (n−1) other steps. This kinetico-thermodynamic form separates the kinetic and thermodynamic factors. The result is extended to the case of a buffer substance. It is promising for distinguishing the influence of kinetic and thermodynamic factors in the complex reaction rate. The developed theory is illustrated by examples taken from heterogeneous catalysis.
Highlights
How do we derive the reaction rate for a complex reaction, e.g., for a complex catalytic reaction?Based on graph theory, this general problem was posed by King and Atman [1] and, Volkenstein and Goldstein [2,3]
The kinetic equation for a single-route catalytic reaction with a linear mechanism can always be presented in the form: Cc in which Cc is the cycle characteristic
In the theory of steady-state kinetic models, the kinetic polynomial is the general description of a single-route catalytic reaction
Summary
How do we derive the reaction rate for a complex reaction, e.g., for a complex catalytic reaction?. The kinetic equation for a single-route catalytic reaction with a linear mechanism can always be presented in the form (see [1,2]): Cc. W in which Cc is the cycle characteristic. The functions f (Cr ), f (C p ) are the products of the reactant and product concentrations raised to certain powers, assuming that the rate of reaction follows the mass-action law formally, as if the overall reaction were an elementary reaction. It represents a “resistance” to the overall reaction rate by p the “resistances” of the individual steps of the catalytic cycle. Equations (4) and (5) are very similar to the well-known Ohm’s Law considering the analogy between the reaction rate and current and between kinetic “driving force” and voltage as well
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