Role of local configurations in a Langmuir–Hinshelwood surface reaction: Kinetics and compensation

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Abstract
We have employed Monte Carlo sampling to calculate the rate coefficient of a Langmuir–Hinshelwood reaction between species A and B on a square lattice. The experimental situation that is simulated is the reaction between a p r e a d s o r b e d overlayer of species A with species B. The preadsorbed overlayer of A is allowed to equilibrate prior to the adsorption of B. Upon adsorption of B, the initial reaction rate is calculated assuming that A is irreversibly adsorbed and immobile, and that the equilibrium between adsorbed B and gas‐phase B is established much more rapidly than the time scale of the reaction between A and B. Reaction is allowed only between nearest‐neighbor A B pairs. We examine the parametrization of the reaction rate coefficient into an effective activation energy and an effective preexponential factor. We find that correlations between nearest‐neighbor particles affect the reaction rate coefficient significantly. We also find that if the distribution of local configurations of nearest‐neighbor pairs of reactant particles changes with temperature, the corresponding Arrhenius plot is nonlinear. The effective activation energy and the effective preexponential factor vary strongly with the fractional coverage of A and show a large compensation effect, similar to that observed experimentally in many desorption and surface‐reaction systems. We conclude that variations in the distribution of local configurations of pairs of reactant molecules is a function of temperature and fractional surface coverage can be responsible for these experimentally observed compensation effects.