Eliana Valencia

Effect of the coordination of the superficial site in the monomer–dimer reaction on a disordered substrate

Abstract Using Monte Carlo simulation experiments, a study is made of the effect of the superficial coordination number in a square lattice of sites for the monomer–dimer surface reaction (Ziff, Gulari and Barshad model) in the case of disordered substrates showing geometric heterogeneity of the sites, such as the percolation clusters. An analysis is made of the change in character of the phase transitions and in the size of the reactive window in the phase diagram, and the results were also compared with mean field theoretical calculations for disordered systems.

Mean-field hierarchical equations for some A+BC catalytic reaction models

A mean-field study of the (A+BC→AC+12B2) system is developed from hierarchical equations, considering mechanisms that include dissociation, reaction with finite rates, desorption, and diffusion of the adsorbed species. The phase diagrams are compared to Monte Carlo simulations.

On the pair approximation method in a nonreactive catalytic system

The nonreactive catalytic system made up of the reduction of NO by CO on a square lattice of sites is studied by means of dynamic equations in the pair approximation, showing some characteristics and limitations of the model in systems with a nontrivial behavior.

The monomer–trimer and dimer–trimer superficial reactions on geometrically disordered substrates

A Monte Carlo study is made of monomer–linear trimer, monomer–bent trimer and dimer–linear trimer surface reactions on substrates made of percolation clusters having varying degrees of surface disorder and on a statistical fractal, the incipient percolation cluster. The phase diagrams show that the branching of the disordered substrate alters the width of the reactive zone, the production value and the character of the irreversible phase transitions. At the ends of the diagrams a linear decrease in the jamming fractions with increasing substrate branching is seen, together with a discontinuous transition between the jamming states and the neighboring absorbent zones.

The Hill-de Boer equation in the adsorption of water on quartz

Abstract Within the limitations imposed by the number of experimental points, it has been possible to establish that the system of water adsorbed on pure and methylated quartz has adsorption isotherms in which the quantity adsorbed increases with increasing temperature when plotted in terms of relative pressure. This behavior can be adequately described by the Hill-de Boer equation, even though the interpretation of the data by means of parameter K 1 of the equation suggests that the water shows only dispersion interactions with the silica surface. This rather anomalous behavior of the system is in agreement with the previously published values of parameter S of the Frenkel-Halsey-Hill equation.

Geometric heterogeneity of the lattice and its effect on the kinetics phase transitions of surface reactions

Abstract Two novel phenomena are discussed in this paper. The first one refers to the effect of the catalyst’s surface heterogeneity on the smoothing of the first-order transition observed in the ( A + B 2 ) reaction (ZGB model). The second effect corresponds to obtaining information on the surface heterogeneity from the shape of the transition curve. Two types of heterogeneity were considered: the structure obtained by the random blocking of reactive sites, and the existence of a distribution in independent strips or terraces on the catalyst’s surface.

Adsorption mechanisms and surface heterogeneity in the oxidation reaction of CO

A Monte Carlo simulation study is made of the sensitivity of the CO oxidation reaction to changes in the characteristics of the catalyst’s surface on which the type of oxygen adsorption mechanism is dependent. Infinite rate models of the Ziff, Gulari, and Barshad (ZGB) type, and mechanisms having kinetics parameters of actual experiments from the literature are studied. It is shown that, if linear adsorption is assumed, the structural insensitivity becomes apparent in the phase diagram but not in the production of CO2. In the case of structural sensitivity it is seen that surface heterogeneity leads to a change in the character of the phase transition curve, and also allows information about the surface to be obtained from the shape of the transition curve.

MONTE CARLO SIMULATIONS AND KINETIC THEORY OF HOMOGENEOUS AND HETEROGENEOUS ADSORPTION WITH LATERAL INTERACTIONS

Using the kinetic form of the Monte Carlo (MC) simulation method, a comparison has been made between the results that predict the phenomenological equations for adsorption kinetics and MC experiments in systems with and without lateral interactions on homogeneous and heterogeneous surfaces with random topography and varying degrees of surface heterogeneity. A very good correspondence exists between the theoretical results and those obtained from the MC experiments.

NEXT NEAREST NEIGHBORS SITES AND THE REACTIVITY OF THE CO-NO SURFACE REACTION

Abstract Using Monte Carlo experiments of the reduction of NO by CO, a study is made of the effect on reactivity due to the formation of N 2 O and to the increased coordination of the sites considering the next nearest neighbors sites (nnn) in a square lattice of superficial sites.

Kinetic phase transitions and reactive windows in reactions of monomers on two-dimensional lattices

Some conceptual considerations are made and Monte Carlo simulation studies are carried out to analyze a series of catalytic reactions of two and three monomers on a square lattice of sites. Two aspects are considered: The increase in the system’s degrees of freedom, leading to the formation of reactive sites that allow a change in the character of one of the kinetic phase transitions from the first order to a second order transition, and the classification and reactivity of the new system class.