The effects of surface defects in a catalysis model

We conducted an extensive study of the effect of defects on a catalyst surface, using the Ziff, Gulari, and Barshad model of carbon monoxide (CO) oxidation. First, we placed a single defect in the center of the system and observed that CO islands form around the defect. The size of those islands scales as a power law of the distance to the spinodal point with the exponent m=−0.73. Then, we studied both randomly distributed and regularly ordered defects. In both cases, we found that as the coverage of defects, θd, increases, the CO poisoning transition occurs at lower partial pressures of CO, yCO, and the first-order discontinuity of the CO poisoning transition decreases. Also, we studied how the arrangement of the defects affects the poisoning transition by using three different arrangements of regularly ordered defects with the same overall defect coverage. These studies have allowed us to better understand why defects cause the system to poison at lower values of yCO and also why the poisoning transition becomes more continuous.