Surface phase transitions at O and CO catalytic reaction on Pd(1 1 1)

The model has been proposed to simulate numerically the reaction O + CO → CO₂ and occurring phase transitions on Pd(1 1 1) surface. We calculate the phase diagram for this system by kinetic Monte Carlo method. It shows the phase transitions p (2 × 2)_O → sqrt(3) × sqrt(3) R 30_O ° and p (2 × 2)_O → sqrt(3) × sqrt(3) R 30_O ° → p (2 × 1)_O with increase of CO coverage for room and intermediate temperatures, respectively, while in the low temperature limit the direct p(2 × 2)_O → p(2 × 1)_O phase transition is observed. We demonstrate that the reaction rate is the crucial factor determining the occurrence of the p(2 × 1)_O phase and vanishing of the sqrt(3) × sqrt(3) R 30_O ° with decrease of temperature. The results indicate that the reaction proceeds inside both the p(2 × 2)_O and sqrt(3) × sqrt(3) R 30_O ° phases, but on the perimeter of the domains of p(2 × 1)_O structure.