Theoretical Inquiry into the Microscopic Origins of the Oscillatory CO Oxidation Reaction on Pt{100}

Abstract

An improved model is presented which simulates temporal behavior in the CO + O 2 reaction on the Pt{100} surface. The model is based on an experimentally determined strongly nonlinear power law for (1 × 1)-CO island growth rate from the hexagonal (hex) phase with an apparent reaction order of about 4 in the local CO coverage on the hex phase. The power law describes the phase transition from the hexagonal phase of the reconstructed Pt surface to the (1 × 1) phase. Rate parameters from recent adsorption and desorption experiments are used in the modeling. The variations of all adsorbate coverages, the reaction rates, and the surface phase are monitored to provide extensive information about the reaction. New insight into the mechanisms driving the experimentally observed oscillations is gained, and an interpretation of the actual dynamics of the underlying surface processes is also given.

A Monte Carlo study of CO oxidation with oscillations induced by site blocking

“…For Pt͑100͒ this change consists of a surface reconstruction from a 1ϫ1 phase to a quasi-hexagonal phase and back. 6,7 The latter is stable without adsorbates and has a low sticking coefficient for oxygen. The former is stabilized by CO adsorption and has a high oxygen sticking coefficient.…”

Theoretical study of pattern formation during the catalytic oxidation of CO on Pt{100} at low pressures

“…͑1͒-͑7͒ take standard chemical kinetic forms based on the model of Gruyters et al, 21 except that we explicitly consider the fraction of sites available to adsorption, trapping, and untrapping processes, and that we ignore the distinction between free and freed sites as this does not seem to be important in our model. Furthermore, our revised model explicitly couples the phase transition with surface diffusion, thereby allowing the development of a spatially extended model, and takes into account the detailed experimental evidence regarding the reaction kinetics.…”

“…The righthand side of Eq. ͑12͒ tends to k 8 ͑ CO hex ͒ n hex for c͑ ͒ ജ 1 and −k 9 ͑1−c͑ ͒͒ 1ϫ1 for c͑ ͒ Ͻ 1, as → ϱ, and is, therefore, a smoothed version of the corresponding discontinuous equation of Gruyters et al 21 We chose = 1000 in order to approximate a discontinuous change. The function c͑ ͒ is defined to be…”

“…We use the same parameters as Gruyters et al, 21 who, in turn, adopted many of them from Hopkinson and King. 11 The coverage-dependent sticking probabilities of CO and oxygen on the 1 ϫ 1 phase are adapted from experimental data as in Ref.…”

“…24. We use the sticking probability of oxygen on "freed" sites, recently made available by CO desorption or CO 2 formation 21 for S O 2 1ϫ1 .…”