Bistability for CO Oxidation: An Understanding from Extended Phenomenological Kinetics Simulations

CO oxidation can exhibit diversely appealing catalytic behaviors on metal surfaces. Exploring such properties is crucial not only for fundamental understanding but also for practical applications. In the present work, we focus on bistability and comprehensively investigate how the bistability is influenced by changes of the apparent rate coefficients of the elementary reaction steps. Such changes are related to the changes of reaction conditions and the design of the catalysts. For CO oxidation at certain lower temperatures and total pressures, there exists a bistability region, where one state, the reactive (R-) state, is predominantly oxygen-covered while CO can still adsorb and react, whereas the other state, the P-state, is CO poisoned and O-2 adsorption is inhibited and the catalyst is inactive. By means of extended phenomenological kinetics (XPK) simulations, we find that the minimum CO pressure for the system to stay at the P-state is determined by the apparent rate coefficients of CO desorption and oxygen adsorption, meanwhile the maximum CO pressure for the system to stay at the R-state is determined by the apparent rate coefficients of CO oxidation and oxygen adsorption. The XPK results reveal that lateral interactions between adsorbates can significantly affect the rate coefficients and thus have a strong impact on the bistability region. With these understandings, we further predicted that the sandwiched PdRuPd(100), PdOsPd(100), and PdCoPd(100) surfaces would be good candidates as catalytic converters to reduce CO pollution from automobile engines under both conditions before and after the catalysts are warmed up to the ignition temperature.