Swallowtail model for predicting the global bifurcation behavior of CO oxidation reactions

Catalytic CO oxidation on platinum group metals exhibits nonlinear phenomena such as hysteresis and bifurcation. Elucidation of the nonlinear mechanisms is important for catalyst design and control of reaction routes. Previous studies have offered initial insights into the local bifurcation behavior of CO oxidation. However, since the bifurcation behavior of CO oxidation is determined by multiple parameters such as temperature, total flux, and CO fraction, it is difficult to predict the global bifurcation behavior in the resulting high-dimensional parameter space. It is for this reason that the observed nonlinear phenomena reflect just the local bifurcation features of CO oxidation. In this paper, an elementary chemical law (topological invariance) concerning the bifurcation behavior of CO oxidation on platinum group metals such as Pd(111) is found from a topological perspective. Following the elementary law, we put forward a topological approach to model the critical criteria for the reaction hysteresis and bifurcation. The model may be applied to predict the global bifurcation behavior of CO oxidation in the high-dimensional parameter space. The topological approach and the model results may be useful as a guide in thinking about the complex reaction mechanism, designing reaction routes, and actively controlling the bifurcation behavior of the CO oxidation reaction.