Competing ternary surface reaction CO + O₂ + H₂on Ir(111)

Abstract

The CO oxidation on platinum-group metals under ultra-high-vacuum conditions is one of the most studied surface reactions. However, the presence of disturbing species and competing reactions are often neglected. One of the most interesting additional gases to be treated is hydrogen, due to its importance in technical applications and its inevitability under vacuum conditions. Adding hydrogen to the reaction of CO and O 2 leads to more adsorbed species and competing reaction steps towards water formation. In this study, a model for approaching the competing surface reactions CO+ O 2 + H 2 is presented and discussed. Using the framework of bifurcation theory, we show how the steady states of the extended system correspond to a swallowtail catastrophe set with a tristable regime within the swallowtail. We explore numerically the possibility of reaching all stable states and illustrate the experimental challenges such a system could pose. Lastly, an approximative first-principle approach to diffusion illustrates how up to three stable states balance each other while forming heterogeneous patterns.

Elementary catastrophes underlying bifurcations of vector fields and PDEs

“…A number of other works have attempted to relate elementary catastrophes to the behaviours of partial differential equations. In [6], the signature shapes of a swallowtail are seen in bifurcation diagrams of an oxidation reaction, and in [21], butterfly sets are then shown in reaction diffusion by limiting to a scalar one species problem, and a similar treatment places cusps in a crowd density problem in [28]. A nice discussion of the problem of detecting high codimension bifurcation points in PDEs can be found in [15], before scalar catastrophe theory is used to develop numerical methods for the purpose.…”