Topological analysis of catalytic reaction networks: Methanol decomposition on Pt(111)

We describe our new reaction route (RR) graph approach as a powerful new tool for topological mechanistic and kinetic analysis of catalytic reaction networks, illustrated here with the help of methanol decomposition on Pt(111). In this approach a graph-theoretic network of molecular reaction steps is first constructed for the overall reaction (OR), on which each mechanistic step is represented by a directed branch interconnected at nodes, such that all conceivable reaction pathways can then be traced on it simply as walks or paths. Further, the network is consistent with the basic laws of flow graphs, so that it is suitable for a quantitative analysis. In fact, a direct analogy can be made to an equivalent wiring diagram, which allows tools of electric circuit analysis, namely, Kirchhoff's laws of current (rate) and potential (affinity), to be directly utilized for a rigorous flux analysis of the network. As a result, the dominant pathways as well as the rate-limiting steps (RLS) become transparent. This furthermore facilitates network pruning to retain only the essential steps and pathways. The RR graph approach when combined with ab initio kinetics, thus, provides a rigorous new framework for analyzing the mechanism and kinetics of catalytic reactions. It is, thus, found that methanol decomposition proceeds exclusively via the initial CH dehydrogenation step rather than through OH bond activation.