How Hard Is Mechanism Elucidation in Catalysis? Combinatorial Analysis of C1 Chemistry

Most chemical reactions occur over multiple steps whose identity is elucidated by experiment, yielding a reaction mechanism. Knowledge of cognitive science suggests that mechanism elucidation can be viewed as a knowledge-guided search within a combinatorial space. The MECHEM computer program searches this space comprehensively for the simplest plausible mechanisms. We use MECHEM to find mechanisms for Fischer-Tropsch chemistry and CO2 re-forming of methane, both heterogeneous catalytic reactions of current importance. The results reveal hundreds of equally simple mechanisms consistent with evidence. Hence, mechanism elucidation in catalysis is a much harder problem than is ordinarily realized.