To develop a molecular level understanding, microkinetic models are constructed considering all possible elementary reactions and intermediate species in the system without a priori assumptions of a rate-limiting step or dominant pathway. As these microkinetic models are quite large, complex, and difficult to create by hand, automated model generation is the focus of many researchers; GRACE and KING are the oldest and use a matrix-based representation of species. Some software packages were designed for specific chemistries, such as EXGAS and COMGEN for combustion, PRIM-O and REACTION for heavy molecules, and RING 9 initially for biomass conversion. Others, like RMG, Genesys, and KinBot 13 are applicable to a variety of different reactions. KinBot uses onthe-fly Density Functional Theory (DFT) calculations to discover novel reaction pathways and determine accurate thermo-kinetic parameters, but doing so is much slower than applying rules and estimates. Many of these mechanism generation tools are reviewed in ref. 14; very few of them can model heterogeneous catalysis and surface reactions.