| One of the challenges facing the use of detailed mechanistic models to describe heterogeneously catalyzed systems is their construction. Algorithms which automate model construction allow the modeler to focus on interpreting the chemistry described by the model rather than on its tedious assembly. Currently, several limitations of existing software for automatic mechanism generation prevent description of a wide range of catalytic chemistries. Since many configurations of adsorbed intermediates exist, incorporation of a catalytic surface must account for possible sites of interaction. Solution of a generated reaction mechanism ultimately requires rate constants, and therefore, the mechanism generator should be linked with methods for their specification. Furthermore, in chemistries where molecular weight growth is important, a chemically-based algorithm must be implemented to halt mechanism generation rationally. Development of these generic capabilities, implemented by constructing a Fischer-Tropsch synthesis model, was carried out.; Another primary focus of this work was the estimation of rate constants during automatic mechanism generation for heterogeneously catalyzed reactions. Linear free energy relationships, using heat of reaction as the reactivity index, were applied and theoretical approaches were used to estimate activation energies and preexponential factors. Calculation of heats of reaction involving surface species presented special challenges due to unknown heats of adsorption for many adsorbates. This problem was addressed by estimating heats of adsorption using two phenomenological approaches which relate the chemisorption energy of multiatomic species to that of adatoms. In order to provide a basis set of values for adsorbed species on Ni(111) and Co(0001) surfaces, the binding energies of carbon, hydrogen, oxygen, CH, CH{dollar}sb2,{dollar} and CH{dollar}sb3{dollar} were calculated using an ab initio method developed for periodic systems. The dependence of the binding energy on adsorption site and surface coverage was probed; the results reported in this thesis present the most comprehensive study to date of the interplay of these two variables for the adsorbates and surfaces studied. The energetics obtained were used in a reaction mechanism describing Fischer-Tropsch synthesis via carbene polymerization that was constructed automatically. The model predictions for Ni(111) and Co(0001) surfaces successfully captured product selectivities observed experimentally over nickel and cobalt catalysts. |
