| As heterogeneous catalysts are studied in more detail, it becomes clear that the description of a catalyst surface as a homogeneous set of catalytic reaction sites is invalid. Rather, the catalytic surface is often nonuniform, comprised of a host of different atomic configurations, leading to a range of chemical environments. These different chemical environments can result in a wide range of reactivities, or molecular reaction rates, on a single catalytic surface. In addition, the presence of other reactive intermediates can have profound effects on the local reaction rates. Therefore, a detailed picture of all catalyst-molecule and adsorbate-adsorbate interactions is needed to fully specify a system. For even medium-size systems, this leads to an unwieldy number of parameters. Fortunately, there is a large experimental database documenting well-defined systems in which specific types of nonuniformity are known to exist. The information gained from studying such systems forms a basis from which investigations of more complex systems can begin.; First principles calculations and information from the literature were synthesized to develop effective nonuniform kinetic models of heterogeneous catalytic reactions. Specifically, models were first developed for model systems. Software was written to solve these mechanisms using both microkinetic modeling and dynamic Monte Carlo methods. The information from these investigations was then used to develop an accurate, nonuniform model of the methanation reaction. This model outperformed all other models in the literature at both fitting and predicting methane production rates. It also provided valuable insight into the state of the catalytic surface under reaction conditions and the controlling kinetic and nonuniform parameters in the system. |
