Getting to the point: Bridging the gap between simple and complex catalytic systems using Temporal Analysis of Products (TAP).

摘要

One of the key issues in the field of catalysis is to relate the catalyst structure/composition to its activity/selectivity. One way to understand this relationship is to understand the individual role each catalyst component plays in the chemical reaction. Industrial catalysts can be extremely complex in structure and to understand their reaction kinetics, researchers often study simpler surfaces such as single crystals using surface science techniques. This introduces a well-known problem in the field of catalysis commonly referred to as the "pressure and materials gap." Typically, industrial catalyst research is performed under process conditions, which means operating pressures of one atmosphere or higher. Under these conditions, it is difficult to extract intrinsic kinetic properties of the catalyst which are properties that are directly related to the catalyst structure and composition. To find these intrinsic kinetic properties, scientists turn to surface science techniques using different types of spectroscopic tools to study reaction properties on single crystal surfaces under ultra-high vacuum (UHV) conditions. Experiments using single crystals and surface science techniques have helped establish that some crystal planes are more active and/or selective than others. Although surface science approaches are successful in obtaining fundamental information on a variety of catalytic reactions on the atomic level, current catalytic reactions are still carried out under atmospheric pressures or greater and on much more complex materials than single crystal surfaces.;This dissertation introduces a new approach to characterize catalysts that vary in compositional/structural complexity in order to understand their performance in a conventional reactor/reaction environment under both atmospheric pressure and ultra-high vacuum conditions. Experiments performed under both pressure regimes were carried out using the same apparatus, the Temporal Analysis of Products (TAP) reactor. The catalysts under investigation are bulk transition metals (Pt), transition metals deposited on metal oxide supports (Pt/SiO2), and mixed metal oxides (VPO). The catalysts are applied to two types of reaction systems, CO oxidation and selective oxidation of hydrocarbons. The goal of the experiments is to understand and distinguish the role of each component of the catalyst during chemical reaction. Using the TAP reactor, the number of active sites, reaction mechanisms, adsorption/desorption rate constants, and rates of reaction can be determined.