ProfessorOffice: Chemistry C127APhone: 970-491-6292Website: http://sites.chem.colostate.edu/rappelabEducation: Ph.D., California Institute of TechnologyEmail: Anthony.Rappe@colostate.edu
Research interests are focused on the theoretical study of catalytic processes. Reactions currently under study include single-site propylene polymerization and hydrocarbon oxygenation. Modern Heterogenous catalysts function at the nanoscale with metal particles in the 10 nm range and metal sulfides with 3-5 nm wafer size. A particularly important question in catalysis is at what size do desirable bulk properties develop? When does a molecule become a solid? For properties such as ionization potential the bulk value is attained rather soon. The electron affinity and associated work function (IP-EA)/2 evolve more slowly, likely requiring hundreds of atoms. A catalytically important property that we are focussed on is the size-development of the solid-vacuum dielectric discontinuity which is present in a solid but absent in a molecular scale cluster. The associated electric field gradient likely plays an important role in stabilizing ionic species such as carbocations on catalyst particle surfaces. Since catalytic processes involve the reaction of relatively large chemical reagents in the condensed state, we, by necessity, are in the business of developing theoretical methodologies as well as validating and applying present-day techniques to catalytic reactions. This effort includes the development of molecular mechanics and dynamics technologies including the development of full periodic table molecular mechanics force fields, the development of functional forms and models consistent with the making and breaking of chemical bonds, and the development and documentation of molecular dynamics procedures for studying reactive species under controlled-temperature and high-pressure conditions. Since molecular mechanics and dynamics procedures, by their empirical nature, provide little insight into the electronic structure of metal ligand bonds and the electronic structural reorganization that accompanies a chemical reaction, we also utilize ab initio electronic structure tools. The types of electronic structure methods utilized generally attempt to include electron correlation (many-body) effects well enough to obtain reasonably accurate descriptions of the ground states of molecules both near equilibrium geometries and as they react. Additionally, correlation is included in a manner so as to permit interpretation and generalization of the electronic structural results into viable chemical concepts. These electronic structure techniques are used to probe the electronic control of catalytic processes through ligand tuning and to understand the character of metal ligand (primarily oxygen) bonding. Important questions here are 1) why do particular metal oxides epoxide olefins, others cis-dihdyroxylate olefins, and still others allylically oxidize olefins? 2) Can over oxygenation (combustion) be shut down by turning off radical autoxidation?