Bimetallic Systems for Heterogeneous Catalysis and Tuning Electronic Properties of Functional Materials

Throughout the past few decades, advancements have been made in altering monometallic materials through addition of a second metal to create a bimetallic material that displays enhanced properties over its monometallic components and optimized attributes toward the intended application. However, a lack of fundamental understanding of the interactions between the two metals and between the metals and their environment can hinder the process of designing enhanced functional materials with desirable properties. In this work, careful analysis of model catalysts and metal-organic frameworks (MOFs) is performed in ultrahigh vacuum, and evaluation of the catalytic activity of the catalysts and electronic properties of the MOFs establishes a relationship between the interactions of the bimetallic materials and their properties. Platinumrhenium surfaces on diverse supports including TiO2, HOPG, and Pt(111) are investigated for the effect of differences in their composition and morphology on their catalytic activity for the water-gas shift (WGS) reaction, as well as their potential for oxidation. Catalysts consisting of Pt with subsurface Re are found to have enhanced activity over Pt alone regardless of the support being used. However, clusters on the TiO2 support have greater activity overall, indicating the oxide support plays a role in facilitating the reaction. The oxidation of Re is enhanced in the presence of Pt on all supports, and is attributed to greater dispersion when Re is intermixed with Pt. The electronic properties of copper-containing MOFs are studied by transmetallating a second metal into the framework, including cobalt, rhodium, iron, manganese, ruthenium, or nickel to form a bimetallic MOF. Alternate secondary building units (SBUs) of monomeric M-HHTP, dimeric M2-BTC and pentameric M5-NIP metal centers are used with the monometallic and bimetallic MOFs to fully investigate the parameters that influence their electronic properties. The bimetallic CuCo-BTC and CuRh-BTC MOFs exhibit more density of states (DOS) near the Fermi edge (EF) than the monometallic Cu-BTC MOF, demonstrating the influence of incorporating a second metal into the framework. However both the monometallic and bimetallic MOFs using the HHTP ligand all have greater DOS near EF than the Cu-BTC MOF; and the Cu-NIP and CuRh-NIP also show enhanced DOS near EF, suggesting the ligand plays an influential role in determining the DOS as well. Thin MOF films of Cu-BTC grown via dip-coating demonstrated successful transmetallation with Co to produce bimetallic CuCo-BTC films with controllable Co concentration based on immersion time and temperature. Films maintained a uniform coverage of the substrate and crystalline structure upon initial growth and after undergoing transmetallation