Site Isolated Vanadium Oxidative Catalysis in Metal Organic Frameworks: Exploring Oxidative Dehydrogenation and Oxidative Polymerization

Aerobic oxidation of simple hydrocarbons represents a sustainable route for producing chemically useful products. Unlike conventional thermal conversions such as direct dehydrogenation, aerobic oxidation can produce olefins under milder conditions. Solid-state catalysts play a central role in facilitating these reactions. Transition-metal oxides, particularly those containing vanadium, molybdenum, cobalt and iron, exhibit favorable oxygen mobility and tunable redox potentials. Traditional metal oxide catalysts are cheap, easy to produce and have high oxidation potential. Conversely this high oxidation potential leads to over oxidation which wastes feedstock and decreases atom efficiency. Challenges with these catalysts include site heterogeneity and the fact that structural changes, like metal migration, can occur during the reaction. These changes can alter surface area, redox behavior, and catalyst lifetime as well as vary selectivity and reproducibility. Efforts are being made to control active sites by supporting the catalysts on surfaces. One such material that allows for atomic level control of active sites are metal organic frameworks. Metal organic frameworks (MOFs) are a versatile class of crystalline porous materials constructed from metal ions or nodes coordinated to organic linkers. These pores result in large surface areas, tunable environments, and structural diversity. As a result, MOFs are prime candidates for a wide range of catalytic applications. This dissertation describes the use of MOFs as supports for high-valent vanadium catalytic sites for the aerobic oxidation of simple hydrocarbons. Specifically, MOFs that contain intrinsic hydroxyl sites on the metal node were post synthetically modified to introduce site isolated vanadium species. Both MIL-53 and UiO-66 were selected as supports for vanadium due to their ability to scale synthetically from low-cost starting materials, their high thermal and chemical stability. The MOF catalysts were able to perform several different reactions. First, the aerobic oxidation of cyclic olefins was investigated. Here, it was found that the catalyst was able to epoxidize and ring open the olefin to form short-chain polyether oligomers. The selectivity for cyclic olefins ix Texas Tech University, Thomas E. Ericson, December 2025 was utilized with the reaction of a bio-derived starting material D-limonene where the terminal olefin was able to be modified post-polymerization. A second reaction class involved cyclic alkanes, where the catalyst was able to directly oxidize cyclohexane to form either poly caprolactone (PCL) species or a polyether depending on the MOF that was used. Lastly, the MOF catalysts were employed as photocatalysts and found to be competent for the aerobic oxidation of cyclic olefins. Lastly covered will be an overview of the Mo ssbauer technique. Addressed will be its use in Fe chemistry. Then given are a few examples of when this technique was employed demonstrating why it was chosen and its result.