One of the greatest challenges in heterogeneous catalysis is the rational design and development of new catalytic systems, due to synthetic limitations in the design of solid catalysts and inhomogeneity of chemical sites at solid surfaces. This obfuscates understanding of catalyst behavior and slows improvements of processes. One approach to circumventing these challenges is the synthesis of well-defined, structurally tunable catalysts like Metal–Organic Frameworks (MOFs). MOFs are crystalline, porous coordination polymers, which are most useful for their structural tunability and molecular precision, allowing the optimization of catalytic performance through precise, structural modification and the elucidation of structure-reactivity relationships. Through a combination of chemical synthesis, materials characterization, catalytic testing, and computational modeling, this work studies zirconium MOFs (Zr-MOFs) for the development of structural parameters for optimizing conversion of hydrocarbon and biomass feedstocks. Chapter 1 introduces approaches towards and challenges in the rational design of solid catalysts. Chapter 2 details the study of the archetypal Zr-MOF, “NU-1000”, as a catalyst support for organotantalum complexes in olefin and alkane metathesis. While the tantalum sites were inactive for these reactions due to over-coordination from the support, the serendipitous observation was made that NU-1000 heterolytically activates H2, leading to 1-butene isomerization. Chapters 3 and 4, detail mechanistic investigations establishing structural parameters for H2 activation and olefin hydrogenation and isomerization (OHI). Basic ligands adsorbed on the Zr6O8 nodes in Zr-MOFs cooperate with adjacent Zr4+ Lewis acid sites in heterolytic cleavage of H2, leading to 1-butene hydrogenation and parallel hydride- and acid-catalyzed pathways for 1-butene isomerization. Increasing Brønsted acidity of protons formed in H2 cleavage trends with increasing activity for 1-butene isomerization, and MOF topology is shown to control the orientation of co-adsorbates during 1,2-insertion, affecting hydrogenation and isomerization activity. Finally, chapter 5 details effects of Zr-MOF topology upon performance in MPV reduction, where more accessible topologies lead to orders of magnitude differences in conversion at the expense of lower product selectivity with bulky substrates. These results are due to 1) more favorable formation of MPV transition states and 2) increases in the quantity of fruitful configurations of co-adsorbed substrates in more accessible topologies.

Creator

• Hicks, Kenton

DOI

• https://doi.org/10.21985/n2-5ks8-wa32

Subject

• Inorganic chemistry
• Chemistry
• Chemical engineering

Language

• en

Alternate Identifier

• etdadmin_upload_996080
• http://dissertations.umi.com/northwestern:16635

Date created

• 2023-01-01

Resource type

• Dissertation

Rights statement

• In Copyright