Browsing by Subject "Metal-organic frameworks"
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Item Bimetallic Active Sites In Metal-Organic Frameworks: Harnessing Bimetallic Cooperativity For Chemoselective Transformations(2020-04) Desai, Sai PuneetHeterogeneous catalysts featuring multiple metal centers account for a significant fraction of US GDP, and new ways to enhance them would have enormous economic, scientific and technological impact. The availability of several modulating sites coupled with the ability to precisely tune the selectivity has enabled the usage of multi-metallic catalysts for a wide array of industrial transformations. Critical to the challenge in engineering such active sites, is to understand and predict how catalysts function at the atomic or molecular level. An emerging approach that facilitates the systematic study of such systems is the installation of molecular precursors onto three-dimensional crystalline supports such as metal-organic frameworks (MOFs). In this vein, a generalized solution-phase-deposition technique was developed wherein pre-assembled bimetallic precursors were deposited onto the MOF NU-1000, such that two metals of choice were delivered in a controlled manner. Rigorous spectroscopic and computational investigations confirmed that the bimetallic active sites were structurally well-defined and site isolated. An important outcome of this study was the identification of a rhodium-gallium (Rh–Ga) bimetallic catalyst for the chemoselective semihydrogenation of alkynes to alkenes. In the absence of the supporting Ga ion, over-hydrogenation to the alkane was observed by the Rh-only analogue. By quantitatively analyzing the initial rates, transition state properties, and thermodynamic profiles, it was concluded that Ga acts as an electronic and structural promoter. Finally, as an extension of this unique strategy, thermally robust Co–M (M = Al, Mn or Co) active sites, prepared by silica nanocasting of NU-1000, mediated industrially relevant chemical transformations such as oxidative dehydrogenation of propane to propylene and oxidation of alcohols. Overall, the design principles developed in this thesis provide compelling solutions to generate ‘multi-metallic single sites’ and add to the arsenal of existing metalation strategies.Item Development of Novel Porous Materials and Thin Membranes For Gas Separations(2020-01) Xue, FengThe development of high-flux, high-selectivity, and low-cost membranes has the potential to improve the energy efficiency in the chemical industry by reducing the reliance on energy-intensive separation processes, such as distillation. To achieve this goal, novel porous materials and membrane fabrication methods are being increasingly sought after. Metal-organic frameworks (MOFs) are a new type of microporous materials with tunable pore structures suitable for gas separations. However, the high manufacturing cost and industrially-unattractive throughput hinder the industrial applications of MOF membranes. Fabrication of thin membranes with high throughput has the potential to overcome this barrier. This dissertation focuses on developing synthesis methods for thin MOF membranes by using two-dimensional (2D) MOF nanosheets and an all-vapor-phase zeolitic imidazolate frameworks (ZIFs) membrane synthesis process named ligand-induced permselectivation (LIPS). Crystal growth strategies for 2D MOFs were developed that yield Zn(Bim)OAc MOF nanosheets with desirable aspect ratio and uniformity for membrane formation. Using the Zn(Bim)OAc nanosheets, uniform coatings were successfully prepared on porous supports by vacuum filtration. A novel vapor growth method combining the support surface modification and ligand vapor treatment was developed to transform the nanosheet deposits into thin propylene-selective membranes. In addition, in an effort to reduce the membrane cost by using low-cost polymers, porous Cu(BDC) MOF nanosheets were incorporated into polymer matrices to form mixed matrix membranes that exhibited significantly improved performance for CO2/N2 separation. Besides solution processing of MOF membranes, a novel, well-controlled and cost-effective all-vapor-synthesis LIPS method with a combination of atomic layer deposition (ALD) and ligand vapor treatment was investigated. It was demonstrated that an ALD processing condition allowing a thin non-permeable ZnO deposit formation, as well as efficient ZnO-to-ZIFs conversion during ligand vapor treatment are very critical to realize consistent high membrane performance. With optimized ALD parameters, support and ligand properties, the membranes exhibit superior separation performance, with propylene permeance above 1.3 ×10-7 mol m-2 s-1 Pa-1 and propylene/propane selectivity above 60, which is highly promising for industrial applications.Item Supporting Information for Mechanism of Methanol Dehydration Catalyzed by Al8O12 Nodes assisted by Linker Amine Groups of the Metal-Organic Framework CAU-1(2022-06-13) Yang, Dong; Chheda, Saumil; Lyu, Yinghui; Li, Ziang; Xiao, Yu; Siepmann, J Ilja; Gagliardi, Laura; Gates, Bruce C; lgagliardi@uchicago.edu; Gaglairdi, Laura; University of Chicago Department of Chemistry; University of Chicago Pritzker School of Molecular Engineering; University of Chicago Chicago Center for Theoretical Chemistry; University of Minnesota Department of Chemical Engineering and Materials Science; University of Minnesota Department of Chemistry; University of Minnesota Chemical Theory CenterThis repository contains the XYZ files of the structures optimized using density functional theory for the investigation of methanol dehydration mechanism catalyzed by metal-organic framework CAU-1.