DOI
https://doi.org/10.25772/KSGC-J058
Author ORCID Identifier
https://orcid.org/0000-0002-2114-8835
Defense Date
2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Chemistry
First Advisor
Dr. Hani El-Kaderi
Abstract
Porous materials provide access to a unique framework for designing materials for a variety of applications. These materials excel in areas that take advantage of the increased opportunity for interaction with the high-surface-area framework. Often, this quality is used effectively in the capture and storage of materials, such as electrical charge storage, separation of metals from water, storage of gaseous fuels, and gas capture applications. Conversely, porous materials can be a host for another active material, used to disperse active sites across a large surface area, enabling the formation of ultrasmall metal nanoparticles that can be used in catalysis. Some materials, such as metal-organic frameworks (MOFs), are dual purpose; high surface area and microporosity are beneficial for increasing physical interactions with the framework and open metal sites on the secondary building units can provide highly dispersed active metal sites throughout the material.
In this dissertation, the effects of synthetic parameters on the textural and chemical properties of heteroatom-doped porous carbons were investigated. A fundamental understanding of the relationships among the chemical activation agent, carbonization temperature, and precursor identity was elucidated. These relationships were leveraged to optimize several porous carbons for toxic gas adsorption, enabling the formation of highly adsorbing and reusable heteroatom-doped porous carbons. According to gas uptake measurements, these nitrogen-doped carbons exhibit exceptional gas adsorption capacity, with BIDC-3-800 adsorbing 21.42 mmol/g SO2 at 298 K and 1 bar, exceeding most reported porous materials and BIDC-2-700 adsorbing 14.26 mmol/g NH3 under the same conditions. The NH3 uptake of BIDC-2-700 surpassed reported activated carbons and is among the best adsorbents including MOFs. It was found that the heteroatom content plays a significant role in the adsorption of NH3 gas, and tuning the chemical properties of the associated porous carbons allowed for significant uptake of NH3, even in samples with a lower surface area. Conversely, the adsorption of SO2 was found to depend largely on textural effects. Tailoring the pore size and volume, even at the expense of the incorporated heteroatom content, enabled a near-record amount of SO2 to be adsorbed.
In the second project, silica-supported Pd and bimetallic catalysts were investigated for their activity in Buchwald-Hartwig Amination (BHA) reaction. The catalysts were synthesized by the strong electrostatic adsorption method, known for producing homogeneously dispersed, ultra-small nanoparticles that are strongly affixed to the silica support increasing the available active Pd sites at the desired loading. Ultra-small Pd nanoparticles were successfully deposited and characterized by XRD, XPS, and HR-TEM/HAADF-STEM. TEM and HAADF-STEM imaging show the particles to be 0.5-3 nm in diameter. After optimization of reaction parameters, it was found that an exogenous phosphine ligand was required for catalytic conversion. Bidentate ligands showed better activity than monodentate ligands with a correlation between increasing bite angle and increased product yield. Silica-supported monometallic Pd in the presence of Xantphos was found to be the optimal system for the BHA test reaction, reaching 99% conversion in 16 h @ 110 °C, outperforming the bimetallic alloyed systems. A variety of sterically and electronically different substrates were tested and shown to be generally high yielding, although the catalyst seems to be more sensitive to variations in the aryl halide than the amine. Recycling studies show that the silica-supported monometallic Pd sample is reusable, retaining 74% of its activity after 5 cycles, though leaching of the active Pd species is of concern, hypothesized to be primarily due to strong binding to the phosphine ligand.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
8-11-2023