Abstract

Carbon nanotubes (CNT) have gained interest for wide use as both support and catalyst due to the ease of uniquely tunable surface chemistry. Increasingly severe greenhouse effects have attracted attention to novel materials and technologies capable of capturing carbon dioxide (CO2). In this context, we develop a CNT based solid state amine for the CO2 capture. CNT are functionalized under various methods as a support for polymeric amines. Polyethyleneimine are physically adsorbed on CNT and are further characterized and studied for reversible CO2 capture. We obtain a high CO2 capture capacity (6.78 mmol∙g-1) for linear polyethyleneimine (LPEI) and 6.18 mmol∙g-1 for branched polyethyleneimine (BPEI). Based on the study of pore structure, we also demonstrate that in a steam post-combustion environment, supported polymeric amines on CNT show higher stability than traditional metal oxides. Besides the increased stability of the support in steam, we also improve the stability of amines under steam conditions by developing a covalent modification method. The CO2 capture capacity of the covalent bonded materials under steam conditions improved by 14% compared to dry conditions. In addition, the loading, chemical properties of PEI, and the surface chemistry of CNT remained stable under steam conditions compared to physically adsorbed PEI on CNT. These results suggest that covalent bonded PEI on CNT can be more suitable for CO2 capture in post-combustion processes. A different CNT application is as a catalyst for oxidative dehydrogenation (ODH) of ethane, and herein we develop a new processing technique for tuning the surface chemistry of the CNT-based catalyst. A one-step, gas-phase hydrogen (H2) surface modification is used to reduce carboxylic groups to phenolic groups on carbon nanotube (CNT) materials. This technique is greener and more facile for large-scale industrial catalysts than what has previously been reported. This method uses fundamental principles of CNT surface chemistry to efficiently reduce the unselective oxidation sites and enhances the active sites used for alkane oxidative dehydrogenation. The resulting catalyst improves the ethylene selectivity and yield by at most 81% and 28% respectively compared to the non-modified catalyst. A clear linear correlation between the functional groups and catalytic activity reveals the effect of specific oxygen species on performance. As the catalyst surface area increases, pretreatments generate more selective active sites instead of over-oxidation sites, providing a guideline for catalyst optimization. We suggest that the gas-phase H2 method is general for reducing carbon catalysts to increase selective oxidation sites for gas phase reactions.

College and Department

Physical and Mathematical Sciences

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2020-03-24

Document Type

Dissertation

Handle

http://hdl.lib.byu.edu/1877/etd11169

Keywords

carbon nanotube, carbon dioxide, capture, catalysis, oxidative dehydrogenation

Language

English

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