Doctor of Philosophy
Chemical and Biochemical Engineering
Dr. Jose Herrera
Single-walled carbon nanotubes (SWCNTs) are materials with unique electronic and mechanical properties suitable for a large number of applications. Although, since their discovery many strategies for SWCNT synthesis have been explored, most of these are either tremendously energy intensive or require complex SWNCT purification strategies. These issues have resulted in expensive SWCNT production processes which in turn have hampered the development of a large range of SWCNT applications. This study deals with the controlled growth of SWCNTs from methane decomposition over iron and cobalt catalysts supported on MgO and the application of the CCVD grown SWCNTs as a catalyst for partial oxidation of ethanol to acetaldehyde. A series of analytical techniques such as nitrogen physisorption, powder X-ray diffraction, diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and temperature programmed reduction techniques were used to examine the catalysts used for SWCNTs synthesis. Similarly, obtained carbon nanotube deposits were characterized by Raman spectroscopy, high resolution electron microscopy, optical absorption spectroscopy, energy dispersive X-ray spectroscopy, temperature programmed oxidation and nitrogen physisorption techniques. The results indicate that the relative aggregation rate of stabilized metallic clusters and methane decomposition rate were balanced such that a high yield of SWCNTs of high quality was achieved. Surface-modified SWCNTs catalysts with oxygen functionalities for partial oxidation of ethanol to acetaldehyde were obtained by thermal treatment of the purified SWCNT materials obtained during the first part of this study in O2/He gas mixture iv between 200-350 ºC. Raman and optical absorption spectroscopy and temperature programmed oxidation (TPO) were used to probe the SWCNTs catalyst before and after partial oxidation. Temperature programmed desorption (TPD) and infrared spectroscopy were used to investigate the nature of oxygen functionalities involved in partial oxidation catalysis. The catalyst displayed high, stable activity and selectivity up to 24 hours time-on-stream. Acetaldehyde selectivity was found to be independent of catalyst pretreatment temperature. The results indicate that an opportunity exists to create highly active and selective nanotube-based catalysts for ethanol partial oxidation resulting in a sustainable metal-free strategy for acetaldehyde production that is free of the environmental burden of toxic transition metals.
Abdullahi, Inusa, "Controlled Synthesis of Single-Walled Carbon Nanotubes by Methane Decomposition and Their Application as Heterogeneous Partial Oxidation Catalyst" (2012). Electronic Thesis and Dissertation Repository. 957.