Synthesis And Characterization Of Single Wall Carbon Nanotubes By Decomposition Of Methane On Como Mgo Catalysts

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.

"Education, arts and social sciences, natural and technical sciences in the United States and Canada".

After a brief introduction to the fundamental properties of graphene, this book focuses on synthesis, characterization and application of various types of two-dimensional (2D) nanocarbons ranging from single/few layer graphene to carbon nanowalls and graphene oxides. Three major synthesis techniques are covered: epitaxial growth of graphene on SiC, chemical synthesis of graphene on metal, and chemical vapor deposition of vertically aligned carbon nanosheets or nanowalls. One chapter is dedicated to characterization of 2D nanocarbon using Raman spectroscopy. It provides extensive coverage for applications of 2D carbon in energy storage including supercapacitor, lithium ion battery and fuel cells.

Alternative energy conversion systems are receiving great attention due to the depletion of fossil fuels and increasing environmental pollution. Due to excellent features such as high energy density, low operating temperature, and high energy conversion efficiency, direct methanol (DMFC) and ethanol fuel cells (DEFC) are promising power sources to address future energy problems. However, their performance is limited by low electrocatalytic activity of anodes for methanol and ethanol oxidations, and the high cost of noble metal platinum (Pt) based catalysts. One approach to enhance catalytic activity and to reduce the cost is to explore novel carbon materials as catalyst supports. In this work, single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and graphene-supported Pt and Pt-Ru catalysts were synthesized by an ethylene glycol (EG) reduction method. Comparative electrochemical measurements of different carbon structure-supported catalysts were conducted using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry techniques. Experimental results show that SWCNT-supported Pt and Pt-Ru catalysts have a higher catalytic activity and lower charge transfer resistance towards methanol and ethanol oxidation in comparison to MWCNT-supported catalysts. The electrocatalytic activities of graphene-supported catalysts were compared with commercial Vulcan XC-72 carbon black-supported catalysts and graphite supported catalysts. Experimental results suggest that graphene-supported Pt and Pt-Ru nanoparticles possess superior electrocatalytic activity than carbon black and graphite supports.