Abstract

In this thesis research, three novel methodologies have been examined for their use in the synthesis of transition metal - carbon nanotube hybrid materials. These newly synthesized materials were assessed as catalysts in various heterogeneous catalysis reactions, including Fischer Tropsch synthesis, the Sabatier reaction, and the Reverse Water Gas Shift reaction. Specifically, this research was aimed at evaluating the relationship between particle size, support material, and activity of the metal-centerednanotube hybrid catalysts as compared to more traditional heterogeneous catalysts. Efforts were centered on establishing the conditions needed to obtain the optimum metal crystallite size deposited on the nanotube support, as required for achieving the best catalytic activity for a particular reaction scheme. This was done by modifying various synthesis parameters such as the reaction temperature and time, as well as reviewing the metals used for the catalyst deposition.

In Fischer Tropsch synthesis, carbon monoxide is hydrogenated over a transition metal catalyst to produce varying length hydrocarbons and olefins. Traditionally, iron, nickel, and cobalt catalysts have been used, and were supported on various oxides and activated carbon. In this thesis research, a series of transition metals, including iron, nickel, cobalt, chromium, and rhodium were deposited on purified single walled carbon nanotubes (SWNTs). SWNTs have recently gained considerable attention do to their unique physical and chemical properties, which can be tailored for the use in numerous applications. In this thesis research, the use of SWNTs as catalyst supports is explored. The large surface area, chemical inertness, mechanical strength, and meso-porous structure, make SWNTs an excellent candidate for a catalyst support material.

Catalyst deposition was achieved in this project through an adsorption technique, a direct reduction technique, and through the pre-reduction of the SWNT surface. In typical catalyst synthesis, the metal particles are reduced onto the catalyst support using flowing H2, however, through the use of the proposed adsorption technique, the transition metal is nucleated onto the surface of the SWNTs at the position of a defect site, and is subsequently reduced with the aid of a reducing agent thus causing the growth of the particle. On the other hand, the direct reduction technique involves the modification of the nanotube reduction potential by pre-reducing the SWNTs with alkali metals, such that the metal catalyst particle will be spontaneously reduced and deposited onto the surface of the SWNTs at the position of a defect site. Lastly, the third technique proposed for the synthesis of the hybrid materials involves the pre-reduction of the SWNT surface with a reducing agent, followed by the direct reduction of the metal catalyst particles. This technique yields pristine-like SWNTs, free of most oxidative defects, and causes the transition metals to be reduced and precipitated evenly over the entire surface of the SWNT material. Of these three techniques, the latter was found to produce hybrid materials with well dispersed metal nanoparticles having(TEM). Additionally, these materials were examined for their use as efficient catalysts in the heterogeneous catalysis reactions named previously. Temperature programmed desorption (TPD) data demonstrated the ability of these materials to catalyze the Fischer Tropsch reaction. Additionally, the Rh- SWNT samples have shown evidence that they can be used as catalysts in the Sabatier and Reverse Water Gas Shift reactions when doped with the appropriate reagents as well.

Library of Congress Subject Headings

Transition metal compounds--Synthesis; Carbon compounds--Synthesis; Transition metal catalysts--Analysis; Nanotubes; Nanostructured materials; Catalysis

Publication Date

2007

Document Type

Thesis

Student Type

Graduate

Degree Name

Chemistry (MS)

Department, Program, or Center

School of Chemistry and Materials Science (COS)

Advisor

Thomas Gennet

Advisor/Committee Member

Terrence Morrill

Comments

Physical copy available from RIT's Wallace Library at QD172.T6 E55 2007

Campus

RIT – Main Campus

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