Date on Master's Thesis/Doctoral Dissertation

8-2010

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Chemical Engineering

Committee Chair

Fu, Xiao-An

Subject

Cerium dioxide; Nanostructured materials; Nanochemistry

Abstract

Cerium dioxide or ceria, CeO2, has been widely used in industry as catalyst for automotive exhaust controls, chemical mechanical polishing (CMP) slurries, and high temperature fuel cells because of its unique metal oxide properties. This well-known rare metal oxide has high thermal stability, electrical conductivity and chemical diffusivity. Proper synthesis method requires knowledge of reaction temperature, concentration, and time effects on the synthesis. In this work, ceria nanomaterials were prepared via the hydrothermal method using a Teflon autoclave. Cerium nitrate solution was used as the source and three different precursors: NaOH, H2O2, and NH4OH were used as the oxidizing agents. CeO2 nanoplates, nanocubes and nanorods were produced and studied using transmission electron microscopy (TEM), BET specific surface area, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Through characterization, CeO2 nanomaterials showed the presence of mixed valence states (Ce3+ and Ce4+) through XPS spectra. Deconvolution was performed to investigate the ratio of Ce3+/Ce4+ concentration in the synthesized CeO2 nanostructures. Nanocubes showed a higher Ce3+ concentration. CeO2 nanomaterials were found to be mesoporous. Nanoplates synthesized with H2O2, and NH4OH were found with surface areas of 95.11 m2/ g and 62.07 m2/ g, respectively. Nanorods and nanocubes showed surface areas of 16.77 m2/ g and 16.55 m2/ g, respectively. The prepared ceria nanoplates, nanocubes and nanorods had crystallite size in the range of 5-25 nm and pore size range of 7-15 nm. XRD spectra confirmed that the peaks were indexed to the cubic phase of CeO2 with fluorite structure and with an average lattice parameter, 5.407 Å. Higher Ce3+ concentration and exposed surface of crystalline planes suggest that nanorods are better catalyst for CO oxidation and oxygen storage capacity (OSC).

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