Date of Award

Summer 2019

Document Type

Open Access Thesis

Department

Chemical Engineering

First Advisor

Erdem Sasmaz

Abstract

Flame spray pyrolysis (FSP) is a method of quickly synthesizing active particles in a flame. Precursors are dissolved in a flammable organic solvent before being sprayed into the flame environment where they rapidly burn. Particle formation occurs on the order of 10 milliseconds. FSP has been shown to be a viable method of producing materials on an industrial scale, capable of producing grams of particles per minute. Metastable structures which exist in the liquid phase, but are difficult to synthesize using traditional impregnation methods can be formed with FSP due to fast quenching times. For example, solid solutions of Ce-Zr synthesized using FSP have been shown to have higher thermal stability when compared to Ce-Zr solid solutions made through traditional wet synthesis methods. Flame made particles have been shown to have higher activity in a variety of catalytic reactions, including oxidation reactions, photocatalytic reactions, and combustion reactions.

Due to the favorable properties of solid solution FSP materials, a flame spray pyrolysis system was built using a premixed flat flame burner and atomizing nozzle for the synthesis of Ce-Mn solid solutions. Liquid solutions with varying ratios of Ce and Mn (1:1, 1:3, 3:1) were synthesized in the FSP system under a variety of different conditions. The liquid to dispersion gas ratio and atomization pressure were altered in order to determine each parameter’s effect on final particle morphology and stability. Particle morphology was characterized using x-ray diffraction and scanning electron microscopywith energy dispersive x-ray spectroscopy. Raman spectroscopy was used to determine the chemical composition of the materials, and TGA was used to determine the amount of water and carbon in the material. The hydrothermal stability of FSP made Ce- Mn solid solutions was also investigated.

Samples at each atomization pressure (P=0, 0.5, 1 bar) exhibited peaks corresponding to both crystalline and amorphous ceria. The presence of amorphous ceria indicates that complete combustion is not achieved. The lattice constants for crystalline samples were calculated using Scherrer’s equation. The flame made Ce-Mn solid solutions had lower lattice constants when compared to the literature value for the lattice constant of ceria (5.411 A), indicating the incorporation of Mn into the ceria lattice. Raman and TGA data show that incomplete combustion is occurring in the flame, which matches well with the XRD data. Characterization of samples after water stability testing revealed an increase in particle size when compared to fresh samples.

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