Date of Award

2010-01-01

Degree Name

Doctor of Philosophy

Department

Chemistry

Advisor(s)

Karina Castillo

Abstract

Silica and nanoparticles of Pt, Au, and Ag supported on silica were tested for the ability to oxidize dibenzothiophene (DBT) to sulfone. High performance liquid chromatography was used to study the removal of DBT from solution. In addition, X- ray diffraction, infrared spectroscopy and Raman Spectroscopy were used to characterize the product of the oxidation reaction. Further studies involved the use X-ray absorption spectroscopy to characterize the nanoparticle catalysts before and after the oxidation reaction.

To better understand the reaction, silica was synthesized at different pHs using three different acids. The acids used to synthesize the silica were HCl, HNO3, and H2SO4. The effect of SiO2 calcination temperature on the reaction was studied by drying silica at different temperatures. In addition, the oxidation reactions were performed at different temperatures and in different solvents. The reaction temperature used to test silica ranged between 115oC and 160oC when using decahydronaphthalene (decalin) as a solvent. Further studies were performed using high boiling point solvents tetrahydronaphthalene (tetralin) and n-dodecane. The percentage removal of DBT was similar when any of the three solvents was used in the reaction. However, when lower boiling point solvents were tested, such as hexane and heptane, no oxidation was observed. Furthermore, oxidation was not observed when the reactions were performed at the boiling point of each tested solvent. Silica synthesized at pH 0 using HCl, removed up to 70% of dibenzothiophene. However, a 90% removal was observed when commercially available silica was tested in this reaction.

Studies were performed to determine activation energy of the reactions using silica and then using the metal nanoparticles supported on silica. The activation energy was determined by testing each catalyst at three different temperatures. Each reaction was sampled every 30 minutes for up to 2 h. The Pt/SiO2 catalyst had an activation energy of 20.26 kJ/mol, the Au/SiO2 catalyst an activation energy of 47.04 kJ/mol, and the activation energy of the Ag/SiO2 catalyst was 77.31 kJ/mol. In addition, the activation energy of SiO2 catalyst was determined to be 115.56 kJ/mol. The Pt/SiO2 catalyst had the lowest activation energy of all the studied catalysts. Recycling studies showed the Au/SiO2 catalyst maintained the highest catalytic activity when tested four consecutive times in the reaction.

Infrared spectroscopy, X-ray diffraction and Raman spectroscopy confirmed that dibenzothiophene was oxidized to dibenzothiophene sulfone in the reaction. Furthermore, extended X-ray absorbed fine structure (EXAFS) showed the metal nanoparticles grew after the reaction. In addition, EXAFS studies also showed the silver catalyst converted to Ag2S after use in the oxidation reaction.

Language

en

Provenance

Received from ProQuest

File Size

108 pages

File Format

application/pdf

Rights Holder

Karina Castillo

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