Date of Award

4-2016

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Prof. Abbas Ahmed Khaleel

Second Advisor

Dr. Yaser Greish

Third Advisor

Prof. Sofian M. Kanan

Abstract

Fe (III)-modified Titania and Fe (III)-Ti (IV) binary oxides have received much less attention as possible catalysts compared to their parent single-metal oxides, Fe2O3 and TiO2. This could be due to the difficulty of obtaining pure desired monophases. In addition, the effect of different preparative conditions on the textural properties of sol-gel-prepared Ti-Fe mixed oxides was rarely studied. Furthermore, the effect of the composition on the reducibility and the catalytic activity of these composites was never studied. In the present work, Ti-Fe mixed oxides were prepared using a modified sol-gel method and their textural properties as well as their reducibility and their catalytic activity were investigated and were compared with those of parent single-metal oxides.

The use of propylene oxides (PO) as a gelation promoter as well as the presence of hetero-ions was found to play a key role in promoting gel formation at certain concentrations. While in the presence of a single metal, colloidal solutions and very fine precipitates were obtained, gels formed readily from mixed solutions containing 5-15% Fe(III) in the presence of PO, and from solutions containing 40 and 66.7% Fe(III) even in the absence of PO.

While Fe (III) concentration as high as 10% was well dispersed in the Titania lattice, which was also associated with enhanced stability of the anatase structure, higher concentrations resulted in the formation of anatase and pserudorutile (Pr) initially, which converted to rutile and pseudobrookite (Pb) upon heating at elevated temperatures. The preparation of a pure Pr phase was possible under the employed preparative conditions starting with a solution containing 40% Fe (III). However, the presence of higher concentrations resulted in the formation of some segregated α- Fe2O3. Xerogel and aerogel mixed oxides possessed significantly higher surface areas than their parent single metal oxides, and the surface area increased as the Fe (III) concentration increased. Furthermore, the mixed oxides showed an enhanced reducibility indicating a more labile lattice oxygen.

The mixed oxides possessed significantly improved catalytic activity compared with their single-metal oxide counterparts, especially at lower temperatures. Using 4% air in the reaction mixture resulted in the formation small amounts of benzene besides CO2 as the major product. However, Using 16% air in the reaction mixture, resulted in deep oxidation to CO2 as the only product. Among the tested catalysts, TiFe67 showed the highest catalytic activity making it a promising catalyst for oxidative degradation of volatile organic compounds, VOCs.

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