Date of Award

1-2013

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering (MSMSE)

Department

Materials Science

First Advisor

Dr. Abbas Khaleel

Second Advisor

Dr. Yaser Afifi

Abstract

Transition-metal ions -doped γ-alumina composites with various dopant concentrations (Cr3+, Fe3+, Ce3+, Zn2+, Mn2+, V2+ and Cu2+) were prepared by straightforward tempIate-free sol-gel method. They were characterized by XRD, FTIR, SEM, NMR and N2 adsorption-desorption isotherm technique. The presence of dopant metal ions, generally, enhanced the gel formation and their behavior was dependent on the nature of the metal ion and its concentration. Certain ions, especially Fe3+, resulted in rapid formation of a transparent gel upon hydro lysis. The presence of the acetylacetonate ions (acac) enhanced the condensation reactions in the sol-gel process and resulted in eventually unique textural properties of the calcined products including high surface areas, small particle size, homogeneous mesopores, and enhanced resistance to sintering especially at high dopant concentrations and elevated calcination temperatures.

The prepared doped γ-alumina powders were weakly crystalline at low dopant ion concentrations, 3%, and became completely amorphous at a concentration of 10%. The morphology of the particles was also dependent on the dopant concentration. While dopant concentration of 2% resulted in nano-particles with significant amount of inter-particle mesopores, 10% concentration led to significant aggregation into larger particles. The prepared doped γ-alumina as well as the undoped γ-alumina showed high surface areas (377 m2/g) and pore volumes (1.65 cc/g) which were largely dependent on the nature of the dopant metal ions and on their concentrations. While composites with low dopant concentration, 2 and 3%, exhibited surface areas and pore volumes comparable to those of undoped γ-alumina, a considerable decrease was associated with higher concentrations. The changes in textural properties were referred to the evident enhanced sintering associated with high dopant concentrations. Composites with low Cr3+ ion concentration, 0.75 and 2%, showed reversible thermochromism where their greenish yellow color changed to red upon calcinations at temperatures between 500 and 700 °C. Based on NMR results, occupation of tetrahedral sites by Cr3+ ions was preferred over octahedral sites at low Cr3+ concentrations. The composites showed unique textural properties comparable with those of high-surf ace-area porous γ-alumina, especially at low concentrations of Cr3+.

The catalytic activity of the doped catalysts as well as that of undoped γ-alumina was studied over 1,2-dichloroethan (DCE) at 300°C using FTIR spectroscopy to monitor the reaction products. γ-alumina catalyst doped with CU(Il) and Cr(Ill) ions showed higher conversion than undoped γ-alumina. The nature of the products was strongly dependent on the presence of dopant ions and on the type of dopant. While pure γ-alumina resulted, mainly, in the formation of C2H3CI, Cu- and Cr-doped catalysts showed significantly stronger capability for deep oxidation of DCE to CO2 on the account of C2H3Cl.

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