Multi-functional porous mix-valent manganese oxide nano-materials and Ru/TiO2 for magnetic, electronic, and catalytic applications

Date of Completion

January 2006

Keywords

Chemistry, Inorganic|Engineering, Chemical|Engineering, Materials Science

Degree

Ph.D.

Abstract

This thesis contains two parts: (1) development of porous mixed-valent manganese oxide octahedral molecular sieve (OMS) nano-materials with controlled tunnel structures and muilt-functionalities and (2) application of H 2 adsorption for metal particle size evaluation on TiO2 supported Ru Fischer-Tropsch catalysts. ^ Manganese oxide OMS with different nano-scale tunnel sizes may result in various microporosities for different selective catalysis and separation applications. A hydrothermal method was developed to synthesize manganese oxide nano-materials with controlled nano-scale tunnel sizes by hydrothermal treatments of layered structure manganese oxides under different pH conditions. Manganese oxides with increasing tunnel sizes of 2.3 Å × 2.3 Å (1×1 tunnel structure), 4.6 Å × 6.9 Å (2×3 tunnel structure), and 4.6 Å × 9.2 Å (2×4 tunnel structure) were synthesized with increasing pH value from 1.0, 7.0, to 13.0, respectively. Phase transformation mechanism of layered precursors to tunnel structures was obtained by characterization of the materials during synthesis using in situ synchrotron X-ray diffraction. The obtained phase transformation mechanism was used for synthesis of better materials such as new l×l/1×2 tunnel structures and controlled BET surface areas. ^ Most manganese oxide OMS materials show paramagnetism at temperatures from 100 to 350 K. A new method was established to measure the average oxidation state (AOS) of mix-valent manganese in OMS materials by describing their paramagnetic behavior using the Curie-Weiss law. Measurement results show a maximum 7% deviation error compared to the reference titration method for 10 different samples. Magnetism of OMS was further explored by doping Fe into KOMS-2 (a 2×2 tunnel structure manganese oxide) to create high temperature ferromagnetism. The possession of both semiconducting and high temperature ferromagnetism in the Fe-doped KOMS-2 created a highly promising new group of functional materials for spintronics applications. ^ In the second part, effects of temperatures, H2 pressures and adsorption equilibration times on H2 adsorption on Ru/TiO 2 were investigated. By assuming that exposed Ru atoms equally contribute to the three low index planes with the highest atomic density [(001), (100), and (110) planes], the average Ru particle size calculated from monolayer H2 chemisorption (4.6 nm) showed good agreement with the TEM measurement results (4.1 nm). ^

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