Title

Heterogeneous photocatalysis and migration of vanadium between zeolite and matrix components in fluid catalytic cracking (FCC) catalysts

Date of Completion

January 1993

Keywords

Chemistry, Inorganic

Degree

Ph.D.

Abstract

The experiments presented here explore the nature of photocatalysis via a model reaction of the photocatalytic oxidation of isopropanol to acetone by two groups of newly developed catalysts, uranyl and manganese oxides. Different than previous reports of uranyl photocatalysis in solution or in static liquid-solid interface reactions, continuous gas-solid interface reactions were carried out in a heterogeneous photocatalytic reactor under room temperature with visible light employed rather than UV light.^ In Chapter 2, various uranyl catalysts with better properties have been developed showing 100 times higher activity than literature reports, 100% selectivity and long lifetime. XPS, EDX, and luminescence spectroscopy studies reveal that uranyl ions, the U(VI) species, are the active centers. Systematic studies of the roles of light, carrier gases and supports suggest that each are very important to the reaction rate and selectivity. Possible reaction mechanisms have been proposed.^ In Chapter 3, amorphous manganese oxides, crystalline manganese oxides (hollandite, todorokite, pyrolusite) and potassium oxalatomanganate complexes have been prepared and used as photocatalysts. The amorphous manganese oxide materials have been successfully explored for the first time as photocatalysts for this reaction having an activity five to six times higher than the best uranyl catalyst and 100% selectivity. Characterization suggest that high activities correlate with higher oxidation state manganese (Mn$\sp{3+}$, Mn$\sp{4+}$) oxides and the presence of oxygen species on the surfaces of these catalysts. An oxygen atmospheres and small particle size catalysts are needed to regenerate the catalysts. A mechanism for the photooxidation reaction involving manganese oxide catalysts has been proposed. This approach not only provides new materials for solar energy usage, but also shows the promise of how to fundamentally study many complicated bio-photochemical processes by investigating inorganic species.^ In Chapter 4, a study of FCC catalysts is described. The migration of vanadium between zeolite and matrix during calcination and regeneration stages was monitored and the behavior of different vanadium precursors under different conditions was studied by various spectroscopic methods. This study clears some confusion in regard to the migration behavior of different vanadium precursors and under different conditions, elucidates the principle of these differences, and proposes information for passivating metal poisons. ^

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