Masters Theses

Date of Award

12-2004

Degree Type

Thesis

Degree Name

Master of Science

Major

Environmental Engineering

Major Professor

Terry L. Miller

Committee Members

Chris D. Cox, Randall W. Gentry

Abstract

The overall goal of this research was to investigate a new class of mesoporous uranium oxide catalyst used to destroy a range of volatile organic compounds (VOCs), including aromatics and chlorinated organic compounds under conditions which are applicable for U.S. Department of Energy (DOE) facilities and U.S. industries.

Uranium oxides are known to have high efficiency and long-term stability when used to destroy volatile organic compounds (VOCs) when compared with some of the commercial catalysts, such as precious metals, TiO2, and Co3O4 catalysts. Two key factors limiting catalytic activities of uranium oxides prepared by conventional methods are small surface area and pore size. To overcome these limitations, mesoporous uranium oxides dispersed on mesoporous oxide hosts were synthesized and tested for VOC destruction efficiency.

This research work consisted of synthesizing potential depleted uranium catalysts, as well as testing and structural characterization. A plug flow microreactor was built and used to measure the catalytic performance of toluene, chlorobenzene, and trichloroethylene (TCE) v. catalyst temperature. These data result in so-called ‘light-off’ curves. Destruction efficiency generally increases with temperature. These VOCs were chosen as typical of those found in anticipated air pollution controls applications.

The catalysts have been tested for the destruction of VOCs at space velocities of 84,000 mlg-1h-1. A gas chromatograph and a sampling mass spectrometer were used to measure conversion and reaction by-products. The X-ray diffraction (XRD), transmission electron microscope (TEM) and Brunauer-Emmett-Teller (BET) adsorption-desorption isotherm surface area measurements were used to provide information about the compositions present in the catalyst.

Catalysts were synthesized using a variety of methods, most notably a method that includes template-moderated co-synthesis of mesoporous oxides. Catalyst activity was improved by supporting the uranium oxide on silica. Dopants (e.g., Cr, Co, K, Br, Fe, Ca, Mg, Cu, Pt, La, Ce, Sr) were added to the urania to improve the catalytic activity. Catalyst performance was compared with that of conventional catalysts. Further improvement was made by supporting uranium on titanium oxide. This co-assembled formulated catalyst was found to be competitive with noble and metal catalysts for catalytic oxidation of VOCs and chlorinated VOCs. The variation in the U:Ti ratio indicated that optimal activity for oxidation of toluene, chlorobenzene, and trichloroethylene was obtained for U:Ti ratio of 1:20 at calcinations temperature of 600˚C. It was stable to deactivation and operates efficiently in the presence of large amounts of water.

The gained experiences of this project can be used in the clean up of emissions from soil vapor extraction wells, which are in use to remove VOCs from ground water at DOE’s Hanford and Savannah River sites.

This work was conducted under the auspices of the U.S. Department of Energy’s (EM-21) Depleted Uranium Research and Development Program.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS