Meng Lu

Date of Award

12-2005

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

Advisor

Brian G. Frederick

Second Committee Member

M. Clayton Wheeler

Third Committee Member

François G. Amar

Abstract

Our interest in studying reactions catalyzed by high surface area W03 powders is based on their potential application as the active material in sensors for low level (ppb) detection of flammable or toxic gases. A series of porous W03 powders with both meso- and micro-porosity have been synthesized by Waghe and Tripp. Preliminary results of the response of sensors fabricated from these materials indicated the possibility of size selectivity on the molecular scale. To provide support for the hypothesis of size selectivity and understand the reaction kinetics of alcohols over the new porous W03 powders for sensor applications, we have designed and verified a new microreactor system to measure the product distribution, reaction rates (activity), and influence of transport through nanoscale and mesocopic pores. This microreactor system is composed of three parts, a quantitative gas source, a microreactor for powder materials, and a GUMS for quantitative analysis of reactant and product concentrations. A detailed account of the design parameters and rationale of the experimental facility are presented, and a quantitative analysis of the uncertainties in the concentration measurements is also shown in this work. Before we started the alcohol oxidation experiments, the system was calibrated, and the instrumental method was optimized. According to the quantitative analysis, the relative uncertainty in concentrations was about 6%, consistent with the design. The oxidation reactions of a series of alcohols (methanol, ethanol, 2-propanol, 2-butanol and 2-hexanol) over A1203 (pure Denstone support media), nonporous WO3/A12O3 and porous WO3/Al2O3 were studied. The product distributions and alcohol conversion as a function of temperature were measured. Dehydration and dehydrogenation products were observed as the main alcohol oxidation products. However, trace amounts of aldol condensation products were also detected in some alcohol oxidation reactions, and the presence of these condensation products was related to the potential effect of water on the alcohol oxidation. Reaction kinetic analysis of 2-butanol on nonporous and porous WO3 suggested a potential effect of the pore size of WO3 to selectivity.

Download

Share