Graduation Year

2007

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Chemical Engineering

Major Professor

John T. Wolan, Ph.D.

Keywords

Supported Au/TiO2, Kinetic modeling, Catalysis, World Gold Council, FTIR

Abstract

This work begins with a brief overview of heterogeneous, characterization techniques, and current hypotheses about gold mechanisms. This is followed by the initial characterization of custom two-phase-method gold nanoparticles provided by the Interfacial Phenomena and Polymeric Materials research group at USF, the anatase TiO2 support and reference Au/TiO2 catalyst provided by the World Gold Council. In order to verify the ability of the two-phase-method GNP catalyst provided to oxidize CO in excess hydrogen, it was necessary to develop an effluent testing protocol. The first experiments involved 24 hour runs to observe catalyst deactivation. Concerns over cycling effects observed in the absorbance integral calculations lead to the introduction of a reference gas. Corrections were made to the carbon monoxide absorbance integral calculations which allowed the direct comparison of results.

These corrections included baseline adjustments for each species and N2 purging to eliminate background CO2 and H2O contamination. After these improvements, the two phase method GNP catalyst CO oxidation ability was investigated. Unfortunately, the supplied two phase method gold catalyst has been unresponsive for CO oxidation applications. One hypothesis for the problems is that the surfactants used to keep the gold nanoparticles from aggregating are preventing carbon monoxide transport to the surface of the particle. Another theory is that the gold may not be adhering to the surface of the TiO2 creating a cohesive metal/support interaction. The kinetics of CO preferential oxidation (PROX) catalyzed by the World Gold Council's nano-Au/TiO2 was studied to evaluate elementary and nonelementary empirical rate expressions. Information is readily available for CO fractional conversion for this catalyst below 0 degrees C.

However, a comprehensive CO PROX kinetic model in which three reactions (CO oxidation, H2 oxidation and the water gas shift reaction) occur simultaneously is lacking. The reaction was carried out in a vertical packed bed micro-reactor testing unit; temperature was varied between 25 and 125 degrees C, and a range of feed rates were tested. In-situ Fourier transform infrared spectroscopy (FTIR) reaction data was analyzed; pre-exponential and activation energies are calculated for each kinetic model. Empirical rate expressions based on power law models were used to fit the experimental data. The reversible water gas shift reaction was found to play an important role when fitting the experimental data precisely and explained the selectivity decrease at higher reaction temperatures. The empirical kinetic model presented will be useful to simulate PROX operation parameters for many applications.

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