Date of Award

Fall 2020

Project Type

Dissertation

Program or Major

Chemical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Nan Yi

Second Advisor

Nan Yi

Third Advisor

Xiaowei Teng

Abstract

Besides being widely used as a probe reaction, carbon monoxide (CO) oxidation has been playing a crucial role in multiple industrial applications, including automotive emission elimination, chemical production, and abatement of toxic waste. Copper (Cu) based catalysts have been extensively investigated for CO oxidation, because of its low cost and comparable activity to precious metal-based catalysts. Meanwhile, the surface properties, such as the oxidation state of copper species and oxygen species, depend on the synthesis process. Surface properties would eventually impact the catalytic performance. Therefore, it is desirable to build the property-activity relationship to understand factors that can affect the performance of copper-based catalysts for carbon monoxide oxidation.

This dissertation applied different approaches to tune the surface properties of titanium dioxide (TiO2) and understand how those surface properties affect reaction rate. The first project aimed at investigating the effect of surface hydroxyl groups on Cu-TiO2 catalysts by adjusting pH values. Our results revealed enhanced catalytic performance could be achieved over Cu-TiO2-pH7 catalyst, which contained less hydroxyl groups and Cu (I) species on the surface. The ratio between Cu (I) and hydroxyl groups correlated well with activity performance. The second project applied different pretreatment to tune surface properties of Cu-TiO2 catalysts. Reductive treatment on Cu-TiO2 improved copper dispersion, thus reinforced its catalytic performance. The third project focused on the impact of introduced nitrogen on the Cu-TiO2 catalyst. Activity results indicated that the promotion effect existed through the addition of nitrogen to TiO2 support. Interstitial nitrogen, which was identified as the dominant nitrogen species, contributed to the improved copper dispersion on the surface. The fourth project studied how TiO2 phases (anatase and rutile) affect the surface properties of Cu-N-TiO2 catalysts. Anatase TiO2 facilitated CO oxidation with lower activation energy and higher reaction rate. Characterization results demonstrated the concentration of oxygen vacancies increased with the addition of nitrogen to TiO2 (anatase).

This dissertation also proposes to consider the spectator species when building the property-activity relationship. As evidenced from four different projects, the consideration of the combined effect of Cu (I) species and surface oxygen species, emphasized the importance of balancing active and spectator species while exploring the catalytic performance.

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