Development and Application of in Situ/Operando Spectroscopic Techniques for Understanding Active Sites and Surface Intermediate Species in Heterogeneous Catalysis

The development and application of advanced steady-state and dynamic spectroscopic techniques have revolutionized the characterization of complex catalytic systems, enabling detailed insights into catalyst structures, reaction intermediates, and mechanisms. This thesis presents the application of innovative methods, including in situ transient Raman spectroscopy, Differential Derivative Reflectance (DDR) UV-Vis Spectroscopy, Modulation Excitation Spectroscopy with Phase-Sensitive Detection (ME-PSD), and isotope modulation techniques, to investigate catalytic systems for propylene metathesis and ethanol oxidation reactions. For propylene metathesis, tungsten-based catalysts supported on silica (zWOX/SiO2) and titania-promoted silica (zWOX/yTiOX/SiO2) were explored. Catalyst preparation via incipient wetness impregnation revealed that titania promotion significantly enhanced catalytic performance by balancing WOX dispersion and resistance to deactivation. Advanced in situ DDR-UV-Vis spectroscopy, Raman, and mass spectrometry elucidated the interplay of WOX and TiOX species, linking these findings to catalytic activity and deactivation mechanisms. In ethanol oxidation studies, vapor-phase reactions on Au catalysts supported on SiO2, TiO2, ZnO, and SrTiO3 were assessed. Operando ME-PSD-DRIFTS revealed critical intermediates such as ethoxy and acetaldehyde, with charge transfer dynamics playing a key role in catalytic behavior. Au/SiO2 exhibited high activity for acetaldehyde formation, while Au/SrTiO3 favored acetate production, consistent with fixed-bed reactor studies. Modulation frequency analysis further highlighted the relative speeds of ethoxy decomposition and acetaldehyde transformations. Isotopic kinetic studies on Au/TiO2 provided deeper mechanistic insights, confirming ethoxy oxidation as the rate-limiting step. These experiments revealed rapid hydrogen diffusion to the Au-TiO2 interface, facilitating O2 activation and the formation of reactive oxygen species. A Langmuir-Hinshelwood model was proposed, integrating spectroscopic and kinetic data to describe surface reactions and charge transfer processes. This work demonstrates the power of integrated spectroscopic and kinetic methodologies for unraveling complex catalytic phenomena, offering pathways for optimizing catalyst design and improving catalytic performance.

Grantor dc:publisher

University of Kansas

Year dc:date.issued

2025

Author dc:creator

• Patil, Bhagyesha Sunil

Advisor dc:contributor.advisor

• Bravo-Suárez, Juan J.

• Chemical engineering
• Heterogeneous Catalysis
• In situ Spectroscopy
• Kinetics
• Operando Techniques
• Reaction Engineering

Statement dc:rights

• This item is protected by copyright and unless otherwise specified the copyright of this thesis/dissertation is held by the author.

Language dc:language.iso

en

Dc Identifier Other

https://www.proquest.com/LegacyDocView/DISSNUM/31839528

OAI identifier oai:identifier

oai:kuscholarworks.ku.edu:1808/37895