Title: 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 innovative methods including: a) in situ Differential Derivative Reflectance (DDR) UV-Vis and transient Raman spectroscopies; b) frequency screening in Modulation Excitation Spectroscopy (FS-MES); and c) isotopic MES as applied to propylene metathesis and ethanol oxidation reactions. In propylene metathesis on silica (zWOX/SiO2) and titania-promoted silica (zWOX/yTiOX/SiO2), I will show that titania promotes significantly the catalytic performance. In situ DDR-UV-Vis spectroscopy, transient Raman, and MS revealed the interplay between WOX and TiOX species by balancing WOX dispersion and resistance to deactivation. In ethanol oxidation on Au supported on SiO2, TiO2, ZnO, and SrTiO3 I will show how FS-ME-DRIFTS revealed critical intermediates such as ethoxy and acetaldehyde, and charge transfer dynamics playing a key role in catalytic behavior. Isotopic MES and kinetic studies provided deeper mechanistic insights, confirming ethoxy oxidation as the rate-limiting step. In Au/TiO2, these experiments revealed rapid hydrogen diffusion to the Au-support 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 in ethanol oxidation. 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.