Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy for Heterogeneous Catalysis: Verbeterde Raman Spectroscopie door Schil-Geïsoleerde Nanodeeltjes voor Heterogene Katalyse

Abstract

The goals of this PhD thesis are as follows: first, to advance SHINERS towards a more stable and universal characterization technique. Second, to apply SHINERS for the observation and characterization of catalytically relevant surface species during in situ and ultimately operando spectroscopy. The first three chapters – Chapters 2, 3 and 4 – will focus on the preparation of SHINs and a better understanding of SHINERS signals observed under catalytic studies. The knowledge obtained in these three chapters are then combined in Chapter 5 to develop extrudate sensors for operando measurements of surface species during heterogeneous catalysis. In Chapter 2, TiO2 and SiO2 SHINs were prepared for application as SHINERS substrates and were tested for their thermal stability. Both SiO2 and TiO2 SHINs were found to be adequate Raman signal enhancers, and maintained their Raman enhancing properties up to temperatures of 400 °C in air. We implemented these nanostructures in Chapter 3 for in situ measurements of CO hydrogenation. The two types of SHINs can be used for probing various metal catalysts supported on two support materials, namely TiO2 and SiO2. During these initial in situ experiments, we ran into difficulties with assigning the Raman signals. This problem was overcome in Chapter 4, by setting up experimental guidelines for the implementation of SHINERS in heterogeneous catalysis. These guidelines involve careful control of experimental conditions to obtain clean substrates for obtaining SHINER spectra without spurious peaks. Finally, in Chapter 5, the knowledge on obtaining optimal SHINERS substrates was applied to prepare extrudate sensors. Using these sensors, we were able to probe the interfaces between metals and support material over three different catalysts: Rh/SiO2, Rh/TiO2 and RhFe/SiO2. This resulted in the observations of chemical species that were previously not observed by conventional spectroscopy methods, such as IR. Furthermore, the extrudates contained, next to SHINs, luminescent NPs for probing the local temperature of a working catalyst. This PhD thesis ends with some concluding remarks and an outlook based on other work found in literature and promising experiments that were performed during various projects that did not make it to the main chapters of this PhD thesis.