Temperature-dependent reaction dynamics of CO-oxidation on Pt nanoparticles

Abstract

Key to the continued development of catalysts is bridging the gap between research and industrial operating conditions, or operando conditions. Additionally, to achieve a deeper understanding of catalytic dynamics, single-particle analysis has gained popularity as a way to mitigate the loss of information brought about by ensembleaveraging effects. In an effort to both bridge the gap between the research and application while allowing probing at the single-particle level, a technique called nanoplasmonic sensing has emerged. Nanoplasmonic sensing relies on the inherent plasmonic properties of catalytic metal nanoparticles to probe catalytic reactions. In this thesis, the temperature-dependent reaction dynamics of CO-oxidation facilitated by Pt nanoparticles on a SiO2 substrate were studied, with a focus on the dynamics of the kinetic phase transitions of Pt nanoparticles between their COpoisoned and catalytically active states. This was investigated at both the ensemble and single-particle levels under operando conditions by performing temperatureprogrammed nanoplasmonic sensing on a nanoreactor chip hosting the Pt nanoparticles and the chemical reaction. Additionally, the effects of particle size and reactant ratio on the reaction dynamics were studied. To complement the nanoplasmonic sensing measurements, a structural analysis involving hyperspectral and SEM imaging was conducted. In this thesis, it was shown that temperature-dependent reaction dynamics could be obtained using nanoplasmonic sensing by applying a newly in-house-developed autofocusing software to counteract the drift in focus caused by the thermal expansion of the nanoparticles. Additionally, the critical temperatures of the kinetic phase transitions were evaluated using a statistical method called the bootstrap approach. One of the observed transitions aligned with the expected critical temperatures. However, an additional lower-temperature transition was also observed, and further analysis is required to evaluate whether this transition represents a real physical phenomenon or a measurement/data-treatment artifact. The nanoplasmonic sensing results were supported by the structural analysis, in which irreversible structural changes were observed in the nanoparticles, alluding to insufficient annealing. When assessing the effect of particle size, differences in the observed dynamics between ensemble and single-particle analyses were found, highlighting the need for further analysis at the single-particle level.