Studying individual catalyst nanoparticles using two-color fluorescence correlation spectroscopy

Summary

Heterogeneous catalysis is widely used in industrial plants, cars, and fuel cells, to accelerate and control chemical reactions. Many catalysts consist of a porous host material (e.g. alumina) supporting active metal or oxide nanoparticles. A gram of catalyst material contains billions of nanoparticles that together determine the catalyst’s performance. Experiments often assess only the macroscopic performance as an average over all particles. Studying individual nanoparticles and individual reactions is challenging, but a necessary next step for a full understanding of catalysis.

This project will develop two-color fluorescence correlation spectroscopy as a microscopic analysis technique for catalytic reactions. This technique provides the single-molecule sensitivity and sub-millisecond time resolution required to measure diffusion, adsorption/desorption, and chemical conversion of individual molecules. A two-color setup will enable me to detect and distinguish both the reactant and the product molecules of a model reaction (conversion of Rhodamine B to Rhodamine 110), in contrast to previous single-molecule studies that observed only the product. Rates associated with the steps in the catalytic process will be extracted from the statistics (i.e., the auto- and cross-correlation functions) of photons emitted by reactant and product molecules.

Accelerating the rates of chemical reactions is what defines catalysis. I will quantify this acceleration, on the level of individual catalytic particles with varying composition (e.g. CdS or TiO2), size, and crystal facets exposed. Even for an ensemble of nominally identical nanoparticles, the catalytic properties may show wide static and dynamic variations. I will measure not only the average properties of an ensemble, but also the best particles, and relate catalytic performance to atomic structure using correlative electron microscopy. These experiments will improve our understanding of what defines an optimal catalyst particle, and thus help in the rational design of new catalysts with optimized performance.

Details

Project number

722.017.002

Main applicant

Dr. F.T. Rabouw

Affiliated with

ETH Zurich, Mechanical and Process Engineering, Institute of Process Engineering

Duration

01/01/2018 to 31/12/2019