Advanced electron microscopy characterization of catalysts

Date: 24 May 2016

Venue: Campus Middelheim, G0.10 - Middelheimlaan 1 - 2020 Antwerpen

Time: 4:00 PM

Organization / co-organization: Department of Physics

PhD candidate: Maria Meledina

Principal investigator: Gustaaf Van Tendeloo & Stuart Turner

Short description: PhD defence of Mrs. Maria Meledina - Department of Physics



Abstract

In our everyday life we constantly use products and processes where catalysts are necessary. For example, in the chemical industry about 85-90% of the products are obtained through catalytic processes. Most of the catalysts in industry are heterogeneous: the catalyst is solid whereas the reactants are present in a gas/liquid phase. For these applications, it is favorable to select materials with a high surface area, for example nanoparticles or porous materials.

Catalysis requires a multidisciplinary knowledge in chemistry, physics, engineering and materials science covering an extremely broad field of study at the steps of catalyst preparation, design of the setting, understanding the mechanisms and optimization of the whole process. It is of great importance to follow the catalyst through a full characterization at the different steps of the process, in order to find and minimize the “weak points” that cause the loss of efficiency and degradation upon cycling. Transmission electron microscopy is a powerful technique, providing information on the morphology, crystallographic structure and chemical composition of the sample. As the heterogeneous catalysts are often nanoparticles or supported nanoparticles, the information obtained by microscopy is able to provide a unique insight into the organization of the catalyst at the atomic scale. Detailed monitoring of the changes happening with the catalyst, such as particle agglomeration and sintering, formation of different crystal structures based on the initially present ones or reduction/oxidation of the elements, is possible using various TEM techniques and provides the necessary data for a smart design of new catalysts.

Materials investigated within this PhD work can be split in three groups: oxide nanoparticles, nanoparticles supported by MOFs and nanoparticles supported by porous silica. Electron microscope was used as the main characterization tool. The most common questions to be asked while characterizing the catalyst are related to the mechanism of the catalytic reactions and the ways to improve the existing material. The information obtained by the different electron microscopy techniques has helped answering some of these questions.