Abstract
Heterogenous catalysts are important for the production of everyday life products, ranging from plastics to pharmaceuticals and energy. Understanding how to improve these catalyst materials allows for the optimization of these current processes. Therefore, studying catalysts in detail and preparing them with high accuracy is essential. This PhD work focuses
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on the controlled design of catalytic (support) materials with nanometer-precision. To achieve this level of control, nanoparticles are synthesized and self-assembled into ordered structures. This self-assembly approach offers significant advantages over conventional methods, particularly in controlling the composition, size, location, and distribution of nanoparticles within the catalyst.
In this project, ordered silica and graphene mesoporous support materials were synthesized, and nickel/silica catalyst prepared. For the preparation of self-assembled mesoporous silica, monodisperse silica nanoparticles were prepared with sizes ranging from 5 to 100 nm. The self-assembly of these nanoparticles within drying emulsion droplets resulted in the formation of "supraparticles," which are spherical 3D assemblies of nanoparticles. These supraparticles feature an interconnected 3D mesoporous network with tunable pore size, symmetry, porosity, and surface chemistry. To demonstrate the applicability of mesoporous supraparticles in catalyst preparation, silica supraparticles were impregnated with nickel to create a nickel/silica catalyst for hydrogenation reactions. Additional synthesis control was achieved through colloidal synthesis of catalytically active nickel nanoparticles. For example, bimetallic nickel-palladium nanoparticles were studied using in situ electron microscopy, revealing that the atoms within these nanoparticles could shift between alloy and core-shell arrangements in response to reducing and oxidizing environments. Such rearrangement of atoms strongly effects the catalytic properties. Another material that was prepared is porous graphene, made using supraparticles of iron oxide nanoparticles as templates in the production ordered mesoporous graphene. The pore properties were controlled by the size and shape of the iron oxide nanoparticles used, and resulted in the production of new graphene materials.
The ordered catalyst (support) materials presented in this thesis are highly suitable for systematic catalyst optimization. The detailed synthesis and electron microscopy characterization moreover demonstrates that nanoparticle synthesis and self-assembly enable the precise tailoring of catalysts at the nanometer scale.
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