Porous ceramic frameworks for CO2 utilization

Abstract

Growing climate challenges are accelerating CO2 utilization research, where catalyst support materials can determine performance and efficiency. The main objective of this thesis was to create an innovative and versatile material platform and to proof the material concept for its applicability to various heterogenous catalysis concepts aiming for CO2 utilization. The freeze-casting technique was successfully combined with polysiloxane-derived Ceramic processing based on photopolymerization-assisted solidification templating (PASST). Macropore morphologies templated from various unary and binary structure-directing solvents were investigated, where photopolymerization-assisted crosslinking was particularly suitable for on-demand fixation of low-temperature states.In the first model case, thermally activated catalytic reactors were examined using CO2 methanation as a gas-phase model reaction. By depositing nickel onto dendritically structured freeze-cast SiOC by wet impregnation, CO2 to CH4 conversions up to 58 % were reached at 400 °C, demonstrating the suitability of the materials concept at elevated temperatures. In the second model case, SiOC-supported ionic liquids for the highly selective production of limonene carbonate by cycloaddition of supercritical CO2 to bio-based epoxides are studied. Here, the ability to modify the affinity of SiOC to water promoted the selectivity of these catalysts.In a third case, the biocompatibility of SiOC with industrially relevant microorganisms (Bacteria Escherichia coli and yeast Komagataella phaffii) was investigated. Neither E. coli nor K. phaffii showed growth inhibition from SiOC. The adsorption of cells to macroporous SiOCs was investigated by electron microscopy, where prevalent biofilms of K. phaffii were observed. Finally, the principle of PASST was expanded from unidirectional freeze-casting to prepare monoliths to an emulsion-based variant to shape porous microspheres (d50 = 199 μm, pore opening diameter = 5.2 μm), enabling future application of SiOC-supported catalysts for other reactor designs.The results on porous SiOC frameworks for a variety of CO2 conversion processes bridge a gap from ceramic engineering to fields like thermal catalysis, organic synthesis, and biotechnology. The findings highlight the potential of porous SiOC-based materials as catalyst supports.