Innovative monolithic catalyst supports based on freeze-cast, polysiloxane-derived silicon oxycarbides (SiOCs) are developed for heterogeneous catalysis in CO₂ utilization applications. Silicon-based polymeric precursors can be modified and shaped in their polymeric state, and with a subsequent heat-treatment, can be converted into ceramic materials. Freeze-casting, in contrast, is a method that uses the phase separation of a solvent from the preceramic solution for pore templating. By choice of the solvent, controlled solidification and subsequent sublimation of solvent, pore morphologies can be precisely controlled.

In this contribution, the combination of solution-based freeze-casting of polymer-derived ceramics with photopolymerization-assisted crosslinking at low temperature is presented, thus avoiding loss of the templated structure upon solvent removal and ceramic conversion. The resulting freeze-cast SiOC monoliths are shown to be compatible with the wet impregnation technique to deposit catalytically active sites. In a first example, the development of catalytic microreactors for CO₂ methanation is discussed: By depositing 25 wt.% Ni onto dendritically structured freeze-cast SiOC, CO₂ conversions up to 58 % were reached at temperatures of 400 °C, demonstrating the suitability of the materials concept at elevated temperatures. The second application example involves organic synthesis: SiOC-supported ionic liquids were developed for the highly selective production of limonene carbonate by cycloaddition of supercritical CO₂ to bio-based epoxides. Here, the ability to modify the affinity of SiOC to water by interrupting the pyrolysis at different conversion states promoted the catalytic performance.

Results on freeze-cast SiOCs as catalyst supports link the in-depth knowledge about the chemistry of polymer-derived ceramics and the macropore tailorability by freeze-casting with promising CO₂ utilization technologies, and thus indicates the versatility and suitability of this specific materials processing concept for various fields of application.