While ceramics exhibit high thermal and chemical stability rendering them suitable candidates for catalyst carriers, conventional powder-based processing is somewhat limited in terms of obtaining porous parts. Catalyst carriers should ideally show hierarchical porosity and tailored pore shapes, as ordered macropores reduce the flow resistance and thus increase the product throughput, while mesopores further increase the surface area and the catalytic activity. In contrast to traditional powder-based routes, polymer-derived ceramics (PDCs) come with significant processing benefits. PDCs can be chemically modified in the precursor state and can be shaped as polymeric liquids. Novel shaping methods like ice-templating are in this regard particularly interesting, as porosity, surface area and pore morphology can be systematically optimized.

In this work, a photocurable poly-silsesquioxane (PSO) solution is combined with the ice-templating method to obtain directionally aligned and porous silicon oxycarbide (SiOC) monoliths for prospective catalysis applications. PSO is functionalized with acrylic groups as crosslinker. The modified preceramic polymer solution can be stabilized in its ice-templated state by light irradiation prior to solvent sublimation and pyrolysis, similarly to previous reports on poly-silazane-derived ceramics.(1, 2) Processing via ice-templating is optimized on a custom-made set-up to control the cooling rate and to monitor the freezing front velocity in a reproducible manner. The pore morphologies obtained by the use of cyclohexane and tert-butanol as macropore templates are studied, cooling rates of 1 to 10 K/min are applied, and the effect of different thermal gradients on the macropore alignment are investigated. Furthermore, the introduction of sacrificial porogens into PSO is evaluated for further increasing the specific surface area .

By adequate knowledge of the effect of selected process parameters on the final material morphology, it can be shown that ice-templating enables the generation and control of porosity at different length scales to create functional structures with hierarchical porosity. The obtained ceramics are thereby a promising starting point for the development of PDC-based catalysts for CO₂ utilization processes.

References

(1) Mikl, G., Obmann, R., Schörpf, S., Liska, R. and Konegger, T., 2019. Pore morphology tailoring in polymer‐derived ceramics generated through photopolymerization‐assisted solidification templating. Advanced Engineering Materials, 21(6), p.1900052.

(2) Obmann, R., Schörpf, S., Gorsche, C., Liska, R., Fey, T. and Konegger, T., 2019. Porous polysilazane-derived ceramic structures generated through photopolymerization-assisted solidification templating. Journal of the European Ceramic Society, 39(4), pp.838-845.