Fabrication of self-supporting structures made of washcoat materials ( γ - Al 2 O 3 - CeO 2 ) by ceramic stereolithography: Towards digital manufacturing of enhanced catalytic converters

Highlights: • A novel fabrication method for catalytic converters using stereolithography is proposed. • A resin made of washcoat materials (γ-Al₂O₃-CeO₂) is printed into self-supporting structures. • The addition of CeO₂ to the plain γ-Al₂O₃ resin significantly reduces the curing depth. • Microstructure characterizations show hierarchical porosity of the printed structures. • Surface area measurements show that CeO₂ stabilized the printed γ-Al₂O₃ at 1100 °C, not 900 °C. Despite increasing interest in the use of alternative fuel, conventional diesel or gasoline powered vehicles still dominate road transportation; removal of their emitted pollutants is a challenge to sustainable transportation. The automotive industry has employed catalytic converters (CCs) to effectively modify or eliminate toxic pollutants emitted by combustion engines. The efficiency of a CC greatly depends on its geometry and is hindered by limitations in fabrication techniques. To go beyond these limits and further enhance the performance of CCs, one can use state-of-the-art ceramic stereolithography (CSL) technology, which enables fabrication of complex-shaped structures. In this work, a novel photocurable ceramic resin made of $\gamma$-${\mathrm{Al}}_2{O}_3$ and ${\mathrm{CeO}}_2$ (the commonly used washcoat materials in CCs) is shaped into the honeycomb and twisted honeycomb structures using CSL. Measurements reveal that upon the addition of ${\mathrm{CeO}}_2$ to the plain $\gamma$-${\mathrm{Al}}_2{O}_3$ resin, the penetration depth of light is significantly decreased from 408.06 $\mu m$ to 75.19 $\mu m$. This research also focuses on the balance between having a high surface area and achieving good physical stability in the printed structures. Accordingly, the appropriately debinded structures are sintered at two different temperatures: 900 $°$C and 1100 $°C$. It is found that the structure sintered at 900 $°$C has a higher surface area, and thus, it is a better candidate for catalytic applications. Furthermore, investigation of the stabilizing effect of ${\mathrm{CeO}}_2$ on printed $\gamma$-${\mathrm{Al}}_2{O}_3$ finds that ${\mathrm{CeO}}_2$ is effective in stabilizing the printed $\gamma$-${\mathrm{Al}}_2{O}_3$ at1100 $°$C but not 900 $°$C. Targeting the realization of green and sustainable transportation, the applied CSL technique in this study enables flexible control in the design and fabrication of self-supporting structures that are expected to open promising ways for the optimization of CCs.