Coaxial 3D Printing of Zeolite-Based Core–Shell Monolithic Cu-SSZ-13@SiO₂ Catalysts for Diesel Exhaust Treatment

Core–shell catalysts with functional shells can increase the activity and stability of the catalysts in selective catalytic reduction of NO_x with ammonia_x. However, the conventional approaches based on multistep fabrication for core–shell structures encounter persistent restrictions regarding strict synthesis conditions and limited design flexibility. Herein, a facile coaxial 3D printing strategy is for the first time developed to construct zeolite-based core–shell monolithic catalysts with interconnected honeycomb structures, in which the hydrophilic noncompact silica serves as shell and Cu-SSZ-13 zeolite acts as core. Compared to a Cu-SSZ-13 monolith which suffers from the interfacial diffusion, the SiO₂ shell layer can increase the accessibility of active sites over Cu-SSZ-13@SiO₂, resulting in a 10–20% higher NO conversion at200−550 °C under 300 000 cm³ g⁻¹ h⁻¹. Meanwhile, a thicker SiO₂ shell enhances the hydrothermal stability of the aged catalyst by inhibiting the dealumination and the formation of CuO_x. Other representative monolithic catalysts with different topological zeolites as shell and diverse metal oxides as the core can be also realized by this coaxial 3D printing. This strategy allows multiple porous materials to be directly integrated, which allows for flexible design and fabrication of various core–shell monolithic catalysts with customized functionalities.