Direct ink writing of Pd-Decorated Al2O3 ceramic based catalytic reduction continuous flow reactor

Continuous flow reactor, due to the characteristics of safety and stability, faster reaction, less solvent demand, smaller occupied area and less energy requirements, is a satisfactory selection for heterogeneous catalysis compared with the traditional intermittent and non-intermittent reactors. Herein, the emerging 3D printing is employed to build the all-Al₂O₃ ceramic based continuous flow reactor (Pd/Al₂O₃ CFR) with the direct ink writing technique, where the outer wall is the dense Al₂O₃ ceramic and the inner is the Pd immobilized porous Al₂O₃ ceramic carrier for catalytic hydrogenation reaction. Polymethylmethacrylate (PMMA) microspheres are used to realize the inside micro-/nanometer porous structures during calcination, which offer plentiful sites for Pd anchoring via the vacuum self-assembly. The Pd/Al₂O₃ CFR therefore exhibits outstanding catalytic performance in the reduction of 4-nitrophenol (4-NP). Importantly, the continuous flow reactor is programmable in diameter, length and shape, and reusable as well. A 3 cm length Pd/Al₂O₃ CFR can be reused for a period of 4 cycles consecutively and still achieve 93.87% catalytic efficiency at 90 s for the reduction of 4-NP with no any post-treatment but washing. Combining the freeform fabrication 3D printing and the porous Al₂O₃ ceramic, the present direct ink writing continuous flow reactor is promising in practical application due to the stability, reusability, and designability etc.