Improving the Hydrogenation Performance of Nano-Catalysts by Constructing a Cavity-Constrained Fluidized System

Nano-catalysts demonstrate exceptional performance in heterogeneous reactions, yet their potential is often underutilized due to a lack of attention to engineering design. In this study, an innovative encapsulated structure is presented for nano-catalysts and a corresponding catalytic system. Using an oil-in-water droplet strategy, millimeter-sized hollow spherical alumina (Al₂O₃-HS) is fabricated with an average diameter of ≈3 mm and a hollow void size of ≈1 mm. This approach enables the one-step encapsulation of nanoscale Pd/Al₂O₃ within the Al₂O₃-HS. The resulting assembly is immobilized within a tubular reactor for the hydrogenation of 2-ethylanthraquinone, with hydrogen introduced from the bottom of the reactor. Remarkably, the encapsulated catalyst achieved twice the H₂O₂ productivity of conventional supported catalysts. This enhancement is attributed to the cavity-constrained fluidization behavior of Pd/Al₂O₃ within the hollow alumina spheres. The design introduces a novel catalytic system that combines shell-immobilization with the fluidization of encapsulated nano-catalysts. As the gas velocity exceeds the minimum fluidization velocity, the Pd/Al₂O₃ particles remain highly accessible while allowing efficient gas and product flow. This hybrid approach integrates the advantages of fixed-bed and fluidized-bed systems, offering a promising solution to the technical challenges limiting the industrial application of nano-catalysts.