Synergetic Catalysis of Pd Single Atom and Subnanometer Cluster Enables Ambient Temperature H2O2 Production via Selective Hydrogenation of 2-Ethylanthraquinone

Low-temperature and highly selective hydrogenation of 2-ethylanthraquinone (EAQ) is still challenging, owing to the high energy barrier for hydrogen dissociation and the lack of multifunctional active sites. Herein, alumina supports with specific crystal planes were synthesized via the modified sol–gel approach using octanol as the crystal growth directing agent. The layered γ-alumina support characterized (100) crystal planes materialized atomic dispersion of palladium species (Pd dispersion 66.3%), comprising Pd single atoms and subnanometer clusters. The dual-site catalyst with a low Pd loading (0.1%) achieved a H2O2 space-time yield of 1273.7 g·H2O2/g·Pd/h and selectivity of 99.4% at room temperature (25 °C) in a fluidized reactor. Moreover, the apparent activation energy for EAQ hydrogenation of the dual-site structure is significantly lower than those of the single-site structures. Systematically, in situ spectroscopic techniques confirmed that Pd single atoms enabled effective hydrogen adsorption and dissociation and the effective anchoring subnanometer Pd clusters endowed moderate adsorption intensity of intermediates and inhibited overhydrogenation. We posit that these results provide guidance for the design and synthesis of supported metal catalyst featuring synergistic single atom and subnanometer cluster active sites for practically selective hydrogenation processes.