Intermetallic PdZn Supported on Porous Carbon Derived from ZIF-8 for Efficient Direct Synthesis of H2O2

Abstract

Design of highly efficient Pd-based catalysts for the direct synthesis of hydrogen peroxide (DSHP) from H₂ and O₂ still remains a challenge. Herein, Zn-doped porous carbon was synthesized via pyrolysis of ZIF-8 under a N₂ atmosphere and then applied as supports of Pd catalysts for DSHP. The results of aberration corrected HAADF-STEM, XRD, XPS, and TEM reveal that the Zn species in the porous carbon support exist mainly in highly dispersed ZnN_x. In the reduction process, Zn atoms are first reduced by spillover hydrogen from adjacent Pd⁰ atoms and then diffuse into Pd particles to form intermetallic PdZn. The pyrolysis temperature appears to be a crucial factor affecting the proportion of PdZn. A catalyst supported on the porous carbon obtained at a pyrolysis temperature of 850 °C has the highest proportion of PdZn (Pd/ZnC-850). The DFT simulations reveal that intermetallic PdZn shifts the d-band center of Pd atoms away from the Fermi level; weakens the adsorption of O₂, *OOH, and H₂O₂; and shortens the length of the O–O bonds of *OOH and H₂O₂. These are favorable for inhibiting cleavage of O–O bonds. Pd/ZnC-850 exhibits a superior H₂O₂ selectivity (89.6%), relatively high H₂ conversion, and good stability. A H₂O₂ productivity of 44,396 mol kg_Pd^–1 h^–1 is achieved.