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

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 ZnNx. 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 kgPd–1 h–1 is achieved.