Sonication-Assisted Synthesis of CuPd-HKUST-1 Catalysts for Cyclohexene Oxidation

The use of sonochemical synthesis opens new opportunities for efficient tuning of the properties of the designed materials. This study introduces the sonochemical route to obtain a bimetallic CuPd-HKUST-1 metal–organic framework (MOF), replacing the conventional solvothermal synthesis method. The developed synthesis method allowed for obtaining bimetallic CuPd-HKUST-1 crystals or a CuPd-HKUST-1-son-def composite with Pd nanoparticles when orthophosphoric acid was used during the sonochemical synthesis. Several techniques, including low-temperature nitrogen adsorption, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared and μRaman spectroscopies, and density functional theory modeling, comprehensively characterized the obtained materials. The sonochemically synthesized CuPd-HKUST-1 is characterized by a significantly increased specific surface area equal to 1792 m2 g–1, which is 41% higher than its conventionally obtained counterpart. The catalytic activity of the obtained materials was tested in a cyclohexene oxidation reaction under 10 bar of O2 conditions. Sonically synthesized CuPd-HKUST-1-son showed exceptional selectivity, promoting the production of cyclohexanol. The enhanced selectivity toward cyclohexanol is due to many well-distributed Cu- and Pd-active sites confirmed by in situ FTIR spectroscopy using CO as a probe molecule. The obtained results confirmed that sonochemistry is a versatile tool for the development and optimization of MOF-based catalysts, allowing the design and tuning of specific functionalities.