Palladium nanoparticles supported on CNT functionalized by rare-earth oxides for solvent-free aerobic oxidation of benzyl alcohol

A series of rare-earth oxide functionalized multi-walled carbon nanotubes (CNTs) were prepared through wet impregnation process. Palladium nanoparticles were deposited over surfaces of functionalized CNT through metal ion adsorption-reduction method and were examined using X-ray diffraction, transmission electron microscopy, in situ adsorbed pyridine Fourier Transform Infrared spectroscopy, and electrochemical measurements. Compared to the non-functionalized Pd/CNT catalyst, the catalytic activities of different rare-earth oxide functionalized CNT supported Pd catalysts were improved for aerobic solvent-free oxidation of benzyl alcohol due to the fine-tuned properties of catalytic active sites, e.g., Pd particle size, size distribution, valence status, metal-support interactions, electron density, surface acidity and basicity. Sm₂O₃ functionalization displayed the highest improvement in catalytic activity whereas the content of Sm₂O₃ had impact on Pd particle size, electrochemical surface area, and metal-support interactions which further influenced the benzyl alcohol conversion and selectivity toward benzyl aldehyde. The catalyst functionalized by an appropriate amount of Sm₂O₃ afforded a remarkably high turnover frequency of 318,760 h^-1 for aerobic oxidation of benzyl alcohol based upon palladium electrochemical active surface areas.