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

Abstract

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 318,760h−1 for aerobic oxidation of benzyl alcohol based upon palladium electrochemical active surface areas.