Synthesis, characterization and catalytic activity of metal nanoparticles in the selective oxidation of olefins in the gas phase

摘要

Shape controlled metal nanoparticles were studied in the epoxidation of olefins. PVP mediated polyol processes were employed to generate silver nanowires/rods, nanocubes and nanopolyhedra. Spherical copper nanoparticles were also obtained by the polyol process. The mean diameter of the silver nanoparticles was around 150 nm. Furthermore, Cu nanoparticles were synthesized in an ethanol solution using CTAB as surfactant and as reducing agent. Additionally Au nanoparticles were synthesized by a phase-transfer system irradiated with 254 nm UV light. The mean diameter of these Au and Cu nanoparticles was around 10 nm. The catalytic activity of these nanoparticles on several supports such as α-Al{sub}2O{sub}3, CaCO{sub}3 and spherical particles of TiO{sub}2 obtained by the Stober method was investigated in the epoxidation of a no-allylic olefin such as styrene, as well as for an allylic olefin, such as propene, using molecular oxygen and N{sub}2O as oxidants. The effect of Cs promotion in the styrene epoxidation was also investigated. The type of metal, the particle size, the support and the oxidant, as well as the addition of promoters such as Cs, showed a strong influence towards the formation of selective oxidation products. The metal nanoparticles were characterized employing various techniques such as X-ray diffraction (XRD), temperature programmed reduction (TPR), UV-visible spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and ICP-AES.