Multiwalled Carbon Nanotubes Modified with Silylated-salicylaldimine Co(II) and Pd(II) Complexes as Precatalysts in Ethylene Oligomerization

Abstract

MWCNTs-Co(II) and Pd(II) were prepared through grafting silylated-salicylaldimine Pd(II) and Co(II) on multiwalled carbon nanotubes(MWCNTs) for ethylene oligomerization. The structures of the two MWCNTs-supported catalysts were characterized by means of scanning electron microscopy( SEM), X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, thermogravimetric analyses(TGA) and nitrogen adsorption and desorption. And the influence of the supported pattern on the catalytic properties for ethylene oligomerization was investigated. The results revealed that the silylated-salicylaldimine complexes were grafted on the inner and outer surfaces of the carbon nanotubes and the pore size and BET surface area of MWCNTs decreased. Compared with the homogeneous catalysts, the two MWCNTs-supported catalysts had higher selectivity for hexene and 1-hexene in the presence of diethylaluminum chloride(DEAC) with a small molecule size due to confinement effect. MWCNTs-Pd exhibited higher activity and higher selectivity for $\rm{C}_{8^+}$ olefin compared to MWCNTs-Co due to electronic factors. The catalytic activities of MWCNTs-Pd and MWCNTs-Co decreased from 24.18×105 g·(mol Pd·h)^-1 and 20.57×10⁵ g·(mol Co·h)^-1 to 19.79×10⁵ g·(mol Pd·h)^-1 and 13.14 × 10⁵ g·(mol Co·h)^-1 after the third recycle reaction, respectively.

Keywords

Ethylene oligomerization / Multiwalled carbon nanotube / Confinement effect / Heterogeneous catalyst

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