Tuning the pore structure of plug-containing Al-SBA-15 by post-treatment and its selectivity for C16 olefin in ethylene oligomerization

Al-SBA-15 containing plug structures inside straight channels have been hydrothermally synthesized through a one-step synthesis strategy in an environmentally friendly acid-free medium. The effects of steaming, alkali, and acid post-treatments on the structural properties were investigated by powder X-ray diffraction (XRD), nitrogen adsorption-desorption at 77 K, transmission electron microscopy (TEM), scanning electron microscopy (SEM), FT-IR spectrum, Al-22 MAS NMR, and inductively coupled plasma (ICP) analyses. The presence of the plugs can significantly enhance structural stability against steaming or alkali post-treatments. Acid post-treatment can be a very simple and convenient technique for adjusting the textural properties of plug-containing Al-SBA-15, and especially for optimizing the accessibility to active sites. Acid post-treatment at the low temperatures of 313 and 323 K results in the formation of a larger specific surface area (905 m(2)/g) and pore volume (0.94 cm(3)/g) through an open door effect in the plugs, without eliminating any of the plugs from the channels. In particular, nearly half of the secondary micropores on the pore walls were preserved. In contrast, raising the acid post-treatment temperature further to 333 and 343 K caused a closed doors effect through the blockage of pores in the plugs by the extracted fragments. After loading with nickel, the catalyst exhibited a higher yield of C10+ olefins in ethylene oligomerization, and more importantly, after steaming and acid post-treatments at higher temperatures, the samples showed shape selectivity for the C-16 olefin. (C) 2013 Elsevier Inc. All rights reserved.