Ni/SIRAL-30 as a heterogeneous catalyst for ethylene oligomerization

Abstract

The oligomerization of ethylene is an important catalytic process for the production of higher olefins, and is also a key step for jet-fuel production from bioethanol. We herein investigated the use of Ni/SIRAL-30 as a heterogeneous catalyst for ethylene oligomerization, as it can be prepared easily and cheaply by the simple impregnation of a Ni precursor on a commercial SIRAL-30 support with a high Brønsted acid site (BAS) density. Pyridine-infrared spectroscopy confirmed that proton species in the bridge-type Si-OH-Al frameworks of SIRAL-30 were partially exchanged with Ni2+ cations without interfering with the Al3+ sites. In addition, the Ni species following catalyst calcination under air and pretreatment with N2 was identified to be the isolated Ni2+ by XPS, EXAFS and CO adsorption. The Ni/SIRAL-30 catalyst gave almost complete ethylene conversion and stability over 100 h at 200 °C, 10 bar pressure, and at a weight hourly space velocity of 0.375 h−1 during continuous ethylene oligomerization. A Ni loading of 4 wt% on SIRAL-30 was optimal for both ethylene conversion and for maximizing the proportion of C10+ products formed, while the pretreatment of Ni(4 wt%)/SIRAL-30 at 550 °C under N2 resulted in the best catalytic activity. Although a degree of deactivation was observed due to the adsorption of heavy oligomers, the initial catalytic activity was restored by heating the used catalyst at 550 °C under air. These results confirm that the Ni(4 wt%)/SIRAL-30 catalyst is both recyclable and an efficient heterogeneous catalyst for continuous ethylene oligomerization.