Improved selectivity to C₈-Olefins for isobutene oligomerization on NiO-W₂O₃/Al₂O₃ catalysts

Isobutene oligomerization on W₂O₃/Al₂O₃ and NiO-W₂O₃/Al₂O₃ catalysts (20 wt.% W₂O₃ and 5 wt.% NiO) was studied. The catalysts were prepared by impregnating ammonium tungstanate and nickel nitrate on a γ-alumina sol-gel support. The XRD patterns of the samples calcined at 500°C show the presence of large W₂O₃ conglomerates on the W₂O₃/Al₂O₃ sample and smaller ones on the NiO-W₂O₃/Al₂O₃ catalyst. Pyridine-FT-IR absorption spectra study shows a higher acidity on the nickel-containing sample. The isobutene oligomerization was carried out in a gas-phase flow reactor (50°-150°C), and selectivity as high as 100% to the formation of the C₈= olefins fraction was obtained. The role of NiO coordinating the π-allyl adsorption of the olefins as well as its role to the high C₈= selectivity were discussed.