Production of Linear Octenes from Oligomerization of 1‑Butene over Carbon-Supported Cobalt Catalysts

Linear octenes were produced in high (70–85%) selectivity from oligomerization of liquid 1-butene using carbon-supported cobalt oxide catalysts in a continuous flow reactor. The liquid products were characterized by two-dimensional gas chromatography–mass spectrometry. Above 95% of the oligomers were C8 olefins, with the other products primarily being branched C12 olefins. The linear octene products at a conversion of 9.77% decreased in selectivity according to 3-octene > trans-2-octene > cis-2-octene > 4-octene. Methyl-heptenes including trans/cis-5-methyl-2-heptene > trans/cis-5-methyl-3-heptene > trans-3-methyl-2-heptene (at the lowest conversion) were the other major products summing to 15.6%. The selectivity of linear octenes decreased from 84 to 78% as the conversion increased from 10% to 29%. The product distribution suggests the reaction pathway involves a head-to-head coupling of two 1-butene molecules to form internal linear octenes. Head-to-tail coupling of two 1-butene molecules or a coupling between 1-butene and 2-butene forms the observed methyl-heptenes. The rate of head-to-head coupling is higher than the rate of head-to-tail or the rate of 1-butene to 2-butene coupling as indicated by the higher selectivity of linear octenes. The activated catalyst contained both Co₃O₄ and CoO as confirmed by X-ray diffraction (XRD), in situ Raman spectroscopy, and X-ray absorption spectroscopy. The cobalt oxide particle size was estimated to be between 5 and 10 nm by high-resolution transmission electron microscopy and XRD. The Co₃O₄/CoO ratio decreased with increasing pretreatment temperature. Metallic cobalt, which has a low catalytic activity, formed at 550 °C.