Homologation of Methanol by Cobalt-Ruthenium Mixed Catalysts

Abstract

The homologation of methanol to ethanol was carried out with the aid of the mixed transition metal catalysts containing cobalt in conjunction with iodide promoters under the compressed synthesis gas (H₂-CO). The Co-Ru system was found to exhibit a remarkable catalytic activity for homologation. The influences of reaction variables such as Ru/Co ratio, pressure, temperature, added iodide and solvents on the methanol conversion, the ethanol selectivity and the formation of by-products were examined in detail. Both the yield and selectivity of ethanol were significantly dependent on the Ru/Co ratio and the composition of synthesis gas. The yield increased with the charge ratio of RuCl₃⋅ n H₂O to Co₂(C0)₈(Ru/Co), reached a maximum and then decreased with larger ratio. The optimum ratio of Ru/Co varied slightly from ca. 0.2 to 0.4 when the temperature and the partial pressure of H₂ were decreased under the otherwise same conditions.
It was also found that ethers such as 1, 4-dioxane, THF, Methyl Cellosolve and Diglyme, served as a good solvent to give the higher yield (ca.60%) and selectivity (ca.80%) of ethanol.