Epoxidation of cyclohexene with O 2 and isobutyraldehyde catalysed by cobalt modified hydrotalcites

Abstract

The paper presents a comparison between the catalytic performances of cobalt modified hydrotalcites obtained from different cobalt precursors in the epoxidation of cyclohexene using molecular oxygen, isobutyraldehyde as reductant, at 25 °C and 1 atmosphere pressure of oxygen in acetonitrile as solvent. Two different types of cobalt containing catalysts were prepared: (i) a hydrotalcite-like compound containing cobalt in the brucite type layer, CoMg/Al, and (ii) three catalysts obtained by impregnation of the as-synthesized hydrotalcite support (HT) with CoCl 2, bis-triphenylphosphine-dichlorocobalt (II) Co[P(C 6H 5) 3] 2Cl 2, (A), and an admixture of complexes (AB) containing bis-triphenylphosphine-dichlorocobalt (II) Co[P(C 6H 5) 3] 2Cl 2 (A) and benzyltriphenyl phosphonium-tetrachlorocobaltate [C 6H 5CH 2P(C 6H 5) 3] 2 +[CoCl 4] 2− (B). The names of these catalysts have been abbreviated as CoCl 2/HT, A/HT and AB/HT. The catalysts were characterized by chemical analyses, DR-UV–vis, DRIFTS, XRD, EDX and texture measurements. The most active and selective catalyst was AB/HT. A linear correlation between the ratio Cl/Co in the resulting solids and the yield to epoxide has been established. For AB precursor the effect of the support has been also investigated using as carriers the mixed oxide CHT derived from the calcination of the parent hydrotalcite, and the reconstructed hydrotalcite RHT obtained by rehydration of CHT.