Oxidation of Ethyl Methyl Ketone to Biacetyl over Cobalt-spinels

Abstract

The catalytic activities of nine spinel oxides containing cobalt were examined for oxidation of ethyl methyl ketone (EMK) to biacetyl. The formation of biacetyl was observed, more or less, over all the oxides in a lower temperature range (473 K to 523 K). The selectivity of biacetyl decreased with the increase in temperature, biacetyl formation being replaced by complete oxidation. Based on the product distribution at 473 K, the oxides were classified into two groups: one were selective for biacetyl and the other favored oxidative scission of EMK. In the first group, Co₂NiO₄ had the highest selectivity for biacetyl, while CuCo₂O₄ showed the highest specific rate for EMK conversion. In the latter group, Co₂MnO₄ gave equimolar amounts of acetic acid and acetaldehyde, but acetaldehyde was obtained predominantly on MgCO₂O₄ and CoAl₂O₄. It was found that the catalytic activities of the cobalt-spinels for biacetyl formation or partial EMK oxidation were dependent on the type of spinel, i. e., (A)M²⁺Co₂³⁺ O₄; (B) Co²⁺M₂³⁺O₄;(C) Co₂²⁺M⁴⁺O₄ Among the spinels of the same type, the activities were well correlated with the electronegativities of metal ion or the heat of formation of component oxides MOn. The deviation of the activities of Co₂NiO₄ and Fe₂CoO₄ from the correlations suggests that the cobalt ions at the A sites (tetrahedral) are more active than those at the B sites (octahedral). Apart from these correlations, temperature programmed desorption measurements revealed that the catalytic activities of the oxides ran parallel with the amount of adsorbed oxygen on the oxides. This fact suggests participation of the adsorbed oxygen in this type of oxidative reaction.