Selective oxidation of n-buthanol to butyraldehyde over MnCo₂O₄ spinel oxides

Partial oxidation of n-butanol to butyraldehyde, propionaldehyde and acetaldehyde over MnCo₂O₄ spinel oxides has been investigated. Physicochemical characteristics of samples, prepared by co-precipitation with different amounts of precipitating agent, were studied by XRD, N₂ adsorption-desorption isotherms, FT-IR, SEM and XPS. The ratio between the precipitating agent and the precursors has a considerable influence both on the structure, which is evidenced by XRD, due to switching from a crystalline structure to an amorphous one and on the surface (XPS) by an obvious change in the ratio Co³⁺/Co²⁺ and Mn⁴⁺/Mn³⁺ and in the content of oxygen vacancies. The reaction rate is not influenced by the oxygen pressure, emphasizing that n-butanol oxidation occurs through the Mars van Krevelen mechanism. The conversion of n-butanol and yield of butyraldehyde are directly proportional to the cobalt content on the surface, while the propionaldehyde yield is proportional to the Mn⁴⁺/Mn³⁺ ratio.