Aerial oxidation of alcohols over CuAl-, CoAl-, NiAl-, ZnAl- layered double hydroxides and their mixed oxides

This paper reports the oxidative conversion of benzyl alcohol, cyclohexanol and allyl alcohol in the presence of CuAl-, CoAl-, NiAl-, ZnAl-layered double hydroxides (LDH) and their corresponding mixed oxides (MAlO) as catalysts. The mixed oxides were obtained by thermal decomposition at different temperatures. The catalysts were characterized by elemental analysis, BET method and X-ray diffraction (XRD). The partial oxidation was carried out with air oxygen and under solvent-free mild conditions. The reaction temperatures were the boiling temperatures of the alcohols. The catalytic activity and selectivity of the used LDHs and of their mixed oxides were evaluated using the air oxidation of mentioned alcohols to benzaldehyde, adipic acid and glycidol as major products. Benzyl benzoate, cyclohexyl ester of 6-hydroxyhexanoic acid and 2-2′-[oxybis(methylene)]dioxirane were determined as by-products. The interactions between catalytically active acid and basic sites and reactants are discussed. Some reaction routes and mechanisms are suggested.