Co–Mn–Al mixed oxides on anodized aluminum supports and their use as catalysts in the total oxidation of ethanol

Abstract

The Co–Mn–Al mixed oxide catalysts over Al2O3/Al supports were obtained by calcination of layered double hydroxide (LDH) precursors formed on anodized aluminum foils during hydrothermal reaction in aqueous solutions containing Co and Mn nitrates. The precursors crystallized as thin curved platelets with nearly perpendicular orientation to the support; the morphology of the deposited LDH films remained preserved after heating at 500°C, when spinel-like mixed oxides were formed. The Mn/Co molar ratio in the range from about 4 to 8 in the nitrate solution was found to be favorable for obtaining catalysts with demanded contents of active components. The supported Co–Mn–Al mixed oxide catalysts were tested in the total oxidation of ethanol and compared with the grained sample obtained from the coprecipitated LDH precursor. The specific activity of the catalysts increased with increasing Mn/Co molar ratio in the solid up to value of about 0.4. Compared to the grained catalyst, the layers of Co–Mn–Al mixed oxides formed over anodized aluminum foils showed slightly higher specific activity in the total oxidation of ethanol (calculated per a weight of the active components Co and Mn). Formation of main reaction intermediate, acetaldehyde did not change practically with increasing Mn/Co molar ratio.