Supported mixed oxide catalysts for the total oxidation of volatile organic compounds

Supported mixed oxide catalysts of various cation composition were obtained by heating (500 °C) of layered double hydroxide (LDH) precursors deposited on Al2O3/Al support (anodized aluminum foil) or grained alumina calcined at various temperatures during hydrothermal reaction in aqueous solutions of Co, Cu, Ni, and Mn nitrates. The MII–(Mn)–Al LDHs (MII = Co, Ni–Co, Ni–Cu, and Co–Cu) with only low Mn content were obtained. NiO-like and spinel-like mixed oxides but no distinct Cu-containing phases were detected in the supported catalysts. A low-temperature peak ascribed to reduction of an amorphous copper oxide was detected in TPR patterns of the supported mixed oxides containing Cu. TPR results indicated reduction of Ni- and Co-containing species at temperatures higher than 400 °C; it can be explained by formation of spinel-like phases and high structural ordering of the calcination products. Heating of grained alumina support at high temperatures (>550 °C) resulted in substantial decrease in surface area and, consequently, the amount of deposited active species. Among the examined catalysts, the Ni–Cu–(Mn)–Al mixed oxide showed the highest catalytic activity. Slight acetaldehyde formation during ethanol deep oxidation over the supported mixed oxides was observed.