Supported layered double hydroxide-related mixed oxides and their application in the total oxidation of volatile organic compounds

Structured mixed oxide catalysts were prepared by the calcination of layered double hydroxides (LDHs) deposited on Al2O3/Al supports (anodized aluminum foil). The deposition of LDH precursors on the supports was carried out under hydrothermal conditions at 140 °C in aqueous solutions of Ni, Co, Cu, and Mn nitrates. MII-(Mn)-Al LDHs (MII = Ni, Co, Ni-Co, Ni-Cu, and Co-Cu) with only slight Mn contents were obtained. An increased pH of the solutions used for deposition enhanced the formation of LDH phases. After heating at 500 °C, spinel-like and/or NiO-like oxides were detected in the supported mixed oxides. Compared to the mixed oxides obtained by calcination of the coprecipitated LDH precursors, the supported mixed oxides exhibited worse reducibility and lower catalytic activity in the total oxidation of ethanol; both the formation of spinel-like phases and high structural ordering of the products deposited on the Al2O3/Al supports could explain the poor reducibility. Among the supported catalysts, the Ni-Cu-(Mn)-Al mixed oxide was the most active in the total oxidation of ethanol. Increasing the pH of solutions used during the hydrothermal deposition of the LDH precursors resulted in improved catalytic activity and selectivity of the supported mixed oxides.