Total oxidation of benzene over cobalt-aluminum mixed oxides prepared from layered double hydroxides: influence of preparation methods

The influence of the preparation methods of Co-Al layered double hydroxides (LDHs) on the structural and catalytic properties of Co-Al mixed oxides for benzene total oxidation was investigated. Various Co-Al LDHs were synthesized via constant pH precipitation, decreasing pH precipitation, and urea homogeneous precipitation. The synthesized samples were characterized by using N2physical adsorption, ICP, XRD, TG–DTA, SEM, and H2-TPR. The characterization results showed that calcination of Co-Al LDHs gave rise to Co-Al mixed oxides consisting of Co(Co, Al)2O4spinel as the main phase, which showed relatively small crystallite size and high specific surface area, i.e., ~12 nm, 90–100 m2gcat−1. The highest catalytic activity was obtained on the Co-Al mixed oxide prepared by decreasing pH precipitation, followed by that prepared by constant pH precipitation, while the Co-Al mixed oxide prepared by urea homogeneous precipitation was much less active. The activity difference can be related to the different reducibility of Co3+species in Co(Co, Al)2O4spinel.