Hydrotalcite-derived aluminum-doped cobalt oxides for catalytic benzene combustion: Effect of calcination atmosphere

Al-doped Co 3 O 4 and CoO are prepared from Co‒Al hydrotalcite by calcination in air and N 2 atmospheres, and characterized by TG-DTA, XRD, SEM, N 2 adsorption, Raman, XPS, and H 2 -TPR. Co‒Al hydrotalcite is oxidized to Co(Co,Al) 2 O 4 in air accompanying with the collapse of layered structure, while in N 2 it decomposes to Co(Al)O that remains the plate morphology of hydrotalcite. In both cases, Al 3+ is doped into the lattice of cobalt oxides, leading to marked changes in the crystal size, surface state, and reducibility. Especially, Al-doped CoO shows smaller crystal size (4.1 nm), larger surface area (172 m 2 g ‒1 ), and higher degree of structural disorder than Al-doped Co 3 O 4 . Meanwhile, the Al-doped cobalt oxides show different reducibilities to those of Co 3 O 4 and CoO, indicating a strong interaction between cobalt and aluminum. The N 2 -calcined sample exhibits higher activity for benzene combustion than the air-calcined sample as well as a relatively good stability during heating/cooling cycles and a good long-time durability. Under the reaction atmosphere, Co(Al)O is transferred to Co(Co,Al) 2 O 4 . The resulting Co(Co,Al) 2 O 4 remains the original plate morphology and textural property and presents abundant surface adsorbed oxygen species, which accounts for its high activity.