The metal oxides such as Al2O3, CaO, Fe2O3, MgO and ZnO were used directly from commercial products. The mixed metal oxides with different Al2O3/CaO/Fe2O3/MgO/ZnO mass ratios (1:1 w/w for binary and 1:1:1 w/w for ternary metal oxides) were prepared by pH controlled co-precipitation method. In brief, appropriate amounts of the metal precursors were dissolved in an aqueous solution containing Na2CO3 and NaOH with mass ratio of 3:1. The solution was stirred at 60 °C using magnetic stirrer for 30 min, and then aged for an additional 1 h After vacuum filtration, the solid precipitate was washed with double distilled water, dried in an oven at 100 °C, and was calcined in a muffle furnace at 550 °C for 4 h The calcined materials were crushed, sieved to the particle size ≤ 100 μm (Tyler standard), and then dried in an oven at 100 °C for 5 h Recovered metal oxides were also prepared by following the same calcination process as described above. The structural characteristics were determined using X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmer–Teller (BET) and Barrett–Joyner–Halenda (BJH) analysis.