Effects of the preparation methods of Co3O4 catalysts on catalytic oxidization performance toward o-xylene

Abstract

The Co₃O₄ catalysts with different precursors (Na₂CO₃, CH₄N₂O) were synthesized and evaluated for its o-xylene catalytic oxidation performance. A series of techniques including BET, XRD, TEM, XPS, H₂-TPR were employed to characterize the physical and chemical properties of catalysts under various preparation conditions. The results indicated that physisorption played an important role in the o-xylene removal and higher calcination temperature destructed the specific surface areas of the Co₃O₄ samples. The enhanced catalytic performance of Co₃O₄N catalyst was mainly attributed to be abundance in active Co³⁺ and lattice oxygen species, while that of Co₃O₄C catalyst was ascribed to the formation of superoxide anion, especially the lower calcination temperature facilitated the generation of active species. In addition, the reaction mechanisms toward o-xylene oxidation over Co₃O₄ catalysts obtained by different preparation methods were explored in detail. The o-xylene molecule preferentially adsorbed onto the Co³⁺ ion sites, and was further oxidized by the lattice oxygen or superoxide anion with the product being o-methyl benzyl alcohol. Soon the benzyl alcohol was transformed into the o-methyl benzaldehyde, and afterward to form benzoic acid. Later, the benzoic acid was converted into small-molecule carboxylate for Co₃O₄N catalyst, whereas for Co₃O₄C catalysts, the benzoic acid was further turned into maleic acid subsequently into acetone. Finally, both the small-molecule carboxylate and acetone species were oxidized to CO₂ and H₂O. This finding offers some valuable insights for designing efficient o-xylene oxidation catalysts and mitigating industrial air pollution.