Enhanced CO catalytic oxidation of flower-like Co3O4 composed of small nanoparticles

Abstract

Three dimensional (3D) flower-like Co₃O₄ composed of nanoparticles (NPs) is synthesized via a hydrothermal route to prepare a precursor and a subsequent calcination process to create the Co₃O₄ phase. Calcination is the key process for controlling the size of the Co₃O₄ NPs and their catalytic performance. The size of NPs in flower-like samples depends strongly on the heating rate and calcination temperature. High temperatures result in the formation of heterogeneous and large particles. In contrast, the NPs in resulting samples pack together or aggregate, and their sizes decrease with an increasing heating rate. Our CO catalytic oxidation investigation indicates that the flower-like Co₃O₄ calcined at 400 °C with a heating rate of 1 °C min⁻¹ exhibits the highest catalytic performance with a 100% conversion ratio at 93 °C. This activity originates from the redistribution of ions on the surface of flower-like Co₃O₄ induced by the calcination process, which generates more Co³⁺ active sites and active oxygen species adsorbed on the surface of the catalyst. The content of inactive Co²⁺ cations is reduced simultaneously. It is suggested that the enhanced catalytic activity is due to the increasing number of Co³⁺ active sites and adsorbed active oxygen species at the surface of flower-like Co₃O₄ that was calcined under optimum conditions. Meanwhile, the increasing specific surface area also provides more reaction sites for CO catalytic oxidation.