Property and Reactivity Relationships of Co₃O₄ with Diverse Nanostructures for Soot Oxidation

Cobalt oxide (Co₃O₄) nanostructures with different morphologies (nanocubes, nanoplates, and nanoflowers) were synthesized by a simple hydrothermal method and used for catalytic oxidation of soot particles. Through the study of the physicochemical properties of the catalysts, the key factors affecting the performance of soot oxidation were investigated. The results showed that all three kinds of Co₃O₄ nanocrystals exhibited excellent low-temperature activity in catalytic oxidation of soot, and the Co₃O₄ nanoflowers showed higher oxidation activity of soot compared with Co₃O₄ nanocubes and Co₃O₄ nanoplates, whose T _m was only 370 °C. The excellent activity of Co₃O₄ nanoflowers was due to the large amount of Co³⁺ and lattice oxygen on their surface and highly defective structure, which promoted the adsorption and activation of oxygen species. The large crystallite size and few surface defects were the main reasons for the poor catalytic performance of Co₃O₄ nanocubes. During soot oxidation, the crystallite size of the catalysts and the contact between the catalysts and soot played a significant role in the catalytic performance.