Growth mechanism and CO oxidation catalytic activity of raspberry-shaped Co₃O₄ nanoparticles

Abstract

Raspberry-shaped Co₃O₄ nanoparticles has a great potential as a CO oxidation catalyst in a wide temperature range because of a high stability and a low-temperature oxidation activity. In this study, primary particle sizes, morphology and crystallite sizes were controlled by changing a synthesis time to enhance the CO oxidation activity and to reveal growth mechanism of the raspberry structure. The primary particle sizes increased while decreasing crystallite size, indicating crystal orientation and particle growth of Co₃O₄ nanoparticles were occurred in multistage, and a single-crystal-like structure formed in the hydrothermal treatment for 3.0 h. Long-time hydrothermal treatment for 12.5 h caused decomposition of the crystallographic orientation and the raspberry structure. H₂-temperature programmed reaction analysis indicated that crystal orientation among multiple Co₃O₄ nanoparticles improved a mobility of bulk oxygen species, and our previous findings that 93% of CO conversion rate for the raspberry-shaped Co₃O₄ nanoparticles was confirmed analytically by the high oxygen mobility in the early 3.0 h-hydrothermal treatment.