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. Longtime 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.