Morphology-dependent reactivity of cobalt oxide nanoparticles in N2O decomposition†
A series of cobalt spinel materials with identical bulk structures were obtained using various synthesis methods. Two types of precursors were obtained by precipitation with ammonium carbonate and hydrothermal treatment with urea. The two precursors were then calcined at 400 and 600 °C. Another sample was prepared in one step, with the use of supercritical water at 380 °C. The final materials were characterized using XRD, Raman spectroscopy, N2-BET, H2-TPR, nanoparticle tracking analysis and TEM. In situ work function experiments were conducted to evaluate the interactions of catalysts' surfaces with adsorbates such as O2. The reactivity in N2O decomposition was tested through a series of steady state experiments in a flow reactor. The different surface electronic properties of the materials, which are responsible for the catalysts' activity, were found to be associated with the morphology of the constituting nanocrystals. The samples with larger, more well-defined crystals were also characterized as having the lowest work function and lowest ability to stabilize adsorbates, such as oxygen species, and exhibited the highest catalytic activity.