Vertically-aligned Co3O4 arrays on Ni foam as monolithic structured catalysts for CO oxidation: effects of morphological transformation

Abstract

A generic hydrothermal synthesis route has been successfully designed and utilized to in situ grow highly ordered Co₃O₄ nanoarray (NA) precursors on Ni substrates, forming a series of Co₃O₄ nanoarray-based monolithic catalysts with subsequent calcination. The morphology evolution of Co₃O₄ nanostructures which depends upon the reaction time, with and without CTAB or NH₄F is investigated in detail, which is used to further demonstrate the growth mechanism of Co₃O₄ nanoarrays with different morphologies. CO is chosen as a probe molecule to evaluate the catalytic performance over the synthesized Co-based oxide catalysts, and the effect of morphological transformation on the catalytic activity is further confirmed via using TEM, H₂-TPR, XPS, Raman spectroscopy and in situ Raman spectroscopy. As a proof of concept application, core–shell Co₃O₄ NAs-8 presenting hierarchical nanosheets@nanoneedle arrays with a low density of nanoneedles exhibits the highest catalytic activity and long-term stability due to its low-temperature reducibility, the lattice distortion of the spinel structure and the abundance of surface-adsorbed oxygen (O_ads). It is confirmed that CO oxidation on the surface of Co₃O₄ can proceed through the Langmuir–Hinshelwood mechanism via using in situ Raman spectroscopy. It is expected that the in situ synthesis of well-defined Co₃O₄ monolithic catalysts can be extended to the development of environmentally-friendly and highly active integral materials for practical industrial catalysis.