Water-induced structural evolution of oxide catalysts is a key issue in heterogeneous catalysis, as it strongly affects the catalysts' active states, stability, and reaction pathways. However, the atomic-scale understanding of how water drives structural reconstruction in oxide catalysts remains unclear.

To address this knowledge gap, a research team led by Profs. FU Qiang and MU Rentao from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences has uncovered the water-induced dynamic structural evolution of oxides. The study reveals at the atomic scale the dynamic mechanisms of oxidative and reductive hydroxylation of cobalt-based oxide (CoO_x) nanostructures in water vapor.

The findings were recently published in National Science Review.

The researchers found that CoO_x nanostructures with different initial structures follow distinct hydroxylation pathways in the presence of water. For CoO, water adsorbs dissociatively on the surface, driving its conversion into Co(OH)₂ and accompanying the oxidation of Co ions.

In contrast, for CoO_2-x surfaces containing both CoO and CoO₂ domains, water first reacts with the CoO domains, converting them into Co(OH)₂ and forming a Co(OH)₂–CoO_2-x interface. Subsequent reaction of this interface with water promotes the removal of lattice oxygen, thereby inducing the reduction and hydroxylation of CoO₂ domains and ultimately leading to their full conversion into Co(OH)₂.

This study clarifies the structural transformation mechanism by which water molecules play both oxidative and reductive roles in different CoO_x structures, providing new insights into the role of water in oxide catalysis.

Schematic of reductive and oxidative hydroxylation of CoO_x nanostructures in H₂O atmosphere. (Image by SUN Xiaoyuan)