In Situ Transmission Electron Microscopy to Study the Location and Distribution Effect of Pt on the Reduction of Co₃...

The addition of Pt generally promotes the reduction of Co₃ O₄ in supported catalysts, which further improves their activity and selectivity. However, due to the limited spatial resolution, how Pt and its location and distribution affect the reduction of Co₃ O₄ remains unclear. Using ex situ and in situ ambient pressure scanning transmission electron microscopy, combined with temperature-programmed reduction, the reduction of silica-supported Co₃ O₄ without Pt and with different location and distribution of Pt is studied. Shrinkage of Co₃ O₄ nanoparticles is directly observed during their reduction, and Pt greatly lowers the reduction temperature. For the first time, the initial reduction of Co₃ O₄ with and without Pt is studied at the nanoscale. The initial reduction of Co₃ O₄ changes from surface to interface between Co₃ O₄ and SiO₂ . Small Pt nanoparticles located at the interface between Co₃ O₄ and SiO₂ promote the reduction of Co₃ O₄ by the detachment of Co₃ O₄ /CoO from SiO₂ . After reduction, the Pt and part of the Co form an alloy with Pt well dispersed. This study for the first time unravels the effects of Pt location and distribution on the reduction of Co₃ O₄ nanoparticles, and helps to design cobalt-based catalysts with efficient use of Pt as a reduction promoter.