The addition of Pt generally promotes the reduction of Co3O4 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 Co3O4 remains unclear. Using ex situ and in situ ambient pressure scanning transmission electron microscopy, combined with temperature-programmed reduction, the reduction of silica-supported Co3O4 without Pt and with different location and distribution of Pt is studied. Shrinkage of Co3O4 nanoparticles is directly observed during their reduction, and Pt greatly lowers the reduction temperature. For the first time, the initial reduction of Co3O4 with and without Pt is studied at the nanoscale. The initial reduction of Co3O4 changes from surface to interface between Co3O4 and SiO2. Small Pt nanoparticles located at the interface between Co3O4 and SiO2 promote the reduction of Co3O4 by the detachment of Co3O4/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 Co3O4 nanoparticles, and helps to design cobalt-based catalysts with efficient use of Pt as a reduction promoter
