Unveiling Reversible Evolution of Single-Atom Catalysts Driven by Reverse Oxygen Spillover of CeO2

The oxygen transfer from the support surface to the metal catalyst, so-called reverse oxygen spillover, is of immense interest in heterogeneous catalysis, but how exactly it influences the structure reconstruction of metal catalysts and evolution of the real active sites during reactions remains unclear. Herein, we reveal the dynamic evolution of the Ni species caused by the reverse oxygen spillover of CeO 2 under the water gas shift reaction conditions using in situ scanning transmission electron microscopy and in situ infrared spectroscopy. The direct, atom-resolved evidence shows that the tiny Ni 0 nanoparticles in situ formed during the reaction subsequently underwent oxidation and collapse as temperature decreased after the reaction and eventually spread out and redispersed on the CeO 2 surface as Ni single atoms. The spontaneous redispersion of the metal during the reaction induced by the reverse oxygen spillover is of general importance for understanding the catalytic mechanisms.