Pt/CeO2 is a promising catalyst for the low temperature water gas shift reaction (WGS).1 Moreover, it is “dynamic” since Pt can be dispersed during an oxidative treatment at moderate temperature leading to single atoms catalysts (SACs) while a reducing treatment triggers 3D particles formation.2 Starting from SACs, suitable redox treatments were previously shown to tailor nanoclusters more active for the low-temperature CO oxidation in the presence of water.3,4 In this work, the influence of different redox treatments on the WGS activity of Pt/CeO2 catalysts has been investigated depending on the Pt surface density. Relationships between physicochemical and catalytic properties have been established based on several complementary characterization methods including in situ/operando techniques. An optimal H2 productivity was observed for a Pt coverage higher than 0.12 at/nm, revealing two different behaviors for high and low loadings. It has been attributed to the increase in Pt reducibility with higher loadings, enabling the formation of more active nanoparticles than initial SACs. Interestingly, reductive pretreatment and oxidative post-treatment after reaction improves the catalytic performances at low Pt loadings by forming active Pt nanoparticles from stable SACs, while it decreases the catalytic activity at higher loadings. Low loadings catalysts were strongly activated by the increase of Pt and ceria reducibility, which enhances the formation of Pt0 nanoparticles under reactive conditions. These results permitted to show that Pt reducibility is a promising factor to manage the activity of the catalysts under water gas shift condition, and can be controlled by the surface content and redox treatments applied. References [1] : Panagiotopoulou, P.; Kondarides, D. I. Catal. Today 2007, 127 (1), 319–329. [2] Moliner, M.; Gabay, J. E.; Kliewer, C. E.; Carr, R. T.; Guzman, J.; Casty, G. L.; Serna, P.; Corma, A. J. Am. Chem. Soc. 2016, 138 (48), 15743–15750. [3] Gänzler, A. M.; Casapu, M.; Vernoux, P.; Loridant, S.; Cadete Santos Aires, F. J.; Epicier, T.; Betz, B.; Hoyer, R.; Grunwaldt, J.-D. Angew. Chem. Int. Ed. 2017, 56 (42), 13078–13082.. [4] Ferré, G.; Aouine, M.; Bosselet, F.; Burel, L.; Aires, F. J. C. S.; Geantet, C.; Ntais, S.; Maurer, F.; Casapu, M.; Grunwaldt, J.-D.; Epicier, T.; Loridant, S.; Vernoux, P. Catal. Sci. Technol. 2020, 10 (12), 3904– 3917.