Pt/CeO2 is a promising catalyst for the low temperature water gas shift reaction (WGS) [1]. Moreover, it is ‘dynamic’ since Pt atoms can be dispersed during an oxidative treatment at moderate temperature leading to single atoms (SAs) while a reducing treatment triggers 3D nanoparticles (NPs) formation [2-4] Starting from SAs, suitable redox treatments were previously shown to tailor more active nanoclusters for the low-temperature CO oxidation in the presence of water [2,3]. In this work, the influence of different redox pre and post-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 high resolution STEM-ADF microscopy, microRaman, CO-TPR followed by in situ DRIFT, near ambient resonant photoemission (NAP ResPES) and operando DRIFT spectroscopies. Ultradispersed PtOx species at the surface of CeO2 were generated by performing an oxidizing pretreatment at 500 °C before the WGS reaction. It was shown that the molar catalytic activity is strongly dependent on the Pt content, increasing up to 0.59 wt% and stabilizing above. A major structural change during reaction was found for Pt contents above 0.59 wt% through the formation of metallic Pt0 NPs from oxidized Pt SAs and clusters. Conversely, for Pt contents below 0.59 wt%, Pt species are strongly interacting with CeO2 limiting the formation of Pt0 NPs under reaction conditions. This strongly suggests that these metallic species are more active than oxidized Pt single atoms and clusters, which are mainly present at low loadings. The importance of PtOx reducibility to achieve high WGS activity was also highlighted. Then, the impact of reductive pre-treatments at 250 and 500 °C for 1 h under H2 (RED250 and RED500, respectively) and oxidative post-treatments under O2 at 230 °C for 10 min and 500 °C for 12 h (ReOx230 and ReOx500, respectively) on the catalytic activity and the nature of Pt species was determined. A 4-fold increase in activity compared to the fresh state was obtained for 0.10 wt% Pt/CeO2 catalyst after RED500 treatment. Such enhancement was explained by reduction and extraction of Pt SACs strongly anchored in the CeO2 subsurface. Catalysts with intermediate and high Pt contents which contain PtOx and Pt0 clusters, were slightly activated after RED250 due to higher number of active sites while they were strongly deactivated after RED500. These pre-treatments irreversibly modify the structure of Pt species since a consecutive oxidative treatment at 500 °C did not allow to recover the initial activity. Furthermore, a regeneration of catalyst activity was demonstrated using ReOx230 post-treatment. Unexpectedly, a strong increase in activity compared to the initial state was observed after ReOx500 for Pt loading below 0.80 wt%. The disappearance of Pt0 NPs during ReOx500 post-treatment was evidenced revealing the redispersion of Pt atoms. However, the initial state of Pt species was not recovered. In fact, this oxidative post-treatment triggers the formation of highly reducible PtOx clusters on the surface of CeO2 for Pt loading lower than 0.80 wt% which in turn increases the amount of small Pt0 NPs in the WGS conditions. Keywords: Pt/CeO2 catalyst, water-gas shift reaction, Pt species, structural dynamics, redox treatments. References [1] P. Panagiotopoulou et al., (2007), Water–gas shift activity of doped Pt/CeO2 catalysts, Catal. Today, 127, 319. [2] A. M. Gänzler et al., (2017), Tuning the Structure of Platinum Particles on Ceria In Situ for Enhancing the Catalytic Performance of Exhaust Gas Catalysts, Angew. Chem. Int. Ed., 56, 13078. [3] G. Ferré et al., (2020), Exploiting the dynamic properties of Pt on ceria for low-temperature CO oxidation, Catal. Sci. Technol., 10, 3904. [4] C. Molinet-Chinaglia et al., (2024), Tuning the metal loading of Pt/CeO2 catalysts for the water-gas shift reaction, Mat. Today Catal., 4, 100046.