This work unveils the chemical evolution of bimetallic Pt0.3Cu0.7 nanoparticles (NPs) when submitted to oxidizing (H2S) and reductive (H2) atmospheres. Time-resolved X-ray absorption measurements were performed at both Pt-L3 and Cu-K edges in dispersive mode (DXAS), during which near-edge spectra (XANES) were collected sequentially and in situ. These results contributed to the modeling of the Pt0 and Cu0 fraction evolution, from which the activation energies for the sulfidation and reduction processes were estimated. We conclude that the addition of Cu in this bimetallic system improved resistance to sulfur poisoning and its diffusion into the NPs when compared to the Pt-Pd nanoalloys, and moreover allows reversing the S contamination, making it an economically attractive catalyst.