Fig. 2. Pd₈Au₉₂/RCT-SiO₂ is subjected to HD exchange reaction after three sequential pretreatments.

a Initial state S0 undergoes O₂ treatment to starting state S1 (treatment A), followed by H₂ treatments to starting states S2 and then S3 (treatments B and C respectively). The hydrogen regime is shaded blue, and the oxygen regime is shaded yellow. b Activity versus temperature for three HD exchange experiments, labeled HD-1 to HD-3, corresponding to three different starting states (S1-S3). The solid and open circles indicate the heating and cooling regimes, respectively. c Normalized XANES collected for the different samples (pink = S0, blue = S1, yellow = S2, orange = S3, and dashed black = Pd foil). The inset shows a shift in the spectral center of mass “c”. d Coordination numbers (blue = Pd–Pd bonds and red = Pd–Au bonds) from NN-XANES are consistent with Pd atoms having more Pd neighbors after O₂ treatment (yellow shade) and less Pd neighbors after H₂ treatment (blue shade). Atomic Pd ensembles in (c) and (d) are depicted with bird’s-eye-view schematics (yellow = Au; green = Pd).