RESEARCH / A0257
Revealing the Interface-Driven Atomic Local Chemical Heterogeneity in Bimetallic Catalysts in Three Dimensions
Read the original paper · 10.1021/jacs.5c12285 ↗
Source figures may contain other techniques and soft X-ray spectra. C, N and O measurements are outside our current hard-XAFS testing range.
Figure 4. Local chemical heterogeneity on the surface of Pd@PtnL nanoparticles. (A) The Pd concentrations in the first three shells of the Pd@ PtnL_1 nanoparticles. Pd@PtnL_1 nanoparticles were “peeled” like an onion from the outside to get the atomic compositions in the first three shells. (B) The fraction of heterogeneous Pd and Pt center atoms to total surface atoms in Pd@PtnL_1 nanoparticles. The distance of the fourth nearestneighbor atoms (fourth valley of the RDF) was used as a threshold to identify where the surface atom is heterogeneous. (C) Histogram of normalized Pd concentrations (cPd) around heterogeneous Pt centers. cPd (on the x-axis) is quantified by atom fractions of Pd/(Pd + Pt). The fraction (on the y-axis) in the histogram is the relative frequency of the total atoms of heterogeneous Pt centers. (D−G) Heterogeneous Pt centers distributed on the surface of Pd@PtnL_1 nanoparticles. Surface atoms where cPd in the interval of 0.05−1 are displayed. The surface contour shapes of the nanoparticles are shown in transparent meshes. (H) XANES at the Pd K-edge for Pd@PtnL nanoparticles and Pd foil. Inset, enlarged view of white line (WL) peak intensity. The peak intensity of the WL region in the inset follows the order: Pd@Pt2L > Pd@Pt5L > Pd@Pt>8L> Pd@Pt<1L > Pd foil, which indicates the electron density of the Pd shell in Pd@PtnL CS-NPs follows the order: Pd@Pt2L < Pd@Pt5L < Pd@Pt8L < Pd@Pt<1L. (I) k3-weighted EXAFS spectra at the R-space for Pd@PtnL CS-NPs and Pd foil. Note that since atomic diameters of Pd and Pt are similar, the shell in the interval of 2−3 Å includes not only the Pd−Pd but also the Pd−Pt coordination information. (J) Comparison of the CNs around Pd atoms, Pd- M (M = Pd, Pt, for the similar radii of the two), which are obtained from EXAFS and AET, respectively. Pd@PtnL_1 is presented here as a representative data set.