In Situ X-ray Absorption Spectroscopic Analysis of Gold–Palladium Bimetallic Nanoparticle Catalysts

Abstract

Gold−palladium core−shell nanoparticles have been previously shown to be extremely effective catalysts for a number of oxidation reactions including the aerobic oxidation of alcohols. However, the novel activity and durability of such catalysts are still poorly understood, and there are several putative mechanisms by which oxidation reactions can proceed. Previously we showed that Pd(II) salts in the presence of Au nanoparticles were also effective catalysts for the room temperature oxidation of crotyl alcohol. Herein we show an in situ X-ray absorption spectroscopy (XAS) study at both the Pd−K and Pd-L III edges of Au nanoparticle/Pd(II) salt solutions in the presence of crotyl alcohol. Liquid cells with X-ray permeable windows were used to obtain quick-scan XAS data during the oxidation of crotyl alcohol, allowing for time-resolved Pd speciation information and information about the reaction mechanism and kinetics. XAS measurements definitively show that the first step of this reaction involves Pd reduction onto the Au nanoparticles; in addition, further studies of the stability of the resulting Au−Pd core−shell nanoparticles toward oxygen gas suggests that the role of Au in such catalysts is to prevent the reoxidation of the catalytically active surface Pd atoms. Catalytic crotyl alcohol oxidation measurements were done which validated that the in situ reduction of Pd(II) in the presence of Au nanoparticles did indeed result in catalytically active AuPd bimetallic catalysts.

Synthesis of Ni/Graphene Nanocomposite for Hydrogen Storage

“…This spectral difference is presumably due to a difference of electronic structure between the Ni and graphene in the Ni/graphene composite; electron density was probably dragged towards defects in the graphene. 35 A similar finding was obtained from the k-weight Fourier transform of Ni K-edge extended X-ray absorption fine structure (EXAFS) spectra as shown in Figure 5h 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 16 (Ni/graphene_0.5 bar) as references to determine the hydrogen uptake and the storage capacity in the hydrogen charged sorbents.…”

Rational design and characterization of bimetallic gold‐palladium nanoparticle catalysts

“…Similar results were seen for other ratios used, which suggested that co‐reduction synthetic strategies led to the formation of near‐alloy particles, albeit with slightly higher Au loadings in the core of the particles. Meanwhile, recent results for sequentially synthesized Au‐Pd core‐shell particles show first shell coordination numbers for Au of ∼10.6 and Pd of ∼7.5, which suggests preferentially Pd surfaces on these particles with Au core . However, the EXAFS results cannot rule out the presence of some surface Au.…”

Bimetallic Dendrimer-encapsulated Nanoparticle Catalysts

“…XRF is a powerful technique to perform the quantitative and qualitative elemental analysis of many kinds of materials including the liquids, solids, thin-film, and loose powders samples. 78,79 The analysis is rapid, precise, accurate, and non-destructive, which usually requires a very flexible range of concentrations at the sample preparation. The obtained spectra are simple and the spectral positions are basically not influenced by the chemical state of the samples.…”