Nanoscale bimetallic catalysts: are they really bimetallic?

Guczi, L.; Bazin, Dominique; Schay, Z.; Kovács, Imre

doi:10.1002/sia.1255

Cited by 5 publications

(5 citation statements)

References 17 publications

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“…The Au/Pd system was chosen because of its remarkable. catalytic properties for many fine chemical fabrications, deep hydrogenation reactions and Co oxidation [4]. Figure 1a shows a HA-ADF image of a nanoparticle of AuPd (1:1 in atomic composition) in which surface roughness is observed; that roughness is consistent with the DFT calculation of a similar particle, shown in Fig.…”

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confidence: 73%

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Imaging Au-Pd Nanoparticles with the Aberration-Corrected STEM/TEM

et al. 2006

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The understanding of the way in which matter organizes into clusters with thousands of atoms is one of the most important and challenging problems in catalysis and nanotechnology. When two species of atoms with different radii are involved, the expected packing will be more complicated and a richer spectrum of structures is anticipated, ranging from quasicrystals and amorphous crystals to well-ordered superlattices and core-shell structures [1]. This plethora of structures has been predicted by theoretical calculations and observed by a number of authors [2], and it is one of the most active and fascinating topics in nanotechnology. It has been known for several years that the addition of a second metal into monometallic nanoparticles significantly changes some of their properties, e.g. optical properties, catalytic properties, electronic properties, etc. [3][4][5][6][7]. When two or more different elements compose one nanoparticle, the differences in atomic radii are going to influence the way the atoms accommodate. However, very little is known about the crystal structure of bimetallic nanoparticles in the size regime from 0.5 to 2nm [5]. For bimetallic nanoparticles composed of a noble metal and a transition metal, recent experimental results indicate that an icosahedral phase structure is preferred over the others [6]. In the present work we are conducting a complete study of the structure, size, shape, optical response and catalytic properties of single, bimetallic and multimetallic nanoparticles. We have made a systematic study of nanoparticles of Au, Ag, Pt, Pd and their alloys, which are the most interesting systems because of their catalytic applications. An aberration-corrected JEOL 2200FS-AC (S)TEM (with a CEOS GmbH corrector on the illumination side) [8] was used for high-angle annular dark-field (HA-ADF) imaging of Au-Pd nanoparticles ranging from pure element end members, through mixtures including Au1Pd5 to Au5Pd1. Images of the nanoparticles were compared with appropriate density functional theory (DFT) calculations of model particles. Examples are given below. The Au/Pd system was chosen because of its remarkable. catalytic properties for many fine chemical fabrications, deep hydrogenation reactions and Co oxidation [4]. Figure 1a shows a HA-ADF image of a nanoparticle of AuPd (1:1 in atomic composition) in which surface roughness is observed; that roughness is consistent with the DFT calculation of a similar particle, shown in Fig. 1b. Both particle and calculations were obtained in conditions of rapid cooling similar to the one that is used in real catalysis. We show that we can predict complex surface structures that are active sites for a number of different reactions. Figure 2a shows nanoparticles in the Au1Pd5 system. It is clear that some atomic columns are significantly brighter than adjacent columns. Figure 2b is an intensity trace over the row of atoms as indicated in Fig 2a. A profile over a single (presumed Pd) atom on the carbon film indicated a peak intensity above background of 40...

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confidence: 73%

“…optical properties, catalytic properties, electronic properties, etc. [3][4][5][6][7]. When two or more different elements compose one nanoparticle, the differences in atomic radii are going to influence the way the atoms accommodate.…”

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confidence: 99%

Imaging Au-Pd Nanoparticles with the Aberration-Corrected STEM/TEM

et al. 2006

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“…There have been numerous efforts to synthesize uniform bimetallic particles spanning a range of compositions; however, most of these studies have shown that although it is possible to prepare binary particles with uniform sizes/shapes and specific compositions, it is extremely difficult to control the uniformity on a particle-by-particle basis [4][5][6][7][8][9][10][11][12][13][14][15]. The composition from particle to particle can vary as much as 0-50% mole fraction with further uncertainty regarding whether the particle is of the ''alloy'' or ''core-shell'' type.…”

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confidence: 99%

The growth of Ag–Au bimetallic nanoparticles on TiO2(110)

2004

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“…While not as easily accessible as other techniques, synchrotron-based X-ray techniques are very promising for fulfilling these criteria. For example, X-ray absorption (EXAFS) has been applied successfully to characterize bimetallic catalysts. , …”

Section: Introductionmentioning

confidence: 99%

Study of Supported PtCu and PdAu Bimetallic Nanoparticles Using In-Situ X-ray Tools

et al. 2010

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A combination of two synchrotron X-ray techniques, X-ray absorption spectroscopy (XAS), and pair distribution function analysis (PDF) with complementary Fourier transform infrared (FTIR) spectroscopy measurement, was used to characterize the composition distributions of PdAu and PtCu bimetallic particles after treatment in H 2 or CO and in the presence of these gases. This is the first reported application of PDF to the study of supported bimetallic nanoparticles. We found that XAS was informative in determining the component distribution of an initial sample, but PDF was better suited to following changes in the distribution upon changing the gas environment. Thus, the surface of a PtCu bimetallic particle of about 2.5 nm after treatment in H 2 was found to be enriched in Cu, while the core was bimetallic. There was no evidence of a componentsegregated core-shell structure. Treatment in CO caused enrichment of Pt to the surface layer, with a concomitant migration of Cu to the core. The average particle size remained the same. For the PdAu bimetallic particles, the surface and core compositions were similar after H 2 treatment, and Pd was enriched in the surface after CO treatment. The X-ray results compared favorably to infrared spectroscopy results. The results demonstrated that the two X-ray techniques in combination can generate new information not available with either technique alone or other techniques, about the elemental distribution of bimetallic particles under conditions relevant to catalysis. They could provide new insight into structure-function relationships and time-on-stream behavior of bimetallic catalysts. † Part of the "D. Wayne Goodman Festschrift".

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Nanoscale bimetallic catalysts: are they really bimetallic?

Cited by 5 publications

References 17 publications

Imaging Au-Pd Nanoparticles with the Aberration-Corrected STEM/TEM

Imaging Au-Pd Nanoparticles with the Aberration-Corrected STEM/TEM

The growth of Ag–Au bimetallic nanoparticles on TiO2(110)

Study of Supported PtCu and PdAu Bimetallic Nanoparticles Using In-Situ X-ray Tools

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