Bimetallic Pt–Ag and Pd–Ag nanoparticles

Lahiri, Debdutta; Bunker, Bruce A.; Mishra, Bhoopesh; Zhang, Zhenyuan; Meisel, Dan; Doudna, C. M.; Bertino, Massimo F.; Blum, Frank D.; Tokuhiro, Akira; Chattopadhyay, Soma; Shibata, Tomohiro; Terry, Jeff

doi:10.1063/1.1888043

Cited by 57 publications

(41 citation statements)

References 37 publications

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“…Ag is believed to be present on the surface because XRD measurements do not indicate the formation of a PtAg alloy, consistent with their complete immiscibility in the bulk [48]. Lahiri et al [49] have shown that Pt and Ag do not alloy at the nanoscale (2 nm Pt core particle), but rather form Ag-Pt coreshell nanoparticles. The deposition and growth of Ag adlayers on Pt(111) leads to monolayer confined mixing, i.e.…”

Section: Characterization and Ethylene Hydrogenation Studies Of Pt/sbmentioning

confidence: 86%

Monodisperse platinum nanoparticles of well-defined shape: synthesis, characterization, catalytic properties and future prospects

et al. 2006

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Monodisperse platinum nanoparticles with well-defined faceting have been synthesized by a modified polyol process with the addition of silver ions. Pt nanoparticles are encapsulated in mesoporous silica during in situ hydrothermal growth of the high surface area support. Removal of the surface regulating polymer, poly(vinylpyrrolidone), was achieved using thermal oxidationreduction treatments. Catalysts were active for ethylene hydrogenation after polymer removal. Rates for ethylene hydrogenation decreased in accordance with the amount of Ag retained in the Pt nanoparticles after purification. Ag is most likely present on the Pt particle surface as small clusters. Future prospects for these catalysts for use in low temperature selective hydrogenation reactions are discussed.

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Section: Characterization and Ethylene Hydrogenation Studies Of Pt/sbmentioning

confidence: 86%

Monodisperse platinum nanoparticles of well-defined shape: synthesis, characterization, catalytic properties and future prospects

et al. 2006

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“…The picture of alloying between Pt and Ag is not so clear, and studies have shown that phase diagrams for alloys can change with particle size 43 . In two separate Xray absorption fine structure (XAFS) studies, no alloying was observed for a Pt-Ag catalyst, even for particle sizes down to 2 nm 44,45 . Pt-Ag bimetallic NP systems have produced Pt(core)/Ag(shell) 46 and also Ag(core)/Pt(shell) 47 structures as indicated by UV-Vis spectroscopy combined with modeling based on Mie theory.…”

Section: Ethylene Hydrogenation On Unetched and Etched Pt(shape)/sba-15mentioning

confidence: 99%

Silver Ion Mediated Shape Control of Platinum Nanoparticles: Removal of Silver by Selective Etching Leads to Increased Catalytic Activity

et al. 2008

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2A procedure has been developed for the selective etching of Ag from Pt nanoparticles of well-defined shape, resulting in the formation of elementally-pure Pt cubes, cuboctahedra, or octahedra, with a largest vertex-to-vertex distance of ~ 9.5 nm from Agmodified Pt nanoparticles. A nitric acid etching process was applied Pt nanoparticles supported on mesoporous silica, as well as nanoparticles dispersed in aqueous solution.The characterization of the silica-supported particles by XRD, TEM, and N 2 adsorption measurements demonstrated that the structure of the nanoparticles and the mesoporous support remained conserved during etching in concentrated nitric acid. Both elemental analysis and ethylene hydrogenation indicated etching of Ag is only effective when [HNO 3 ] ≥ 7 M; below this concentration, the removal of Ag is only ~ 10 %. Ethylene hydrogenation activity increased by four orders of magnitude after the etching of Pt octahedra that contained the highest fraction of silver. High-resolution transmission electron microscopy of the unsupported particles after etching demonstrated that etching does not alter the surface structure of the Pt nanoparticles. High [HNO 3 ] led to the decomposition of the capping agent, polyvinylpyrollidone (PVP); infrared spectroscopy confirmed that many decomposition products were present on the surface during etching, including carbon monoxide. and energy dispersive X-ray spectroscopy) indicated Ag was not present in the NPs after removing excess AgCl, it was later found that residual Ag of up to ~ 20 at %, is still present in the NP system (metal NP plus stabilizing polymer). In a subsequent paper, we found that Ag acts as a poison in the hydrogenation of ethylene by Pt and the amount of Ag in the NPs can be directly correlated to the decrease in catalytic activity. This is in agreement with studies of highly dispersed Pt-Ag catalysts on silica gel; in that study, rates of 1-hexene hydrogenation decreased exponentially with increasing Ag content . The dependence of etching on temperature, HNO 3 concentration, and silver particle size (mm-range) is well-documented [24][25][26][27] . The reaction proceeds with the overall stoichiometry at HNO 3 concentrations between 3.8 and 4.9 M:For [HNO 3 ] of 4.9 -7.1 M, the stoichiometry isPlatinum, on the other hand, is resistant to etching by nitric acid, usually being dissolved with aqua regia (70 % concentrated hydrochloric acid and 30 % concentrated nitric acid). Using this difference in reactivity towards nitric acid, we are able to modify the Pt-Ag NPs after synthesis to pure platinum nanoparticles of well-defined shapes.

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“…The referred data are from: solid circles, [15] solid squares, [16] solid prisms, [46] solid triangles, [47] open circles, [48] open triangles, [49] open squares [50] and open prisms [51] (sizes are estimated from the TEM images). [32] All the solid symbols denote the compositions and sizes for the particles that have been alloyed, while all the open symbols represent that for non-alloyed particles.…”

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confidence: 99%

Size‐, Shape‐ and Composition‐Dependent Alloying Ability of Bimetallic Nanoparticles

Xiong

Huang

et al. 2011

ChemPhysChem

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Based on the surface-area-difference model, the formation enthalpies and the formation Gibbs free energies of bimetallic nanoparticles are calculated by considering size and shape effects. Composition-critical size diagrams were graphed for bulk immiscible bimetallic nanoparticles with the developed model. The results reveal that both the formation enthalpy and formation Gibbs free energy decrease with the decrease of particle size. The effect of rising temperature is similar to the diminishing of particle size on reducing the formation Gibbs free energy. Contrary to the positive formation enthalpy of the bulk immiscible system, a negative formation enthalpy is obtained when the particles are smaller than a critical size. With the decrease of size, the alloying process first takes place in the dilute solute regions, then broadens to the dense solute regions and finally, particles with all compositions can be alloyed. The composition-critical size diagram is classified into three regions by the critical size curves with shape factors of 1 and 1.49, that is, the non-alloying region, alloying region and possible alloying region. The model predictions correspond well with experimental evidences and computer simulation results for Cu-Ag, Au-Ni, Ag-Pt and Au-Pt systems.

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Bimetallic Pt–Ag and Pd–Ag nanoparticles

Cited by 57 publications

References 37 publications

Monodisperse platinum nanoparticles of well-defined shape: synthesis, characterization, catalytic properties and future prospects

Monodisperse platinum nanoparticles of well-defined shape: synthesis, characterization, catalytic properties and future prospects

Silver Ion Mediated Shape Control of Platinum Nanoparticles: Removal of Silver by Selective Etching Leads to Increased Catalytic Activity

Size‐, Shape‐ and Composition‐Dependent Alloying Ability of Bimetallic Nanoparticles

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