Bimetallic Palladium−Platinum Dendrimer-Encapsulated Catalysts

Scott, Robert W. J.; Datye, Abhaya K.; Crooks, Richard M.

doi:10.1021/ja034176n

Cited by 320 publications

(263 citation statements)

References 10 publications

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“…Results of the type described here are enabled by the high degree of monodispersity resulting from the dendrimer templating approach to nanoparticle synthesis. We recently discovered that this same templating approach can be used to control the composition 3,20,21 and structure 21 of metal nanoparticles, and therefore we are presently studying the effect of these variables on catalyst performance.…”

Section: Published On Web 03/17/2006mentioning

confidence: 99%

Effect of Pd Nanoparticle Size on the Catalytic Hydrogenation of Allyl Alcohol

et al. 2006

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We report that the rate of hydrogenation of allyl alcohol is a function of the diameter of the Pd nanoparticles (1.3-1.9 nm) used to catalyze the reaction. Furthermore, kinetic data indicate that this effect is electronic in nature for particles having diameters <1.5 nm, but for larger particles it depends primarily on their geometric properties. This is a significant finding, because it represents a particle size effect for hydrogenation over unsupported Pd nanoparticle catalysts in a size range that has not been widely studied.Dendrimer templates have been used to exert a high degree of control over the size, composition, and structure of catalytically active nanoparticles in the <3 nm size range. 1 Because of this, dendrimer-encapsulated nanoparticles (DENs) are well-suited for studying the effect of particle size on catalytic function. 1 We have previously briefly noted a qualitative link between the size of DENs and their catalytic properties. 2,3 This paper represents our first quantitative analysis of the origin of these trends.The procedure used to prepare Pd DEN catalysts has been previously reported. 2 For the experiments reported here, the total moles of Pd used for each hydrogenation reaction was maintained constant for all experiments, but the Pd/dendrimer ratio was varied to yield DENs having different sizes. Specifically, sixth-generation, hydroxyl-terminated polyamidoamine dendrimers (G6-OH) were used to synthesize Pd DENs containing an average of 55, 100, 147, 200, or 250 Pd atoms (G6-OH(Pd n ), where n is the average number of atoms per particle). These particles have measured (by TEM, Figures S1 and S2, Supporting Information) and calculated (in parentheses) diameters of 1.3 (1.2), 1.4 (1.4), 1.5 (1.6), 1.7 (1.8), and 1.9 (1.9) nm, respectively. 4,5 Alkene hydrogenation occurs via the Horiuti-Polanyi mechanism, which involves dissociative adsorption of H 2 onto the catalyst surface, followed by stepwise hydrogenation of the CdC double bond. 6 Here, the rate of hydrogenation of allyl alcohol was determined by measuring hydrogen uptake. 7 Briefly, 20.0 mL of the catalyst solution (3.0 µmol of Pd) was transferred to a Schlenk flask. The system was sealed and purged with H 2 for 10 min and then stirred for an additional 10 min. Allyl alcohol was added, and differential H 2 pressure measurements were obtained every 10 s for 10 min. 7 Turnover frequencies (TOFs, mol H 2 /mol active siteh) were determined from the slope of plots of turnover (mol H 2 /mol catalyst) versus time. Figure 1a shows that the rate of hydrogen consumption increases significantly as the measured particle diameter increases. However, this relationship does not correlate to a simple change in the total number of surface Pd atoms. This is because the total amount of Pd used in all these experiments is fixed, and therefore the number of catalyst particles present is smaller for the larger particles. This point is illustrated in Figure 1b. Here, the total number of Pd atoms present at particular locations on cuboctahedra are plotte...

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Section: Published On Web 03/17/2006mentioning

confidence: 99%

Effect of Pd Nanoparticle Size on the Catalytic Hydrogenation of Allyl Alcohol

et al. 2006

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“…Additionally, the gas-phase catalytic activity for CO oxidation is higher for the bimetallic catalysts than that for the corresponding Pd-only and Au-only monometallics. 2,3 It has previously been shown that 1-3-nm diameter alloy and core-shell bimetallic PdPt, 4,5 PdAu, 6 PdRh, 7 and AuAg 8 nanoparticles can be synthesized within dendrimer templates. 1 The resulting materials are characterized by a high degree of uniformity in size, structure, and elemental composition, and in some cases they have enhanced solution-phase catalytic activities compared to the analogous monometallic materials.…”

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“…10 For example, G4-NH 2 (Pd 27.5 Au 27.5 ) was synthesized as follows: 0.0924 g of a 14.2 wt % solution of G4-NH 2 in MeOH and 20 µL of 0.3 M HCl were added to 1 L of 99% MeOH, followed by 255 µL of a 0.10 M K 2 PdCl 4 solution. The HCl was added to prevent crosslinking of the G4-NH 2 dendrimer by Pd 2+ (Pd 2+ is used to designate PdCl 4 2-and all its hydrolysis products). 19 After being stirred for 10 min, 255 µL of a 0.10 M HAuCl 4 solution was added.…”

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Titania-Supported PdAu Bimetallic Catalysts Prepared from Dendrimer-Encapsulated Nanoparticle Precursors

et al. 2005

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In this communication, we report the synthesis and characterization of TiO 2 -supported PdAu bimetallic nanoparticle catalysts prepared using dendrimer-encapsulated nanoparticles (DENs). 1 The key result is that the compositional fidelity of the original bimetallic DENs, and to some extent their size, is retained in the supported catalyst after removal of the dendrimer template by calcination at 500°C. Additionally, the gas-phase catalytic activity for CO oxidation is higher for the bimetallic catalysts than that for the corresponding Pd-only and Au-only monometallics. 2,3 It has previously been shown that 1-3-nm diameter alloy and core-shell bimetallic PdPt, 4,5 PdAu, 6 PdRh, 7 and AuAg 8 nanoparticles can be synthesized within dendrimer templates. 1 The resulting materials are characterized by a high degree of uniformity in size, structure, and elemental composition, and in some cases they have enhanced solution-phase catalytic activities compared to the analogous monometallic materials. [4][5][6][7] There are also a few examples of dendrimer/nanoparticle composites of various sorts being used to prepare supported Pt, 9 Pd, 10 Au, 10 CuO, 11 and Fe 2 O 3 nanoparticles. 12 In some cases, these were shown to be catalytically active. 9,12 To the best of our knowledge, however, there is only one very recent example of a heterogeneous catalyst prepared from a bimetallic DEN precursor. 13 The DEN approach to bimetallic nanoparticles is potentially simpler than many alternative methods. For example, organometallic cluster precursors containing two different metals have been used to prepare supported bimetallic catalysts, but continuous variation of the elemental composition of the resulting particles requires large precursor libraries. [14][15][16] Most other methods for preparing supported bimetallic nanoparticles in the <5-nm size range lead to phase segregation of the two metals and thus poor control over the composition of individual particles, 17 although limited success has been achieved using surfactant-stabilized nanoparticles. 18 We prepared DENs consisting of PdAu alloys within fourthgeneration, amine-terminated poly(amidoamine) (PAMAM) dendrimers (G4-NH 2 (Pd n Au 55-n )) by co-complexation of the two corresponding metal salts followed by chemical reduction of the dendrimer/metal-ion composite. 6 The synthesis was carried out in a 99% methanol solution using a procedure we previously reported for preparing DENs within amine-terminated dendrimers. 10 For example, G4-NH 2 (Pd 27.5 Au 27.5 ) was synthesized as follows: 0.0924 g of a 14.2 wt % solution of G4-NH 2 in MeOH and 20 µL of 0.3 M HCl were added to 1 L of 99% MeOH, followed by 255 µL of a 0.10 M K 2 PdCl 4 solution. The HCl was added to prevent crosslinking of the G4-NH 2 dendrimer by Pd 2+ (Pd 2+ is used to designate PdCl 4 2-and all its hydrolysis products). 19 After being stirred for 10 min, 255 µL of a 0.10 M HAuCl 4 solution was added. After being stirred for an additional 2 min, 1 mL of a 1.0 M NaBH 4 solution was added (20× molar excess). The s...

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“…In the nanorods, with a cleaner metallic surface available to perform the reaction and a less effective particle protection, the catalytic activity is better. The catalytic activity measured for both types of BSAfunctionalized nanocrystals was greater than the activity reported for dendrimer-encapsulated platinum nanocrystals [TOF = 50 mol H2/(mol Pt 9 h)] (Scott et al 2003). Platinum particles studied in this work remain stable for months.…”

Section: Triangular Face Atomsmentioning

confidence: 54%

Influence of morphology in the catalytic activity of bioconjugated platinum nanostructures

et al. 2010

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Platinum nanoparticles stabilized by a protein, bovine serum albumin, have been synthesized successfully with two different morphologies such as cuboctahedra and nanorods. They have been characterized by the use of different techniques such as XPS, PCS, TEM, and STEM-HAADF. These nanoparticles have been applied as catalysts for the hydrogenation of allyl alcohol in an aqueous solution. A key finding of this article is the superior catalytic activity of the nanorods compared to the cuboctahedral particles. This difference in the catalytic activity was justified because of the variation in the amount of protein to stabilize the nanorods. A model for the nanorods and equations that describe the proportion of atoms in the different sites of the particle (face, vertex, edge, or interior) is used to calculate the percentage of atoms that are located on the nanorod surface. The stability of these particles as catalysts was also studied. The results showed that Pt nanorods and Pt cuboctahedra particles were degraded after 24 h of reaction.

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Bimetallic Palladium−Platinum Dendrimer-Encapsulated Catalysts

Cited by 320 publications

References 10 publications

Effect of Pd Nanoparticle Size on the Catalytic Hydrogenation of Allyl Alcohol

Effect of Pd Nanoparticle Size on the Catalytic Hydrogenation of Allyl Alcohol

Titania-Supported PdAu Bimetallic Catalysts Prepared from Dendrimer-Encapsulated Nanoparticle Precursors

Influence of morphology in the catalytic activity of bioconjugated platinum nanostructures

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