Decomposition and Activation of Pt-Dendrimer Nanocomposites on a Silica Support

Deutsch, D. Samuel; Lafaye, Gwendoline; Liu, Dongxia; Chandler, Bert D.; Williams, Christopher T.; Amiridis, Michael D.

doi:10.1023/b:catl.0000038575.79498.c3

Cited by 69 publications

(110 citation statements)

References 14 publications

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“…Both of these values are consistent with studies of other supported Pt catalysts prepared from DENs and with traditionally prepared Pt catalysts. 27,28,31 All of the bimetallic catalyst spectra ( Figure 1) were red-shifted 10-15 cm -1 from the high-coverage value. Infrared spectra attributable to CO bound to Cu sites (ν CO between 2180 and 2100 cm -1 ) were not observed, indicating that surface Cu is present as Cu 0 (vide infra).…”

Section: Resultsmentioning

confidence: 98%

“…Our study is consistent with studies from other labs in that UVvis spectra of mixtures of PtCl 4 2-and PAMAM dendrimers cease to change after approximately 2 days. 21,28,41,42 However, detailed 195 Pt NMR studies by Murphy and co-workers indicate that as many as 10 days may be required to equilibrate the various aqueous Pt(II) species with dendrimer amine groups. 41 Our current results are also consistent with Ploehn's studies, which indicate that, during borohydride reduction, Pt species are particularly mobile and can escape dendrimer interiors.…”

Section: Resultsmentioning

confidence: 99%

“…18,26 In the absence of a solvent, however, supported intact DENs are inactive catalysts and do not bind CO. After being dried, the organic dendrimer apparently collapses onto the nanoparticle, poisoning the metal surface. [26][27][28] Because the amide architecture is relatively unstable at elevated temperatures, 29,30 DENs can be "activated" by heating under oxidizing and/or reducing atmospheres to remove the organic template. 27 Provided activation temperatures are moderate (ca.…”

Section: Introductionmentioning

confidence: 99%

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Tuning Supported Catalyst Reactivity with Dendrimer-Templated Pt−Cu Nanoparticles

2006

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The effects of particle composition on heterogeneous catalysis were studied using dendrimer-encapsulated nanoparticles (DENs) as precursors to supported Pt-Cu catalysts. Bimetallic Pt-Cu DENs with varying Pt/Cu ratios were prepared in an anaerobic aqueous solution and deposited onto a high-purity commercial alumina support. The dendrimer template was then thermally removed to yield supported nanoparticle catalysts, which were studied with toluene hydrogenation and CO oxidation catalysis as well as infrared spectroscopy of adsorbed CO. Incorporating Cu into Pt nanoparticles had opposite effects on the two test reactions. Cu acted as a mild promoter for CO oxidation catalysis, and the promoting effect was independent of the amount of Cu present. Conversely, Cu acted as a strong poison for toluene hydrogenation catalysis, and the normalized rate tracked inversely with Cu content. Infrared spectroscopy of the supported nanoparticles indicated that electronic effects (electron donation from Cu to Pt) were minimal for these materials. Consequently, the catalysis results are interpreted in terms of potential structural differences as a function of Cu incorporation and reaction conditions. IntroductionHighly dispersed supported metal nanoparticle catalysts are an important class of industrial materials, as one-third of material U. S. gross national product involves a catalytic process somewhere in the production chain. 1 State of the art heterogeneous catalysts often contain dopant metals, which are incorporated to promote a desired reaction, prevent undesirable side reactions, or enhance catalyst longevity. 2,3 Traditional preparative routes involve impregnating metal salts onto high-surfacearea supports, followed by various thermal activation steps. 3 Most important industrial supports can also be employed as separation media; consequently, chromatographic separation of salt precursors as they pass through the support pore structure is unavoidable. Further, nanoparticle preparation via traditional routes depends on the surface (and even gas phase) mobility of the species present during the thermal treatments. 4,5 These processes vary widely for different metals and are poorly understood, at best. 4,5 Consequently, bimetallic materials prepared by such methods are often complicated, have significant compositional inhomogenaity from one particle to the next, and are difficult to characterize.Recent advances in computational methods are beginning to shed light onto the fundamental properties of bimetallic catalyst systems, and predictive models are beginning to emerge. [6][7][8][9] The potential to controllably tune catalyst properties through the nanoscale design of bimetallic nanoparticles is becoming apparent, and designed bimetallic catalysts with novel behavior for important reactions already appear in the recent literature. [10][11][12] However, the utilization of traditional preparative techniques and the complicated materials that arise from these methods remain a significant hurdle to studying new catalysts, eva...

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Tuning Supported Catalyst Reactivity with Dendrimer-Templated Pt−Cu Nanoparticles

2006

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“…However, as will be discussed below, the dendrimer was shown to be stable on the titania. The bands associated with various dendrimer functional groups were analyzed via literature values (Deutsch et al 2004(Deutsch et al , 2007Ye et al 2004). The respective bands at 2,972, 2,921, and 2,849 cm -1 match asymmetric C-H methyl stretching, asymmetric C-H methylene stretching, and symmetric C-H methylene stretching.…”

Section: Batch Metal Ion Remediation Studies By Immobilized Dendrimersmentioning

confidence: 99%

Metal ion remediation by polyamidoamine dendrimers: a comparison of metal ion, oxidation state, and titania immobilization

Castillo

Barakat

Ramadan

et al. 2013

Int. J. Environ. Sci. Technol.

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The exceptional ability of dendrimers to coordinate metal ions yields the potential for many applications including wastewater remediation, which is the focus of this study. Here, the comparison of metal ion removal rate from simulated wastewater by generation 4 dendrimers with external hydroxyl functional groups (G4-OH) is evaluated for Ni 2? , Fe 2? , and Fe 3? ions. Ni 2? to amine complexation occurred more rapidly than Fe 3? , which was more rapid than Fe 2? complexation. These results indicate that both charge density and d-electron configuration are important toward the chelation rate. The impact of both factors is discussed in light of existing models in which precursor aquation rates have been proposed as a key intermediate step. Additionally, the application of the dendrimers as chelation agents is further advanced by immobilizing the dendrimer to titania and re-evaluating its chelation ability for Ni 2? removal. The dendrimer immobilization decreased the pseudo-first-order rate coefficient for Ni 2? -amine complexation at a pH of 7 by a factor of 7.5. This result is significant as it suggests that mass transfer becomes important following immobilization of the dendrimer to titania.

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“…Several research groups have prepared dendrimer-metal nanocomposites [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The internal tertiary nitrogens of poly(amido amine) (PAMAM) dendrimers are well suited to the formation of complexes with transition metal and noble metal ions at the appropriate pH.…”

Section: Introductionmentioning

confidence: 99%

Cobalt–poly(amido amine) superparamagnetic nanocomposites

2008

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Metallic cobalt-dendrimer nanocomposites were prepared using generation 5 Poly(amido amine) dendrimers with primary amino termini. Cobalt loading of ~38 atoms per dendrimer was determined by atomic absorption spectrophotometry. Magnetic properties of the cobalt-dendrimer nanocomposites were investigated across the temperature range from 2-300 K by SQUID magnetometry. Magnetization as a function of temperature and applied field strength was studied in zero field cooled samples. Magnetization-demagnetization curves (hysteresis loops) were also acquired at temperatures between 10 -300 K. These results clearly indicate superparamagnetism for the nanocomposites with a characteristic blocking temperature of ~50 K.

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Decomposition and Activation of Pt-Dendrimer Nanocomposites on a Silica Support

Cited by 69 publications

References 14 publications

Tuning Supported Catalyst Reactivity with Dendrimer-Templated Pt−Cu Nanoparticles

Tuning Supported Catalyst Reactivity with Dendrimer-Templated Pt−Cu Nanoparticles

Metal ion remediation by polyamidoamine dendrimers: a comparison of metal ion, oxidation state, and titania immobilization

Cobalt–poly(amido amine) superparamagnetic nanocomposites

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