Bimetallic Dendrimer-encapsulated Nanoparticle Catalysts

Wang, Hui; Rempel, Garry L.

doi:10.1080/15583724.2015.1110167

Cited by 22 publications

(12 citation statements)

References 64 publications

(97 reference statements)

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“…One method that overcomes some of the synthetic limitations mentioned heretofore, especially those associated with ligand removal, is called dendrimer encapsulation. Dendrimer-encapsulated nanoparticles (DENs) are synthesized by taking advantage of highly dendritic polymers, or dendrimers, as synthetic templates for NP formation. ,, The typical size of DENs is in the range of just a few atoms to ∼300 atoms, making them very well suited for comparison to theory. ,− Commercially available poly(amidoamine) (PAMAM) dendrimers are the most commonly employed for the synthesis of DENs; however, the use of other dendrimers, − such as poly(propyleneimine) (PPI), has been reported …”

Section: Tools and Techniques For Comparing Experiments To Theorymentioning

confidence: 99%

“…In a basic synthesis of DENs, a metal salt precursor is added to a solution of dendrimers and subsequently reduced with BH 4 – at room temperature (Figure ). This synthetic method leads to one zerovalent NP per dendrimer while allowing for good synthetic control over both size and composition. , In addition to monometallic DENs, alloy and core@shell DENs can also be prepared. − For example, Au M ( M = Pd, Pt, Rh) alloys, ,, as well as PdAu@Pt alloy-core@shell DENs, , have recently been successfully synthesized and employed as electrocatalysts. While a wide variety of DEN structures can be prepared, enhanced atomic diffusion in such small NPs can sometimes lead to structural and compositional rearrangements during, or even before, electrocatalysis. , …”

Section: Tools and Techniques For Comparing Experiments To Theorymentioning

confidence: 99%

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Well-Defined Nanoparticle Electrocatalysts for the Refinement of Theory

et al. 2019

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The relationship between experiment and theory in electrocatalysis is one of profound importance. Until fairly recently, the principal role of theory in this field was interpreting experimental results. Over the course of the past decade (roughly the period covered by this review), however, that has begun to change, with theory now frequently leading the design of electrocatalytic materials. Though rewarding, this has not been a particularly easy union. For one thing, experimentalists and theorists have to come to grips with the fact that they rely on different models. Theorists make predictions based on individual, perfect structural models, while experimentalists work with more complex and heterogeneous ensembles of electrocatalysts. As discussed in this review, computational capabilities have improved in recent years, so that theory is better represented by the structures that experimentalists are able to prepare. Likewise, synthetic chemists are able to make ever more complex electrocatalysts with high levels of control, which provide a more extensive palette of materials for testing theory. The goal of this review is to highlight research from the last ∼10 years that focuses on carefully controlled electrocatalytic experiments which, in combination with theoretical predictions, bring us closer to bridging the gap between real catalysts and computational models.

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Section: Tools and Techniques For Comparing Experiments To Theorymentioning

confidence: 99%

Section: Tools and Techniques For Comparing Experiments To Theorymentioning

confidence: 99%

Well-Defined Nanoparticle Electrocatalysts for the Refinement of Theory

et al. 2019

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“…Catalysis with other elements, particularly the more affordable and abundant first-row transition metals, like Fe, Co, and Ni, has few precedents. 36 These metals are prone to aggregation due to their ferromagnetism in the metallic state generated during the synthesis of clusters. Furthermore, they are vulnerable to oxidation when exposed to air, which complicates the formation of clusters.…”

Section: ■ Outlookmentioning

confidence: 99%

Supported Dendrimer-Encapsulated Metal Clusters: Toward Heterogenizing Homogeneous Catalysts

Zhukhovitskiy²,

Deraedt

et al. 2017

Acc. Chem. Res.

136

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Recyclable catalysts, especially those that display selective reactivity, are vital for the development of sustainable chemical processes. Among available catalyst platforms, heterogeneous catalysts are particularly well-disposed toward separation from the reaction mixture via filtration methods, which renders them readily recyclable. Furthermore, heterogeneous catalysts offer numerous handles-some without homogeneous analogues-for performance and selectivity optimization. These handles include nanoparticle size, pore profile of porous supports, surface ligands and interface with oxide supports, and flow rate through a solid catalyst bed. Despite these available handles, however, conventional heterogeneous catalysts are themselves often structurally heterogeneous compared to homogeneous catalysts, which complicates efforts to optimize and expand the scope of their reactivity and selectivity. Ongoing efforts in our laboratories are aimed to address the above challenge by heterogenizing homogeneous catalysts, which can be defined as the modification of homogeneous catalysts to render them in a separable (solid) phase from the starting materials and products. Specifically, we grow the small nanoclusters in dendrimers, a class of uniform polymers with the connectivity of fractal trees and generally radial symmetry. Thanks to their dense multivalency, shape persistence, and structural uniformity, dendrimers have proven to be versatile scaffolds for the synthesis and stabilization of small nanoclusters. Then these dendrimer-encapsulated metal clusters (DEMCs) are adsorbed onto mesoporous silica. Through this method, we have achieved selective transformations that had been challenging to accomplish in a heterogeneous setting, e.g., π-bond activation and aldol reactions. Extensive investigation into the catalytic systems under reaction conditions allowed us to correlate the structural features (e.g., oxidation states) of the catalysts and their activity. Moreover, we have demonstrated that supported DEMCs are also excellent catalysts for typical heterogeneous reactions, including hydrogenation and alkane isomerization. Critically, these investigations also confirmed that the supported DEMCs are heterogeneous and stable against leaching. Catalysts optimization is achieved through the modulation of various parameters. The clusters are oxidized (e.g., with PhICl) or reduced (e.g., with H) in situ. Changing the dendrimer properties (e.g., generation, terminal functional groups) is analogous to ligand modification in homogeneous catalysts, which affect both catalytic activity and selectivity. Similarly, pore size of the support is another factor in determining product distribution. In a flow reactor, the flow rate is adjusted to control the residence time of the starting material and intermediates, and thus the final product selectivity. Our approach to heterogeneous catalysis affords various advantages: (1) the catalyst system can tap into the reactivity typical to homogeneous catalysts, which conventional heterogeneous cata...

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“…Various alloy or core–shell nanoparticles have been used as catalysts. One of the most significant advantages of the dendrimer template for multimetallic clusters is controllability of the ratio of metals in one particle. − Because the nanoparticles were obtained from the assembled metal ions or salts in the dendrimer structure, the content ratios can be regulated in a manner similar to metal complexes (Figure ).…”

Section: Multimetallic Nanoparticles In a Dendrimermentioning

confidence: 99%

New Horizon of Nanoparticle and Cluster Catalysis with Dendrimers

et al. 2019

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Among various approaches synthesizing metal nanoparticles and tiny clusters, a template method using dendrimers has significant advantages over other chemical approaches with respect to their synthetic precision and the scalability. A dendrimer of polydentate ligands assembles metal ions or salts into the interior allowing production of metal nanoparticles in the dendrimer. The dendrimer-encapsulated nanoparticles (DENs) exhibit unique and remarkable catalytic properties depending on the size and elemental formula. Recent advances in dendrimer chemistry even enabled the atom precise synthesis of subnanometer metal clusters that have been impossible to prepare by wet chemical methods. In addition, not only for the synthesis of metal nanoparticles and clusters, the dendrimer itself can also provide the modulation of activity and selectivity in the catalysis. In this review, we summarized the most relevant research in which the dendrimer was employed as the template, modulator, or stabilizer for nanoparticle synthesis for catalytic applications.

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Bimetallic Dendrimer-encapsulated Nanoparticle Catalysts

Cited by 22 publications

References 64 publications

Well-Defined Nanoparticle Electrocatalysts for the Refinement of Theory

Well-Defined Nanoparticle Electrocatalysts for the Refinement of Theory

Supported Dendrimer-Encapsulated Metal Clusters: Toward Heterogenizing Homogeneous Catalysts

New Horizon of Nanoparticle and Cluster Catalysis with Dendrimers

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