Isolated Effects of Surface Ligand Density on the Catalytic Activity and Selectivity of Palladium Nanoparticles

Vargas, Kevin M.; San, Khin Aye; Shon, Y.

doi:10.1021/acsanm.9b01696

Cited by 10 publications

(11 citation statements)

References 47 publications

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“…It is worthwhile to note that the steric hindrance of the ligand is highly related to the polarity of the solvent, the chain length of the ligand, and the bonding conformation of the ligand. − Mechanistically, the construction of thiolate ligands varies upon the selection of different types of solvents (polar or nonpolar), leading to different available spaces for reagent contact. , The different chain lengths of ligands also change the local density of catalytic active sites (i.e., surface coverage of ligands), altering the selectivity of the catalytic reaction, which will be discussed in detail in the section on the following topic. − The different bonding conformations of ligands somehow change the interfacial microenvironment of the metal–ligand interface (or surface coverage of ligands) and can induce very different styrene hydrogenation activities …”

Section: The Beneficial Effects Of Ligands For Nanocatalysismentioning

confidence: 99%

The Critical Impacts of Ligands on Heterogeneous Nanocatalysis: A Review

2021

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Ligand utilization is a necessary and powerful technique for the colloidal synthesis of nanoparticles (NPs) with controllable sizes and regulated morphologies. For catalysis applications, it is commonly believed that surface ligands on metal NPs block the active catalytic sites and reduce the catalytic activity. Nevertheless, since 2010, an increasing number of research groups have demonstrated the unexpected benefits of ligands that improve catalytic activity and/or selectivity. These benefits can be ascribed to the construction of an inorganic−organic interface, through which a series of factors, such as steric, electronic, and solubility effects, can be utilized to produce favorable changes to the interfacial environment. Considering the tremendous number of developments in this emerging research field, it is necessary to compile a comprehensive and systematic overview of recent advances. In this Review, we summarize the critical impacts of ligands on heterogeneous nanocatalysis. First, we introduce the vital roles of ligands in colloid syntheses for controllable sizes and regulated shapes. Second, the detrimental effects of ligands for nanocatalysis are described on the basis of traditional views. Third, a series of strategies for ligand removal are reviewed and compared. Fourth, on the basis of research that has been conducted in the past decade, the three main beneficial ligand effects (steric, electronic, and solubility) on heterogeneous nanocatalysis are classified and discussed. For each effect, the possible corresponding beneficial mechanism is presented, and typical examples are provided. Recent advances regarding density functional theory (DFT) calculations and the regulation of ligand surface coverage have been dedicated to explaining the ligand-promotion mechanism in nanocatalysis and searching for optimal nanocatalysts. Fifth, the stabilities of cutting-edge ligand-capped nanocatalysts before and after catalytic reactions are discussed. Finally, we highlight the remaining challenges and propose future perspectives. Although much progress has been achieved, the impacts of ligands on the catalytic activities of nanocatalysts are multifaceted and still debatable. We hope this Review will deepen readers' understanding of the actual impacts ligands have on heterogeneous catalysis.

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Section: The Beneficial Effects Of Ligands For Nanocatalysismentioning

confidence: 99%

The Critical Impacts of Ligands on Heterogeneous Nanocatalysis: A Review

2021

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“…This condition was also used for the synthesis of other PdNPs using constitutional isomers of pentyl thiosulfate. In addition to achieving the necessary stability in organic solvents, the surface ligand density should be similar between the nanoparticles to minimize variability on catalytic activity due to the surface density (Vargas et al, 2019 ). Since the constitutional isomers of ligands are used for surface capping, the direct comparison of organic weight fraction to metal fraction would be sufficient as long as the average core sizes of nanoparticles are comparable.…”

Section: Resultsmentioning

confidence: 99%

“…Our research group utilizes the thiosulfate method to assemble alkanethiolate ligands onto metal nanoparticles (Gavia et al, 2014 ; San et al, 2017 ; Vargas et al, 2019 ). The subsequent cleavage of the ionic sulfite moiety after surface adsorption and the presence of hydrophobic monolayer delaying the further passivation of ionic alkyl thiosulfate ligands allow controlling the ligand density on palladium nanoparticles (PdNPs) as described in the previous publications.…”

Section: Introductionmentioning

confidence: 99%

“…These straight chain alkanethiolate-capped PdNPs were shown to selectively catalyze the isomerization of allylic alcohols to carbonyl compounds and the mono-hydrogenation of isolated, conjugated, and cumulated dienes in the presence of H 2 (Zhu and Shon, 2015 ; Maung et al, 2017 ; Chen and Shon, 2018 ). The surface ligand density of alkanethiolate on PdNPs with same average core size was also found to have a great influence on both the activity and selectivity of PdNPs (Vargas et al, 2019 ). These catalytic reactions take place in homogeneous conditions that normally promote catalytic efficiency and selectivity and complete under the mild condition of room temperature and atmospheric pressure.…”

Section: Introductionmentioning

confidence: 99%

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Proximity Effects of Methyl Group on Ligand Steric Interactions and Colloidal Stability of Palladium Nanoparticles

2020

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Metal nanoparticle catalysts functionalized with small, well-defined organic ligands are important because such systems can provide a spatial control in the catalyst-substrate interactions. This article describes the synthesis, stability, and catalytic property evaluations of four different Pd nanoparticles capped with constitutional isomers of pentanethiolate ligands that have either a straight chain or an alkyl chain with one methyl group at different locations (α, β, or γ from the surface-bound sulfur). The structure and composition analyses of Pd nanoparticles confirm that they have similar average core sizes and organic ligand contents. The presence of methyl group at α position is found to lower the capping ability of short ligands and thus make Pd nanoparticles to lose their colloidal stability during the catalytic reactions. The overall activity and selectivity for hydrogenation and isomerization of pentene and allylbenzene derivatives are investigated for each combination of ligand and substrate. Catalysis results indicate that steric interactions between the ligands on the metal catalyst surface and the alkene substrates are a factor in controlling the activity of Pd nanoparticles. In particular, Pd nanoparticles capped with pentanethiolate isomer having a methyl group at α position exhibit poor and inconsistent catalytic activity due to its low colloidal stability. The presence of a methyl group at β position mildly interferes the adsorption of alkene group on the nanoparticle surface resulting in lower conversion yields. Interestingly, a methyl group at γ position only has a minimal effect on the catalytic property of Pd nanoparticles exhibiting similar catalysis results with Pd nanoparticles capped with straight chain pentanethiolate ligands. This indicates the proximity of steric group at the reactive site controls the nanoparticle activity for surface oriented reactions, such as hydrogenation and isomerization of alkenes in addition to their colloidal stability.

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“…Examples for the latter case present the quantification of elements such as sulfur present in certain dyes or cleavable probes [64,89,127], or the use of metal ion containing reporters [173]. ICP-OES has been used to quantify FG on various NM such as carbon-based NM, noble metal NP, polymer beads, and lanthanide-based NP [127,[174][175][176][177]. ICP-MS has been frequently used to quantify FGbearing ligands on gold NP [169,173,[178][179][180], but has also been applied to quantify FG and ligands on other NM such as silica NP, polymeric beads, and semiconductor QD [126,Fig.…”

Section: Mass Spectrometry and Atomic Spectroscopymentioning

confidence: 99%

Analyzing the surface of functional nanomaterials—how to quantify the total and derivatizable number of functional groups and ligands

et al. 2021

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Functional nanomaterials (NM) of different size, shape, chemical composition, and surface chemistry are of increasing relevance for many key technologies of the twenty-first century. This includes polymer and silica or silica-coated nanoparticles (NP) with covalently bound surface groups, semiconductor quantum dots (QD), metal and metal oxide NP, and lanthanide-based NP with coordinatively or electrostatically bound ligands, as well as surface-coated nanostructures like micellar encapsulated NP. The surface chemistry can significantly affect the physicochemical properties of NM, their charge, their processability and performance, as well as their impact on human health and the environment. Thus, analytical methods for the characterization of NM surface chemistry regarding chemical identification, quantification, and accessibility of functional groups (FG) and surface ligands bearing such FG are of increasing importance for quality control of NM synthesis up to nanosafety. Here, we provide an overview of analytical methods for FG analysis and quantification with special emphasis on bioanalytically relevant FG broadly utilized for the covalent attachment of biomolecules like proteins, peptides, and oligonucleotides and address method- and material-related challenges and limitations. Analytical techniques reviewed include electrochemical titration methods, optical assays, nuclear magnetic resonance and vibrational spectroscopy, as well as X-ray based and thermal analysis methods, covering the last 5–10 years. Criteria for method classification and evaluation include the need for a signal-generating label, provision of either the total or derivatizable number of FG, need for expensive instrumentation, and suitability for process and production control during NM synthesis and functionalization. Graphical abstract

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Isolated Effects of Surface Ligand Density on the Catalytic Activity and Selectivity of Palladium Nanoparticles

Cited by 10 publications

References 47 publications

The Critical Impacts of Ligands on Heterogeneous Nanocatalysis: A Review

The Critical Impacts of Ligands on Heterogeneous Nanocatalysis: A Review

Proximity Effects of Methyl Group on Ligand Steric Interactions and Colloidal Stability of Palladium Nanoparticles

Analyzing the surface of functional nanomaterials—how to quantify the total and derivatizable number of functional groups and ligands

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