Pd Clusters Research Articles

Isomorphous Substitution of Organic Cage Crystal by Pd Nanoclusters for Selective Hydrogenation.

For supporting active metal, the cavity confinement and mass transfer facilitation lie not in one sack, a trade-off between high activity and good stability of the catalyst is present. Porous organic cages (POCs) are expected to break the trade-off when metal particles are properly loaded. Herein, three organic cages (CC3, RCC3, and FT-RCC3) are employed to support Pd nanoclusters for catalytic hydrogenation. Subnanometer Pd clusters locate differently in different cage frameworks by using the same reverse double-solvents approach. Compared with those encapsulated in the intrinsic cavity of RCC3 and anchored on the outer surface of CC3, the Pd nanoclusters orderly assembled in FT-RCC3 crystal via isomorphous substitution exhibit superior activity, high selectivity, and good stability for semi-hydrogenation of phenylacetylene. Isomorphous substitution of FT-RCC3 crystal by Pd nanoclusters is originated from high crystallization capacity of FT-RCC3 and specific interaction of each Pd nanocluster with four cage windows. Both confinement function and H2 accumulation capacity of FT-RCC3 are fully utilized to support active Pd nanoclusters for efficient selective hydrogenation. The present results provide a new perspective to the heterogeneous catalysis field in terms of crystalizing metal nanoclusters in POC framework and outside the cage for making the best use of both parts.

Unraveling the structural, electronic and magnetic properties of Mn1Pd n-1, Mn 2Pd n-2 and Pd n(n=13) clusters

This work presents a systematic study of the geometric, electronic and magnetic properties of Pd clusters pristine and mono- and bi[1]doped with Mn: Pdn, Pdn−1Mn, Pdn−2Mn2 where n ≤13. We have used the density functional formalism with the spin polarized generalized gradient approximation. From the variety of possible structures with thirteen atoms, we found the icosahedral configuration to be the most stable as compared to the hexagonal, cub-octahedral and buckled bi-planar. The change in magnetic behavior of Pd clusters after doping with Mn has been observed. This communication is an attempt to understand that behaviour.

Carbon Monoxide Oxidation on Ceria-Supported Nanoclusters.

Periodic density functional theory is used to evaluate the minimum energy pathways of CO oxidation on cerium oxide-supported platinum and palladium nanoclusters (Pt/CeO2 and Pd/CeO2). For Pt/CeO2, the oxidation process involves the participation of lattice oxygen from CeO2 at the boundary sites of the cluster-ceria interface, which exhibits an exceptionally low energy barrier. Conversely, on Pd/CeO2, oxidation predominantly occurs through oxygen species bound to the Pd cluster. Experimental analysis using the temperature-programmed reduction of the oxidized Pd/CeO2 catalyst reveals a lower CO oxidation temperature compared to Pt/CeO2. This observation aligns with the anticipated decrease in the energy barrier for CO oxidation due to the oxygen coverage of the Pd cluster.

C2H2 semi-hydrogenation over Pdn/TiO2 and PdnCO/TiO2 catalysts: Probing into the roles of Pd cluster size and pre-adsorbed CO in tuning catalytic performance

The size effect of Pd catalyst and CO as a selective accelerator in C2H2 semi-hydrogenation over Pd catalyst are two main factors to affect catalytic performance. In this work, density functional theory calculations were used to unravel the roles of Pd cluster size and introduced CO over the anatase TiO2 supported Pdn (n = 2, 3, 4, 7, 13) clusters in tuning catalytic performance of C2H2 semi-hydrogenation. The results show that as the increasing of Pdn cluster size over Pdn/TiO2 catalysts, C2H4 selectivity generally presents a volcanic-type curve, and the activity of C2H4 and green oil presents an inverted volcanic-type curve. Compared with Pdn/TiO2 catalysts, the introduction of CO greatly improves C2H4 selectivity over Pd2/TiO2 and Pd3/TiO2 catalysts, enhances C2H4 formation activity over Pdn/TiO2 (n = 3, 4, 7, 13), and decreases green oil production over Pd2/TiO2 and Pd13/TiO2 catalysts. Meanwhile, the activation free energy of C2H4 hydrogenation and C2H3 coupling reaction can be used as the evaluate index to quantitatively predict the selectivity of C2H4 and green oil, respectively. The different geometric and electronic effects induced by the introduction of CO could tune catalytic performance. The screened Pd4/TiO2 and Pd2CO/TiO2 catalysts are the most suitable catalysts in the Pdn/TiO2 and PdnCO/TiO2 catalysts, respectively. The relationship of Pdn cluster size and CO introduction with C2H4 selectivity and formation activity would provide valuable structural clue for the construction of C2H2 semi-hydrogenation catalyst with highly catalytic performance.

Unveiling Static and Dynamic Structures of Pd Clusters Influenced by Al2O3 Surfaces: DFT and AIMD Studies

Unveiling Static and Dynamic Structures of Pd Clusters Influenced by Al₂O₃ Surfaces: DFT and AIMD Studies

Facet-engineered TiO2 drives photocatalytic activity and stability of supported noble metal clusters during H2 evolution

Metal clusters supported on TiO2 are widely used in many photocatalytic applications, including pollution control and production of solar fuels. Besides high photoactivity, stability during the photoreaction is another essential quality of high-performance photocatalysts, however systematic studies on this attribute are absent for metal clusters supported on TiO2. Here we have studied, both experimentally and with first-principles simulation methods, the stability of Pt, Pd and Au clusters prepared by ball milling on nanoshaped anatase nanoparticles preferentially exposing {001} (plates) and {101} (bipyramids) facets during the photogeneration of hydrogen. It is found that Pt/TiO2 exhibits superior stability than Pd/TiO2 and Au/TiO2, and that {001} facet-based photocatalysts always are more stable than their {101} analogous regardless of the considered metal species. The loss of stability associated with cluster sintering, which is facilitated by the transfer of photoexcited carriers from the metal species to the neighbouring Ti and O atoms, most significantly and detrimentally affects the H2-evolution photoactivity.

Experimental and computational study of the catalytic activity of Pd and PdCu nanoparticle catalysts and clusters supported on reduced graphene oxide and graphene acid for the suzuki cross-coupling reaction

The catalytic activity of Pd and PdCu nanoparticle catalysts and clusters supported on reduced graphene oxide (RGO) and graphene acid (GA) toward the Suzuki cross-coupling reaction between bromobenzene and phenylboronic acid is investigated experimentally and computationally. The experimental results indicate that the bimetallic PdCu nanoparticle catalysts supported on RGO or GA outperform the supported Pd catalysts and that the PdCu/RGO catalyst exhibits superior activity, reaching a full conversion to the biphenyl product in only 15 min under ambient conditions. The experimental results show that both the Pd and PdCu catalysts have higher activities when supported on RGO than when supported on GA. The computational results using density functional theory show that the RGO provides relatively better support for the C-C coupling reaction than GA. Investigations based on the charge analysis have further revealed that the RGO is a better charge donor and acceptor than GA, facilitating both the reaction's oxidative addition and reductive elimination steps by reducing the respective barrier heights. Doping a Cu atom near the Pd reaction site is shown to enhance this effect further. The relative reactivity trends of RGO- and GA-supported Pd and PdCu clusters obtained from the DFT calculations show exact agreement with the experimental results.

Pd Loaded NiCo Hydroxides for Biomass Electrooxidation: Understanding the Synergistic Effect of Proton Deintercalation and Adsorption Kinetics.

The key issue in the 5-hydroxymethylfurfural oxidation reaction (HMFOR) is to understand the synergistic mechanism involving the protons deintercalation of catalyst and the adsorption of the substrate. In this study, a Pd/NiCo catalyst was fabricated by modifying Pd clusters onto a Co-doped Ni(OH)2 support, in which the introduction of Co induced lattice distortion and optimized the energy band structure of Ni sites, while the Pd clusters with an average size of 1.96 nm exhibited electronic interactions with NiCo support, resulting in electron transfer from Pd to Ni sites. The resulting Pd/NiCo exhibited low onset potential of 1.32 V and achieved a current density of 50 mA/cm2 at only 1.38 V. Compared to unmodified Ni(OH)2, the Pd/NiCo achieved an 8.3-fold increase in peak current density. DFT calculations and in-situ XAFS revealed that the Co sites affected the conformation and band structure of neighboring Ni sites through CoO6 octahedral distortion, reducing the proton deintercalation potential of Pd/NiCo and promoting the production of Ni3+-O active species accordingly. The involvement of Pd decreased the electronic transfer impedance, and thereby accelerated Ni3+-O formation. Moreover, the Pd clusters enhanced the adsorption of HMF through orbital hybridization, kinetically promoting the contact and reaction of HMF with Ni3+-O.

Pd Loaded NiCo Hydroxides for Biomass Electrooxidation: Understanding the Synergistic Effect of Proton Deintercalation and Adsorption Kinetics

AbstractThe key issue in the 5‐hydroxymethylfurfural oxidation reaction (HMFOR) is to understand the synergistic mechanism involving the protons deintercalation of catalyst and the adsorption of the substrate. In this study, a Pd/NiCo catalyst was fabricated by modifying Pd clusters onto a Co‐doped Ni(OH)2 support, in which the introduction of Co induced lattice distortion and optimized the energy band structure of Ni sites, while the Pd clusters with an average size of 1.96 nm exhibited electronic interactions with NiCo support, resulting in electron transfer from Pd to Ni sites. The resulting Pd/NiCo exhibited low onset potential of 1.32 V and achieved a current density of 50 mA/cm2 at only 1.38 V. Compared to unmodified Ni(OH)2, the Pd/NiCo achieved an 8.3‐fold increase in peak current density. DFT calculations and in situ XAFS revealed that the Co sites affected the conformation and band structure of neighboring Ni sites through CoO6 octahedral distortion, reducing the proton deintercalation potential of Pd/NiCo and promoting the production of Ni3+−O active species accordingly. The involvement of Pd decreased the electronic transfer impedance, and thereby accelerated Ni3+−O formation. Moreover, the Pd clusters enhanced the adsorption of HMF through orbital hybridization, kinetically promoting the contact and reaction of HMF with Ni3+−O.

Pd cluster decorated free standing flexible cathode for high performance Li-oxygen batteries

Pd cluster decorated free standing flexible cathode for high performance Li-oxygen batteries

Principle on Selecting the Coordination Ligands of Palladium Precursors Encapsulated by Zeolite for an Efficient Purification of Formaldehyde at Ambient Temperature.

High-performance zeolite-supported noble metal catalysts with low loading and high dispersion of active components are the most promising materials for achieving the complete oxidation of formaldehyde (HCHO) at room temperature. In this work, palladium nanoparticles (Pd NPs) with different sizes were successfully encapsulated inside the silicalite-1 (S-1) zeolite framework by using diverse stabling ligands via the one-pot method. Thereafter, the rule on selecting the coordinative ligands for palladium was clarified: more N atoms, a short carbon chain, a smaller branch chain, and bidentate coordination are characteristics of an ideal ligand. Accordingly, the best-performing 0.2Pd@S-1(Ethylenediamine) catalyst exhibited outstanding performance for HCHO oxidation, achieving 100% conversion even at room temperature. High-resolution high-angle annular dark-field scanning transmission electron microscopy (HR HAADF-STEM) and density functional theory (DFT) calculations indicate that the chelate is formed by complexation of Pd2+ ions with ethylenediamine, displaying the smallest spatial site resistance simultaneously with the zeolite synthesis, resulting in Pd located mostly within the 5-membered ring (5-MR) channels of S-1 after calcination, thus limiting the growth of Pd clusters and promoting their dispersion.

Electrochemical Hydrogen Peroxide Production on Single Atoms and Atomic Clusters

The electrochemical oxygen reduction reaction (ORR) involving the transfer of two electrons (2-electron ORR) offers a sustainable alternative for the production of hydrogen peroxide (H2O2) on-site. Minimizing the use of expensive noble metal catalysts and maximizing their atomic utilization can be achieved by reducing the size of the catalysts. While previous studies have primarily focused on the relationship between particle size and oxygen reduction activity in the 4-electron ORR using Pt-based catalysts, less attention has been paid to the 2-electron ORR for H2O2 production. In this study, we prepared a series of size-controlled Pd clusters and investigated the oxygen reduction in acidic conditions to understand the relationship between cluster size and catalytic performance. Our results showed that larger Pd clusters favored the 4-electron ORR and the production of H2O, while smaller clusters favored the 2-electron ORR and the production of H2O2. To estimate the contribution of single atoms in the catalysts to their performance, we introduced CO. Using in-situ attenuated total reflection-surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS), we observed a range of CO vibrational signatures that correlated with specific ORR behaviors depending on the particle/cluster size.

DFT study of Pd4 and Pd3P supported on modified graphene for hydrogen storage

In this study, density functional theory (DFT) calculations were utilized to investigate the feasibility of using Pd4 and Pd3P clusters for hydrogen adsorption and spillover, with a focus on their potential as hydrogen storage materials. Four different modified graphene slabs were examined and the results showed that pristine graphene (PG), phosphorus-doped pristine graphene (PPG), and phosphorus-doped single vacancy graphene (PSVG) are not suitable surfaces for decorating Pd4 and Pd3P clusters for hydrogen adsorption and spillover. Our results showed that Pd4/SVG and Pd3P/SVG materials exhibited high binding energies of −5.37 eV and −4.49 eV respectively, which indicated their potential to prevent desorption of Pd–H hydrides with H2 desorption. The stability of Pd4/SVG and Pd3P/SVG was also confirmed by molecular dynamics at a temperature of 500 K. Moreover, the decoration of Pd3P on SVG resulted in hydrogen adsorption with an average energy of 0.25 eV/H2, falling within the ideal useable range. At full saturation, the energy barrier for spillover decreased from 0.86 eV to 0.75 eV, and the system could store up to 5.74 wt% of hydrogen. Furthermore, the spillover reaction occurred rapidly at room temperature within 0.68 s. Our findings suggest that Pd3P decorated single vacancy graphene represents a promising hydrogen storage material, providing valuable insights into the development of effective hydrogen storage technologies.

Highly Selective Hydrogenation of Phenol to Cyclohexanone Using WO3 Supported Tiny Pd Clusters Catalysts

Highly Selective Hydrogenation of Phenol to Cyclohexanone Using WO3 Supported Tiny Pd Clusters Catalysts

Selective coordination activation regulating the selectivity for photocatalytic hydrogenation of α, β-unsaturated aldehyde over Pd/MIL-100(FeaCub)

Here, the mixed metal nodes MOFs, Pd/MIL-100(FeaCub), were constructed as photocatalysts for hydrogenation of α, β-unsaturated aldehyde (UAL) under visible light. 1 wt% Pd/MIL-100(Fe0.81Cu0.19) can convert a range of UAL to saturated aldehydes (SAL) with a high efficiency (≈ 100 %) and selectivity (≈ 98 %). The results of XPS and in situ DRIFTS reveal that UAL can be selectively activated via a coordination of -CC- on Cu2+ sites, determining the high selectivity of the photocatalytic reaction. The mixed metal nodes and Pd clusters can improve the transformation and separation of photogenerated electrons-holes. EPR result suggests that photogenerated carriers can facilitate the generation of H·on Pd/MIL-100(Fe0.81Cu0.19), enhancing the catalytic activity. A possible mechanism is proposed for elucidating the catalytic processes at the molecular level. This work provides a valuable strategy for tailoring the selectivity of photocatalytic hydrogenation via selective coordination activation.

Demystifying the influence of ferroptosis on Alzheimer’s and Parkinson’s diseases: A network and systems biology approach

Research into the pathophysiology of Alzheimer’s disease (AD) and Parkinson’s disease (PD) has spanned decades, unraveling deregulated signaling cascades in these diseases. Recently, the discovery of the link between ferroptosis and neurodegeneration has opened new avenues for neurodegenerative disease research. Despite this, the key players in the ferroptotic pathway potentially governing the progression of neurodegenerative disease remain unidentified. Thus, in the present study, we reconstructed two protein–protein interaction networks (PPINs) for AD and PD with their respective differentially expressed genes from post-mortem tissues and identified 21 highly connected clusters within the AD PPIN and 17 clusters within the PD PPIN. Then, we identified 8 ferroptotic transcription factors (FerrTFs) that regulate hub genes from the 7 deregulated clusters of AD and 6 FerrTFs from the 4 deregulated clusters of PD. Functional enrichment analysis of these clusters revealed impairment in important neurological functions. Finally, we identified 681 drugs with potential therapeutic effects against the 8 FerrTFs associated with AD and 633 drugs against the 6 FerrTFs linked to PD. In addition, 126 and 114 miRNAs might silence 7 and 5 FerrTFs against AD and PD, respectively. This exploratory study identifies potential markers of ferroptosis that could exacerbate these neurodegenerative diseases and also suggests possible therapeutic measures against them.

Enhanced bifunctional electrocatalytic performance of NiFe-layered double hydroxide activated by ultrasonic-assisted loading of Pd nanoclusters

In this study, metallic Pd nanocrystals loaded on NiFe-layered double hydroxide (Pd/NiFe-LDH-u) electrocatalyst for water splitting is synthesized via a novel ultrasonic-assisted ion exchange and in situ reduction method. The ultrasonic-assisted loaded Pd clusters (with an average size 2.84 nm) are in high crystallinity. The optimized Pd/NiFe-LDH-u displays remarkable oxygen evolution reaction (OER) catalytic activity with a low overpotential of 267 mV at 20 mA cm−2. The hydrogen evolution reaction (HER) mass activity of Pd/NiFe-LDH-u is up to 6.37 A mg−1 at an overpotential of 300 mV, which is nearly 10 times higher than that of bare Pd and outperforming most reported Pd-based catalysts. Both the experimental results and density functional theory (DFT) calculations prove that the ultrasonic-assisted loading effectively strengthens the interaction between Pd and NiFe-layered double hydroxide (NiFe-LDH), resulting in improved dispersion uniformity, catalytic stability, electrical conductivity and bifunctional catalytic activities.

Self-assembled synthesis of Pd/SPEn from polyelectrolyte membranes for efficient direct synthesis of H2O2 via inhibiting the dissociation of O − O bond

Although a high-activity yield of hydrogen peroxide (H2O2) can be achieved by direct synthesis from hydrogen and oxygen, developing an extreme catalyst with high activity and stability is still very challenging, which limits its industrial application. Here, we reported a catalyst Pd/SPE with polyelectrolyte membranes SPE as an electronic acceptor to anchor Pd, which achieves H2O2 selectivity of 90.1% and productivity of 5764.4 mmol∙gPd-1∙h−1. The results of TEM, XRD and ICP-MS, XPS, CO-DRIFT, O2-TPD, synchrotron radiation and density functional theory (DFT) simulations reveal that the electrons of Pd are transferred into polyelectrolyte membranes and Pd clusters are strongly chemisorbed on SPE, which is beneficial for O2 adsorption and inhibits the dissociation of O-O bond, leading to significantly enhanced H2O2 productivity and selectivity.

Pd(II) and Rh(I) Catalytic Precursors for Arene Alkenylation: Comparative Evaluation of Reactivity and Mechanism Based on Experimental and Computational Studies.

We combine experimental and computational investigations to compare and understand catalytic arene alkenylation using the Pd(II) and Rh(I) precursors Pd(OAc)2 and [(η2-C2H4)2Rh(μ-OAc)]2 with arene, olefin, and Cu(II) carboxylate at elevated temperatures (>120 °C). Under specific conditions, previous computational and experimental efforts have identified heterotrimetallic cyclic PdCu2(η2-C2H4)3(μ-OPiv)6 and [(η2-C2H4)2Rh(μ-OPiv)2]2(μ-Cu) (OPiv = pivalate) species as likely active catalysts for these processes. Further studies of catalyst speciation suggest a complicated equilibrium between Cu(II)-containing complexes containing one Rh or Pd atom with complexes containing two Rh or Pd atoms. At 120 °C, Rh catalysis produces styrene >20-fold more rapidly than Pd. Also, at 120 °C, Rh is ∼98% selective for styrene formation, while Pd is ∼82% selective. Our studies indicate that Pd catalysis has a higher predilection toward olefin functionalization to form undesired vinyl ester, while Rh catalysis is more selective for arene/olefin coupling. However, at elevated temperatures, Pd converts vinyl ester and arene to vinyl arene, which is proposed to occur through low-valent Pd(0) clusters that are formed in situ. Regardless of arene functionality, the regioselectivity for alkenylation of mono-substituted arenes with the Rh catalyst gives an approximate 2:1 meta/para ratio with minimal ortho C-H activation. In contrast, Pd selectivity is significantly influenced by arene electronics, with electron-rich arenes giving an approximate 1:2:2 ortho/meta/para ratio, while the electron-deficient (α,α,α)-trifluorotoluene gives a 3:1 meta/para ratio with minimal ortho functionalization. Kinetic intermolecular arene ethenylation competition experiments find that Rh reacts most rapidly with benzene, and the rate of mono-substituted arene alkenylation does not correlate with arene electronics. In contrast, with Pd catalysis, electron-rich arenes react more rapidly than benzene, while electron-deficient arenes react less rapidly than benzene. These experimental findings, in combination with computational results, are consistent with the arene C-H activation step for Pd catalysis involving significant η1-arenium character due to Pd-mediated electrophilic aromatic substitution character. In contrast, the mechanism for Rh catalysis is not sensitive to arene-substituent electronics, which we propose indicates less electrophilic aromatic substitution character for the Rh-mediated arene C-H activation.

Mizoroki-Heck Macrocyclization Reactions at 1 M Concentration Catalyzed by Sub-nanometric Palladium Clusters.

The synthesis of cyclized organic compounds with more than ten atoms (macrocycles) is traditionally based on reversible reactions under highly diluted conditions, typically <0.05 M, in order to circumvent the formation of intermolecular products. These reaction conditions severely hamper industrial productivity and the use of solid catalysts. Herein, it is shown that the intramolecular Mizoroki-Heck reaction of ω-iodide cinnamates proceeds at 1 M concentration when catalyzed by few-atom Pd clusters, either in solution or supported on a solid, to give different macrocycles in good yields. This paradigmatic increase in reaction concentration not only opens the door for macrocycle production with high throughputs but also enables the use of solid catalysts for a macrocyclization reaction in flow.