Palladium Nanoclusters Research Articles

Tandem selective reduction of nitroarenes catalyzed by palladium nanoclusters

Five categories of valuable N-containing compounds can be selectively synthesized by the catalytic tandem reduction of nitroarenes with in situ generated Pd nanoclusters as the catalyst.

Size-dependent electrocatalytic activity of ORR/OER on palladium nanoclusters anchored on defective MoS2monolayers

The catalytic performance of MoS2monolayer for oxygen reduction/evolution can be effectively tuned by carefully controlling the sizes of the deposited Pd clusters.

A novel nanosensor for detecting tetracycline based on fluorescent palladium nanoclusters

Tetracycline (TC) is considered one of the most widely used antibiotic medicines, and ranks the second highest in global production and usage among all antibiotics.

Hydrogen-gas sensing at low concentrations using extremely narrow gap palladium nanoclusters prepared by resistive spectroscopy

Isolated palladium nanostructures expand when they are exposed to hydrogen gas, and the gaps between them become narrower, thereby decreasing the electrical resistance. This behavior is applicable for the hydrogen-gas sensing, and several types of nanogap structures have been developed. However, the resistance change is significantly small at a low hydrogen-gas concentration because of insignificant lattice expansion. In the present study, this problem is solved by using the palladium nanoclusters with extremely narrow gaps, which is achieved by our original method, resistive spectroscopy, and hydrogen-induced structural stabilization. The nanoclusters are fabricated by interrupting deposition just before forming the continuous film, in which palladium clusters are nearly touching each other, and exposing them to hydrogen gas. In conventional studies using nanoclusters, hydrogen gas is detected through a decrease in the surface electric resistance caused by gap narrowing/closing. However, in this study, we observe an increase in the resistance when the gap distance between the cluster is extremely small, which is attributed to the restriction of electron tunneling between the palladium nanoclusters because of hydrogen adsorption on their surface. We confirm that this mechanism allows ultrahigh sensitivity hydrogen-gas sensing, achieving a limit of detection of 0.25-ppm hydrogen gas. In addition, we find that an optimized structure for the present detection mechanism is different from those in conventional sensors based on the gap-narrowing/closing mechanism.

Formation of Transient Anionic Metal Clusters in Palladium/Diene-Catalyzed Cross-Coupling Reactions.

Despite their considerable practical value, palladium/1,3‐diene‐catalyzed cross‐coupling reactions between Grignard reagents RMgCl and alkyl halides AlkylX remain mechanistically poorly understood. Herein, we probe the intermediates formed in these reactions by a combination of electrospray‐ionization mass spectrometry, UV/Vis spectroscopy, and NMR spectroscopy. According to our results and in line with previous hypotheses, the first step of the catalytic cycle brings about transmetalation to afford organopalladate anions. These organopalladate anions apparently undergo SN2‐type reactions with the AlkylX coupling partner. The resulting neutral complexes then release the cross‐coupling products by reductive elimination. In gas‐phase fragmentation experiments, the occurrence of reductive eliminations was observed for anionic analogues of the neutral complexes. Although the actual catalytic cycle is supposed to involve chiefly mononuclear palladium species, anionic palladium nanoclusters [PdnR(DE)n]−, (n=2, 4, 6; DE=diene) were also observed. At short reaction times, the dinuclear complexes usually predominated, whereas at longer times the tetra‐ and hexanuclear clusters became relatively more abundant. In parallel, the formation of palladium black pointed to continued aggregation processes. Thus, the present study directly shows dynamic behavior of the palladium/diene catalyst system and degradation of the active catalyst with increasing reaction time.

Benzalaniline from nitrobenzene and benzaldehyde catalyzed efficiently by an atomically precise palladium nanocluster

Nanoclusters with a precise number of atoms may exhibit unique and often unexpected catalytic properties. Here, we report an atomically precise Pd3 nanocluster as an efficient catalyst, whose catalytic performance differs remarkably from typical Pd nanoparticle catalysts, with excellent reactivity and selectivity in the one-pot synthesis of benzalaniline from nitrobenzene and benzaldehyde. We anticipate that our work will serve as a starting point for the catalytic applications of these tiny atomically precise nanoclusters in green chemistry for the one-pot syntheses of fine chemicals.

Composite Microneedle Arrays Modified With Palladium Nanoclusters for Electrocatalytic Detection of Peroxide

The fabrication of conductive composite microneedle (MN) patches modified with palladium clusters for the electrocatalytic detection of peroxide is described in this letter. Micromolding techniques are utilized in which carbon nanoparticles are bound within a polystyrene matrix resulting in the production of a 10 × 10 array of needles of length 700 μm. Electrochemical anodization of the carbon particles increases the interfacial carboxyl group population which facilitates the capture of Pd 2+ ions. Their subsequent electroreduction yields a catalytic interface with a high sensitivity toward the electroreduction of peroxide (-0.3 V:49.7+/-2.8 μA·mM -1 ·cm -2 ; -0.5 V:102.1+/-2.32 μA·mM -1 ·cm -2 ). The MN sensing system and the various modification stages has been characterized using mechanical testing (fracture testing), cyclic voltammetry, and high-resolution X-ray photoelectron spectroscopy.

Computational modelling of an amide functionalized single-walled carbon nanotube based H2S gas sensor

Abstract Due to the importance of detection of hydrogen sulphide in some industries, we are seeking to design a real-time H 2 S gas sensor with high sensitivity and very low detection limit. Here, we have investigated the sensitivity of amido-functionalized semiconducting single-walled carbon nanotube (SWCNT), interconnected between two gold electrodes , in terms of electrical conductance behavior. For this reason, we have used the non-equilibrium Green's function method and density functional theory and compared our results to our previous study (SWCNT functionalized with palladium nanoclusters) to find the best H 2 S gas sensor with high sensitivity. Initially, the optimized structure of the SWCNT functionalized with amide groups with and without H 2S gas is computed. Then, the electrical properties of the sensor prior to and after the exposure to H2S gas are computed and compared at different bias voltages. The highest sensitivity is found to be at 40 mV bias voltage with a current change of 1 order of magnitude in response to H2 S gas which in comparison to SWCNT functionalized with palladium nanoclusters , the current change, and as a result the sensitivity, are more significant. So it is inferred that amido-functionalized SWCNT can act as an effective detector with a considerable current change.

Emergence of magnetism in bulk amorphous palladium

Magnetism in palladium has been the subject of much work and speculation. Bulk crystalline palladium is paramagnetic with a high magnetic susceptibility. Palladium under pressure and palladium nanoclusters have generated interest to scrutinize its magnetic properties. Here we report another possibility: Palladium may become an itinerant ferromagnet in the amorphous bulk phase at atmospheric pressure. Atomic palladium is a d$^{10}$ element, whereas bulk crystalline Pd is a d$^{10-x}$(sp)$^{x}$ material; this, together with the possible presence of 'unsaturated bonds' in amorphous materials, may explain the remnant magnetism reported herein. This work presents and discusses magnetic effects in bulk amorphous palladium.

Palladium Nanoclusters Uniformly Enveloped Electrochemically Activated Graphene for Highly Sensitive Hydrogen Peroxide Sensor

AbstractNonenzymatic sensors based on a metals nanocomposite with high sensitivity, selectivity, and stability has been received considerable interest. In this study, a novel electrochemical nanocomposite sensor based on palladium nanoclusters (PdNCs) decorated electrochemically activated graphene (EAGr) was established for highly sensitive nonenzymatic H2O2 sensor. The PdNCs/EAGr nanocomposite was fabricated via an electrochemical activation of Gr by the potential cycling in the range of +0.6 to −1.8 V, followed by the electrodeposition of PdNCs at −0.4 V applied potential. The homogeneous dispersion of PdNCs/EAGr nanocomposite were characterized by scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and linear sweep voltammetry (LSV). The PdNCs/EAGr nanocomposite electrode showed higher electrocatalytic activity towards the reduction of H2O2 in pH 7.0 of 0.1 M PBS by significantly enhancing the reduction peak current and reduced the reduction overpotential as well as eliminated other interfering species responses. The PdNCs/EAGr electrode displayed a wide linear range for H2O2 reduction from 1.0 to 1100 μM with limit of detection 0.02±0.01 μM. The higher sensitivity and selectivity as well as long‐time stability and excellent reproducibility obtained, indicating the proposed sensor is an effective H2O2 based sensor. In addition, the analytical application of the nancomposite sensor was successfully examined for the determination of H2O2 in the real sample of human urine indicating that the appreciable practicality of the nonenzymatic sensor for the determination of H2O2 in physiological fluids.

Cover Picture: Activation and Spillover of Hydrogen on Sub‐1 nm Palladium Nanoclusters Confined within Sodalite Zeolite for the Semi‐Hydrogenation of Alkynes (Angew. Chem. Int. Ed. 23/2019)

Cover Picture: Activation and Spillover of Hydrogen on Sub‐1 nm Palladium Nanoclusters Confined within Sodalite Zeolite for the Semi‐Hydrogenation of Alkynes (Angew. Chem. Int. Ed. 23/2019)

Activation and Spillover of Hydrogen on Sub‐1 nm Palladium Nanoclusters Confined within Sodalite Zeolite for the Semi‐Hydrogenation of Alkynes

AbstractThe search for efficient nontoxic catalysts able to perform industrial hydrogenations is a topic of interest, with relevance to many catalytic processes. Herein, we describe a mechanistic phenomenon for the activation and spillover of hydrogen for remarkable selectivity in the semi‐hydrogenation of acetylene over sub‐1 nm Pd nanoclusters confined within sodalite (SOD) zeolite (Pd@SOD). Specifically, hydrogen is dissociated on the Pd nanoclusters to form hydrogen species (i.e., hydrogen atoms and hydroxyl groups) that spill over the SOD surfaces. The design and utilization of the small‐pore zeolite SOD (six‐membered rings with 0.28×0.28 nm channels) is crucial as it only allows H2 diffusion into the channels to reach the encapsulated Pd nanoclusters and thus avoids over‐hydrogenation to form ethane. Pd@SOD exhibits an ethylene selectivity of over 94.5 %, while that of conventional Pd/SOD is approximately 21.5 %.

Activation and Spillover of Hydrogen on Sub-1 nm Palladium Nanoclusters Confined within Sodalite Zeolite for the Semi-Hydrogenation of Alkynes.

The search for efficient nontoxic catalysts able to perform industrial hydrogenations is a topic of interest, with relevance to many catalytic processes. Herein, we describe a mechanistic phenomenon for the activation and spillover of hydrogen for remarkable selectivity in the semi-hydrogenation of acetylene over sub-1 nm Pd nanoclusters confined within sodalite (SOD) zeolite (Pd@SOD). Specifically, hydrogen is dissociated on the Pd nanoclusters to form hydrogen species (i.e., hydrogen atoms and hydroxyl groups) that spill over the SOD surfaces. The design and utilization of the small-pore zeolite SOD (six-membered rings with 0.28×0.28 nm channels) is crucial as it only allows H2 diffusion into the channels to reach the encapsulated Pd nanoclusters and thus avoids over-hydrogenation to form ethane. Pd@SOD exhibits an ethylene selectivity of over 94.5 %, while that of conventional Pd/SOD is approximately 21.5 %.

Design and fabrication of surface capped palladium nanoclusters for the subnanomolar sensing of glutathione

In this work, a palladium atomic cluster modified glassy carbon electrode (PdAC/GCE) was developed by potentiodynamic electrodeposition in the presence of an anionic surfactant for the electrochemical detection of glutathione (GSH).

Dimethylformamide-stabilised palladium nanoclusters catalysed coupling reactions of aryl halides with hydrosilanes/disilanes.

N,N-Dimethylformamide-stabilised Pd nanocluster (NC) catalysed cross-coupling reactions of hydrosilane/disilane have been investigated. In this reaction, the coupling reaction proceeds without ligands with low catalyst loading. N,N-Dimethylacetamide is a crucial solvent in these reactions. The solvent effect was considered by various techniques, such as transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The Pd NCs can be recycled five times under both hydrosilane and disilane reaction conditions.

NHC stabilized Pd nanoclusters in the Mizoroki–Heck reaction within microemulsion: exploring the role of imidazolium salt in rate enhancement

Significant rate enhancement of the Mizoroki–Heck reaction by in situ generated palladium nanoclusters within the confined space of water-in-oil mixed microemulsion in the presence of novel imidazo[1,5-α]pyridinium chlorides as N-heterocyclic carbene (NHC) precursors is reported.

Biogenic palladium nanoclusters supported on hybrid nanocomposite 2-hydroxypropyl-β-cyclodextrin/alginate as a recyclable catalyst in aqueous medium

This paper develops a simple and green process of synthesizing palladium nanoclusters (PdNCs) capped on the hybrid nanocomposite based on biodegradable polysaccharides, 2-hydroxypropyl-β-cyclodextrin (HPCD) and alginate (Alg) through an ionotropic gelation mechanism. PdNCs were biosynthesized from aqueous extract of Burdock root (BR), Arctium lappa. The nanocomposite PdNCs/HPCD/Alg was characterized by techniques like UV–Vis, FTIR, EDX, FESEM, TEM, HR-TEM and TG-DTA. The crystal palladium nanoparticles were found to distribute in cluster shape with a size of 4–10nm. EDX data showed that average amount of palladium capped on the hybrid nanocomposite was approx. 4.7% (w/w). PdNCs/HPCD/Alg exhibited highly catalytic activity for degradation of pollutants including 4-nitrophenol, methyl orange and rhodamine B in wastewater and leaching mechanism of the nanocatalyst was showed. In particular, the nanocomposite showed excellent aqueous-phase catalytic performance for free-triphenylphosphine Sonogashira cross-coupling reaction. The nanocatalyst could be efficiently reused without much compromising with its activity.

Ultra-low loading of Pd5 nanoclusters on carbon nanotubes as bifunctional electrocatalysts for the oxygen reduction reaction and the ethanol oxidation reaction

How to reduce the usage of precious metals in electrocatalysts is a big challenge for the development of fuel cells. Metal nanoclusters (NCs) are highly desirable as active catalysts, but palladium nanoclusters (Pd NCs) have been less well developed than other metal clusters, such as gold, silver and copper, owing partly to the difficulties in size-controlled synthesis. Here, based on N, N-dimethylformamide (DMF)-mediation and ligand-exchange reaction, atomically precise Pd5(C12H25S)13 nanoclusters are successfully synthesized. By loading the as-prepared Pd5 nanoclusters on multiwalled carbon nanotubes (MWCNTs) and the following pyrolysis to remove the thiolate ligands, the surface-cleaned Pd5 clusters (Pd5 NCs/MWCNTs) can serve as efficient electrocatalysts for the oxygen reduction reaction (ORR) and the ethanol oxidation reaction (EOR). With ultra-low mass loading of Pd (2%), the Pd5 NCs showed higher mass and specific activities and better durability than the commercial Pd/C catalyst (5 wt%) for the ORR. At 0.8 V, the mass and specific activities of Pd5 NCs/MWCNTs are 5.70 and 4.53 times higher than the commercial Pd/C catalyst, respectively. As for the EOR, the Pd5 NCs/MWCNTs exhibited lower onset potential (0.39 V) and peak potential (0.81 V) than the commercial Pd/C catalyst (0.44 and 0.89 V). Electrochemical impedance spectroscopy (EIS) measurements indicated that for the EOR, the Pd5 nanoclusters have a much smaller charge transfer resistance (Rct) than the commercial Pd/C. The high-performance electrocatalytic properties of Pd5 NCs for the ORR and EOR could be ascribed to the relatively high surface area-to-volume ratio and high density of exposed surface atoms of the Pd5 nanoclusters.

A new efficient, highly dispersed, Pd nanoparticulate silica supported catalyst synthesized from an organometallic precursor. Study of the homogeneous vs. heterogeneous activity in the Suzuki-Miyaura reaction

A new Pd(0) catalyst supported on silica UVM-7 has been synthesized from the organometallic [Pd2{μ-(C6H4) PPh2}2(CH3CN)4](BF4)2 precursor, characterized by the high dispersion, activity, and small size of the palladium nanoclusters fixed on the silica surface. The catalyst was tested for the Suzuki-Miyaura (SM) reaction of different 4-substitutedphenyl halides with phenylboronic acid. The kinetic study concurs with most of the catalytic action was carried out by Pd species originated by the partial solubilization of Pd immobilized on mesoporous silica. The Schmidt’s analysis of differential selectivity (SADS) in several competitive SM reactions, together the STEM-HAADF and HRTEM images of the catalyst surface taken along several reuse cycles support the conclusions of the kinetic study. Furthermore, this hypothesis was critically investigated using different classic approaches to distinguish between homogeneous and heterogeneous catalysis as the three phases test, poisoning, and hot filtrate experiments.

Palladium nanoclusters decorated partially decomposed porous ZIF-67 polyhedron with ultrahigh catalytic activity and stability on hydrogen generation

Metal-organic frameworks have attracted extensively attentions due to their unique structural properties such as high porosity, good crystallinity, and three-dimensional networking. However, to the best of our knowledge, there is no report concerning the application of partially decomposed metal-organic frameworks based catalyst for sodium borohydride hydrolysis for H2 generation. Herein, the partially decomposed cobalt-based zeolitic imidazolate frameworks supported Pd nanoclusters are fabricated by evaporation solvent assisted method followed by subsequent annealing under H2 atmosphere. Our results show that catalytic performance of the designed catalyst can be largely improved by optimizing the Pd loading and the annealing temperatures. The optimized catalyst exhibits a high catalytic activity towards hydrolysis of alkalized sodium borohydride with a specific H2 generation rate of 20.6 l min−1 mgPd−1 and turnover frequency of 495.0 mol min−1 molPd−1 at 25 °C, which is the highest reported so far among the similar catalysts. Moreover, the resulted catalyst also demonstrates a high level of stability. Based on structural characterization and experimental optimization, the extraordinary performance of the fabricated catalyst is mainly contributed to the synergetic effect of highly dispersed Pd nanoclusters with partially decomposed cobalt-based zeolitic imidazolate frameworks.