Pd Nanocatalysts Research Articles

Aptamer-Regulated Gold Nanosol Plasmonic SERS/RRS Dimode Assay of Trace Organic Pollutants Based on TpPa-Loaded PdNC Catalytic Amplification.

As with excellent catalytic performance, palladium nanoclusters (PdNCs) have a wide range of applications. However, the traditional PdNCs are easy to agglomerate in the analysis system and lose their catalytic activity. A covalent organic framework (COF) has a definite structure, good stability, and easy surface functionalization. So, it is of great significance to develop stable PdNCs with high catalytic activity and then combine with advanced analysis techniques to analyze ultratrace small-molecule pollutants in the environment. In this research, a stable PdNC dispersed on a COF (PdTpPa) catalyst is prepared and we find it with strong catalysis for the NaH2PO2-HAuCl4 catalytic reaction. Furthermore, this nanocatalytic indicator reaction can be tracked by surface-enhanced Raman spectroscopy (SERS) and resonance Rayleigh scattering (RRS) dual-mode. Combined with a highly specific aptamer-modifying technique, a highly sensitive and selective SERS/RRS dimode assay platform for trace organic pollutants has been developed. The detection limits of oxytetracycline (OTC), glyphosate (GLY), tetracycline (TEC), and bisphenol A (BPA) are 0.64, 0.03, 6.2 × 10-3, and 0.53 × 10-3 ng/mL, respectively. This work also provides ideas for the application of COF materials and Pd nanocatalysts in the molecular spectral detection of trace pollutants.

Palladium Immobilized on a Polyimide Covalent Organic Framework: An Efficient and Recyclable Heterogeneous Catalyst for the Suzuki–Miyaura Coupling Reaction and Nitroarene Reduction in Water

An efficient and recyclable Pd nano-catalyst was developed via immobilization of Pd nanoparticles on polyimide linked covalent organic frameworks (PCOFs) that was facilely prepared through condensation of melamine and 3,3′,4,4′-biphenyltetracarboxylic dianhydride. The Pd nanoparticles (Pd NPs) catalyst was thoroughly characterized by FT-IR, XRD, SEM, TEM. Furthermore, the catalytic activity of Pd NPs catalyst was evaluated by Suzuki–Miyaura coupling reaction and nitroarene reduction in water, respectively. The excellent yields of corresponding products revealing revealed that the Pd NPs catalyst could be applied as an efficient and reusable heterogeneous catalyst for above two reactions.

Highly selective semi-hydrogenation of alkynes with a Pd nanocatalyst modified with sulfide-based solid-phase ligands

• Metallic sulfide-based solid-phase ligands are employed for alkyne semi-hydrogenation. • Detailed reaction kinetics has been obtained on various alkyne substrates. • Marked improvements in alkene selectivity have been demonstrated. • The solid-phase ligands are noted for high reusability with no contamination of products. Soluble small molecular/polymeric ligands are often used in Pd-catalyzed semi-hydrogenation of alkynes as an efficient strategy to improve the selectivity of targeted alkene products. The use of soluble ligands requires their thorough removal from the reaction products, which adds significant extra costs. In the paper, commercially available, inexpensive, metallic sulfide-based solid-phase ligands (SPL8-4 and SPL8-6) are demonstrated as simple yet high-performance insoluble ligands for a heterogeneous Pd nanocatalyst (Pd@CaCO 3 ) toward the semi-hydrogenation of alkynes. Based on the reactions with a range of terminal and internal alkyne substrates, the use of the solid-phase ligands has been shown to markedly enhance the selectivity of the desired alkene products by efficiently suppressing over-hydrogenation and isomerization side reactions, even during the long extension of the reactions following full substrate conversion. A proper increase in the dosage or a reduction in the average size of the solid-phase ligands enhances such effects. With their insoluble nature, the solid-phase ligands have the distinct advantage in their simple, convenient recycling and reuse while without contaminating the products. A ten-cycle reusability test with the SPL8-4/Pd@CaCO 3 catalyst system confirms its well-maintained activity and selectivity over repeated uses. A mechanistic study with x-ray photoelectron spectroscopy indicates that the solid-phase ligands have electronic interactions with Pd in the supported catalyst, contributing to inhibit the binding and further reaction of the alkene products. This is the first demonstration of solid-phase ligands for highly selective semi-hydrogenation of alkynes, which show strong promise for commercial applications.

Ultrafine Pd nanoparticles@g-C3N4 for highly efficient dehalogenation of chlorinated environmental pollutant: Structure, efficacy and mechanisms

Catalytic hydrodechlorination represents one of the most promising strategies for the remediation of chlorinated environmental pollutants. However, the wide application of this approach in the practical settings is hampered by the efficiency and stability of catalysts as well as the danger of using molecular hydrogen as hydrogen source. By combining the advantages of both palladium nanocatalyst and graphitic carbon nitride (g-C3N4) as support, here we report the preparation of a hybrid material with ultrafine Pd nanoparticles (NPs, ca. 2 nm) finely embedded inside the well-ordered geometric structure of g-C3N4 by making use of the unique interaction between metal and nitrogen functional groups, and for the first time apply this catalyst for the remediation of chlorinated environmental pollutant. This catalyst (Pd NPs@g-C3N4) exhibited significantly better catalytic performance than any catalysts reported previously with catalytic activity as high as ca. 101 mmol•g−1Pd•min−1 and the ability to achieve rapid complete dechlorination of 1.0 mM 4-chlorophenol (4-CP) within 2 min by using a very low dosage of NaBH4 (2 equivalent) as hydrogen source. The distinctive catalytic dehalogenation property of Pd NPs@g-C3N4 was attributed to i) the ultrafine Pd NPs that activated molecular hydrogen into numerous reactive species (e.g., atomic hydrogen) and ii) the electron-deficient nature of Pd nanocatalyst due to the presence of g-C3N4 support that greatly facilitated the electron transfer on the catalyst surface. This hybrid Pd NPs@g-C3N4 catalyst displayed a rapid dechlorination ability, wide pH applicability, good stability and recyclability. This study provides a promising alternative catalyst for highly efficient dehalogenation of chlorinated environmental pollutants and can shed light onto developing other powerful catalysts for the remediation of these recalcitrant contaminants in water. This work provides new insights into the preparation of ultrafine metal catalyst by using nitrogen functional groups and the possible effect of support to the electronic structure of Pd nanocatalyst.

Ternary supportless Pd@Cd-Ag core-shell as advanced nanocatalysts towards electro-oxidation performance of ethanol

Developing highly active Pd-based nanocatalysts with a well-organized structure is desired for direct alcohol fuel cell commercialization. In this study, room temperature seed mediated growth strategy has been successfully developed to prepare ternary [email protected]x-Agy core-shell as advanced novel non-Pt anode nanocatalysts for ethanol oxidation reaction EOR in alkaline electrolyte. The introduction of oxophilic Cd and Ag metals into Pd nanocatalysts can reduce the adsorption energy of OHads on the [email protected]x-Agy nanocatalysts and inhibit the COads on the Pd surface. Morphological characterization demonstrates that the as-synthesized [email protected]x-Agy nanocatalysts are well-organized core-shell nanostructure with Pd NPs as the core and Cd-Ag alloy as the shell. Moreover, electrochemical results indicate that the [email protected]1-Ag1 core-shell catalyst exhibit a remarkable electrochemical activity (2995.76mAmgPd−1), excellent CO tolerance and long-term durability compared to those of [email protected] (1285.9mAmgPd−1), [email protected] (2423.52mAmgPd−1) and commercial Pd/C (JM) (477.4mAmgPd−1) nanocatalysts. The excellent catalytic activity and stability of [email protected]1-Ag1 nanocatalyst can be associated to their huge electrochemical active surface area, positive influence of Cd-Ag NPs on Pd NPs and the unique well-organized core-shell nanostructure. These results suggested that the as-synthesized [email protected]Cdx-Agy core-shell could serve as advanced catalysts towards alkaline DEFCs.

PEDOT-supported Pd nanocatalysts – oxidation of formic acid

Palladium (Pd) nanocatalysts are obtained by electroless deposition of Pd on pre-reduced poly(3,4-ethylenedioxythiophene) (PEDOT) layers doped with either polystyrenesulfonate (PSS) or dodecylsulfate (SDS) ions. The PEDOT-supported Pd catalysts are investigated with respect to formic acid (FA) oxidation in slightly acidic solution under voltammetric and chronoamperometric conditions. Atomic force microscopy (AFM) and Scanning electron microscopy (SEM) studies are carried out before and after exposure to FA. It is established that the dopant used for the synthesis of PEDOT does affect not only the distribution of the Pd nanoparticles on the polymer surface but also the stability of the composites upon electrochemical treatment in the presence of FA. It is found that PEDOT-PSS undergoes structural rearrangement, and significant loss of the Pd catalyst is observed. In comparison, PEDOT-SDS is more resistant to FA exposure since aggregated Pd nanoparticles are providing additional stability of the polymer structure.

Highly tunable selectivity to benzaldehyde over Pd/ZrO2 catalysts in Oppenauer oxidation of benzyl alcohol using acetone as H-acceptor

The development of novel bifunctional catalysts with high selectivity is the key to achieving the goals of sustainable chemical synthesis. Here, we report the synthesis of mesoporous zirconia and transition metal-doped zirconia by inverse micelle approach. Also, meso-zirconia supported Pd nanocatalysts via the deposition-precipitation method. Highly crystalline Pd/ZrO2 nanoparticles were formed, as evidenced in the pXRD and TEM analyses. The acid-base quantification was investigated using TPD-NH3 and TPD-CO2. Interestingly, the integration of the intrinsic chemical properties of the multi-component catalyst is significant in tailoring the catalytic activities. Interactions between the adsorbates and the moderate acid-base pair sites rather than a single dominating acid or base site mediate the higher selectivity for the aldehyde product. The 100 % chemoselectivity to benzaldehyde is ascribed to the strong synergy between Pd-Zr, which generated the moderate acid-base property. The Pd/ZrO2 is reusable, with selectivity retained after ten cycles.

Facile one-pot synthesis of superfine palladium nanoparticles on polydopamine-functionalized carbon nanotubes as a nanocatalyst for the Heck reaction

Heterogeneous Pd nanocatalysts are efficient catalysts for the Heck reaction but require multi-step, sophisticated procedures and harsh reaction conditions. In this work, a green and facile strategy has been developed to decorate Pd nanoparticles on polydopamine (PDA)-coated multi-walled carbon nanotubes (Pd/CNTs-PDA) via a one-pot method. The obtained nanoparticles were characterized by various techniques including transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, which proved that Pd NPs are well-dispersed on the PDA and between the surfaces of the PDA and CNTs. The resultant Pd/CNTs-PDA catalysts exhibit excellent catalytic reactivity toward the Heck reaction at low temperatures. Moreover, by DFT simulation, we found that during the PDA polymerization process, a large number of unsaturated N and CO species are more active than the groups on the PDA end product to anchor Pd NPs. The results provide evidence that the catalyst synthesized by the one-pot method exhibited good activity because sufficient active sites could be created to effectively promote Pd NPs dispersion during the dopamine polymerization process. Additionally, the Pd/CNTs-PDA catalyst was successfully employed in Heck cross-coupling reactions with various functionalized substrates. This method opens a window for the fabrication of high-performance nanocomposite catalysts under mild conditions using simple methods and has several potential applications.

Ferrocenyl-terminated polyphenylene-type "click" dendrimers as supports for efficient gold and palladium nanocatalysis.

Although dendrimer supports have been known as key parts of nanocatalysts, the capability of rigid dendrimers for this function has not yet been reported. Here, the study is focused on ferrocenylmethylenetriazolyl-terminated dendrimers (FcMTPD) as supports of remarkably efficient nanogold and nanopalladium catalysts. A biphasic system is elaborated to evaluate the catalytic activity of FcMTPD-supported Au and Pd nanoparticles (NPs) for the reduction of 4-nitrophenol to 4-aminophenol by NaBH4 at 20 °C, and FcMTPD-supported PdNPs are found to be the best nanocatalysts with a rate constant kapp = 7.8 × 10-2 s-1. Excellent catalytic results are also obtained in this reaction for FcMTPD-supported AuNPs with a rate constant kapp = 5.6 × 10-2 s-1. For both Pd NPs and AuNPs, the kinetic results are shown to strongly depend on the method of preparation of these NPs that influences the NP size and thus their catalytic efficiency. The FcMTPD-stabilized PdNPs are easily recovered and reused at least 13 times, and their catalytic performance displays only a slight decrease during the first seven runs.

The twinned Pd nanocatalyst exhibits sustainable NRR electrocatalytic performance by promoting the desorption of NH3

The Pd icosahedron with a twin structure accelerates the desorption of NH3 and improves the utilization of active sites due to which it maintains continuous excellent catalytic activity.

Recent advances in the development of palladium nanocatalysts for sustainable organic transformations

In this review, we highlighted Pd nanocatalysts which have been used in the development of sustainable organic transformations including transfer hydrogenation, C–H bond activation, and some carbon–carbon couplings in the last five years.

Ligand-Protected Ultrasmall Pd Nanoclusters Supported on Metal Oxide Surfaces for CO Oxidation: Does the Ligand Activate or Passivate the Pd Nanocatalyst?

Herein, we report on the synthesis of ultrasmall Pd nanoclusters (∼2 nm) protected by L-cysteine [HOCOCH(NH2 )CH2 SH] ligands (Pdn (L-Cys)m ) and supported on the surfaces of CeO2 , TiO2 , Fe3 O4 , and ZnO nanoparticles for CO catalytic oxidation. The Pdn (L-Cys)m nanoclusters supported on the reducible metal oxides CeO2 , TiO2 and Fe3 O4 exhibit a remarkable catalytic activity towards CO oxidation, significantly higher than the reported Pd nanoparticle catalysts. The high catalytic activity of the ligand-protected clusters Pdn (L-Cys)m is observed on the three reducible oxides where 100 % CO conversion occurs at 93-110 °C. The high activity is attributed to the ligand-protected Pd nanoclusters where the L-cysteine ligands aid in achieving monodispersity of the Pd clusters by limiting the cluster size to the active sub-2-nm region and decreasing the tendency of the clusters for agglomeration. In the case of the ceria support, a complete removal of the L-cysteine ligands results in connected agglomerated Pd clusters which are less reactive than the ligand-protected clusters. However, for the TiO2 and Fe3 O4 supports, complete removal of the ligands from the Pdn (L-Cys)m clusters leads to a slight decrease in activity where the T100% CO conversion occurs at 99 °C and 107 °C, respectively. The high porosity of the TiO2 and Fe3 O4 supports appears to aid in efficient encapsulation of the bare Pdn nanoclusters within the mesoporous pores of the support.

Palladium-Nanoparticles Biohybrids in Applied Chemistry

Applied nanotechnology has experienced tremendous advance over the last decade. In this study, the efficient synthesis of highly stable palladium-nanoparticles (PdNPs) biohybrids based on the application of an enzyme, which induces in situ the generation of spherical nanoparticles on the protein network, has been described. A heterogeneous material was synthesized formed with PdNPs with average sizes between 1.5 to 5 nm. These Pd nanocatalysts were successfully applied in different chemical processes: C-C bonding reactions (Suzuki and Heck reactions) and cascade processes combining enzymatic and metallic activities (hydrolysis-reduction, esterification-racemization).

Assessment of a Pd–Fe3O4-biochar nanocomposite as a heterogeneous catalyst for the solvent-free Suzuki-Miyaura reaction

The objective of this study was the development of a novel, biochar-based Pd nanocatalyst and its evaluation for the promotion of the Suzuki-Miyaura coupling reaction. The Fe3O4–Pd-biochar composite was successfully characterized through a range of spectroscopic and elemental analysis techniques. Its catalytic activity was initially assessed using p-NO2C6H4I as a model reactant and later for the production of biaryls from a wide range of aryl halides, under microwave irradiation and solvent-free conditions. The optimum yield of 99% was obtained at a catalyst dosage of 8 mg, microwave irradiation of 400 W, 6 min residence time, using K2CO3 as the base. Furthermore, the catalyst promoted the Suzuki-Miyaura reaction of aryl iodides and bromides (yields in the range of 88–97 and 86–97%, respectively), but was less successful for aryl chlorides (yields 78–83%). The presence of Fe3O4 allowed for the quick recovery of the catalyst, whereas repeated runs established its recyclability.

Study of Deactivation in Suzuki Reaction of Polymer-Stabilized Pd Nanocatalysts

This work is addressed to the phenomenon of catalyst deactivation taking place during the repeated uses in the reaction of Suzuki-Miyaura (S-M) cross-coupling, which is widely applied in industry for C-C bond formation. Ligandless catalysts based on Pd(0) NPs supported on hyper-cross-linked polystyrene (HPS) of two types (non-functionalized and bearing tertiary amino groups) were studied in a model S-M reaction between 4-bromoanisole and phenylboronic acid. Synthesized catalysts were shown to be highly active under mild reaction conditions. HPS allows stabilization of Pd(0) NPs and prevents their agglomeration and detectable Pd leaching. However, the loss of catalytic activity was observed during recycling. The deactivation issue was assigned to the hydrophobic nature of non-functionalized HPS, which allowed a strong adsorption of cross-coupling product during the catalyst separation procedure. A thorough washing of Pd/HPS catalyst by hydrophobic solvent was found to improve to the big extent the observed catalytic activity, while the replacement of non-functionalized HPS by a one containing amino groups increased the catalyst stability at the expense of their activity.

Structural and Kinetics Understanding of Support Effects in Pd-Catalyzed Semi-Hydrogenation of Acetylene

In this study, the support effects on the Pd-catalyzed semi-hydrogenation of acetylene have been investigated from the structural and kinetic perspectives. According to the results of kinetic analysis and X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, temperature-programmed hydride decomposition, and in situ X-ray diffraction measurements, using carbon nanotubes as support for Pd nanocatalysts with various sizes instead of α-Al 2 O 3 decreases the Pd 0 3d binding energy and suppresses the formation of undesirable palladium hydride species, thus increasing the ethylene yield. Furthermore, X-ray absorption spectroscopy, high-resolution transmission electron microscopy, and C 2 H 4 temperature-programmed desorption studies combined with density-functional theory calculations reveal the existence of a unique Pd local environment, containing subsurface carbon atoms, that produces positive geometric effects on the acetylene conversion reaction. Therefore, tailoring the Pd local environment and electronic properties represents an effective strategy for the fabrication and design of highly active and selective Pd semi-hydrogenation catalysts.

Hyaluronic Acid-Guided Synthesis of Pd Nanocatalysts for Transfer Hydrogenation of 4-Nitrophenol

Herein Pd nanocatalysts for transfer hydrogenation were synthesized by using hyaluronic acid (HA) as both the reductant and the stabilizer. The effects of molecular weight of HA, molar ratio of [HA]/[Na2PdCl4] and reduction temperature, were evaluated in Pd-catalyzed transfer hydrogenation of 4-nitrophenol. The most active Pd NPs show the TOF value of 131.07 h−1 at 50 °C with the equimolar mixture of formic acid and sodium formate. Further, uniformly distributed Pd NPs were successfully synthesized through the reduction of Pd (II) precursors on HA-modified magnetic NPs, which were constructed through electrostatic layer-by-layer assembly. The hybrid catalysts also exhibit high activity with the mixed hydrogen source. This work paves a promising way to construct highly active hybrid catalysts through the combination of in-situ reduction and electrostatic layer-by-layer methods.

Toward Overcoming the Challenges in the Comparison of Different Pd Nanocatalysts: Case Study of the Ethanol Oxidation Reaction

Precious metal nanoparticles, in particular palladium nanomaterials, show excellent catalytic properties and are key in the development of energy systems. For instance, ethanol fuel cells are promising devices for sustainable energy conversion, where Pd-based catalysts are key catalysts for the related ethanol oxidation reaction (EOR). Pd is a limited resource; thus, a remaining challenge is the development of efficient and stable Pd-based catalysts. This calls for a deeper understanding of the Pd properties at the nanoscale. This knowledge can be gained in comparative studies of different Pd nanomaterials. However, such studies remain challenging to perform and interpret due to the lack of cross-studies using the same Pd nanomaterials as a reference. Here, as-prepared sub 3 nm diameter surfactant-free Pd nanoparticles supported on carbon are obtained by a simple approach. The as-prepared catalysts with Pd loading 10 and 30 wt % show higher activity and stability compared to commercially available counterparts for the EOR. Upon electrochemical testing, a significant size increase and loss of electrochemical active surface are observed for the as-prepared catalysts, whereas the commercial samples show an increase in the electrochemically active surface area and moderate size increase. This study shines light on the challenging comparison of different catalysts across the literature. Further advancement in Pd (electro)catalyst design will gain from including self-prepared catalysts. The simple synthesis detailed easily leads to suitable nanoparticles to be used as a reference for more systematic comparative studies of Pd catalysts across the literature.

Magnetic methylene-based mesoporous organosilica composite-supported IL/Pd: a powerful and highly recoverable catalyst for oxidative coupling of phenols and naphthols

A novel magnetic methylene-based mesoporous organosilica composite-supported IL/Pd complex (Fe3O4@MePMO-IL/Pd) was synthesized and characterized, and its catalytic performance was investigated. The preparation of the Fe3O4@MePMO composite was achieved through coating of Fe3O4 nanoparticles with a mixture of tetramethoxysilane, bis(triethoxysilyl)methane, and (3-chloropropyl)-trimethoxysilane in the presence of cetyltrimethylammonium bromide surfactant. The Fe3O4@MePMO was then modified with alkyl imidazolium ionic liquid and palladium species to deliver the Fe3O4@MePMO-IL/Pd nanocatalyst. This catalyst was characterized using Fourier transform infrared, thermal gravimetric, wide-angle powder X-ray diffraction, low-angle powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometer, energy-dispersive X-ray, and nitrogen adsorption–desorption analyses. The Fe3O4@MePMO-IL/Pd was effectively used as a highly recoverable and durable catalyst for the selective oxidative coupling of phenols and 2-naphthols under aerobic conditions.

Oxygen reduction reaction on Pd nanocatalysts prepared by plasma-assisted synthesis on different carbon nanomaterials

In this work He/H2 plasma jet treatment was used to reduce Pd ions in the aqueous solution with simultaneous deposition of created Pd nanoparticles to support materials. Graphene oxide (GO) and nitrogen-doped graphene oxide (NrGO) were both co-reduced with the Pd ions to formulate catalyst materials. Pd catalyst was also deposited on the surface of carbon black. The prepared catalyst materials were physically characterized using transmission electron microscopy, scanning electron microscopy and x-ray photoelectron spectroscopy. The plasma jet method yielded good dispersion of small Pd particles with average sizes of particles being: Pd/rGO 2.9 ± 0.6 nm, Pd/NrGO 2.3 ± 0.5 nm and Pd/Vulcan 2.8 ± 0.6 nm. The electrochemical oxygen reduction reaction (ORR) kinetics was explored using the rotating disk electrode method. Pd catalyst deposited on nitrogen-doped graphene material showed slightly improved ORR activity as compared to that on the nondoped substrate, however Vulcan carbon-supported Pd catalyst exhibited a higher specific activity for oxygen electroreduction.