Formation Of Pd Nanoparticles Research Articles

Dynamic Behavior of Pd/P4VP Catalyst during the Aerobic Oxidation of 2-Propanol: A Simultaneous SAXS/XAS/MS Operando Study

The behavior of a Pd(OAc)2/P4VP catalyst submitted to different pretreatments (prereduced, preoxidized, and untreated) during the aerobic oxidation of 2-propanol to acetone in the gas phase has been investigated. Synchronous, time-resolved, SAXS/XAS/MS techniques coupled with operando DRIFT spectroscopy (which gave information on the destiny of the acetate ligands) and ex situ HR-TEM (to detect the formation of Pd nanoparticles and to obtain their size distribution) were employed to accomplish a dynamical picture of the changes occurring to the Pd phase under transient reaction conditions. In addition, the catalytic performances were qualitatively explored by means of a CATLAB microreactor, with the final aim to establish structure–activity relationships. Our approach clearly demonstrates that highly isolated Pd2+ cationic species, either atomically dispersed or in the form of ultrasmall Pd2+–oxo clusters, are efficient and very stable active sites for the gas-phase aerobic oxidation of 2-propanol to acet...

Microbial synthesis of metallic molybdenum nanoparticles

The production of nanoparticles through biosynthesis is a reliable, non-toxic, and sustainable alternative to conventional chemical and physical methods of production. While noble metals, such as palladium, gold, and silver, have been formed via bioreduction, biologically-induced reduction of electroactive elements to a metallic state has not been reported previously. Herein, we report the reduction of an electroactive element, molybdenum, via microbial reduction using Clostridium pasteurianum. C. pasteurianum was able to reduce 88% of the added Mo6+ ions. The bioreduced molybdenum was shown to be metallically bonded in a prototypical crystal structure with an average particle size of 15 nm. C. pasteurianum was previously shown to degrade azo dyes using in situ formed Pd nanoparticles, but this study shows that in situ formed Mo particles also act as catalysts for degradation of azo dyes. C. pasteurianum cultures with the bioformed Mo nanoparticles were able completely degrade 155 μM methyl orange within 6 min, while controls with no Mo took 36 min. This research demonstrates, for the first time, that the bioreduction of active elements and formation of catalytic particles is achievable.

Evaluation of Pd Nanoparticle-Decorated CeO2-MWCNT Nanocomposite as an Electrocatalyst for Formic Acid Fuel Cells

In this work, CeO2-modified Pd/CeO2-carbon nanotube (CNT) electrocatalyst for the electro-oxidation of formic acid has been investigated. The support CNT was first modified with different amounts (5–30 wt.%) of CeO2 using a precipitation-deposition method. The electrocatalysts were developed by dispersing Pd on the CeO2-CNT supports using the borohydride reduction method. The synthesized electrocatalysts were analyzed for composition, morphology and electronic structure using x-ray diffraction (XRD), scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) techniques. The formation of Pd nanoparticles on the CeO2-CNT support was confirmed using TEM. The activity of Pd/CeO2-CNT and of Pd-CNT samples upon oxidation of formic acid was evaluated by using carbon monoxide stripping voltammetry, cyclic voltammetry, and chronoamperometry. The addition of moderate amounts of cerium oxide (up to 10 wt.%) significantly improved the activity of Pd/CeO2-CNT compared to the unmodified Pd-CNT. Pd/10 wt.% CeO2-CNT showed a current density of 2 A mg−1, which is ten times higher than that of the unmodified Pd-CNT (0.2 A mg−1). Similarly, the power density obtained for Pd/10 wt.% CeO2-CNT in an air-breathing formic acid fuel cell was 6.8 mW/cm2 which is two times higher than Pd-CNT (3.2 mW/cm2), thus exhibiting the promotional effects of CeO2 to Pd/CeO2-CNT. A plausible justification for the improved catalytic performance and stability is provided in the light of the physical characterization results.

Ammonia strengthened graphene/CNT-wrapped polyaniline-nanofiber composites loaded with palladium nanoparticles for coin cell supercapacitors

Supercapacitors with high specific capacitance, energy and power densities as well as high cycle stability are demonstrated in this work. A newly developed palladium nanoparticle loaded reduced graphene oxide/CNT hydrogel (rGO/CNT@Pd) was synthesized and combined with polyaniline nanofibers (rGO/CNT@Pd + PANI Nf). The prepared materials were synthesized by a hydrothermal route, simultaneously reducing graphene oxide and PdCl2. Including pre-synthesized PANI nanofibers in the process led to formation of a 3D rGO/CNT matrix incorporating PANI and effectively preventing swelling/shrinkage damage during electrochemical testing. Subsequent ammonia treatment led to strengthening of the 3D matrix which further improved supercapacitor cycling stability. Material characterizations using scanning and transmission electron microscopy as well as X-ray diffraction and Raman spectroscopy were performed and Pd nanoparticle formation and uniform distribution in the rGO/CNT hydrogel was observed. The materials were used to construct CR2032 coin cell supercapacitors and tested by 2-electrode cyclic voltammetry and galvanostatic charge-discharge with 2 M H2SO4 electrolyte. Ammonia strengthened rGO/CNT@Pd + PANI Nf exhibited excellent electrochemical performance with a specific capacitance of 611.8 F g−1 and energy and power densities of 85 Wh kg−1 and 10.2 kW kg−1 at a current of 1.5 A g−1. Ammonia treatment effectively increased the cycle life of the composite and 84.3% of capacitance was retained after 10000 charge-discharge cycles.

Palladium-scavenging self-assembled hybrid hydrogels - reusable highly-active green catalysts for Suzuki-Miyaura cross-coupling reactions.

A hybrid hydrogel based on 1,3:2,4-dibenzylidene sorbitol (DBS) modified with acyl hydrazides combined with agarose was used for in situ reduction and binding of palladium from aqueous mixtures without the need for an external reducing agent. Palladium uptake was monitored and the formation of Pd nanoparticles (PdNPs) trapped within the gel and located close to the nanofibres was confirmed. This gel effectively scavenges palladium from solution to concentrations < 0.04 ppm - well below the recommended limits for pharmaceutical products. The resulting hybrid hydrogel with embedded PdNPs was used as a catalyst for Suzuki-Miyaura cross-coupling reactions. The gel network stabilises PdNPs, preventing aggregation/leaching and giving excellent catalytic lifetimes. The gel acts as a simple reaction dosing form, being simply added to reactions performed in green solvents in air. Once reactions are complete, the gel can be simply removed, recycled and reused (>10 times). Reactions were purified by simple washing protocols, and leaching of Pd from the gels is limited (<1 ppm). The gels were also used in flow-through mode, giving efficient, rapid reactions, with easy work-up. These catalytic gels combine advantages of homogeneous and heterogeneous catalysts - they are solvent compatible with the reaction taking place in a solution-like environment, while the solid-like gel network enables catalyst recycling. In summary, these hydrogels scavenge 'waste' palladium and convert it into gel 'wealth' capable of efficient, environmentally-friendly Suzuki-Miyaura catalysis.

Operando study of palladium nanoparticles inside UiO-67 MOF for catalytic hydrogenation of hydrocarbons.

Functionalization of metal-organic frameworks with metal nanoparticles (NPs) is a promising way for producing advanced materials for catalytic applications. We present the synthesis and in situ characterization of palladium NPs encapsulated inside a functionalized UiO-67 metal-organic framework. The initial structure was synthesized with 10% of PdCl2bpydc moieties with grafted Pd ions replacing standard 4,4'-biphenyldicarboxylate linkers. This material exhibits the same high crystallinity and thermal stability of standard UiO-67. Formation of palladium NPs was initiated by sample activation in hydrogen and monitored by in situ X-ray powder diffraction and X-ray absorption spectroscopy (XAS). The reduction of PdII ions to Pd0 occurs above 200 °C in 6% H2/He flow. The formed palladium NPs have an average size of 2.1 nm as limited by the cavities of UiO-67 structure. The resulting material showed high activity towards ethylene hydrogenation. Under reaction conditions, palladium was found to form a carbide structure indicated by operando XAS, while formation of ethane was monitored by mass spectroscopy and infra-red spectroscopy.

Electrostatic adsorption-microwave synthesis of palladium nanoparticles on graphene for improved cross-coupling activity

Graphene materials as catalyst supports have shown tremendous promise for improving catalytic activity. Pd nanoparticles supported by graphene defects have been shown to improve catalytic activity in Suzuki reactions, but understanding their formation and factors that affect their formation is still elusive. In order to gain a better understanding of this phenomenon, a new synthetic method was developed combining strong electrostatic adsorption method for directed ionic Pd precursor uptake with a new solventless microwave irradiation method to simultaneously form Pd nanoparticles and graphene defect sites. Catalytic activities an order of magnitude higher than commercial Pd-carbon catalysts were obtained using this new method with low microwave powers, short reaction times, under atmospheric conditions, and without the use of reducing agents or solvents. The systematic comparison of catalysts synthesized from four different graphene materials and two different Pd precursors revealed Pd-graphene defects form through three routes that are affected by the initial oxygen content of graphene support and choice of ionic Pd precursor.

Design of Pd@Graphene oxide framework nanocatalyst with improved activity and recyclability in Suzuki-Miyaura cross-coupling reaction

We describe a new method to synthesize a catalyst comprising of Pd nanoparticles encapsulated in a graphene oxide framework (Pd@GOF). GO was first intercalated with benzene-1,4-diboronic acid to afford a three-dimensional (3D) framework with uniform interlayer spaces, in which Pd nanoparticles were generated through salt reduction. Thus formed Pd nanoparticles were highly dispersed and stabilized inside a graphitic gallery space with a narrow particle size distribution. Thus obtained Pd@GOF catalyst exhibited an outperforming activity toward the Suzuki-Miyaura cross-coupling reaction in both polar and apolar solvents. Moreover, it can be reused for at least five cycles without any significant loss of the activity, while commercial Pd/C and Pd/GO exhibited a clear drop in the activity. These findings would establish the GOF as a promising scaffold to host noble metal nanoparticles and to construct desired metal@GOF nanocatalysts with improved activity and durability, which must be attractive for a broad range of practical applications.

Synthesis of Water-Soluble Palladium Nanoparticles Stabilized by Sulfonated N-Heterocyclic Carbenes.

A strategy involving the decomposition of palladium(II) organometallic complexes with sulfonated N-heterocyclic carbene ligands leads to the formation of stable and water-soluble Pd nanoparticles. Three different methodologies (thermal decomposition, reduction under 13 CO atmosphere, and reduction with H2 ) gave particles with different shapes and sizes, ranging from 1.5 to 7 nm. The structures of the organometallic intermediates and organic decomposition products were elucidated by NMR spectroscopy. To check the accessibility of the surface, the nanoparticles were tested as catalysts for the chemoselective hydrogenation of styrene in water. An effect of the particle size on the catalyst activity was observed. The aqueous phase was recycled up to ten times without any precipitation of metallic palladium.

Kinetic Profile and Catalytic Activity of Transition Metal‐Based Ionic Liquids for Reduction of Nitroarenes via In Situ Formation of Nanoparticles

AbstractThe experimentally determined apparent rate constant (kapp) shows that the [BmIm]2[PdCl4] and [BmIm]2[NiCl4] act as effective catalysts for the reduction of nitroarenes to aminoarenes in the presence of NaBH4. The TEM, XPS, XRD and dynamic light scattering studies show that there is in situ formation of Pd and Ni metal Nanoparticles (NPs) from the reduction of [BmIm]2[PdCl4] and [BmIm]2[NiCl4], respectively which are responsible for the enhancement in the catalytic activity. Thus, in the presence of the ionic liquid stabilized metal NPs show higher catalytic activity in comparison to the NPs stabilized with other capping agents as reported. The order of kapp as 1) PNP &gt; 2‐BrPNP &gt; 2‐APNP and 2) PNP &gt; ONP &gt; 2‐NR for reduction of nitroarenes using [BmIm]2[PdCl4] and [BmIm]2[NiCl4] and its correlation explained on the basis of electronic structure and hydrogen bonding ability of nitroarenes. The thermodynamic parameters such as Ea, ▵H#, ▵S# and ▵G# are in agreement with the surface catalyzed reduction reaction of PNP in the presence of NPs as catalyst. The kapp values illustrated the reduction reaction follow the Langmuir‐Hinshelwood (L‐H) mechanism.

Supercritical fluid-assisted immobilization of Pd nanoparticles in the mesopores of hierarchical porous SiO2 for catalytic applications

Pd nanoparticles were successfully immobilized in the mesopores of hierarchical porous SiO2 and TiO2 using supercritical carbon dioxide (scCO2)-acetone solution. The hierarchical porous SiO2 with macropores and mesopores demonstrated remarkable properties as a support for noble metal nanoparticle catalysts. The nanoparticle precursor, palladium(II) acetate (Pd(OAc)2), was impregnated into the mesopores of hierarchical porous SiO2 and TiO2 microparticles using scCO2. These samples were subsequently reduced by treatment in a stream of H2 at 473K. During reduction, the formed Pd nanoparticles were dispersed within the hierarchical porous SiO2, with a uniform three-dimensional distribution of nanoparticles in the mesopores revealed by TEM images. The resulting Pd@hierarchical porous SiO2 exhibited high activity for the heterogeneous catalytic hydrogenation reaction of styrene in methanol solution. The catalytic activity of the Pd@hierarchical porous SiO2 was higher than that of Pd@conventional porous SiO2 without hierarchical porosity or the Pd@hierarchical porous TiO2.

A New Mode of Operation of Pd-NHC Systems Studied in a Catalytic Mizoroki–Heck Reaction

Metal complexes bearing N-heterocyclic carbene (NHC) ligands are typically considered the system of choice for homogeneous catalysis with well-defined molecular active species due to their stable metal–ligand framework. A detailed study involving 19 different Pd-NHC complexes with imidazolium, benzimidazolium, and triazolium ligands has been carried out in the present work and revealed a new mode of operation of metal-NHC systems. The catalytic activity of the studied Pd-NHC systems is predominantly determined by the cleavage of the metal–NHC bond, while the catalyst performance is strongly affected by the stabilization of in situ formed metal clusters. In the present study, the formation of Pd nanoparticles was observed from a broad range of metal complexes with NHC ligands under standard Mizoroki–Heck reaction conditions. A mechanistic analysis revealed two different pathways to connect Pd-NHC complexes to “cocktail”-type catalysis: (i) reductive elimination from a Pd(II) intermediate and the release of...

Enhancing both selectivity and coking-resistance of a single-atom Pd1/C3N4 catalyst for acetylene hydrogenation

Selective hydrogenation is an important industrial catalytic process in chemical upgrading, where Pd-based catalysts are widely used because of their high hydrogenation activities. However, poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns. In this work, atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride (g-C3N4) using atomic layer deposition. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle (NP) formation. During selective hydrogenation of acetylene in excess ethylene, the g-C3N4-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/Al2O3 and Pd/SiO2 catalysts. In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C3N4 likely plays an important role in the catalytic performance enhancement. More impressively, the single-atom Pd1/C3N4 catalyst exhibited both higher ethylene selectivity and higher coking resistance. Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.

The effect of microemulsion composition on the morphology of Pd nanoparticles deposited at the surface of TiO2 and photoactivity of Pd-TiO2

A series of microemulsion (ME) system, constituted by different water to surfactant molar ratios (Wo) and oil to surfactant mass ratios (S), have been applied for Pd-TiO2 preparation. The effect of ME properties on the morphology of Pd nanoparticles formed at TiO2 surface and an effect of Pd size and distribution on the surface and photocatalytic properties of Pd-TiO2 were investigated. Microemulsion systems were characterized by means of viscosity, density, dynamic light scattering as well as surface tension measurements to find a correlation between the conditions of Pd nanoparticles formation, their morphology and photocatalyst features. The photocatalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), UV–vis diffuse-reflectance spectroscopy (DRS), BET surface area and elemental analysis. The photocatalytic properties of Pd-modified TiO2 particles were studied in a model reaction of phenol photodegradation under Vis irradiation, as well as active species involved in the photocatalytic reaction were determined. Microemulsion composition was found to be a crucial parameter in determining the features of the TiO2-based photocatalysts covered by metallic nanoparticles. The highest photocatalytic activity under Vis radiation was observed for the Pd-TiO2 sample (average diameter 2.4nm) obtained using 0.1mol% Pd in the ME system containing 1.5wt% of water and 82.8wt% of cyclohexane with average droplet size of 2.83±0.18nm. In this regard, synthesis of such metal-semiconductor composites through the microemulsion route should always be preceded by investigation of ME properties in order to the eliminate the inhibitory effect of ME internal structure.

Laser-induced in situ synthesis of Pd and Pt nanoparticles on polymer films

We present the localized in situ formation of Pd and Pt nanoparticles embedded in chitosan solid films. This is achieved by the photo-induced reduction of metallic precursors, previously incorporated in chitosan films, through controlled UV pulsed laser irradiation. Interestingly, at high number of laser pulses, Pd and Pt follow different formation pathways, contrary to their common photoreduction mechanism occurring at low irradiation pulses. Specifically, in the case of the Pd, a photofragmentation process takes place fracturing the previously formed nanoparticles into smaller ones; whereas in the case of Pt, the prolonged irradiation promotes the nanoparticles agglomeration. The combination of both precursors in a binary solid system results in the combined formation of both Pd and Pt nanoparticles in the polymer film upon laser irradiation. The herein reported approach is an efficient and precise tool to generate size- and density-controlled Pd and Pt nanoparticles in desired areas of polymeric films, rendering this method a potential candidate for the fabrication of flexible polymeric devices for gas-sensing or electro-catalysis applications. Schematic representation of Pd, Pt and Pd–Pt combined NPs formation mechanisms under pulsed laser irradiation

Green synthesis of Pd nanoparticles at Apricot kernel shell substrate using Salvia hydrangea extract: Catalytic activity for reduction of organic dyes

For the first time the extract of the plant of Salvia hydrangea was used to green synthesis of Pd nanoparticles (NPs) supported on Apricot kernel shell as an environmentally benign support. The Pd NPs/Apricot kernel shell as an effective catalyst was prepared through reduction of Pd2+ ions using Salvia hydrangea extract as the reducing and capping agent and Pd NPs immobilization on Apricot kernel shell surface in the absence of any stabilizer or surfactant. According to FT-IR analysis, the hydroxyl groups of phenolics in Salvia hydrangea extract as bioreductant agents are directly responsible for the reduction of Pd2+ ions and formation of Pd NPs. The as-prepared catalyst was characterized by Fourier transform infrared (FT-IR) and UV–Vis spectroscopy, field emission scanning electron microscopy (FESEM) equipped with an energy dispersive X-ray spectroscopy (EDS), Elemental mapping, X-ray diffraction analysis (XRD) and transmittance electron microscopy (TEM). The synthesized catalyst was used in the reduction of 4-nitrophenol (4-NP), Methyl Orange (MO), Methylene Blue (MB), Rhodamine B (RhB), and Congo Red (CR) at room temperature. The Pd NPs/Apricot kernel shell showed excellent catalytic activity in the reduction of these organic dyes. In addition, it was found that Pd NPs/Apricot kernel shell can be recovered and reused several times without significant loss of catalytic activity.

Synthesis of Monometallic (Au and Pd) and Bimetallic (AuPd) Nanoparticles Using Carbon Nitride (C3N4) Quantum Dots via the Photochemical Route for Nitrophenol Reduction.

In this study, we report the synthesis of monometallic (Au and Pd) and bimetallic (AuPd) nanoparticles (NPs) using graphitic carbon nitride (g-C3N4) quantum dots (QDs) and photochemical routes. Eliminating the necessity of any extra stabilizer or reducing agent, the photochemical reactions have been carried out using a UV light source of 365 nm where C3N4 QD itself functions as a suitable stabilizer as well as a reducing agent. The g-C3N4 QDs are excited upon irradiation with UV light and produce photogenerated electrons, which further facilitate the reduction of metal ions. The successful formation of Au, Pd, and AuPd alloy nanoparticles is evidenced by UV-vis, powder X-ray diffraction, X-ray photon spectroscopy, and energy-dispersive spectroscopy techniques. The morphology and distribution of metal nanoparticles over the C3N4 QD surface has been systematically investigated by high-resolution transmission electron microscopy (HRTEM) and SAED analysis. To explore the catalytic activity of the as-prepared samples, the reduction reaction of 4-nitrophenol with excellent performance is also investigated. It is noteworthy that the synthesis of both monometallic and bimetallic NPs can be accomplished by using a very small amount of g-C3N4, which can be used as a promising photoreducing material as well as a stabilizer for the synthesis of various metal nanoparticles.

Pd Nanoparticle Formation during Constant Potential Electrodepositions in Ionic Liquids

Electrodepositions in ionic liquids (ILs) allow for opportunities to improve deposited morphologies, access redox potentials that cannot be achieved in aqueous baths, and utilize less hazardous bath compositions. The driver to utilize ILs for Pd electrodeposition is to minimize hydrogen embrittlement challenges commonly associated with Pd electrodeposition in aqueous electrolytes. Generally, the resulting Pd deposits in ILs are thin films, loosely adhered fine powders or dendritic structures, depending upon the IL selected and the electrochemical parameters used(1, 2). Recently, it has also been shown that electroreduction of Pd in ILs can result in nanoparticles being formed in solution, rather than on an substrate electrode when high overpotentials are used(3). Previously, we showed Pd nanosphere formation can be controlled through potentiostatic pulse deposition in 1-butyl, 3-methylimidazolium chloride [Bmim][Cl] onto Ni electrode substrates(4). The nanosphere size was found to be a function of cycle time. In contrast, using 1-buty, 1-methylpyrrolidinum dicyanamide [Bmpyrr][DCA] under constant potential conditions, thin film Pd layers on nickel electrode substrates were obtained(5). We will present how, upon further investigation, these Pd “thin films” formed from constant potential deposition in [Bmpyrr][DCA] are actually agglomerates of nanoparticles that can be scraped off the Ni substrate and dispersed in solution in an unagglomerated state. These nanoparticles have an average size of 6.3 ± 1.6 nm when deposited at -2.3V vs. Fc/Fc+. Further investigation into the conditions for electrodeposition in ILs where it was thought that thin films were formed will also be discussed to better understand if the resulting deposits were truly thin films and not nanoparticle agglomerations.

ChemInform Abstract: Amino Acid‐Derived N‐Heterocyclic Carbene Palladium Complexes for Aqueous Phase Suzuki—Miyaura Couplings.

AbstractFive novel PEPPSI‐type Pd‐NHC complexes are synthesized.

Pd Nanoparticle Formation during Constant Potential Electrodepositions in Ionic Liquids

The palladium film deposited on a nickel substrate in 1-butyl-1-methylpyrrolidinium dicyanamide using a constant potential electrodeposition method was shown to be composed of nanoparticles under transmission electron microscopy. The electrodeposition was carried out by applying a potential hold of -2.3 V vs Fc/Fc+ for 16 h. The size distribution of palladium nanoparticles was unimodal and narrow with an average size of 6.3 ± 1.6 nm. The Pd nanoparticles were polycrystalline with (111) plane being the most prevalent. The implications of this include the having to reconsider the properties of electrodeposited Pd thin films from ionic liquids and opening further applications of electrodeposition of Pd to include nanoparticle synthesis.