Size Of Pd Nanoparticles Research Articles

Application of Pd Nanoparticles Supported on Mesoporous Hollow Silica Nanospheres for the Efficient and Selective Semihydrogenation of Alkynes

AbstractHerein, the preparation of a heterogeneous catalyst consisting of 1–2 nm sized Pd nanoparticles supported on amino‐functionalized mesoporous hollow silica nanospheres and its use for the semihydrogenation of mono‐ and disubstituted alkynes is reported. By utilizing this Pd nanocatalyst together with the green poisoning agent DMSO, high yields of the desired alkenes could be achieved, while suppressing the degree of over‐reduction to alkanes. To our delight, the Pd nanocatalyst displayed remarkable chemoselectivity towards the alkyne moiety, allowing the transformation to be carried out in the presence of other reducible functionalities, such as halogens, carbonyl, and nitro groups.

Effects of Pd Nanoparticle Size and Solution Reducer Strength on Pd/C Electrocatalyst Stability in Alkaline Electrolyte

The degradation of two commercial (E-TEK) electrocatalysts, made of palladium nanoparticles supported on Vulcan XC-72 (Pd/C) and differing by their average Pd nanoparticles diameter, was studied in alkaline and acidic solutions. The fate of the electrocatalysts upon accelerated stress test (AST) in 0.1 M NaOH was compared to that in 0.1 M H2SO4. Whereas Pd/C nanoparticles suffer dramatic degradation in 0.1 M H2SO4, electrochemical measurements combined with Identical-Location Transmission Electron Microscopy (ILTEM) demonstrate their higher stability in 0.1 M NaOH at 25°C than reported in the literature for Pt/C electrocatalysts (supported on the same support). As palladium is an efficient anodic material for direct alkaline fuel cells, the stability of Pd/C was investigated in the presence of reducing species in the alkaline electrolyte: alkaline electrolytes containing hydrogen or hydrazine borane yield slightly larger instability for the Pd/C nanoparticles, and the effect is less pronounced for large Pd/C nanoparticles than for small ones.

Catalytic hydrodechlorination reaction of chlorophenols by Pd nanoparticles supported on graphene

Chlorophenols are widely used as industrial chemicals such as herbicides, insecticides, wood preservatives, and disinfectants. However, chlorophenols are very toxic materials and they have become the cause of current environmental issues. Hydrodechlorination (HDC) reaction is a more environmentally friendly removal method of chlorophenols than other methods. In this paper, Pd–modified graphene was prepared and applied to HDC reaction. Pd supported on graphene (refer to Pd/G) was prepared using the recently reported microwave irradiation method. The Pd(II)/GO was made by impregnation methods of palladium precursors in solution phase and was subsequently reduced to Pd/G by microwave irradiation. The morphological and chemical structure of the Pd/G was characterized by XRD, SEM, ICP-MS, EDS, and TEM. It was found that the graphene-based Pd catalyst showed the highest catalytic performance among Pd/Y, Pd/MCM-41, and Pd/G catalysts. This is attributed to the smaller particle size and higher dispersions of Pd nanoparticles on the graphene surface. The catalytic HDC of chlorophenols was investigated. For HDC reaction, 100 ppm solution of chlorophenols such as 4-chlorophenol, six isomers of dichlorophenol, and 2,3,5-trichlorophenol in isopropanol was treated with catalyst and base, such as Na2CO3 and K2CO3, under a hydrogen gas at ambient pressure. The progress of the chlorophenol decomposition was analyzed with GC. All chlorophenols were completely decomposed within 2 h in the 3 % Pd/G catalyst. The reaction pathway of chlorophenols was elucidated from the conversion of chlorophenols and selectivities of products. The reuse of the catalyst was also studied. The performance of the recycled catalyst in HDC reaction up to six successive runs was observed.

Catalytic applications of alkali-functionalized carbon nanospheres and their supported Pd nanoparticles

Carbon nanospheres (CNSs) prepared by hydrothermal approach and post-functionalization with alkali solutions were employed as solid base catalysts in aldol condensation. The negative charge and alkalinity of CNS surfaces were controlled by the concentration of alkali solutions, leading to the high selectivity superior to aqueous NaOH as the traditional catalyst. Furthermore, CNSs with varying surface alkalinity can be adopted as proper supports for highly dispersed Pd nanoparticles with well-controlled size distribution. The optimized alkaline CNS-supported Pd catalysts demonstrated enhanced reactivities in the solvent-free selective oxidation of benzyl alcohol and the aerobic oxidation of glycerol. In-depth characterizations of their structural and electronic properties by transmission electron microscope (TEM), field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscope (FTIR) and X-ray photoelectron spectroscopy (XPS) were performed to elucidate the nature of the active sites and the mechanism. The effect of electron density, size of Pd nanoparticles as well as the surface alkalinity of supports on the catalytic performance has been unveiled.

Advances in Pd Nanoparticle Size Decoration of Mesoporous Carbon Spheres for Energy Application.

Pd nanoparticles with different sizes and diameter distributions were successfully deposited on the surface of disordered mesoporous carbon spheres (DMHCS). The size and diameter distribution of the Pd particles were controlled by the application of different experimental conditions. Two methods of synthesis (reflux and impregnation) and two Pd precursors (palladium (II) acetyloacetonate (Pd(acac)2) and palladium (II) acetate (Pd(OAc)2)) were investigated and compared for the preparation of Pd-decorated DMHCS. The hydrogen storage properties of the pristine DMHCS and Pd-modified DMHCS at 40 °C and a pressure range of 0–45 bar were studied. The results showed that Pd-supported carbon samples synthesized in the presence of Pd(OAc)2 exhibited enhanced hydrogen storage capacity in respect to the pristine DMHCS. The maximum hydrogen storage of 0.38 wt.% exhibited the sample with the Pd nanoparticle diameter distribution of 2–14 nm and the average Pd crystallite size of 7.6 nm. It was found that the Pd nanoparticle content, size, and diameter distribution have a noticeable influence on H2 storage capacity.

Layer‐by‐layer assembly of {chitosan/Pd}n multilayer film based on in‐situ photochemical reduction with excellent electrocatalytic properties

Chitosan/palladium {CTS/Pd}n composite multilayer film was assembled based on layer‐by‐layer self‐assembly technique and in‐situ photo‐chemical reduction reaction, in which the CTS plays the role of a photo‐reduction agent and an assembly reagent. Transmission electron microscopy (TEM) shows that spherical Pd nanoparticles with diameter of 20 nm are well‐dispersed in the composite multilayer films, and the size of Pd nanoparticles increased gradually with the extension of illumination time. Besides, the {CTS/Pd}n composite multilayer film exhibits linear, uniform and regular layer‐by‐layer growth. Furthermore, the {CTS/Pd}n composite multilayer film presents an excellent catalytic properties for oxygen reduction, and it has potential application in energy, chemical synthesis and biological processes. Copyright © 2015 John Wiley & Sons, Ltd.

High performance Pd catalysts supported on bimodal mesopore silica for the catalytic oxidation of toluene

A series of bimodal mesoporous silica (BMS-x)-supported Pd catalysts were successfully prepared by a facile sol-gel approach, followed by an impregnation method. The synthesized catalysts were characterized by several analytical techniques and the oxidation of toluene was used to evaluate their catalytic performance. Textural analysis showed that all samples had high surface areas (∼1000 m2/g), large pore volumes (∼1.2 cm3/g) and uniform mesopore size (∼2.6 nm). Defining the level of ammonia solution to within a certain range resulted in the catalysts possessing a typical bimodal mesoporous structure with an intraparticle framework mesopore and an interparticle textural mesopore (18–40 nm). Transmission electron microscopy observations and CO chemisorption results revealed that this unique bimodal mesoporous structure helped to decrease the particle size of Pd nanoparticles and could further enhance their dispersion. Activity tests revealed the Pd/BMS-5–Pd/BMS-20 catalysts with a bimodal mesopore structure possessed superior catalytic performance for the oxidation of toluene compared to Pd/BMS-30 with a unimodal mesopore structure. More importantly, compared with the Pd/MCM-41 and Pd/MCM-48 catalysts, Pd/BMS-15 had improved hydrothermal stability and catalytic performance at a high gas hourly space velocity of 70000 h−1. These results indicate the potential application of the catalysts for the elimination of volatile organic compounds.

Effect of processing parameters on size, density and oxygen reduction reaction (ORR) activity of Pd nanoparticles grown by spin coating

To study oxygen reduction reaction (ORR) activity Pd nanoparticles were grown on flat (Si and glass) substrate via spin coating of Pd2+ ions solution followed by chemical reduction in aqueous hydrazine hydrate solution. Growth of Pd nanoparticles was confirmed by x-ray diffraction and x-ray photoelectron spectroscopy techniques. UV–vis-NIR spectroscopy was used to optimize reduction time, whereas scanning electron microscopy was utilized to study size and distribution of grown Pd nanoparticles. It was observed that most of the Pd nanoparticles grow with unique preferable size. The preferable size and density of grown Pd nanoparticles can be precisely controlled by processing parameters (rpm, ramp and reducing agent concentration). The grown Pd nanoparticles are thermally stable up to 450°C. The ORR activity was found to be dependent on size as well as density of Pd nanoparticles.

Synthesis of p-aminophenol from p-nitrophenol reduction over Pd@ZIF-8

p-Aminophenol was synthesized by the catalytic reduction of p-nitrophenol over Pd@ZIF-8 prepared by an assembly method that involves the construction of ZIF-8 crystals around the pre-synthesized polyvinylpyrrolidone (PVP)-stabilized palladium nanoparticles. The catalyst was characterized in detail by XRD, FESEM, HRTEM, XPS, ICP, N2 sorption, TGA and FT-IR. The analysis results show that the hybrid material Pd@ZIF-8 has a rhombic dodecahedral structure like ZIF-8, the particle size of Pd@ZIF-8 is about 400 nm, which is much greater than that of ZIF-8 due to the promotion of PVP, and the pre-synthesized Pd nanoparticle with a diameter of 2–5 nm can be well dispersed within the ZIF-8 crystals. The as-prepared Pd@ZIF-8 catalyst exhibits much higher catalytic activity than the commercial Raney Ni in the reduction of p-nitrophenol to p-aminophenol, and can be reused at least five times without obvious loss in catalytic activity. Furthermore, the Pd@ZIF-8 shows outstanding catalytic selectivity for the synthesis of p-aminophenol, and only target product p-aminophenol is formed in the p-nitrophenol reduction. The better catalytic performance of Pd@ZIF-8 may be caused by the small size and high dispersion of Pd nanoparticles confined within the ZIF-8 framework.

Hierarchical porous Ca(BO2)2 microspheres: Hydrothermal–thermal conversion synthesis and their applications in heavy metal ions adsorption and solvent-free oxidation of benzyl alcohol

Hierarchical three-dimensional (3D) porous structures are of great significance for their versatile applications in diverse fields. Herein, uniform Ca4B10O19·7H2O microspheres were successfully fabricated via a facile hydrothermal method, followed by a thermal conversion (700°C, 2.0h) without any additives, leading to the 3D hierarchical porous calcium metaborate (Ca(BO2)2) microspheres with well-preserved spherical morphology and high crystallinity. When employed as adsorbents, the adsorption isotherms of Pb2+ and Cd2+ onto porous Ca(BO2)2 microspheres were well fitted with the Langmuir adsorption model, giving rise to the maximum adsorption capacities for Pb2+ and Cd2+ as 140.2 and 110.6mgg−1, respectively. When utilized as catalyst support, the good dispersion and smaller size of metallic Pd nanoparticles (NPs) as well as more and stronger acid sites on the catalyst resulted in the 1.05wt% Pd/Ca(BO2)2 catalyst, by using which the conversion of benzyl alcohol and selectivity to benzaldehyde with O2 as oxidant reached 94.3% and 96.0%, respectively. The resultant supported catalyst also exhibited satisfactory high conversion and especially excellent selectivity during 10 cycles of catalysis, revealing the as-prepared porous Ca(BO2)2 microspheres as superior catalyst carrier. The present hierarchical porous Ca(BO2)2 microspheres afforded promising and competitive candidates for water treatment and heterogeneous catalysis.

Simple Preparation of Pd Core Nanoparticles for Pd Core/Pt Shell Catalyst and Evaluation of Activity and Durability for Oxygen Reduction Reaction

Pd core nanoparticles less than 5 nm in mean size were prepared on carbon black (CB) without any stabilizer by using palladium acetate as a precursor and CO as a reducing agent, and then used for preparing Pd core/Pt shell nanoparticles-loaded CB (Pt/Pd/CB). The mean size of Pd nanoparticles could be controlled by the concentration of palladium acetate and the CO bubbling time. The cyclic voltammograms of two Pd nanoparticles-loaded CB (Pd4.2/CB, Pd3.3/CB) electrodes whose mean size was 4.2 and 3.3 nm, respectively, had characteristics similar to a Pt electrode after the formation of a Pt monolayer shell, suggesting that the Pd core nanoparticles were almost covered with the Pt monolayer shell. The oxygen reduction reaction (ORR) on both Pt/Pd/CB proceeded in 4-electron reduction mechanism. Both Pt/Pd/CB electrodes was ca. 1.5 times higher in ORR activity per electrochemical surface area of Pt (specific activity, SA) than the commercial Pt nanoparticles-loaded CB (Tanaka Kikinzoku Kogyo, Pt/CB-TKK) electrode, and the Pt/Pd3.3/CB electrode had higher SA than the Pt/Pd4.2/CB electrode. The ORR activity per unit mass of Pt for both Pt/Pd/CB electrodes was 5.0 and 5.5 times as high as that for the Pt/CB-TKK electrode, respectively. The durability of both Pt/Pd/CB electrodes was comparable to that of Pt/CB-TKK.

One-pot synthesis of carbon-supported monodisperse palladium nanoparticles as excellent electrocatalyst for ethanol and formic acid oxidation

Electrocatalysts of ultrafine and surface-clean nanoparticles uniformly dispersed on high-surface-area conducting supports are among the prime requests for large-scale application of fuel cells. We report a facile one-pot synthesis of carbon-supported monodisperse and ultrafine Pd nanoparticles (Pd/C) in N,N-dimethylformamide by using amine–borane as reducing agent in the absence of any surfactants. The ultrasmall size, monodispersity and surfactant-free surface of Pd nanoparticles make the resulted Pd/C catalyst exhibit excellent electrocatalytic performance toward the oxidation of organic fuels. For formic acid oxidation reaction, it exhibits a similar onset potential to that of the commercial Pd/C (BASF) but about 2.6 times increase in current density, which can be attributed to the increased electrochemically surface area (ECSA); while for ethanol oxidation, it shows about 140 mV negative shift of the onset potential as well as the current increase much beyond that expected by the increased ECSA, indicating that the reduction of Pd particle size not only increases the ECSA, but also enhances the intrinsic activity of surface Pd atoms. The different activity enhancing behaviors for the formic acid and ethanol oxidation have been discussed in terms of the reaction mechanisms. Chronoamperometric measurements show that the home-made Pd/C is also much more durable.

Activated Carbon Supported Palladium Nanoparticle Catalysts Synthesized by Atomic Layer Deposition: Genesis and Evolution of Nanoparticles and Tuning the Particle Size

We report a novel method of synthesizing uniform Pd nanoparticle catalysts with tunable particle size on activated carbon (AC) supports. Pd is deposited on AC supports by atomic layer deposition (ALD) using Pd hexafluoroacetylacetonate and HCOH as the precursors. The ALD surface reaction becomes saturated with long precursor exposures. The saturated Pd loading is roughly linear to the number of ALD cycle. The increased number of ALD cycles leads to growth in particle density and particle size. Modifying the surface chemical state of the AC support provides an alternative method of controlling the size of Pd nanoparticles. Acid treatment and high temperature calcination are applied to the AC to adjust the type and concentration of surface functional groups. In order to investigate the genesis and evolution of Pd nanoparticles, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and X-ray diffraction characterizations are carried out after each step of Pd ALD on the AC suppor...

Pd–MnO2–Fe2O3/C as electrocatalyst for the formic acid electrooxidation

Pd–MnO2–Fe2O3/C and Pd/C (for comparison to the former) were synthesized by NaBH4 reduction method and then annealed at 500 °C. The catalysts were characterized physically by various techniques including XRD, TEM, EDX, XPS and ICP. The results showed that both MnO2 and Fe2O3 are in the amorphous form while Pd is crystalline for both catalysts. The particle size of Pd nanoparticles in Pd–MnO2–Fe2O3/C and Pd/C catalysts were found to be 11.6 nm and 10.9 nm, respectively. The total metal weight percent in Pd–MnO2–Fe2O3/C was determined as 18% and the metal molar ratios of Pd:Mn:Fe was calculated as 49:20:31. By cyclic voltammetry (CV) and chronoamperometry (CA), the ternary catalyst showed a superior electrocatalytic activity, namely of ≈3.4 times higher than Pd/C. The results also indicated that amorphous third parties may play a crucial role to improve the catalyst activity towards formic acid oxidation. All of these results are reported and discussed in details herein.

Size-dependent electrocatalytic reduction of CO2 over Pd nanoparticles.

Size effect has been regularly utilized to tune the catalytic activity and selectivity of metal nanoparticles (NPs). Yet, there is a lack of understanding of the size effect in the electrocatalytic reduction of CO2, an important reaction that couples with intermittent renewable energy storage and carbon cycle utilization. We report here a prominent size-dependent activity/selectivity in the electrocatalytic reduction of CO2 over differently sized Pd NPs, ranging from 2.4 to 10.3 nm. The Faradaic efficiency for CO production varies from 5.8% at -0.89 V (vs reversible hydrogen electrode) over 10.3 nm NPs to 91.2% over 3.7 nm NPs, along with an 18.4-fold increase in current density. Based on the Gibbs free energy diagrams from density functional theory calculations, the adsorption of CO2 and the formation of key reaction intermediate COOH* are much easier on edge and corner sites than on terrace sites of Pd NPs. In contrast, the formation of H* for competitive hydrogen evolution reaction is similar on all three sites. A volcano-like curve of the turnover frequency for CO production within the size range suggests that CO2 adsorption, COOH* formation, and CO* removal during CO2 reduction can be tuned by varying the size of Pd NPs due to the changing ratio of corner, edge, and terrace sites.

Enhanced activity for CO oxidation over Pd/Al2O3 catalysts prepared by atmospheric-pressure cold plasma

Atmospheric-pressure dielectric barrier discharge (DBD) cold plasma was employed to prepare Pd/Al2O3 catalysts by simple incipient wetness impregnation using Pd(NO3)2 and PdCl2 as precursors, respectively. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and N2 adsorption–desorption measurement were used to characterize the Pd/Al2O3 catalysts. CO catalytic oxidation reaction was adopted to investigate the activity of the catalysts. The activity for the Pd/Al2O3 samples prepared by cold plasma using the same Pd precursor was higher than that prepared by thermal reduction method, which indicated that cold plasma is an efficient method for preparing high-performance Pd/Al2O3 catalysts. The results also showed that the Pd/Al2O3 catalysts prepared using Pd(NO3)2 as precursor possess smaller size of Pd nanoparticles, and most of the Pd nanoparticles were distributed on the surface of the Al2O3 support. In addition, a certain amount of chemisorbed oxygen species were detected on the surface of Al2O3 support due to the oxygen-containing Pd precursor. Therefore, they exhibited significantly enhanced activity for CO oxidation than that prepared using PdCl2 as Pd precursor. Atmospheric-pressure DBD cold plasma is a fast and facile method (just 6-min reduction) for fabricating high-performance Pd/Al2O3 catalysts using Pd(NO3)2 as Pd precursor.

High-Efficiency Palladium Nanoparticles Supported on Hydroxypropyl-β-Cyclodextrin Modified Fullerene [60] for Ethanol Oxidation

In this paper, Palladium nanoparticles with uniform size and high dispersion have been successfully assembled on hydroxypropyl-β-Cyclodextrin (HP-β-CD) modified C60 (abbreviated as HP-β-CD-C60) via a sodium borohydride reduction process. According to the transmission electron microscopy (TEM) measurements, the average particle size of the as-prepared Pd nanoparticles dispersed on HP-β-CD modified C60 is 2.7nm. Electrochemical studies reveal that the Pd/HP-β-CD-C60 modified electrode shows a significantly high electrocatalytic activity, much more negative onset potentials and better stability than electrodes modified by other electrocatalysts for ethanol oxidation, which indicates that it is a better potential candidate for application in a direct ethanol fuel cell (DEFC).

Ethanol oxidation on Pd/C promoted with CaSiO3 in alkaline medium

In this paper, CaSiO3 was prepared using a thermal decomposition approach and added to Vulcan XC-72 carbon black as support material. The X-ray diffraction and Transmission electron microscopy results show that the addition of CaSiO3 does not significantly change the particle size and distribution of Pd nanoparticles. The X-ray photoelectron spectroscopy reveals the interaction between Pd and CaSiO3. In addition, the electrochemical CO-striping measurement reveals that the Pd/50CaSiO3/C catalyst exhibits the largest electrochemical active surface and best CO tolerance. Moreover, cyclic voltammetry and chronoamperometry tests demonstrate that the Pd supported by CaSiO3 and C (50:50 in wt.%) possesses a much higher current density (1408mAmg−1) than that of the Pd/C catalyst (743mAmg−1) towards ethanol oxidation in alkaline media, and better stability as well. These results support the suitability of Pd/50CaSiO3/C catalyst developed in this work as a promising candidate for direct ethanol fuel cells application

Improved performance of carbon nanofiber-supported palladium particles in the selective 1,3-butadiene hydrogenation: Influence of carbon nanostructure, support functionalization treatment and metal precursor

Two types of commercial carbon nanofibers with different graphitic structure, Pyrograph PR24-HHT (NFHHT) and PR24-PS (NFPS) were chemically modified to introduce oxygen groups or SO3H-containing species on their surface. Incorporation of these surface groups was confirmed by temperature programed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Palladium catalysts using these modified supports and PdCl2 as precursor were prepared, and subsequently tested in the partial hydrogenation of 1,3-butadiene under conditions of excess hydrogen. The effect of using a different Pd precursor (PdSO4) was also studied. All the prepared catalysts were characterized by transmission electron microscopy to determine the Pd nanoparticle sizes and by X-ray photoelectron spectroscopy to obtain the surface composition and the oxidation state characteristics of the Pd surface species. The carbon nanofiber structure seems to determine the Pd particle size and morphology, probably due to different metal–support interaction. Selectivities to butenes higher than 95% were obtained with the catalysts prepared on SO3H-modified supports or with the PdSO4 precursor, while over-hydrogenation to butane took place over the Pd on oxidized supports. Catalytic activity–structure correlations have been derived and it is proposed that the catalytic behaviour depends on the type of sulfur species, functional group or adsorbed residual sulfur. Furthermore, variations in 1-butene selectivity and 2-butene trans/cis ratio between the two series of catalysts were also detected and ultimately related to the different nanostructure of the carbon nanofiber.

Determination of Parameters Useful for the Control of the Average Size of Pd Nanoparticles for C–Pd Composite

Carbon–palladium composites have been investigated by the method of transmission electron microscopy. The composites have been obtained by two different processes: physical vapor deposition (PVD) and chemical vapor deposition (CVD). The relation between the average size of a palladium particle, the time, and temperature has been carried out. The samples were annealed at different temperatures—from \(500\,^{\circ }\hbox {C}\) to \(750\,^{\circ }\hbox {C}\) but also for three different times, that is, 5 min, 10 min, and 30 min. Activation energies were calculated from the Arrhenius equation. Obtained values for PVD and PVD/CVD samples are: \(64.6\,\hbox {kJ}{\cdot }\hbox {mol}^{-1}\) and \(38.8\,\hbox {kJ}{\cdot }\hbox {mol}^{-1}\), respectively. Determination of the activation energy will be useful in controlling the growth of palladium grains. Significant differences in values for both series resulted from encapsulation in graphite–palladium particles, which were obtained in the PVD/CVD process. Those graphite planes are formed at temperatures above \(600\,\,^{\circ }\hbox {C}\) and significantly slow down the growth of palladium particles.