Pd Black Research Articles

High C1 selectivity in alkaline ethanol oxidation reaction over stable Lewis pairs of Pd-MxC@CNT (M = W, Mo and Cr)

Pd-based catalysts have been widely studied as electrocatalysts for ethanol oxidation reaction (EOR) because of their higher oxygenophilic properties. However, there are still some disadvantages such as low activity, poor stability and poor selectivity, which hinder the development of EOR. Herein, a method through strong metal-support interaction (SMSI) and heterostructure of Pd-MxC@CNT (M = W, Mo and Cr) to construct a stable Lewis acid-base pair is proposed. Pd-W2C@CNT nanomaterial showed the highest mass activity (13.9 A mgPd−1), C1 selectivity (74.15%) and stability, better than Pd Black (3.5 A mgPd−1, 7.2%) and Pd@CNT (4.1 A mgPd−1, 7.6%). Ex situ and in situ electrochemical experiments reveal that the introduction of W2C became a stable electron donor for Pd, increasing the electron density of Pd atoms and forming a stable Lewis acidity Pd atoms to weaken the adsorption of intermediates. Reducing the electron density of W2C and forming a stable Lewis basicity W2C to provide sufficient OH adspecies for the reaction, thereby increasing the selectivity of the C1 pathway. Furthermore, the Pd-MxC@CNT synthesized by this method also exhibited excellent EOR activity, stability and C1 selectivity and glycerol oxidation reaction (GOR) performance.

3D-ordered porous nitrogen and sulfur Co-Doped carbon supported PdCuW nanoparticles as efficient catalytic cathode materials for Li-O2 batteries

3D-ordered porous nitrogen and sulfur co-doped carbon (NS/C) is synthesized from the functionalized fluidic acrylonitrile telomer (ANT) as C, N and S source. The dispersed PdCuW nanoparticles with an average size of 5.25 nm are supported on the walls of the NS/C by a glycol reduction method. Compared with 20%Pd black (Pd/C), NS/C and 20%Pd-NS/C, it is found that PdCuW-NS/C composite with 11.4 wt% Pd exhibits superior catalytic activity for oxygen reduction reaction (ORR) in alkaline solution. Moreover, PdCuW-NS/C possesses higher capacities, lower overpotentials and better cyclic stability as cathode materials for Li-O2 batteries; the cyclic retention of more than 70 cycles are achieved at 300 mA g−1 with the restricted capacity at 500 mAh g−1.

Ultrafast synthesis of flower-like ordered Pd3Pb nanocrystals with superior electrocatalytic activities towards oxidation of formic acid and ethanol

Ordered intermetallic nanocrystals with high surface area are highly promising as efficient catalysts for fuel cell applications because of their unique electrocatalytic properties. The present work discusses about the controlled synthesis of ordered intermetallic Pd3Pb nanocrystals in different morphologies at relatively low temperature for the first time by polyol and hydrothermal methods both in presence and absence of surfactant. Here for the first time we report surfactant free synthesis of ordered flower-like intermetallic Pd3Pb nanocrystals in 10 s. The structural characteristics of the nanocrystals are confirmed by powder X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. The as synthesized ordered Pd3Pb nanocrystals exhibit far superior electrocatalytic activity and durability towards formic acid and ethanol oxidation over commercially available Pd black (Pd/C). The morphological variation of nanocrystals plays a crucial role in the electrocatalytic oxidation of formic acid and ethanol. Among the catalysts, the flower-like Pd3Pb shows enhanced activity and stability in electrocatalytic formic acid and ethanol oxidation. The current density and mass activity of flower-like Pd3Pb catalyst are higher by 2.5 and 2.4 times than that of Pd/C for the formic acid oxidation and 1.5 times each for ethanol oxidation.

Pd black decorated by Pt sub-monolayers as an electrocatalyst for the HCOOH oxidation

Pd black was modified by a very low amount of Pt corresponding to a sub-monolayer (ML). Spontaneous displacement method was employed. The catalysts with 0.02–0.12 ML were characterized by cyclic voltammetry and COads stripping and were tested for HCOOH oxidation under the potentiodynamic and potentiostatic conditions. All the Pt@Pd catalysts were more active for HCOOH oxidation than Pd black. The Pt@Pd with 0.08 ML of Pt exhibited the highest activity with the maximum current density under the potentiodynamic conditions of 8 mA cm−2 (vs. 2.7 mA cm−2 on Pd black). Contrasting HCOOH oxidation kinetics on Pt@Pd and Pt@Au catalysts revealed that the current densities are higher, and the poisoning rate is lower on Pt@Pd catalyst. This was ascribed to an optimal strength of the Pt–adsorbate bond when Pt is supported on Pd and to a possible influence of the Pt atoms on the Pd substrate.

Formation of porous Pd black induced by in situ catalytic reaction

The in situ heterogeneous catalytic reaction of formic acid decomposition was applied as a ‘reaction template’ in the synthesis of porous Pd black. The obtained porous Pd black was characterized by transmission electron microscopy, electrochemical measurements and x-ray photoelectron spectroscopy. It was found that the porous Pd black had a high electrochemical active surface area of about 40.2 m2 g−1 and a clean surface. It could be used directly as a catalyst in many fields such as fuel cells.

Effect of the nature of the acido ligand in the precursor on the properties of nanosized palladium-based hydrogenation catalysts modified with elemental phosphorus

The effect of the nature of the acido ligand in the precursor and the modifying action of elemental phosphorus on palladium catalysts for hydrogenation are reported. The large turnover frequency (TOF) and turnover number (TON) values observed for styrene hydrogenation on the Pd blacks prepared in situ by PdCl2 reduction with hydrogen in DMF are due to the formation of fine-particle catalyst with a base particle size of 6–10 nm. This is explained by the high PdCl2 reduction rate and by the formation of a palladium cluster stabilizer—dimethylammonium chloride—in the reaction system via the catalytic hydrolysis of the solvent (DMF). The modifying action of elemental phosphorus on the properties of the palladium catalysts depends on the nature of the acido ligand in the precursor. In the case of oxygen-containing precursors at small P/Pd ratios, elemental phosphorus exerts a promoting effect, raising the TON and TOF values by a factor of about 9. In the case of palladium dichloride as the precursor, white phosphorus exerts an inhibiting effect. At the same time, it enhances the stability of the catalyst, raising the TON value at P/Pd = 0.3. The causes of these distinctions are considered.

Preparation and catalytic properties of bis(imino)pyridine palladium(II) complexes as efficient catalysts for Suzuki cross‐coupling reaction in water

AbstractAir‐stable bis(imino)pyridine palladium(II) complexes were synthesized and complex 12 proved to be a highly efficient catalyst for the Suzuki cross‐coupling reaction between aryl bromides and arylboronic acids in air using water as solvent. The coupling reaction proceeded smoothly under mild conditions to provide biaryls in excellent yields and Pd black was not observed. The recycling of the catalysts was also investigated, for up to three cycles, and complex 12 still exhibited good activity. Copyright © 2009 John Wiley & Sons, Ltd.

New Synthetic Approach to the Bicyclo[3.1.0]hexane Ring System from (+)-(1R,4R)-4-(Benzyloxymethyl)-4-(hydroxymethyl)cyclopent-2-enol.

A methanocarba approach to conformationally constrain the sugar ring in nucleosides and nucleotides was introduced by Marquez and co-workers. Thus, a bicyclo[3.1.0]hexane system has been constrained in a North ((N), 2'-exo) or South ((S), 2'-endo) conformation, according to the pseudorotational cycle. In many studies of the ribose ring conformation of nucleosides and nucleotides binding to G proteincoupled receptors (GPCRs), novel (N)-ligands for adenosine receptors and P2Y receptors provided favorable receptor affinity and/or selectivity compared to their corresponding (S)-conformers. In addition, (N)-bicyclo[3.1.0]hexane nucleosides, -tides and oligonucleotides, including 2'-deoxy analogues, were good candidates for the development of a potent antiherpes agent, as an inhibitor of (cytosine C5)methyltransferase, for using in oligonucleotides and as a mechanistic probe of base flipping by Hhal DNA methyltransferase. Since the biological relevance of (N)-bicyclo[3.1.0]hexane derivatives is so high, additional effort is warranted to overcome the drawbacks of the previous synthetic pathways described in earlier publications. Those methods involved two or three operationally demanding steps and gave unexpectedly low yields when applied to a gram-scale synthesis (Figure 1). The preparation of (N)-bicyclo[3.1.0]hexanes in quantity is crucial to progress in the related research fields; thus, improving the yield of existing synthetic steps or developing novel synthetic pathways is desirable. In this letter we describe the conversion of (+)(1R,4R)-4-(benzyloxymethyl)-4-(hydroxymethyl)cyclopent2-enol into a key intermediate (+)-bicyclo[3.1.0]hexane alcohol 1. The starting material 2 contains a quaternary carbon, which eliminates the need for harsh conditions usually associated with the construction of a quaternary carbon center. Although there remain aspects for further refinement, this work provides a novel route to obtain the crucial intermediate (+)-bicyclo[3.1.0]hexane 1. The synthesis of (+)-(1R,4R)-4-(benzyloxymethyl)-4(hydroxymethyl)cyclopent-2-enol 2 was done according to the previously reported method. The versatility of diol 2 was demonstrated previously with the synthesis of the (N)locked bicyclo[2.2.1]heptane system. Preparation of silyl acetonide 3 from 2 followed a well-established method. The published report gave a synthetic method to a silyl triol, which was protected as the acetonide to afford silyl acetonide 3 (Scheme 1). Removal of the benzyl group with Pd/C in the presence of hydrogen in a variety of conditions was also accompanied by the unexpected deprotection of the silyl group. Treatment of silylated acetonide 3 with Pd black

Surface State and Composition of a Disperse Pd Catalyst after Its Exposure to Ethylene

Pd black was exposed to ethylene alone or in its mixture with hydrogen at 300 and 573 K. The samples were investigated by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Room temperature introduction of C(2)H(4) (also in the presence of H(2)) induced a binding-energy (BE) shift in the Pd 3d doublet and changed its full width at half-maximum (fwhm). The UPS features indicate shifting of electrons from the Pd d-band to Pd-H, Pd-C, and even Pd-OH species. Vinylidene (BE approximately 284.1 eV) may be the most abundant individual surface species on disperse Pd black, along with carbon in various stages of polymerization: "disordered C" (BE approximately 284 eV), graphite (approximately 284.6 eV), and ethylene polymer (approximately 286 eV), and also some "atomic" C (BE approximately 283.5 eV). Introduction of H(2) followed by ethylene brought about stronger changes in the state of Pd than exposure in the reverse sequence. This may indicate that the presence of some surface C may hinder the decomposition of bulk PdH. Formation of Pd hydride was blocked when ethylene was introduced prior to H(2). The C 1s intensity increased, the low-binding-energy C components disappeared, and graphitic carbon (BE approximately equal to 284.6 eV) prevailed after ethylene treatment at 573 K. The loss of the Pd surface state and "PdH" signal were observed in the corresponding valence band and UPS spectra. Hydrogen treatment at 540 K was not able to decrease the concentration of surface carbon and re-establish the near-surface H-rich state. UPS showed overlayer-type C in these samples. The interaction of Pd with components from the feed gas modified its electronic structure that is consistent with lattice strain induced by dissolution of carbon and hydrogen into Pd, as indicated by the d-band shift and the dilution of the electron density at E(F).

Pd Black in Water as an Efficient Catalyst of the Suzuki Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Successive Hydrogenation and Dechlorination Systems Using Palladized Ion Exchange Membranes

Pd black was deposited on a cation or anion exchange membrane by electroless plating and the subsequent electroplating. Total amount of Pd black deposited on the ion exchange membranes was about one eighth of the mass of the corresponding Pd sheet used in the previous work. A hydrogenation system of styrene and a dechlorination system of 4-chlorotoluene were successfully constructed using a two-compartment cell separated by the resulting palladized ion exchange membranes. The sole hydrogenation product was ethylbenzene, and the dechlorination product was only toluene. In each case current efficiency for ethylbenzene and toluene production was markedly improved by using methanol with high polarity and was not less than that on a Pd sheet or palladized one as a reference. Considering these results, the plausible mechanism of the hydrogenation and dechlorination on the palladized ion exchange membranes was discussed. © 2003 The Electrochemical Society. All rights reserved.

Enantioselective hydrogenation of isophorone over Pd catalysts in the presence of(−)-dihydroapovincaminic acid ethyl ester: The effect of reduction method of Pd blacks on the enantiomeric excess

The enantioselective heterogeneous catalytic hydrogenation of isophorone in the presence of apovincaminic acid ethyl ester was investigated. Various Pd black catalysts differing in their preparation method were studied. The catalysts were characterized by different methods such as physical adsorption and chemisorption, SEM and XPS. An explanation was created for the different enantioselectivity of the catalysts being precipitated by different reducing agents.

Surface Composition of Palladium Blacks of Different Methods of Preparation

The surface composition of two Pd blacks was monitored by XPS. The samples contained ∼75% Pd with carbon and oxygen impurities. The sample reduced in aqueous medium contained also Na plus K impurities (∼1% each). Their possible organic counter ions appeared in the carbon region although no quantitative agreement could be established. The possible influence of the possible surface dipoles (with the alkali pointing outwards) on selective hydrogenation processes is pointed out.

Interaction of ethylene and hydrogen with a commercial Pd black: carbon accumulation and possible adsorbate-induced rearrangement

The interaction of hydrogen, ethylene and their mixtures with a commercial Pd black was studied. Hydrogen treatment at 300 K created a rather clean Pd surface with some residual carbon. Ethylene introduced in high hydrogen excess exerted hardly any influence on the metallic properties of Pd, as shown by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). The carbon content did not change. Contacting Pd with ethylene in low excess of H2 or without any hydrogen changed the Pd 3d line, indicating its chemical interaction with C. Simultaneously, a new component appeared in the C 1s region at BE∽283.5 eV. It indicated the formation of Pd–C bonds, responsible for changes in the Pd valence state. Intensity drop at the near-Fermi edge region in UPS corroborated this interaction. Pd also underwent considerable structural rearrangement, as shown by the appearance of a large peak in the UP spectra at ∽8 eV, corresponding to the enrichment of the sodium carbonate impurity on the surface. This component proved to be a good indicator of surface flexibility.

Characterization of Pd blacks by temperature programmed oxidation

Using different reduction conditions Pd powders have been prepared and characterized by chemisorption and TPO (Temperature Programmed Oxidation) measurements. The amount of carbon deposits introduced during preparation seems to be peculiar to the preparation procedure. The O2 consumption curves attributed to PdO formation have shown two peak minima suggesting strong differences in the accessibility of Pd particles.

Palladium‐Assisted Electrodehalogenation of 1,1,2‐Trichloro‐1,2,2‐trifluoroethane on Lead Cathodes Combined with Hydrogen Diffusion Anodes

In this work, the efficiency and product formation in the electroreduction of 1,1,2‐trichloro‐1,2,2‐trifluoroethane (CFC 113) to obtain completely dechlorinated products has been studied using constant‐current electrolysis at different current densities, gas chromatography, scanning electron microscopy, and energy dispersive x‐ray. While chlorotrifluoroethene was the main product obtained from CFC 113 in MeOH‐water solutions containing , different and suitable conditions which lead to its complete dechlorination are described in this paper. In the presence of small amounts of in solution, a very thin film of Pd black was electrodeposited on the Pb cathode and the efficiency of the CFC 113 electroreduction was about 98%. The efficiency was much smaller and the product composition very different in the absence of in solution, even in the presence of Pd black electrodeposited on the cathode. In the presence of , the main products in the gas phase were difluoroethene and trifluoroethene. Small amounts of 1,2‐dichloro‐1,1,2‐trifluoroethane, chlorotrifluoroethene, difluoroethane, and fluroethane were also present in the gas phase. The liquid composition was enriched in the less volatile compounds. A possible reaction pathway involving the removal of halides by successive reactions is discussed. The anode employed in these experiments was a thin Pd foil with electrodeposited Pd black, which permitted hydrogen diffusion and its further oxidation to . Because of this reaction, contamination of the working‐electrolyte by other oxidation products such as or MeOH derivatives were avoided. This system allows new electrosynthetic processes along with CFC electrodegradation.

Adsorption of methane and ethane, 2. Studies of metal blacks in a dynamic system

The irreversible adsorption of methane and ethane increases with increasing temperature on Pt, Pd and Rh blacks. Data indicate a one-carbon attachment of ethane on Pt and Pd. A two-carbon attachment of ethane is observed upon adsorption on Rh.

Heterogenized metal complex catalysts based on Pd black

By the reduction of π-allyl compounds of palladium such as [Pd-Cl(C 3H 5)] 2, [Pd(C 3H 5)(C 5H 5)] and [Pd 2(C 3H 5)(C 5H 5)(PPh 3) 2] by sodium borohydride and hydrazine hydrate, a new type of catalysts has been synthesized in which the Pd black serves as a support on whose surface palladium complexes, stabilized by organic ligands, are fixed. The chemical and phase compositions of the catalysts have been determined. In the presence of organometallic compounds, a highly dispersed metal phase is formed having a narrow particle size distribution. A mechanism for the formation of Pd blacks from the organometallic compounds is proposed, whereby such blacks form via the emergence of pre-crystalline associates of reduced palladium whose structures are subsequently ordered after hydrogen treatment. It is found that, besides metallic palladium, the catalyst surfaces also contain additional active centres associated with electron-deficient palladium. The activity and selectivity of such blacks in the liquid-phase hydrogenation of organic compounds increase with increasing dispersion of the catalyst and with their fixed complex content. A model is suggested for the structure of Pd blacks generated from organometallic compounds.

Oxidation of propylene by benzoyl peroxide to allyl acetate catalyzed by a palladium cluster and Pd black

Oxidation of propylene by benzoyl peroxide to allyl acetate catalyzed by a palladium cluster and Pd black

ChemInform Abstract: HYDROGENATION OF OXYGEN‐CONTAINING HETEROCYCLIC COMPOUNDS ON GROUP VIII METALS

The hydrogenation of a number of oxygen-containing heterocyclic compounds on Pt, Pd, and Rh blacks in the liquid phase at atmospheric pressure was investigated. The results are compared with data on H-D exchange with D2O and are interpreted from the point of view of the theory of π-complex adsorption.