Preparation of magnetic Fe3O4/P (GMA‐DVB)‐PEI/Pd highly efficient catalyst with core‐shell structure

In this paper, a simple route for palladium (Pd) nanoparticles attached to the surface of hollow magnetic Fe₃O₄/P (GMA‐DVB)‐polyethyleneimine (PEI) microspheres was established. Due to the large amount of imidogen groups and tertiary amine groups presenting in the PEI, Pd²⁺ ions could be anchored to the support by complexation with a polyfunctional organic ligand. Thereafter, a magnetic Pd catalyst having a high loading amount and good dispersibility was obtained by reducing Pd²⁺ ions. Afterwards, the prepared catalyst was characterized by TEM, SEM, FTIR, XRD, TGA, VSM, and UV–vis in detail. Ultimately, their catalytic activity was evaluated using the reduction of 4‐nitrophenol (4‐NP). Research showed that the Fe₃O₄/P (GMA‐DVB)‐PEI/Pd catalyst possessed high catalytic performances for the reduction of 4‐NP with a conversion rate of 98.43% within 540 s. Furthermore, the catalyst could be easily recovered and reused at least for nine successive cycles.     

Highly Selective Pd–Cu/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for Liquid-Phase Hydrogenation: The Influence of the Pd: Cu Ratio on the Structure and Catalytic Characteristics

The structure and catalytic characteristics of a series of Pd–Cu/α-Al₂O₃ catalysts with Pd: Cu ratio varied from Pd₁–Cu_0.5 to Pd₁–Cu₄ were studied. The use of α-Al₂O₃ with a small surface area (S_sp = 8 m²/g) as a support made it possible to minimize the effect of diffusion on the catalytic characteristics and to study the structure of Pd–Cu nanoparticles by X-ray diffraction (XRD) analysis. The XRD analysis and transmission electron microscopy (TEM) data indicated the formation of uniform bimetallic Pd–Cu nanoparticles (d = 20–60 nm), whose composition corresponded to a ratio between the metals in the catalyst, and also the absence of monometallic Pd⁰ and Cu⁰ nanoparticles. The study of catalytic properties in the liquid-phase hydrogenation of diphenylacetylene (DPA) showed that the activity of the catalysts rapidly decreased with the Cu content increase; however, in this case, the yield of a desired alkene compound significantly increased. The selectivity of alkene formation on the catalysts with the ratios Pd: Cu = 1: 3 and 1: 4 was superior to the commercial Lindlar catalyst.     

Fe3O4‐SAHPG‐Pd0 nanoparticles: A ligand‐free and low Pd loading quasiheterogeneous catalyst active for mild Suzuki–Miyaura coupling and C?H activation of pyrimidine cores

This paper reports a green magnetic quasiheterogeneous efficient palladium catalyst in which Pd⁰ nanoparticles have been immobilized in self‐assembled hyperbranched polyglycidole (SAHPG)‐coated magnetic Fe₃O₄ nanoparticles (Fe₃O₄‐SAHPG‐Pd⁰). This catalyst has been used for effective ligandless Pd catalyzed Suzuki–Miyaura coupling reactions of different aryl halides with substituted boronic acids at room temperature and in aqueous media. Herein, SAHPG is used as support; it also acts as a reducing agent and stabilizer to promote the transformation of Pd^II to Pd⁰ nanoparticles. Also, this environmental friendly quasiheterogeneous catalyst is employed for the first time in the synthesis of new pyrimido[4,5‐b]indoles via oxidative addition/C? H activation reactions on the pyrimidine rings, which were obtained with higher yield and faster than when Pd(OAc)₂ was used as the catalyst. Interestingly, the above‐mentioned catalyst could be recovered in a facile manner from the reaction mixture by applying an external magnet device and recycled several times with no significant decrease in the catalytic activity.     

Support-Free Pd3Co NCs as an Efficient Heterogeneous Nanocatalyst for New Organic Transformations of C−C Coupling Reactions

A support-free heterogeneous Pd₃Co nanostructured composite (NC), synthesized through a hydrothermal route, acted as an effective catalytic system in multivariate Heck-, Sonogashira-, and Suzuki-type coupling reactions of iodonium ylides. The XPS analysis of the bimetallic Pd₃Co NCs confirmed the elemental composition as 75 % palladium and 25 % cobalt. Furthermore, high-resolution (HR) TEM analysis confirmed the spherical morphology of the Pd₃Co bimetallic nanoparticles. The average diameter of the NCs is 14.8 nm. The coupling reaction proceeded through the generation of α-iodoenones with simultaneous migration of the phenyl group, thereby giving a scaffold with higher atom economy. The heterogeneous Pd₃Co NCs were recycled and reused without any significant change in catalytic ability for up to five reaction cycles. The high concentration of Pd and association of cobalt into the lattice of palladium appears to enhance its catalytic ability for the diverse coupling reactions in comparison with its monometallic counterparts as well as with bimetallic NCs with a comparatively lesser amount of Pd.     

Self‐Assembly Film of Zeolite Y Nanocrystals Loading Palladium on an Au Electrode for Electrochemical Applications

Nano‐scale zeolite Y crystals were synthesized, and palladium nanoparticles were prepared in the supercage of the zeolite by “ship‐in‐a‐bottle” approach. A novel method to fabricate zeolite‐modified electrode (ZME) loading Pd nanoparticles was developed, in which the zeolite Y loading Pd²⁺ ions was self‐assembled on (3‐mercaptopropyl) trimethoxysilane‐attached Au surface to form the stable and density packed multilayers (SAM‐ZME). The structures of zeolite Y and the SAM‐ZME were investigated by using TEM, XRD and SEM techniques. Pd²⁺ ions in the SAM‐ZME were converted into Pd nanoparticles (Pd_n⁰) by two steps consisting of the electrochemical reduction as well as the succeeding admission and release of CO. The redox couple [Fe(CN)₆]^3?/4? was used to probe the electron‐transfer barrier properties during self‐assembling process. Moreover, the special properties of the SAM‐ZME loading Pd_n⁰ were studied by using cyclic voltammetry and CO‐probe in situ FTIR spectroscopy. The results illustrated that Pd_n⁰ in the SAM‐ZME exhibits higher electrocatalytic activity for oxidation of adsorbed CO than that of ZME prepared in our previous study by zeolite coating method. The present study is of importance in design and preparation of SAM‐ZME, which poccesseses excellent properties for the immobilization of electrocatalysts or biomolecules.     

Composition Control Synthesis and Catalytic Properties in the Suzuki Reaction of Bimetallic PdSn Nanoparticles

We have successfully prepared 6.5 nm palladium tin (PdSn) alloy nanoparticles (NPs) with tunable compositions by high‐temperature reduction of tin acetate and palladium bromide in the presence of oleylamine and trioctylphosphine. The catalytic activities of PdSn NPs with different compositions were evaluated through Suzuki reactions. The PdSn nanocatalysts show better catalytic activity on Suzuki reactions than an equal amount of pure Pd NPs, and their catalytic activities are highly composition dependent. Among these NPs, Pd₆₃Sn₃₇/C NPs exhibited the highest catalytic performance with higher reaction activity, lower Pd leaching properties, and higher stability even after eight recycle reactions.     

Bimetallic palladium–gold nanoparticles synthesized in ionic liquid microemulsion

The palladium and gold precursors were dissolved in dispersive and continuous phase of ionic liquid microemulsion (H₂O/Triton X-100 (TX-100)/1-butyl-3-methylimidazolium hexafluorophosphate), respectively. [PdCl₆]^2? ions were reduced in situ by TX-100 in dispersive phase (H₂O) to prepare Pd nanoparticles (NPs) and then [AuCl₄]^? crossed through the interface film and reacted with the as-prepared Pd NPs to form Pd₄Au NPs. The as-prepared Pd₄Au NPs were characterized by transmission electronic microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and ultraviolet–visible spectroscopy. The as-prepared Pd₄Au NPs suspension and carbon nanotubes (CNTs) suspension were vigorously stirred to prepare the electrocatalyst supported on the CNTs with a total metal loading of 20?wt.% (denoted by Pd₄Au/CNTs). Cyclic voltammetry and chronoamperometry tests show that the Pd₄Au/CNTs are very promising for the oxidation of ethanol in alkaline medium. The result can be attributed to the synergistic effect between Pd and Au during the catalytic process.     

One Step Preparation of Reduced Graphene Oxide/Pd–Fe3O4@Polypyrrole Composites and Their Application in Catalysis

The simple preparation of catalysts with superior catalytic activity and good reusability is highly desirable. Herein, we report a novel strategy to construct reduced graphene oxide (rGO)/Pd–Fe₃O₄@polypyrrole (PPy) catalysts with Pd and Fe₃O₄ nanoparticles anchored on a rGO nanosheet surface and wrapped in a PPy shell. The synthesis and assembly of both the Pd and Fe₃O₄ nanoparticles, the preparation of the PPy layer, and the reduction of graphene oxide nanosheets were finished in one step. In the system, the PPy layer not only prevented aggregation of Pd and Fe₃O₄ nanoparticles, but also generated a synergistic effect with precursor Pd²⁺ ions, which led to a high dispersity of as‐prepared Pd nanoparticles. Although the procedure was simplified to one step, the catalytic activity and reusability were not sacrificed. In the reduction of 4‐nitrophenol, their catalytic performance was better than that in recent reports. Moreover, the catalysts showed good reusability owing to their magnetic properties.     

Nanosized hydrogenation catalyst based on palladium bisacetylacetonate and phosphine: Formation,the origin of activity,and properties

The nature and catalytic properties of a hydrogenation catalyst based on Pd(acac)₂ and PH₃ are considered. As demonstrated by a variety of physicochemical methods (IR and UV spectroscopy, ³¹P and ¹H NMR, electron microscopy, and X-ray powder diffraction), nanoparticles consisting of various palladium phosphides (Pd₆P, Pd_4.8P, and Pd₅P₂) and Pd(0) clusters form under the action of dihydrogen during catalyst preparation. The promoting effect of phosphine at low PH₃: Pd(acac)₂ ratios is mainly due to the ability of phosphine to increase the extent of dispersion of the catalyst.     

Pd2+-Initiated Formic Acid Decomposition: Plausible Pathways for C-H Activation of Formate

Formic acid (HCOOH, FA) has long been considered as a promising hydrogen-storage material due to its efficient hydrogen release under mild conditions. In this work, FA decomposes to generate CO₂ and H₂ selectively in the presence of aqueous Pd²⁺ complex solutions at 333 K. Pd(NO₃)₂ was the most effective in generating H₂ among various Pd²⁺ complexes explored. Pd²⁺ complexes were in situ reduced to Pd⁰ species by the mixture of FA and sodium formate (SF) during the course of the reaction. Since C−H activation reaction of Pd²⁺-bound formate is occurred for both Pd²⁺ reduction and H₂/CO₂ gas generation, FA decomposition pathways using several Pd²⁺ species were explored using density functional theory (DFT) calculations. Rotation of formate bound to Pd²⁺, β-hydride elimination, and subsequent CO₂ and H₂ elimination by formic acid were examined, providing different energies for rate determining step depending on the ligand electronics and geometries coordinated to the Pd²⁺ complexes. Finally, Pd²⁺ reduction toward Pd⁰ pathways were explored computationally either by generated H₂ or reductive elimination of CO₂ and H₂ gas.     

Effect of Transition Element Ions on the Catalytic Activity of Titanium Dioxide during Chemical Deposition of Metallic Copper

We have established the high catalytic activity of TiO₂, modified by Pd²⁺, Cu²⁺, Fe³⁺, and Co²⁺ ions, in reduction of Cu²⁺ ions by formaldehyde in solution. We propose a likely scheme for the electronic processes that occur, including injection of electrons from the reducing agent into the conduction band and formation of metallic nanoparticles on the surface that effectively catalyze deposition of metallic copper.     

The Role of Pd2+/Pd0 in Hydrogenation by [Pd(2‐pymo)2]n: An X‐ray Absorption and IR Spectroscopic Study

The metal–organic framework (MOF) [Pd(2‐pymo)₂]_n (2‐pymo=2‐pyrimidinolate) was used as catalyst in the hydrogenation of 1‐octene. During catalytic hydrogenation, the changes at the metal nodes and linkers of the MOF were investigated by in situ X‐ray absorption spectroscopy (XAS) and IR spectroscopy. With the help of extended X‐ray absorption fine structure and X‐ray absorption near edge structure data, Quick‐XAS, and IR spectroscopy, detailed insights into the catalytic relevance of Pd²⁺/Pd⁰ in the hydrogenation of 1‐octene could be achieved. Shortly after exposure of the catalyst to H₂ and simultaneously with the hydrogenation of 1‐octene, the aromatic rings of the linker molecules are hydrogenated rapidly. Up to this point, the MOF structure remained intact. After completion of linker hydrogenation, the linkers were also protonated. When half of the linker molecules were protonated, the onset of reduction of the Pd²⁺ centers to Pd⁰ was observed and the hydrogenation activity decreased, followed by fast reduction of the palladium centers and collapse of the MOF structure. Major fractions of Pd⁰ are only observed when the hydrogenation of 1‐octene is almost finished. Consequently, the Pd²⁺ nodes of the MOF [Pd(2‐pymo)₂]_n are identified as active centers in the hydrogenation of 1‐octene.     

Pd/Co双金属纳米颗粒的制备及催化制氢性能

采用聚乙烯吡咯烷酮(PVP)保护的化学共还原法制备了Pd/Co双金属纳米颗粒, 研究了PVP及还原剂(NaBH₄)的用量、金属盐浓度、金属比例等对Pd/Co双金属纳米颗粒催化NaBH₄制氢性能的影响. 透射电子显微镜(TEM)的结果表明, 所制备的Pd/Co双金属纳米颗粒的平均粒径在1.5-2.8 nm之间. Pd/Co双金属纳米颗粒(BNPs)的催化活性远高于Pd与Co单金属纳米颗粒的活性; 当Pd/Co的理论原子比为1/9时, 双金属纳米颗粒的催化活性最高可达15570 mol·mol^-1·h^-1 (文中纳米颗粒的催化活性均为每摩尔Pd的活性). 密度泛函理论(DFT)的计算结果表明, Pd原子与Co原子之间发生电荷转移, 使得Pd原子带负电而Co原子带正电, 荷电的Pd和Co原子进而成为催化反应的活性中心. 所制备的Pd/Co双金属纳米颗粒具有很好的催化耐久性, 即使重复使用5次后, 该催化剂仍具有较高的催化活性, 且使用后的纳米颗粒催化剂也没有出现团聚现象. 双金属纳米颗粒催化NaBH₄水解反应的活化能约为54 kJ·mol^-1.     

Pincer‐Type Heck Catalysts and Mechanisms Based on PdIV Intermediates: A Computational Study

Pincer‐type palladium complexes are among the most active Heck catalysts. Due to their exceptionally high thermal stability and the fact that they contain Pd^II centers, controversial Pd^II/Pd^IV cycles have been often proposed as potential catalytic mechanisms. However, pincer‐type Pd^IV intermediates have never been experimentally observed, and computational studies to support the proposed Pd^II/Pd^IV mechanisms with pincer‐type catalysts have never been carried out. In this computational study the feasibility of potential catalytic cycles involving Pd^IV intermediates was explored. Density functional calculations were performed on experimentally applied aminophosphine‐, phosphine‐, and phosphite‐based pincer‐type Heck catalysts with styrene and phenyl bromide as substrates and (E)‐stilbene as coupling product. The potential‐energy surfaces were calculated in dimethylformamide (DMF) as solvent and demonstrate that Pd^II/Pd^IV mechanisms are thermally accessible and thus a true alternative to formation of palladium nanoparticles. Initial reaction steps of the lowest energy path of the catalytic cycle of the Heck reaction include dissociation of the chloride ligands from the neutral pincer complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(Cl)] [X=NH, R=piperidinyl ( 1 a ); X=O, R=piperidinyl ( 1 b ); X=O, R=iPr ( 1 c ); X=CH₂, R=iPr ( 1 d )] to yield cationic, three‐coordinate, T‐shaped 14e^? palladium intermediates of type [{2,6‐C₆H₃(XPR₂)₂}Pd]⁺ ( 2 ). An alternative reaction path to generate complexes of type 2 (relevant for electron‐poor pincer complexes) includes initial coordination of styrene to 1 to yield styrene adducts [{2,6‐C₆H₃(XPR₂)₂}Pd(Cl)(CH₂?CHPh)] ( 4 ) and consecutive dissociation of the chloride ligand to yield cationic square‐planar styrene complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(CH₂?CHPh)]⁺ ( 6 ) and styrene. Cationic styrene adducts of type 6 were additionally found to be the resting states of the catalytic reaction. However, oxidative addition of phenyl bromide to 2 result in pentacoordinate Pd^IV complexes of type [{2,6‐C₆H₃(XPR₂)₂}Pd(Br)(C₆H₅)]⁺ ( 11 ), which subsequently coordinate styrene (in trans position relative to the phenyl unit of the pincer cores) to yield hexacoordinate phenyl styrene complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(Br)(C₆H₅)(CH₂?CHPh)]⁺ ( 12 ). Migration of the phenyl ligand to the olefinic bond gives cationic, pentacoordinate phenylethenyl complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(Br)(CHPhCH₂Ph)]⁺ ( 13 ). Subsequent β‐hydride elimination induces direct HBr liberation to yield cationic, square‐planar (E)‐stilbene complexes with general formula [{2,6‐C₆H₃(XPR₂)₂}Pd(CHPh?CHPh)]⁺ ( 14 ). Subsequent liberation of (E)‐stilbene closes the catalytic cycle.     

Carboxymethylcellulose‐supported palladium nanoparticles generated in situ from palladium(II) carboxymethylcellulose as an efficient and reusable catalyst for ligand‐ and base‐free Heck–Matsuda and Suzuki–Miyaura couplings

A novel palladium(II) carboxymethylcellulose (CMC‐Pd^II) was prepared by direct metathesis from sodium carboxymethylcellulose and PdCl₂ in aqueous solution. Its catalytic activities were explored for Heck–Matsuda reactions of aryldiazonium tetrafluoroborate with olefins, and Suzuki–Miyaura couplings of aryldiazonium tetrafluoroborate with arylboronic acid. Both reactions proceeded at room temperature in water or aqueous ethanol media without the presence of any ligand or base, to provide the corresponding cross‐coupling products in good to excellent yields under atmospheric conditions. The CMC‐Pd^II and carboxymethylcellulose‐supported palladium nanoparticles (CMC‐Pd⁰) formed in situ in the reactions were characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, inductively coupled plasma atomic emission spectrometry, and scanning and transmission electron microscopies. The homogeneous nature of the CMC‐Pd⁰ catalyst was confirmed via Hg(0) and CS₂ poisoning tests. Moreover, the CMC‐Pd⁰ catalyst could be conveniently recovered by simple filtration and reused for at least ten cycles in Suzuki–Miyaura reactions without apparently losing its catalytic activity. The catalytic system not only overcomes the basic drawbacks of homogeneous catalyst recovery and reuse but also avoids the need to fabricate palladium nanoparticles in advance. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation,characterization and catalytic application of PdPt bimetallic nanoparticles stabilized by 15‐membered triolefinic macrocycle‐terminated poly(propylene imine) dendrimer

PdPt bimetallic nanoparticles stabilized by 15‐membered triolefinic macrocycle‐stabilized poly(propylene imine) dendrimer (G3‐M(Pd_x Pt_10−x ) DSNs) have been prepared via synthesis of a 15‐membered triolefinic macrocycle‐modified third‐generation poly(propylene imine) dendrimer (G3‐M) and then synchronous ligand exchange with Pd(PPh₃)₄/Pt(PPh₃)₄ complexes. The structure and catalytic activity of the DSNs were characterized using Fourier transform infrared, ¹H NMR, transmission electron microscopy, energy‐dispersive X‐ray and X‐ray photoelectron analyses. As a novel catalyst system, it can be concluded that the composition of the bimetallic nanoparticles has an influence on the catalytic activity of the hydrogenation reaction of acrylonitrile–butadiene rubber, which can be related to synergistic effect. Furthermore, the selectivity and recyclability of G3‐M(Pd_x Pt_10−x ) DSN catalyst are also discussed.     

Mild and Selective Catalytic Hydrogenation of the C=C Bond in α,β‐Unsaturated Carbonyl Compounds Using Supported Palladium Nanoparticles

Chemoselective reduction of the C=C bond in a variety of α,β‐unsaturated carbonyl compounds using supported palladium nanoparticles is reported. Three different heterogeneous catalysts were compared using 1 atm of H₂: 1) nano‐Pd on a metal–organic framework (MOF: Pd⁰‐MIL‐101‐NH₂(Cr)), 2) nano‐Pd on a siliceous mesocellular foam (MCF: Pd⁰‐AmP‐MCF), and 3) commercially available palladium on carbon (Pd/C). Initial studies showed that the Pd@MOF and Pd@MCF nanocatalysts were superior in activity and selectivity compared to commercial Pd/C. Both Pd⁰‐MIL‐101‐NH₂(Cr) and Pd⁰‐AmP‐MCF were capable of delivering the desired products in very short reaction times (10–90 min) with low loadings of Pd (0.5–1 mol %). Additionally, the two catalytic systems exhibited high recyclability and very low levels of metal leaching.     

DFT Comparison the Performance of Pd10Sn5 and Pd10Ag5 Electrocatalyst for Reduction of CO2

CO₂ electrocatalysis as a hydrocarbon is a promising means of achieving economical CO₂-mediated hydrogen energy cycling. Hydrocarbons are renewable hydrogen storage materials. The development of reliable metal alloy electrocatalysts is an urgent but challenging task associated with such systems, although there is still a lack of precise reaction mechanism design. In this study, the performance of Pd₁₀Ag₅ alloy nanoparticles (NPs) and Pd₁₀Sn₅ alloy nanoparticles (NPs) on the electrocatalytic reaction of CO₂ was compare. The kinetic and density functional theory (DFT) calculations show that the selectivity of the Pd-based bimetallic catalyst to the C2 product is greater than that of C1, and the stability of Pd₁₀Ag₅ is better and less affected by the reaction environment. However, the catalytic performance of the Pd₁₀Sn₅ electrocatalyst in the liquid phase is the best. The insight obtained from the calculations is used to develop criteria for identifying new and improved catalysts for electrochemical CO₂ reduction.     

Hydrogen evolution-assisted one-pot aqueous synthesis of hierarchical trimetallic PdNiRu nanochains for hydrazine oxidation reaction

A hydrogen evolution-assisted one-pot aqueous approach was developed for facile synthesis of trimetallic Pd Ni Ru alloy nanochain-like networks(Pd Ni Ru NCNs) by only using KBH_4 as the reductant, without any specific additive(e.g. surfactant, polymer, template or seed). The products were mainly investigated by transmission electron microscopy(TEM), X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS). The hierarchical architectures were formed by the oriented assembly growth and the diffusioncontrolled deposition in the presence of many in-situ generated hydrogen bubbles. The architectures had the largest electrochemically active surface area(ECSA) of 84.32 m~2 g~(–1) Pdthan Pd Ni nanoparticles(NPs,65.23 m~2 g~(–1) Pd), Pd Ru NPs(23.12 m~2 g~(–1) Pd), Ni Ru NPs(nearly zero), and commercial Pd black(6.01 m~2 g~(–1) Pd), outperforming the referenced catalysts regarding the catalytic characters for hydrazine oxygen reaction(HOR). The synthetic route provides new insight into the preparation of other trimetallic nanocatalysts in fuel cells.