Sonication-Assisted Synthesis of Bimetallic Hg/Pd Alloy Nanoparticles for Catalytic Reduction of Nitrophenol and its Derivatives

In this article, we report a facile approach for the synthesis of an inexpensive catalyst of bimetallic Hg/Pd alloys comprising nanoparticles with various structures using a unique ultrasonic reaction that is conducted without the use of any reducing agent. The nanoparticles of Hg/Pd alloys (HgPd and Hg₂Pd₅) were achieved for the first time by sonicating an aqueous solution of Palladium (II) nitrate with metallic liquid mercury, as evidenced by XRD. EDS further confirmed the presence of Pd and Hg elements in the alloy. The surface morphology and structure of the nanoparticles have been systematically investigated by HRSEM, HRTEM and SAED pattern. In order to explore the catalytic activity of the as-synthesized nanoalloys, the catalytic reduction of 4-nitrophenol and a few other nitrophenol derivatives were investigated. Excellent catalytic activity was obtained for Hg/Pd (1:1) alloy, and the rate constant for the reduction of 4-NP with Hg/Pd at room temperature was found to be 58.4 × 10⁻³ s⁻¹, which is possibly the highest ever reported. The catalyst exhibited superior stability and reusability when compared with those reported in the literature for other catalysts based on noble metals.     

Synthesis of a Au‐on‐Pd Heteronanostructure Stabilized by Citrate and its Catalytic Application

The preparation of Au‐on‐Pd heteronanostructure (HNS) using citrate‐stabilized polycrystalline Pd nanoparticles (NPs) as the seeds is described. The resulting Au‐on‐Pd HNS is characterized and it is found that the formation of Au‐on‐Pd HNS depends greatly on a ratio between Pd seeds and AuCl₄^? ions added and the optimal molar ratio is 10:1. If fewer AuCl₄^? ions are added (Pd/Au ratio is 100:1), the growth of Au NPs only occurs on part of the Pd seeds’ surface. The addition of more AuCl₄^? ions (Pd/Au ratio is 5:1) hinders the growth of Au NPs on the Pd seeds’ surface. To demonstrate the catalytic performance, the electrochemistry oxidation of ethanol and the reduction of p‐nitrophenol by NaBH₄ are chosen to examine the catalytic activity of Au‐on‐Pd HNS. Pd seeds, Au NPs, and poly(vinyl pyrrolidone) (PVP)‐stabilized PdAu nanoalloy are used as the references for comparison. In the first reaction, the catalytic reactivity of Au‐on‐Pd HNS is better than that of corresponding pure Pd or Au NPs, while the opposite occurs for the latter reaction. The catalytic activity of Au‐on‐Pd HNS is much higher than that of PVP‐stabilized PdAu nanoalloy.     

Palladium nanoparticles as catalysts for reduction of Cr(VI) and Suzuki coupling reaction

Herein, six kinds of PdNPs (including icosahedron, sphere, spindle, cube, rod, and wire) were synthesized via simple methods. The catalytic activities were investigated by the reduction reaction of Cr(VI) and Suzuki coupling reaction. Chemically synthesized morphologies of the six catalysis were characterized by transmission electron microscopy, field emission scanning electron microscopy, and X-ray diffraction, etc. Pd icosahedron shows a better catalytic property than other PdNPs with a rate constants 0.42 min^?1 for the reduction of Cr(VI). Moreover, the electrocatalyst shows that Pd icosahedron possesses a bigger surface area of 8.56 m²/g than other nanoparticles, which is attributed to the better catalyst. The Pd icosahedron possesses a better catalytic property, attributing to the abundant exposed {111} facets with high activity on Pd icosahedron. The catalytic activities are closely related to the surface area with the following order: icosahedrons ≥ sphere > rod > spindle > cube > wire. The Pd icosahedron catalyst represents a strong activity for Suzuki coupling reaction as well, outweighting is 80%. The results reveal that Pd icosahedron acts as an efficient catalyst compared to other PdNPs (wire, rod, sphere, spindle, and cube).     

Pd/Au纳米结构制备和粒子组分自旋的谱学性能研究

为研究Pd/Au纳米结构制备和电催化性能、控制粒子大小组分和自旋,用油浴热分解方法制备了核/壳纳米结构Pd/Au双金属合金纳米颗粒,采用PVP和多元醇作表面活性剂和稳定剂,依据溶液浓度、颗粒大小、吸附能控制晶相获得了均匀、一致的2层和3层Pd/Au纳米样品,并采用HAADF和HRTEM测试了纳米结构尺寸形貌,用EDS测试了成分分布,试验产物用TEM/XRD进行了表征,结果表明,Pd/Au具有面心立方八面体结构,与Au/Pd核壳不同,纳米Pd/Au具有活性、耐久性、电催化性和稳定性。     

Preparation of functionalized platinum nanoparticles: a comparison of different methods and reagents

Au–Pd core–shell nanocubes and triangular nanoparticles were systematically synthesized from a few Pd layers up to fully grown morphologies by a modified seed-mediated growth method. The shape evolution of Au–Pd core–shell nanoparticles from single crystal and singly twinned seed to final concave nanocube and triangular plates are presented at atomic level by Cs-corrected scanning transmission electron microscopy (STEM). The growth mechanism of both morphologies was studied throughout different sizes. It was found that the concave nanocubes grew from octahedral Au seeds due to fast growth along 〈111〉 directions; while the triangular nanoparticles grew from singly twinned Au seeds, growing twice as fast in 〈110〉 directions along the twin boundary; compared to the 〈111〉 direction perpendicular to the twin boundary. Both the concave nanocubes and triangular nanoparticles presented high index facet (HIF) surfaces that will increase the catalytic activity of different reactions.     

Catalytic Decomposition of Ammonia on Coatings Consisting of Organoboron and Platinum Nanoparticles

Comparative characteristics of catalytic activity of electroneutral and positively charged coatings consisting of organoboron nanoparticles with a composition (C₂B₁₀H₄)_n or platinum in ammonia decomposition have been obtained for the first time. The charge on the coatings was created by the supply of a positive voltage of +6 or +10 V. It has been found that, for the same mass of the coatings at 700 K and a pressure of 5 × 10^–7 Torr, the rate of ammonia decomposition on a coating consisting of organoboron nanoparticles is 28–43% of the rate of NH₃ decomposition on the coating consisting of platinum nanoparticles depending on the voltage supplied to the coatings.     

Synthesis of monodisperse palladium nanocubes and their catalytic activity for methanol electrooxidation

The single crystalline palladium nanocubes with an average size of 7 nm were prepared in the presence of poly (vinyl pyrrolidone) (PVP) and KBr using the polyol method. The as-prepared Pd nanocubes were highly uniform in both size and shape. The ordered packing structures including monolayer and multilayer can be fabricated via the rate-controlled evaporation of solution solvent. The electrochemical catalytic activity of these Pd nanocubes towards methanol oxidation was found to be higher than that of spherical Pd nanoparticles of similar size.     

Rapid,Microwave‐Assisted,and One‐Pot Synthesis of Magnetic Palladium–CoFe2O4–Graphene Composite Nanosheets and Their Applications as Recyclable Catalysts

Here, a microwave‐assisted approach has been demonstrated to rapidly prepare magnetic Pd–CoFe₂O₄–graphene (GE) composite nanosheets in ethylene glycol (EG) solvent. The generation of both Pd and CoFe₂O₄ nanoparticles is accompanied with the reduction process of graphene oxide (GO) by EG. The surface morphologies and chemical composition of the composite nanosheets are characterized by transmission electron microscopy (TEM), energy‐dispersive X‐ray spectrometer (EDS), powder X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) measurements. The as‐prepared Pd–CoFe₂O₄–GE composite nanosheets exhibit a remarkable catalytic activity towards the reduction of 4‐nitrophenol by sodium borohydride (NaBH₄) at room temperature. The apparent kinetic rate constant (K _app) of this catalytic reaction could reach about 11.0 × 10^?3 s^?1. Moreover, the CoFe₂O₄ component exhibits a magnetic property, which could make the Pd–CoFe₂O₄–GE composite nanocatalysts separated from the suspension system. The catalytic conversion of the 4‐nitrophenol to 4‐aminophenol could reach 87.2% after four cycles. This work presents a simple, rapid, and versatile method to fabricate both metal and spinel‐type complex oxides on GE nanosheets, providing a new opportunity for their applications in the recyclable catalytic reaction.     

基于粒子群算法的Pt-Pd合金纳米粒子的稳定结构研究

Pt-Pd合金纳米粒子相对于Pt及Pd单晶纳米粒子均具有更好的催化活性和选择性, 研究它的稳定结构对进一步了解催化性能具有重要意义. 本文采用粒子群算法和量子修正Sutton-Chen多体势对不同尺寸、 不同组成比例的二十四面体Pt-Pd合金纳米粒子的结构稳定性进行研究. 结果表明: Pt-Pd合金纳米粒子中Pt原子趋向于分布在纳米粒子内层, 而Pd原子趋向于分布在纳米粒子外层, 且Pt, Pd原子的分布越对称有序, 其能量越低, 结构越稳定; 随着Pt原子比例的增加, 三种不同尺寸的合金纳米粒子的Warren-Cowley化学短程有序值都逐渐升高, 即纳米粒子更趋向于偏聚分布状态; 在相同比例下, 小尺寸纳米粒子的偏聚程度比大尺 寸纳米粒子的大. 关键词： 合金纳米粒子 粒子群算法 稳态结构     

Pd/WO<Subscript>3</Subscript>/C nanocomposite with APTMS-functionalized tungsten oxide nanosheet for formic acid electrooxidation enhancement

A Pd/WO₃/C nanocomposite with 3-aminopropyltrimethoxysilane (APTMS)-functionalized tungsten oxide nanosheets (Pd/WO₃/C-APTMS) was synthesized and applied as the efficient anode catalyst for direct formic acid fuel cells (DFAFCs). The mechanism for synthesizing the nanocomposite is as follows: initially, [PdCl₄]^2? was assembled onto the tungsten oxide nanosheets modified with APTMS. Following this, Pd nanoparticles were reduced via traditional impregnation reduction of [PdCl₄]^2? with NaBH₄. The transmission electron microscope (TEM) images revealed that the Pd nanoparticles were uniformly dispersed on WO₃ nanosheets and were approximately 2.7 nm in size. The electrochemical test results showed that enhanced electrocatalytic activity for the formic acid oxidation reaction (FAOR) was obtained on the Pd/WO₃/C catalyst compared with Pd/C. The higher electrocatalytic activity might be attributed to the uniform distribution of Pd with smaller particles. Furthermore, it is likely that the improvement in catalytic stability for the Pd/WO₃/C catalyst is due to the hydrogen spillover effect of WO₃ particles. These results indicate that this novel Pd/WO₃/C-APTMS nanocomposite exhibits promising potential for use as an anode electrocatalyst in DFAFCs.     

Ultrasonic-assisted preparation of ultrafine Pd nanocatalysts loaded on Cl−-intercalated MgAl layered double hydroxides for the catalytic dehydrogenation of dodecahydro-N-ethylcarbazole

N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NEC/H12-NEC) is a promising LOHC, and the development of a catalyst with high activity and stability is the key to realizing its reversible hydrogen storage process. In this paper, ultrafine Pd nanocrystalline catalysts (Pd/LDHs-us) supported on Cl^--intercalated MgAl LDHs were prepared by a simple ultrasonic-assisted reduction method and applied in the dehydrogenation of 12H-NEC. In the process of ultrasonic-assisted reduction, the instantaneous high temperature generated by cavitation decomposed part of the CO₃^2– in LDHs interlayer, and promoted PdCl₄^2- to enter the interlayer and become new intercalated ions. At the same time, hydroxyl groups on the surface of LDHs were excited to generate hydrogen radicals (•H) with strong reducibility, which reduced PdCl₄^2- to Pd nanoparticles (PdNPs) in situ. The remaining Cl^- ions continued to exist in the interlayer as intercalated ions. The agglomeration of PdNPs was effectively inhibited, and the average particle size was 1.8 nm, which was uniformly dispersed on LDHs, which improved the catalytic activity of Pd/LDHs-us. The coordination between PdNPs and oxygen in the hydroxyl groups on the surface of LDHs improved its catalytic stability. Using Pd/LDHs-us catalyst, the conversion rate of H12-NEC was 100.0 %, and the dehydrogenation efficiency was 99.3 % at 180℃. When the reaction temperature drops to 170℃, the dehydrogenation efficiency can still reach 94.6 %, showing excellent catalytic performance. The study of dehydrogenation kinetics shows that the apparent activation energy of Pd/LDHs-us catalyst is only 90.97 kJ/mol. This provides a new method and idea for the preparation of efficient dehydrogenation catalysts in the future.     

Electroreduction of oxygen on Pd catalysts supported on Ti-modified carbon

Carbon supports modified with well dispersed anatase TiO₂ (C–Ti-X; X (0.25, 0.5, 0.75, and 1.0) represents mass ratio of Ti precursor to carbon) were synthesized with various Ti loadings and used to support Pd catalysts for oxygen reduction. The anatase nanoparticles increased in size with increasing Ti loading. Pd dispersion improved with increasing Ti loading up to the C–Ti-0.75, which resulted in the best catalytic activity. Although the Pd dispersion was lowest on the C–Ti-1.0, it showed better catalytic performance than the catalysts supported on C–Ti-0.25 and C–Ti-0.5. At 0.8 V (vs. RHE), the best catalytic activity achieved was respectively 2.7 and 2.7 times the mass and specific activities of Pd supported on un-modified carbon. The interaction between Pd and highly dispersed TiO₂ is believed to improve the catalytic activity of Pd supported on TiO₂-modified carbons.     

Poly(sodium-p-styrenesulfonate) assisted microwave synthesis of ordered mesoporous carbon supported Pd nanoparticles for formic acid electro-oxidation

Pd nanoparticles highly dispersed onto the surface of ordered mesoporous carbons (OMCs) were synthesized successfully by poly(sodium-p-styrenesulfonate) (PSS) assisted microwave synthesis. Here, PSS served as a bifunctional molecule both for solubilizing and dispersing OMCs into aqueous solution and for jointing Pd²⁺ to facilitate the subsequent uniform formation of Pd nanoparticles on their surfaces. The effects of PSS on structural and electrochemical properties of Pd/OMCs were investigated. It was found that the addition of PSS facilitated Pd nanoparticles to disperse on the carbon surface. Electrochemical properties showed that Pd catalysts prepared with addition of PSS displayed better electrochemical activity and stability for formic acid electro-oxidation than those without PSS.     

Electrooxidation of formic acid catalyzed by Pd Nanoparticles supported on multi-walled carbon nanotubes with sodium oxalate

This paper repots a highly catalytic palladium nanoparticle catalyst dispersed on the purified multi-walled carbon nanotubes (P-MWCNTs) for the electrooxidation of formic acid, in which sodium oxalate is employed as both a dispersant and a coordination agent. The nanostructured catalysts have been characterized by X-ray diffraction technique and transmission electron microscopy. It is found that the as-prepared face-centered cubic crystal Pd nanoparticles are uniformly dispersed on the surface of MWCNTs with an average particle size of 5.6 nm. Fourier transform infrared spectroscopy and thermogravimetric analysis revel that sodium oxalate is a tractable ligand with the aid of a suitable solution. Cyclic voltammetry and chronoamperometry tests demonstrate that the obtained Pd/P-MWCNT catalyst from typical experiment has better catalytic activity and stability for formic acid electrooxidation than acid-oxidation treatment MWCNT (AO-MWCNT)-supported Pd catalyst from the control experiment. Therefore, the as-prepared Pd/P-MWCNTs would be a potential candidate as an anode electrocatalyst in direct formic acid fuel cells.     

Pd/C催化剂在乙炔选择加氢反应中的催化性能：载体效应

Pd/C catalysts were prepared by deposited Pd nanoparticles (NPs) on different carbon supports including activated carbon (AC), graphite oxide (GO), and reduced graphite oxide (rGO) using sol-immobilization method. Through transmission electron microscopy, powder X-ray di raction, and X-ray photoelectron spectroscopy, the role of the carbon supports for the catalytic performances of Pd/C catalysts was examined in selective hydrogenation of acetylene. The results indicate that Pd/AC exhibited higher activity and selectivity than Pd/GO and Pd/rGO in the gas phase selective hydrogenation of acetylene. Thermal and chemical treatment of AC supports also have some effect on the catalytic performance of Pd/AC catalysts. The differences in the activity and selectivity of various Pd/C catalysts were partly attributed to the metal-support interaction.     

Pd-Cu双金属催化剂上加氢反应的仲氢诱导超极化研究

本文通过多相催化-仲氢诱导超极化（HET-PHIP）核磁共振（NMR）技术研究了Pd-Cu/SiO₂双金属催化剂上丙炔选择性加氢反应.首先利用等体积浸渍法和连续浸渍法合成了一系列不同Pd/Cu比例和形貌的Pd-Cu/SiO₂双金属催化剂.通过ALTADENA（Adiabatic Longitudinal Transport After Dissociation Engenders Net Alignment）方法发现,催化剂的Pd/Cu比例和形貌均对PHIP的极化效率有较大影响.随着Pd-Cu双金属催化剂中Pd比例的增大,PHIP极化效率降低,同时反应活性增强.在同Pd/Cu比例下,相对于等体积浸渍法,连续浸渍法制备的层叠形貌催化剂具有较弱的极化效率以及较强的催化活性,这是由于催化剂表面暴露出的Pd数量增多,导致催化活性增强;同时单个Pd集簇表面积增大,使得氢原子移动范围扩大,从而造成极化效率降低.     

Characterisation of Sonochemically Produced PdO Nanoparticles by X‐ray Absorption Near Edge Structure Spectroscopy

Brij‐35 [polyoxyethylene(23) lauryl ether] stabilised palladium nanoparticles, obtained on attempted sonochemical reduction of PdCl₂ by sodium sulfite in water under Argon, instantaneously oxidized to PdO. The particles obtained were stable and have narrow size distribution with an average size of 10 nm diameter. PdO nanoparticles were reduced to Pd nanoparticles in an autoclave by treatment with 50 bar hydrogen at 140 °C. The catalytic behaviour of Pd nanoparticles, thus obtained, is unusual in comparison with conventional Pd catalysts. The nanoparticles were characterized by UV‐Vis spectroscopy, TEM and their X‐ray Absorption Near Edge Structure (XANES) at the Pd‐L‐III edge.     

Synthesis of carbon supported palladium nanoparticles catalyst using a facile homogeneous precipitation-reduction reaction method for formic acid electrooxidation

A highly dispersed and ultrafine carbon supported Pd nanoparticles (Pd/C) catalyst is synthesized by a facile homogeneous precipitation-reduction reaction method. Under the appropriate pH conditions, [PdCl₄]²⁻ species in PdCl₂ solution are slowly transformed into the insoluble palladium oxide hydrate (PdO·H₂O) precipitation by heat treatment due to a slow hydrolysis reaction, which results in the generation of carbon supported PdO·H₂O nanoparticles (PdO·H₂O/C) sample with the high dispersion and small particle size. Consequently, a highly dispersed and ultrafine Pd/C catalyst can be synthesized by PdO·H₂O → Pd⁰ in situ reduction reaction path in the presence of NaBH₄. As a result, the resulting Pd/C catalyst possesses a significantly electrocatalytic performance for formic acid electrooxidation, which is attributed to the uniformly sized and highly dispersed nanostructure.     

XAS analysis of iron and palladium bonded to a polysaccharide produced anaerobically by a strain of Klebsiella oxytoca

Klebsiella oxytoca BAS‐10 ferments citrate to acetic acid and CO₂, and secretes a specific exopolysaccharide (EPS), which is able to bind different metallic species. These biomaterials may be used for different biotechnological purposes, including applications as innovative green biogenerated catalysts. In production of biogenerated Pd species, the Fe(III) as ferric citrate is added to anaerobic culture of K. oxytoca BAS‐10, in the presence of palladium species, to increase the EPS secretion and improve Pd‐EPS yield. In this process, bi‐metallic (FePd‐EPS) biomaterials were produced for the first time. The morphology of bi‐metallic EPS, and the chemical state of the two metals in the FePd‐EPS, are investigated by transmission electron microscopy, Fourier transform infra‐red spectroscopy, micro‐X‐ray fluorescence, and X‐ray absorption spectroscopy methods (XANES and EXAFS), and compared with mono‐metallic Pd‐EPS and Fe‐EPS complexes. Iron in FePd‐EPS is in the mineralized form of iron oxides/hydroxides, predominantly in the form of Fe³⁺, with a small amount of Fe²⁺ in the structure, most probably a mixture of different nano‐crystalline iron oxides and hydroxides, as in mono‐metallic Fe‐EPS. Palladium is found as Pd(0) in the form of metallic nanoparticles with face‐centred cubic structure in both bi‐metallic (FePd‐EPS) and mono‐metallic (Pd‐EPS) species. In bi‐metallic species, Pd and Fe nanoparticles agglomerate in larger clusters, but they remain spatially separated. The catalytic ability of bi‐metallic species (FePd‐EPS) in a hydrodechlorination reaction is improved in comparison with mono‐metallic Pd‐EPS.     

Sonochemically synthesized core-shell structured Au–Pd nanoparticles supported on γ-Fe2O3 particles

A sample of Au–Pd bimetallic nanoparticles supported on γ-Fe₂O₃ was synthesized in a sonochemically one-pot process. The structural analyses of the synthesized sample were performed by the techniques of X-ray Absorption Fine Structure (XAFS), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and UV–vis spectrometry. Results indicated that the synthesized sample formed a core-shell structure in which a gold core was surrounded by a thin palladium shell. The reaction rate constant for the hydrogenation of cyclohexene of the present sample showed higher value than that of Pd nanoparticles supported on γ-Fe₂O₃ and core-shell structured Au–Pd nanoparticles supported on SiO₂. The present sample is a promising catalyst material which has a high catalytic activity.