Properties of Pd–Ag/C catalysts in the reaction of selective hydrogenation of acetylene

Samples of Pd/C and Pd–Ag/C, where C represents carbon nanofibers (CNFs), are synthesized by methane decomposition on a Ni–Cu–Fe/Al₂O₃ catalyst. The properties of Pd/CNF are studied in the reaction of selective hydrogenation of acetylene into ethylene. It is found that the activity of the catalyst in hydrogenation reaction increases, while selectivity decreases considerably when the palladium content rises. The obtained dependences are caused by the features of palladium’s interaction with the carbon support. At a low Pd content (up to 0.04 wt %) in the catalyst, the metal is inserted into the interlayer space of graphite and the catalytic activity is zero. It is established by EXAFS that the main share of palladium in catalysts of 0.05–0.1 wt % Pd/CNF constitutes the metal in the atomically dispersed state. The coordination environment of palladium atoms consists of carbon atoms. An increase in the palladium content in a Pd/CNF catalyst up to 0.3 wt % leads to the formation of highly dispersed (0.8–1 nm) Pd particles. The Pd/CNF samples where palladium is mainly in the atomically dispersed state exhibit the highest selectivity in the acetylene hydrogenation reaction. The addition of silver to a 0.1 wt % Pd/CNF catalyst initially probably leads to the formation of Pd–Ag clusters and then to alloyed Pd–Ag particles. An increase in the silver content in the catalyst above 0.3% causes the enlargement of the alloyed particles and the palladium atoms are blocked by a silver layer, which considerably decreases the catalytic activity in the selective hydrogenation of acetylene.     

Argon glow discharge plasma‐reduced palladium nanoparticles supported on activated carbon for Suzuki and Heck coupling reactions

Palladium nanoparticles supported on activated carbon were prepared by argon glow discharge plasma reduction (Pd/C‐P) without any chemical reducing agents and protective agents. The as‐prepared Pd/C‐P catalyst was characterized using nitrogen adsorption–desorption, X‐ray diffraction and transmission electron microscopy analyses. The results showed that the palladium nanoparticles reduced by plasma are well dispersed with a smaller particle size than commercial Pd/C. Pd/C‐P exhibited a high catalytic activity in Suzuki and Heck coupling reactions. Moreover, there was no obvious loss of catalytic activity even after eight repeated cycles, showing good reactivity and recyclability.     

Palladium supported on chitosan as a recyclable and selective catalyst for the synthesis of 2-phenyl ethanol

Two different chitosan supported palladium based catalysts were prepared, wherein dispersed palladium nanoparticles were obtained via chemical reduction supported on chitosan (Pd/CTS) and amine functionalized modified chitosan (Pd/AFCTS). The catalytic activity of the Pd-based catalysts, Pd/CTS and Pd/AFCTS, were assessed in the hydrogenation of styrene oxide to 2-phenyl ethanol. Both Pd-based catalysts enhanced the formation of the desired 2-phenyl ethanol in contrast to a conventional Pd/C catalyst without the assistance of inorganic or organic base. A considerable influence on the conversion and selectivity was observed in the case of Pd/AFCTS, consisting of palladium nanoparticles stabilized and dispersed on amine-functionalized chitosan matrix, affording complete conversion of styrene oxide with 98% selectivity to 2-phenyl ethanol. The catalyst Pd/AFCTS has also been recycled without significant loss of activity and selectivity.     

Mesoporous carbon supported ultrasmall palladium particles as highly active catalyst for Suzuki‐Miyaura reaction

A fast and efficient eco‐friendly two‐step preparation of a palladium‐containing mesoporous carbon catalyst ( C1 ) from green and readily available carbon precursors (phloroglucinol and glyoxal), a porogen template (pluronic F‐127) and PdCl₂ is described. Catalyst C1 contains ultra‐small Pd nanoparticles (1.2 nm) uniformly dispersed in the carbon network and shows an outstanding activity for Suzuki‐Miyaura reactions in pure water: extremely low amounts of palladium (10 μequiv. in most cases) are sufficient to afford almost palladium‐free products (containing <0.25 ppm of precious metal without further purification steps).     

ZIF-8原位负载Pd纳米粒子及其在Suzuki-Miyaura反应中的应用(英文)

将PdCl2与ZIF-8的反应原料ZnO和2-甲基咪唑按照一定的比例,采用机械化学法原位将Pd2+负载在ZIF-8上(Pd2+/ZIF-8)。然后用NaBH4将Pd2+/ZIF-8进行还原,得到均匀分散的Pd纳米颗粒(Pd/ZIF-8)。通过XRD、N2吸附、透射电镜、ICP-AES、XPS等对Pd/ZIF-8的结构、形貌、价态等进行了表征。结果表明用机械化学法原位制备的Pd/ZIF-8具有分散均匀、容易大量制备的优点。该催化剂不仅能高效催化Suzuki-Miyaura交叉偶联反应,并且能够多次循环利用。     

Palladium Nanoparticles Supported on a Porous Organic Polymer: An Efficient Catalyst for Suzuki‐Miyaura and Sonogashira Coupling Reactions

A new porous organic polymer (POP) with high thermal stability and large surface area has been synthesized and applied in the preparation of Pd/POP catalyst. Pd/POP was characterized by XRD, TGA, SEM and TEM. The catalyst consists of highly dispersed palladium nanoparticles of 0.9–4 nm size on POP with a large surface area of 650 m²/g. It presents high catalytic activity for Suzuki‐Miyaura and Sonogashira reactions. The catalyst was reusable for three to five times without significant loss of activity.     

Palladium Nanoparticles Bonded to Two‐Dimensional Iron Oxide Graphene Nanosheets: A Synergistic and Highly Reusable Catalyst for the Tsuji–Trost Reaction in Water and Air

Low cost, high activity and selectivity, convenient separation, and increased reusability are the main requirements for noble‐metal‐nanocatalyst‐catalyzed reactions. Despite tremendous efforts, developing noble‐metal nanocatalysts to meet the above requirements remains a significant challenge. Here we present a general strategy for the preparation of strongly coupled Fe₃O₄ and palladium nanoparticles (PdNPs) to graphene sheets by employing polyethyleneimine as the coupling linker. Transmission electron microscopic images show that Pd and Fe₃O₄ nanoparticles are highly dispersed on the graphene surface, and the mean particle size of Pd is around 3 nm. This nanocatalyst exhibits synergistic catalysis by Pd nanoparticles supported on reduced graphene oxide (rGO) and a tertiary amine of polyethyleneimine (Pd/Fe₃O₄/PEI/rGO) for the Tsuji–Trost reaction in water and air. For example, the reaction of ethyl acetoacetate with allyl ethyl carbonate afforded the allylated product in more than 99 % isolated yield, and the turnover frequency reached 2200 h^?1. The yield of allylated products was 66 % for Pd/rGO without polyethyleneimine. The catalyst could be readily recycled by a magnet and reused more than 30 times without appreciable loss of activity. In addition, only about 7.5 % of Pd species leached off after 20 cycles, thus rendering this catalyst safer for the environment.     

Pd supported on graphene modified g-C3N4 hybrid: a highly efficient catalyst for hydrogenation of nitroarenes

Graphitic carbon nitride (g-C₃N₄) and graphene (GO) have been greatly utilized as supports in the field of heterogeneous catalysis. In this work, layered C₃N₄ polymer/graphene hybrid (CNNS/rGO₂₀) with heterostructure was fabricated by a hydrothermal method followed by loading Pd nanoparticles on the hybrid. The palladium was well dispersed uniformly (1.31 nm) owing to the layered and porous heterostructure of CNNS/rGO₂₀. The obtained catalyst was used for the transfer hydrogenation of a series of nitro-compounds to give the corresponding aromatic amines with outstanding activity by employing formic acid as hydrogen donor under mild conditions. The catalytic activity of the heterogeneous catalyst showed no significant loss after five continuous use.     

Highly dispersed palladium nanoclusters incorporated in amino‐functionalized silica spheres for the selective hydrogenation of succinic acid to γ‐butyrolactone

Highly dispersed palladium nanoclusters incorporated on amino‐functionalized silica sphere surfaces (Pd/SiO₂‐NH₂) were fabricated by a simple one‐pot synthesis utilizing 3‐(2‐aminoethylamino)propyltrimethoxysilane (AAPTS) as coordinating agent. Uniform palladium nanoclusters with an average size of 1.1 nm can be obtained during the co‐condensation of tetraethyl orthosilicate and AAPTS owing to the strong interaction between palladium species and amino groups in AAPTS. The palladium particle size can be controlled by addition of AAPTS and plays a significant role in the catalytic performance. The Pd/SiO₂‐NH₂ catalyst exhibits high catalytic activity for succinic acid hydrogenation with 100% conversion and 94% selectivity towards γ‐butyrolactone using 1,4‐dioxane as solvent at 240°C and 60 bar for 4 h. Moreover, the Pd/SiO₂‐NH₂ catalyst is robust and readily reusable without loss of its catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Carbon nanospheres with well‐controlled nano‐morphologies as support for palladium‐catalyzed Suzuki coupling reaction

Uniform carbon nanospheres (UCS) with well‐controlled nano‐morphologies were fabricated by hydrothermal carbonization of sucrose in the presence of kayexalate. Highly dispersed and ultrafine palladium nanoparticles were supported on the UCS through a facile co‐reduction process with NaBH₄ as reducing agent. The obtained Pd@UCS exhibited efficient catalytic activity for the Suzuki coupling reaction. Moreover, the as‐prepared catalyst could be recycled and reused at least five times without significant loss of its catalytic activity.     

Easy conversion of nitrogen‐rich silk cocoon biomass to magnetic nitrogen‐doped carbon nanomaterial for supporting of Palladium and its application

In this study, magnetic nitrogen‐doped carbon (MNC) was fabricated through facile carbonization and activation of natural silk cocoons containing nitrogen and then combined with Fe₃O₄ nanoparticles to create a good support material for palladium. Palladium immobilization on the support resulted in the formation of magnetic nitrogen‐doped carbon‐Pd (MNC‐Pd). The prepared heterogeneous catalyst was well characterized using FT‐IR, TGA, EDX, FE‐SEM, XRD, VSM, and ICP‐OES techniques. Thereafter, the synthesis of biaryl compounds was conducted to investigate the catalyst performance via the reaction of aryl halides and phenylboronic acid. Further, the catalyst could be used and recycled for six consecutive runs without any significant loss in its activity.     

Palladium nanoparticles supported on poly (N-vinylpyrrolidone)-grafted silica as new recyclable catalyst for Heck cross-coupling reactions

Novel catalytic system based on palladium nanoparticles supported on poly (N-vinylpyrrolidone) (PVP) grafted silica was prepared. Aminopropylsilica was reacted with acryloyl chloride to form acrylamidopropylsilica, and onto this functionalized silica vinylpyrrolidone monomer was polymerized by free-radical polymerization. The complexation of PVP-grafted silica with PdCl₂ was carried out to obtain the heterogeneous catalytic system. X-ray diffraction (XRD) technique and transmission electron microscopy (TEM) image showed that palladium dispersed through the support in nanometer size. This catalytic system exhibited excellent activity in cross-coupling reactions of aryl iodides, bromides and also chlorides with olefinic compounds in Heck-Mizoraki reactions in short reaction time and high yields. Elemental analysis of Pd by inductively coupled plasma (ICP) technique and hot filtration test showed low leaching of the metal into solution from the supported catalyst. The catalyst can be reused several times in repeating Heck reaction cycles without considerable loss in its activity.     

聚苯并噁嗪固载钯基纳米催化剂在芳香醇氧化反应中的应用

以球状聚苯并噁嗪为载体, 采用浸渍热解法合成了钯炭纳米催化剂. 通过透射电子显微镜观察发现, 钯纳米粒子几乎全部均匀分布在载体上, 且尺寸均一, 平均直径约为3.5 nm. 结果表明, 载体表面含有丰富的含氮含氧官能团, 氮和氧原子与钯之间存在相互作用, 从而使聚苯并噁嗪能够有效固载钯纳米粒子. 采用相同的方法进一步合成Pd-Au/C和Pd-Pt/C双金属催化剂, Pd-Au和Pd-Pt纳米粒子也展现出良好的分散性, 无明显团聚现象, 平均直径分别为4.3和4.2 nm, 进一步说明聚苯并噁嗪对金属活性组分的有效固载. 将催化剂应用于苯甲醇氧化反应, 其中Pd₁-Au₁/C在2 h的转化率为98%, 对产物苯甲醛的选择性大于99%, 该催化剂经过焙烧可恢复催化活性, 表现出良好的循环稳定性, 并能将不同取代基的芳香醇氧化为相应的醛, 是一种良好的醇氧化催化剂.     

Development of magnetic,ferrite supported palladium catalysts for 2,4-dinitrotoluene hydrogenation

Cobalt, copper, and nickel ferrite spinel nanoparticles have been synthesized by using a combination of sonochemical treatment and combustion. The magnetic nanoparticles have been used as supports to prepare ~4 wt% palladium catalysts. The ferrites were dispersed in an ethanolic solution of Pd(II) nitrate by ultrasonication. The palladium ions were reduced to metallic Pd nanoparticles, which were then attached to the surface of the different metal oxide supports. Thus, three different catalysts (Pd/CoFe₂O₄, Pd/CuFe₂O₄, Pd/NiFe₂O₄) were made and tested in the hydrogenation of 2,4-dinitrotoluene (DNT). A possible reaction mechanism, including the detected species, has been envisaged based on the results. The highest 2,4-diaminotoluene (TDA) yield (99 n/n%) has been achieved by using the Pd/NiFe₂O₄ catalyst. Furthermore, the TDA yield was also reasonable (84.2 n/n%) when the Pd/CoFe₂O₄ catalyst was used. In this case, complete and easy recovery of the catalyst from the reaction medium is ensured, as the ferrite support is fully magnetic. Thus, the catalyst is very well suited for applicationy in the hydrogenation of DNT or other aromatic nitro compounds.     

Preparation of the Pd/C catalysts: A molecular-level study of active site formation

This review summarizes the results of molecular-level studies on the mechanism of Pd/C catalyst formation from the PdCl₂ precursor. Two processes occur in acidic media during the contact of H₂PdCl₄ with carbon: (a) adsorption of palladium chloride to form surface complexes and (b) redox interaction between PdCl₂ and carbon with the formation of palladium metal particles. The ratio between these adsorbed palladium species depends on the conditions of adsorption and especially on the size of carbon support grains and the oxidative atmosphere. The observations are explained by the fact that carbon support exhibits electrochemical and ligand properties. X-ray diffraction, X-ray scattering, XPS, and high-resolution electron microscopy revealed that the nanostructure of carbon materials, in particular the extent of their three-dimensional ordering, is crucial for the ligand properties. The presence of two forms, metallic and ionic, of sorbed palladium determines the bimodal size distribution of the metal. After the reduction of ionic species, metal particles are “blocked” with support. The nature of the ionic forms of palladium (mostly (PdCl₂)_n) clusters chemically and epitaxially bound to the carbon surface suggests the mechanisms of the bimodal distribution of the supported metal particles on the surface and the methods for the control of the ratio between “blocked,” low-dispersed, and highly-dispersed particles in the catalyst. One of these methods is the use of palladium polynuclear hydroxo complexes (PHCs) with low oxidation potentials as starting compounds for catalysts preparation. The data on the PHC structure in a solution and its change upon the adsorption of PHC on the surface of the carbon material obtained by the¹⁷O,²³Na,¹³³Cs, and³⁵Cl NMR techniques are discussed. PHCs are shown to be a clew of the [Pd(OH)₂]_n polymeric filament, whose fractions are bound with alkali metal ions. When PHC is adsorbed on the surface of the carbon support and then dried, palladium oxide is formed from which highly dispersed metal particles are formed during reduction. The nature of alkali metal ions in PHC affects the activity of the Pd/C catalyst. An important role of the ligand, electrochemical, and lyophilic properties of carbon material during the formation of the species of the active catalyst component is discussed.     

Finely dispersed palladium on silk‐fibroin as an efficient and ligand‐free catalyst for Heck cross‐coupling reaction

A palladium–fibroin complex (Pd/Fib.) was prepared by the addition of sonicated fibroin fiber in water to palladium acetate solution. Pd (OAc)₂ was absorbed by fibroin and reduced with NaBH₄ at room temperature to the Pd(0) nanoparticles. Powder‐X‐ray diffraction, scanning electron microscopy–energy‐dispersive X‐ray spectroscopy, Fourier transform‐infrared, CHN elemental analysis and inductively coupled plasma‐atomic emission spectroscopy were carried out to characterize the Pd/Fib. catalyst. Catalytic activity of this finely dispersed palladium was examined in the Heck coupling reaction. The catalytic coupling of aryl halides (‐Cl, ‐Br, ‐I) and olefins led to the formation of the corresponding coupled products in moderate to high yields under air atmosphere. A variety of substrates, including electron‐rich and electron‐poor aryl halides, were converted smoothly to the targeted products in simple procedure. Heterogeneous supported Pd catalyst can be recycled and reused several times.     

A comparison between two Pd‐Ni catalysts supported on two different supports toward Suzuki‐Miyaura coupling reaction

When a single metal fails to promote an efficient Suzuki‐Miyaura coupling reaction at ambient temperature, the synergistic cooperation of two distinct metals might improve the reaction. To examine the synergistic effect of palladium and nickel for catalyzing Suzuki coupling reaction, g‐C₃N₄ supported metal nanoparticles of PdO, NiO and Pd‐PdO‐NiO were prepared, characterized and their catalytic activities evaluated over different aryl halides at room temperature and 78 °C. The morphological characterization of Pd‐PdO‐NiO/g‐C₃N₄ demonstrated that the bimetallic particles were uniformly dispersed over the g‐C₃N₄ layers with diameters ranging from 3.5‐7.7 nm. XPS analysis showed that nanoparticles of Pd‐PdO‐NiO consisted of Pd(II), Pd(0) and Ni(II) sites. The experiments performed on the catalytic activity of Pd‐PdO‐NiO/g‐C₃N₄ showed that the prepared catalyst demonstrated an efficient activity without using toxic solvents.     

Physical and electrochemical characterizations of nanostructured Pd/C and PdNi/C catalysts for methanol oxidation

Pd and PdNi nanoparticles supported on Vulcan XC-72 carbon were prepared by a chemical reduction with formic acid process. The catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry, and chronoamperometry. The results showed that the Pd and PdNi nanoparticles, which were uniformly dispersed on carbon, were 2–10 nm in diameters. The PdNi/C catalyst has higher electrocatalytic activity for methanol oxidation in alkaline media than a comparative Pd/C catalyst and shows great potential as less expensive electrocatalyst for methanol electrooxidation in alkaline media in direct methanol fuel cells.     

Palladium nanoparticles encapsulated in a metal-organic framework as efficient heterogeneous catalysts for direct C2 arylation of indoles

Highly dispersed palladium nanoparticles (Pd NPs) encapsulated in the mesoporous cages of the metal-organic framework (MOF) MIL-101(Cr) have been prepared by using the wetness impregnation method. The Pd NPs were characterized by powder X-ray diffraction (PXRD), N(2) adsorption, transmission electron microscopy, inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The particles size ((2.6±0.5) nm) of the obtained Pd NPs was in good agreement with the cage diameters (2.9 and 3.4 nm) of the MOF. The resulting Pd/MIL-101(Cr) catalyst exhibited extremely high catalytic activities in the direct C2 arylation of substituted indoles by using only 0.1 mol% of the Pd catalyst. Moreover, the catalyst is easily recoverable and can be reused several times without leaching into solution and loss of activity. The combination of the highly dispersible Pd NPs within the accessible mesoporous cages and the favorable adsorption of the aryl halides on MIL-101 are suspected to be the main reasons for the observed high activities of the Pd/MIL-101(Cr) catalyst in the direct C2 arylation of indoles.     

超临界二氧化碳中功能化聚乙二醇稳定的钯纳米粒子催化醇的选择氧化反应

 以超临界二氧化碳 (scCO2)/聚乙二醇 (PEG) 两相为反应介质, 双齿氮配体功能化聚乙二醇稳定的 Pd 纳米颗粒作为催化剂, 进行了醇的需氧氧化反应. 系统研究了催化剂制备条件和反应条件对苯甲醇需氧氧化反应的影响. 结果表明, 以氢气为还原剂制备的 Pd 纳米粒子的催化活性最高. 反应结束后, 可以利用 scCO2 直接进行原位萃取得到产物, 实现了催化剂与产物的有效分离和催化剂的循环使用. 反应中没有检测到钯的流失. 催化剂经过 5 次循环利用后转化率仍可达 98%.