Synthesis of highly dispersed Pd/C electro-catalyst with high activity for formic acid oxidation

In this study, we present a simple process to obtain highly dispersed palladium nanoparticles on Vulcan XC-72R carbon support without any protective agent. To obtain high metal loading Pd/C catalyst without any surfactant, we modified the polyol process by employing NH₃ species as a mediation to control the reaction pathway to avoid the precipitation of Pd(OH)₂, and hence the agglomeration of Pd nanoparticles. The obtained Pd/C sample was characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques. The results show that highly dispersed Pd/C catalyst with an average diameter of 3.0 nm could be obtained in this novel process. The activity of formic acid oxidation on this Pd/C catalyst was examined via cyclic voltammetry technique and it is found that the catalytic activity is greatly enhanced due to the reduced particle size and the improved dispersion of palladium nanoparticles on the carbon surface.     

Gold, palladium and gold–palladium supported on silica catalysts prepared by sol–gel method: synthesis, characterization and catalytic behavior in the ethanol steam reforming

Noble-metal-based catalysts supported on silica (Au/SiO₂, Pd/SiO₂ and Au–Pd/SiO₂) were prepared by the sol–gel method and were evaluated in the steam reforming of ethanol for hydrogen production. The catalysts were characterized by N₂ physisorption (BET/BJH methods), X-ray diffraction, temperature programmed reduction analysis, H₂ chemisorption, atomic absorption spectrophotometry and Raman spectroscopy. The structural characterization of the Au- and Pd-containing catalysts after calcination showed that the solids are predominantly formed by Au⁰, Pd⁰ and PdO species and was observed that the metallic Pd dispersion diminished in the presence of Au⁰. The results revealed that the catalytic behavior could be influenced by the experimental conditions and the nature of the catalyst employed. The Pd/SiO₂ catalyst showed the best performance among the catalysts tested at the highest reaction temperature (600 °C) due to the more effective action of the metallic active phase, which covers a greater area in this sample. At this same reaction temperature, the Au–Pd/SiO₂ catalyst showed a significant deactivation, probably due to the lower Pd dispersion presented by this catalyst.     

Highly active palladium/activated carbon catalysts for Heck reactions: correlation of activity, catalyst properties, and Pd leaching

A variety of palladium on activated carbon catalysts differing in Pd dispersion, Pd distribution, Pd oxidation state, and water content were tested in Heck reactions of aryl bromides with olefins. The optimization of the catalyst (structure-activity relationship) and reaction conditions (temperature, solvent, base, and Pd loading) allowed Pd/C catalysts with very high activity for Heck reactions of unactivated bromobenzene (turnover number (TON) approximately 18000, turnover frequency (TOF) up to 9000, Pd concentrations down to 0.005 mol %) to be developed. High Pd dispersion, low degree of reduction, sufficient content of water, and uniform Pd impregnation are criteria for the most active system. The catalysts combine high activity and selectivity under ambient conditions (air and moisture), easy separation (filtration), and quantitative recovery of palladium. Determination of Pd in solution after and during the reaction, and catalyst characterization before and after the reaction (transmission electron microscopy (TEM), X-ray diffraction (XRD)), indicate dissolution/reprecipitation of palladium during the reaction. The Pd concentration in solution is highest at the beginning of the reaction and is a minimum (< 1 ppm) at the end of the reaction. Palladium leaching correlates significantly with the reaction parameters.     

有序介孔有机金属 Pd(II) 的制备及其催化水介质中的 Suzuki 反应

 以有机金属 Pd 硅烷和乙基桥联硅烷为混合硅源, 在表面活性剂作用下进行共缩聚反应, 制备了有序介孔有机金属 Pd(II) 催化剂 Pd(II)-PMO(Et). 采用傅里叶变换红外光谱、核磁共振谱、X 射线衍射、透射电子显微镜和 N2 吸附脱附等手段对催化剂进行了表征. 结果表明, 与后嫁接法相比, 共聚法制得的催化剂活性位分散均匀, 孔道不易堵塞, 同时乙基修饰的孔壁增强了催化剂表面疏水性, 有利于反应物在孔道内的扩散和吸附. 在水介质 Suzuki 反应中, Pd(II)-PMO(Et) 的催化活性与均相催化剂 Pd(PPh3)2Cl2 的相当, 且可重复使用.     

Catalytic Hydrodechlorination of 1,2,4,5‐Tetrachlorobenzene over Various Supports Loaded Palladium Catalysts

Water pollution by polychlorinated aromatic hydrocarbons has always been a global issue. In this work, we reported a synthesis of supported palladium catalysts Pd/C, Pd/CeO₂, Pd/SBA‐15, Pd/ZrO₂,Pd/SiO₂, and Pd/Al₂O₃ as well as their catalytic activities on hydrodechlorination (HDC) of 1,2,4,5‐tetrachlorobenzene (TeCB). These Pd catalysts were characterized by Brunauer‐Emmett‐Teller (BET) specific surface area, Transmission electron microscopy (TEM), X‐ray diffraction (XRD), energy Dispersive X‐ray Fluorescence (EDXRF), CO‐chemisorption, and H2‐temperature programmed reduction (H2‐TPR) analysis. Pd/C, Pd/CeO₂ and Pd/SBA‐15 catalysts showed relatively high catalytic activities. The catalytic activities were associated with dispersion of Pd, metal surface area, and reaction temperature, etc.     

Influence of Pd precursors on the catalytic performance of Pd–H4SiW12O40/SiO2 in the direct oxidation of ethylene to acetic acid

The effects of palladium precursors (PdCl₂, (NH₄)₂PdCl₄, Pd(NH₃)₂Cl₂, Pd(NO₃)₂ and Pd(CH₃COO)₂) on the catalytic properties in the selective oxidation of ethylene to acetic acid have been investigated for 1.0 wt% Pd–30 wt% H₄SiW₁₂O₄₀/SiO₂. The structures of the catalysts were characterized using X-ray diffraction, N₂ adsorption, H₂-pulse chemical adsorption, infrared spectrometry of the adsorbed pyridine, H₂ temperature-programmed reduction and X-ray photoelectron spectroscopy. The present study demonstrates that the different palladium precursors can lead to the significant changes in the dispersion of palladium. It is found that Pd dispersion decreases as follows: PdCl₂ > (NH₄)₂PdCl₄ > Pd(NO₃)₂ > Pd(NH₃)₂Cl₂ > Pd(C₂H₃O₂)₂, which is nearly identical to the catalytic activity. This indicates that the dispersion of palladium plays an important role in the catalytic activity. Furthermore, density of Lewis (L) and Brönsted (B) acid sites are also strongly dependent on the palladium precursors. It is also demonstrated that an effective catalyst should possess a well combination of Brönsted acid sites with dispersion of palladium.     

Catalytic methanol decomposition to carbon monoxide and hydrogen over Pd/CeO2-ZrO2-La2O3 with different Ce/Zr molar ratios

The catalytic behaviors of Pd (1.4 wt%) catalysts supported on CeO₂-ZrO₂-La₂O₃ mixed oxides with different Ce/Zr molar ratios were investigated for methanol decomposition. Nitrogen adsorption-desorption (BET), X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (H₂-TPR), X-ray diffraction (XRD) and Pd dispersion analysis were used for their characterization. Pd/Ce_0.76Zr_0.18 La_0.06O_1.97 catalyst showed the highest BET surface area, best Pd dispersion capability and strongest metal-support interaction. Moreover, XPS showed that there was lattice defect oxygen or mobile oxygen. According to the result of O 1s measurements the lattice defect oxygen or mobile oxygen helped to maintain Pd in a partly oxidized state and increased the activity for methanol decomposition. The Pd/Ce_0.76Zr_0.18La_0.06O_1.97 catalyst exhibited the best activity. A 100% conversion of methanol was achieved at around 260 °C, which was about 20-40 °C lower than other catalysts     

高效组合型 Pd/C 催化剂用于 Suzuki 偶联反应

 采用有机金属 Pd2(dba)3 (dba 为二亚苄基丙酮) 还原分解法制得均匀分布的 Pd 纳米颗粒 (粒径为 3~6 nm) 混合液, 并用活性炭直接吸附得到了组合型 Pd/C 纳米催化剂. 采用透射电子显微镜、X 射线光电子能谱和 X 射线衍射等手段测定了催化剂表面 Pd 颗粒大小分布、晶型和化学态等. 将该催化剂用于 Suzuki 碳-碳偶联反应, 其催化活性比浸渍法制备的 Pd/C 催化剂高 2 倍以上. 以溴代芳烃为底物时, 在 80 oC 下 0.5 h 后偶联产物收率可达 98% 以上. 以邻氯硝基苯为底物时, 在 110 oC 下 1 h 后偶联产物收率可达 64%; 延长反应时间, 产物收率可达 90% 以上.     

Green synthesis of palladium nanoparticles using Pistacia atlantica kurdica gum and their catalytic performance in Mizoroki–Heck and Suzuki–Miyaura coupling reactions in aqueous solutions

A one‐pot green method for the synthesis of palladium nanoparticles (Pd‐NPs) supported on Pistacia atlantica kurdica (P. a. kurdica) gum is described. This natural gum is used as a reducing and stabilising agent. The formation of the Pd‐NPs/P. a. kurdica gum catalyst was verified using several techniques, such as Fourier transform infrared spectroscopy, ultraviolet–visible spectrophotometry, scanning and transmission electron microscopies, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, dynamic light scattering and wavelength‐dispersive X‐ray spectroscopy. The Pd‐NPs stabilised by P. a. kurdica gum were employed as a heterogeneous catalyst in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions at low palladium loading (0.1 mol%) under aerobic, phosphine‐free and ligand‐free conditions in water. Product yields of up to 98%, a facile work‐up, no evidence of leached palladium from the catalyst surface and smooth recovery of the catalyst, which can be reused at least eight times, confirm the efficiency of the catalysts in the reactions investigated. Copyright © 2015 John Wiley & Sons, Ltd.     

树枝状钯纳米结构的控制合成及硝基苯加氢反应的催化活性

以氯钯酸为前驱体, 苯甲醇为还原剂和溶剂, 十六烷基吡咯烷酮(PVP)为稳定剂, 在微波辐射下制备了分散均匀、形貌均一的树枝状钯纳米结构. 产物用透射电子显微镜(TEM), X射线粉末衍射(XRD), X射线光电子能谱(XPS)进行了表征, 表明所制备的Pd纳米颗粒呈树枝状, 形貌单一, 分散均匀, 是由许多近似圆形的小颗粒自组装而成的二级结构. 对树枝状钯催化硝基苯加氢反应进行探究, 表明树枝状钯的催化活性比市售的钯碳催化剂的催化活性高.     

Novel and efficient bridged bis(N-heterocyclic carbene)palladium(II) catalysts for selective carbonylative Suzuki–Miyaura coupling reactions to biaryl ketones and biaryl diketones

Bridged N,N′-substituted bisbenzimidazolium bromide salts (L1, L2, and L3) were synthesized and fully characterized. Reactions of palladium acetate with L1, L2, and L3 afforded corresponding new bridged bis(N-heterocyclic carbene)palladium(II) complexes (C1, C2, and C3) in high yields. The X-ray structure of complex C1 showed that the Pd(II) ion is bonded to the two carbon atoms of the bis(N-heterocyclic carbene) and two bromido ligands are in the cis position, resulting in a distorted square planar geometry. The three Pd(NHC)₂Br₂ complexes C1, C2, and C3 were evaluated in carbonylative Suzuki–Miyaura coupling reactions of aryl boronic acids with aryl halides and displayed high catalytic activity with low catalyst loading. The coupling reactions of aryl bromides were selective towards the carbonylation product at higher carbon monoxide pressure.     

A series of (NHC)Pd(N˄O)(OAc) complexes: synthesis,characterization and catalytic activities towards desulfinative Sonogashira coupling of arylsulfonyl hydrazides with arylalkynes

A series of well-defined N-heterocyclic carbene palladium (II) complexes with general formula (NHC)Pd(N^˄O)(OAc) were prepared through reaction of Pd (NHC)(OAc)₂(H₂O) with 1-methyl-1H-pyrazole-3-carboxylic acid or 1-methyl-1H-indazole-3-carboxylic acid in the presence of K₂CO₃. These complexes were then used for desulfinative Sonogashira coupling of arylsulfonyl hydrazides with terminal alkynes. With low catalyst loading, all synthesized palladium compounds exhibited moderate to high catalytic activities for the reactions.     

Synthesis and characterization of N-heterocyclic carbene palladium complex and its application on direct arylation of benzoxazoles and benzothiazoles with aryl bromides

A mixed-halogen bis(1-(4-tert-butylbenzyl)-3-(2, 4, 6-trimethylbenzyl)-1H-benzo[d]imidazol-2-ylidene) palladium(II) complex, trans-[Pd(Cl_0.7Br_0.3)₂(C₂₈H₃₂N₂)₂], has been synthesized and characterized by elemental analysis, ¹H-NMR, ¹³C-NMR, and IR spectroscopy, and single crystal X-ray diffraction. The palladium in the mononuclear complex is four-coordinate in a square-planar configuration with two carbenes of two benzo[d]imidazole rings and two halides. The two halides are disordered between Br and Cl, with the Cl: Br ratio approximately 0.7 : 0.3. The angles C1–Pd1–Br1, 88.63(11)° and C1ⁱ–Pd1–Br1ⁱ, 91.37(11)° (i: 1?x, 1?y, 1?z) in the coordination sphere are very close to the ideal value of 90°. The Pd–X distance is slightly longer than other carbene derivative Pd–Cl single bond distances and slightly shorter than Pd–Br single bond distances. These results agree with the Cl/Br disorder at the halogen position. The palladium–carbene complex was tested as a catalyst in the direct arylation reaction of benzoxazoles and benzothiazoles with aryl bromides.     

N‐Heterocyclic carbene/phosphite synergistically assisted Pd/C‐catalyzed Suzuki coupling of aryl chlorides

An N‐heterocyclic carbene and phosphite synergistically enhanced Pd/C catalyst system has been developed for Suzuki coupling of aryl chlorides and aryl boronic acids from commercially available Pd/C with sterically demanding N,N′‐bis(2,6‐diisopropylphenyl)imidazolylidene and trimethylphosphite. A remarkable increase in catalytic activity of Pd/C was observed when used along with 1 equiv. N,N′‐bis(2,6‐diisopropylphenyl)imidazolium chloride and 2 equiv. phosphite with respect to palladium in appropriate solvents that were found to play a crucial role in Pd/C‐NHC‐P(OR)₃‐catalyzed Suzuki coupling. A dramatic ortho‐substitution effect of carbonyl and nitrile groups in aryl chlorides was observed and explained by a modified quasi‐heterogeneous catalysis mechanism. The Pd/C catalyst could be easily recovered from reaction mixtures by simple filtration and only low palladium contamination was detected in the biparyl products. A practical process for the synthesis of 4‐biphenylcarbonitrile has therefore been developed using the N‐heterocyclic carbene/phosphite‐assisted Pd/C‐catalyzed Suzuki coupling. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

A new palladium complex supported on magnetic nanoparticles and applied as an catalyst in amination of aryl halides,Heck and Suzuki reactions

A simple, efficient and less expensive protocol for the phosphine-free C–C coupling reactions and synthesis of anilines in the presence of 2-aminobenzamide complex of palladium supported on Fe₃O₄ magnetic nanoparticles (Pd(0)-ABA-Fe₃O₄) has been reported. The Suzuki reaction was carried out in water or PEG using phenylboronic acid (PhB(OH)₂) or sodium tetraphenyl borate (NaBPh₄). Pd(0)-ABA-Fe₃O₄ has been found promising for Heck reaction of butyl acrylate, styrene or acrylonitrile with aryl halides (including Cl, Br and I). Also, Pd(0)-ABA-Fe₃O₄ has been found as efficient catalyst for the amination of aryl halides using aqueous ammonia. The products have been obtained in short reaction times and high yields. The catalyst was easily separated using an external magnet from the reaction mixture and reused for several runs without significant loss of its catalytic efficiency or palladium leaching. The leaching of catalyst has been examined by hot filtration and ICP-OES technique. The nanomagnetical catalyst was characterized by FTIR, TGA, XRD, VSM, TEM, SEM, EDS, DLS and ICP-OES techniques.     

Suzuki–Miyaura cross-coupling reaction assisted by palladium nanoparticles-decorated zeolite 13X nanocomposite: a greener approach

Heterogeneous catalysts govern the field of catalysis due to their easy separation from a reaction mixture, reusability, and prevention of agglomeration, making them more efficient catalysts than homogeneous catalysts. Herein, we report the eco-friendly synthesis of a novel heterogeneous catalyst, viz. palladium nanoparticles (Pd NPs) decorated over zeolite 13X nanocomposite using dried fruits of Terminalia chebula Retz. as the reducing and stabilizing agent and its performance as a promising catalyst for the Suzuki–Miyaura coupling reactions. The particle size, crystallinity, morphology, and textural properties of the catalyst were identified using Fourier transform-infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HR-TEM), thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) analysis which confirmed the presence of palladium nanoparticles on the surface of zeolite 13X. The FESEM images revealed the presence of spherical-shaped Pd NPs over the cubical particles of zeolite 13X. The average particle size of the palladium nanoparticles was found to be in the range of 6–7 nm and was polycrystalline in nature. From BET analysis, it was inferred that the decoration of Pd NPs decreased the surface area of zeolite 13X (615.5 m²/g to 548.334 m²/g), thus leaving pores unoccupied. This study showed the efficiency of this novel catalyst in the formation of biaryl derivatives using low palladium loadings (0.0012 mol%) giving good to excellent yields (90–99%) within short reaction times (10–225 min) with high TONs (>?79,000) and TOFs (>?21,000). Both electron-donating and electron-withdrawing aryl halides and aryl boronic acids reacted smoothly in the presence of K₂CO₃ as a base and EtOH/H₂O (1:1) as the solvent. Besides, the catalyst could be recycled and reused for 5 consecutive runs with minimal loss of its efficiency. The supremacy of this catalyst could well be exploited in future for various organic transformations.

Graphical abstract

     

Preparation and catalytic performance of monolayer-dispersed Pd/Ni bimetallic catalysts for hydrogenation

Pd/Ni bimetallic catalysts were prepared by replacement reactions, characterized by X-ray diffraction, CO chemisorption and H₂ temperature-programmed desorption, and evaluated for hydrogenation of cyclohexene, styrene and acetone. The results show that Pd atoms are monolayer-dispersed on the Ni surface in these Pd/Ni catalysts. Consequently, Pd/Ni catalysts are much more active than Pd/Ni and Pd/c-Al₂O₃ with the same Pd loading prepared by the conventional impregnation method. __________ Translated from Chinese Journal of Catalysis, 2007, 28(8): 676–680 [译自: 催化学报]     

Catalytic oxidation of methane at low temperature over Pd-containing perovskite type oxides

Two types of catalysts with the same palladium loading, palladium-substituted perovskite La_0.95Ce_0.05Co_0.95Pd_0.05O₃ and perovskite-supported palladium catalyst Pd/La_0.95Ce_0.05CoO₃ were prepared by the combustion and impregnation method, respectively. The catalyst structure was characterized by X-ray diffraction (XRD), BET measurements, temperature-programmed reduction (TPR) and the methane oxidation activity of the catalysts were investigated in detail. It was found that the activity performance of Pd/La_0.95Ce_0.05CoO₃ was higher than that of La_0.95Ce_0.05Co_0.95Pd_0.05O₃, and this was owing to the ease of reduction of palladium in the former.     

FeOx Coating on Pd/C Catalyst by Atomic Layer Deposition Enhances the Catalytic Activity in Dehydrogenation of Formic Acid

Hydrogen generation from formic acid (FA) has received significant attention.The challenge is to obtain a highly active catalyst under mild conditions for practical applications.Here atomic layer deposition (ALD) of FeO_x was performed to deposit an ultrathin oxide coating layer to a Pd/C catalyst,therein the FeO_x coverage was precisely controlled by ALD cycles.Transmission electron microscopy and powder X-ray diffraction measurements suggest that the FeO_x coating layer improved the thermal stability of Pd nanoparticles (NPs).X-ray photoelectron spectroscopy measurement showed that deposition of FeO_x on the Pd NPs caused a positive shift of Pd3d binding energy.In the FA dehydrogenation reaction,the ultrathin FeO_x layer on the Pd/C could considerably improve the catalytic activity,and Pd/C coated with 8 cycles of FeO_x showed an optimized activity with turnover frequency being about 2 times higher than the uncoated one.The improved activities were in a volcanoshape as a function of the number of FeO_x ALD cycles,indicating the coverage of FeO_x is critical for the optimized activity.In summary,simultaneous improvements of activity and thermal stability of Pd/C catalyst by ultra-thin FeO_x overlayer suggest to be an effective way to design active catalysts for the FA dehydrogenation reaction.