负载型钯-金催化剂催化合成醋酸乙烯酯

采用等体积浸渍法制备了由硫代氨基脲硫醇化改性活性炭负载的钯-金催化剂,将该催化剂用于乙烯气相氧化法合成醋酸乙烯酯(VA)的反应,利用AAS和XPS分析手段对催化剂的组成进行表征,并考察了不同钯/金质量比的催化剂用于乙烯气相氧化法合成VA的催化活性。实验结果表明,当催化剂中钯/金质量比为1.11时,钯和金元素的负载率最大,分别为89.40%和105.60%,该催化剂在乙烯气相氧化法合成VA的时空收率和选择性达最佳值,分别为825.0 g/(L·h)和95.1%。表征结果显示,活性组分钯、金在催化剂上的化学形态主要是由钯的氮化物或氧化物和金单质组成。

Au-Pd/MnO_2纳米催化剂消除挥发性有机物

采用水热法和聚合物保护的硼氢化钠还原法制备了α-MnO_2及其负载Au-Pd的催化剂,考察了催化消除乙酸乙酯、间二甲苯及二者混合物的性能.XRD、SEM和TEM以及H2-TPR表征催化剂的物化性质.在反应物浓度为1000 mg/L,与O_2摩尔比为1:400,空速为40000 m L/(g·h)的条件下,0.91Au0.48Pd/α-MnO_2比α-MnO_2的催化性能优越与其具有更好的低温还原性能有关.

不同状态Au对甲酸在Pd催化剂上电催化性能的影响

合成并比较了碳载Au(Au/C)、碳载Pd(Pd/C)、碳载高合金化Pd-Au(Pd-Au/C-T)和碳载非合金化Pd-Au(Pd-Au/C-H)催化剂对甲酸氧化的电催化活性和稳定性.结果表明,Au/C对甲酸氧化基本没有电催化活性,而Pd/C对甲酸氧化有较好的电催化性能,Au的加入能进一步提高Pd催化剂对甲酸氧化的电催化活性和稳定性,特别是Pd-Au/C-T对甲酸氧化的电催化活性和稳定性要好于Pd-Au/C-H,更远好于Pd/C催化剂.相关反应机理有待进一步揭示.

金-钯合金催化剂催化双氧水直接合成成功

据报道，美国和英国的研究者发明了一种新的金钯合金催化剂，这种催化剂使双氧水的直接合成获得了成功。这种化合物用于消毒剂和漂白剂，目前生产用的是间接法。曾有人尝试比较直接的方法去合成，却造成了双氧水的分解，但是卡迪夫大学及利哈伊大学的科学家称他们已经解决了这个问题。

Oxidation of glycerol with H_2O_2 on Pb-promoted Pd/γ-Al_2O_3 catalysts

A series of bimetallic Pd-Pb catalysts with a constant Pd content of 1 wt%and Pb/Pd atomic ratio from 0 to 1.6 supported on γ-Al2O3 were prepared and used for glycerol oxidation with H2O2 as the oxidizing agent at atmospheric pressure,45℃ and pH =11.The morphology and dispersion of the catalysts were characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy（SEM-EDX） and transmission electron microscopy（TEM）.The presence of an alloy phase in the bimetallic catalyst was detected by X-ray photoelectron spectroscopy（XPS）.Glycerol conversion obtained with the monometallic Pd catalyst was 19%,which was increased to 100%with the addition of Pb.The four bimetallic PdPb catalysts were able to oxidize glycerol to dihydroxyacetone（DIHA） and the selectivity to DIHA reached 59%,58%,34%and 25%for PdPb0.25,PdPb0.50,PdPb1.00 and PdPbl.60 catalysts,respectively.

Promotional effects of Sb on Pd-based catalysts for the direct synthesis of hydrogen peroxide at ambient pressure

TiO2‐supported Pd‐Sb bimetallic catalysts were prepared and evaluated for the direct synthesis of H2O2 at ambient pressure.The addition of Sb to Pd significantly enhanced catalytic performance,and a Pd50Sb catalyst showed the greatest selectivity of up to 73%.Sb promoted the dispersion of Pd on TiO2,as evidenced by transmission electron microscopy and X‐ray diffraction.X‐ray photoelectron spectroscopy indicated that the oxidation of Pd was suppressed by Sb.In addition,Sb2O3 layers were formed and partially wrapped the surfaces of Pd catalysts,thus suppressing the activation of H2 and subsequent hydrogenation of H2O2.In situ diffuse reflection infrared Fourier transform spectroscopy for CO adsorption suggested that Sb homogenously located on the surface of Pd‐Sb catalysts and isolated contiguous Pd sites,resulting in the rise of the ratio of Pd monomer sites that are favorable for H2O2 formation.As a result,the Sb modified Pd surfaces significantly enhanced the non‐dissociative activation of O2 and H2O2 selectivity.

Supported metal catalysts at the single-atom limit – A viewpoint

An account of recent work on supported single‐atom catalyst design is given here for reactions as diverse as the low‐temperature water‐gas shift,methanol steam reforming,selective ethanol dehydrogenation,and selective hydrogenation of alkynes and dienes.It is of fundamental interest to investigate the intrinsic activity and selectivity of the active metal atom site and compare them to the properties of the corresponding metal nanoparticles and sub‐nm clusters.It is also important to understand what constitutes a stable active metal atom site in the various reaction environments,and maximize their loadings to allow us to design robust catalysts for industrial applications.Combined activity and stability studies,ideally following the evolution of the active site as a function of catalyst treatment in real time are recommended.Advanced characterization methods with atomic resolution will play a key role here and will be used to guide the design of new catalysts.

Fabrication of Pd-based metal-acid-alkali multifunctional catalysts for one-pot synthesis of MIBK

The one-pot synthesis of methyl isobutyl ketone（MIBK） from acetone using multifunctional catalysts is an important sustainable organic synthesis method with high atom and energy efficiency.Herein. we report a series of Pd supported on mixed metal oxide（MMO） catalysts with controllable acidic/basic/metallic sites on the surface. We study the relationship between the nature, synergy,and proximity of active sites and the catalytic performance of the multifunctional catalyst in the tandem reaction, in detail. In the existence of Lewis acid and base sites, the catalysts with medium-strength acidic/basic sites show preferred activity and/or MIBK selectivity. For multifunctional catalysts, the catalytic properties are more than just a collection of active sites, and the Pd/Mg_3Al-MMO catalyst possessing 0.1% Pd loading and ~0.4 acid/base molar ratio exhibits the optimal 42.1% acetone conversion and 37.2% MIBK yield, which is among the best reported so far for this tandem reaction under similar conditions. Moreover, the proximity test indicates that the intimate distance between acidic/basic/metallic sites can greatly shorten the diffusion time of the intermediate species from each active site, leading to an enhancement in the catalytic performance.

Gold-doping of carbon-supported palladium improves reduction catalysis

Bimetallic palladium-gold （PdAu） catalysts have better catalytic performance than monometallic catalysts for many applications. PdAu catalysts with controlled nanostructures and enhanced activi- ties have been extensively studied but their syntheses require multiple and occasionally complicated steps, In this work, we demonstrated that supported PdAu catalysts could be simply prepared by doping a supported Pd catalyst with gold through wet impregnation and calcination. Resulting PdAu-on-carbon （PdAu/C） catalysts were tested for the room-temperature, aqueous-phase hydro- dech/orination of trichloroethene. The most active PdAu/C catalyst （Pd 1.0 wt%, Au 1.1 wt%, dried/air/H2 process] had an initial turnover frequency （TOF] of 34.0×10^-2 mOITcE mOled-1 S-1, which was 〉15 times higher than monometallic Pd/C （Pd 1,0 wt%, initial TOF of 2.2 ×10^-2 molTCE molpd^-1s^-1）. Through X-ray absorption spectroscopy, the gold kept Pd from oxidizing under calcination at 400℃. Probable nanostructure evolution pathways are proposed to explain the observed catalysis,

Boosting fuel cell catalysis by surface doping of W on Pd nanocubes

The development of active and durable non-Pt electrocatalysts with well-defined microstructure is of great importance to both fuel cell applications and fundamental understanding.Herein,we report a surface-doping process to prepare well-defined W-doped Pd nanocubes with a tunable atomic percent of W from 0 to 1.5%by using the Pd nanocubes as seeds.The obtained 1.2%W-doped Pd nanocubes/C exhibited greatly enhanced electrocatalytic performance toward oxygen reduction reaction in alkaline media,presenting an enhancement factor of 4.7 in specific activity and 2.5 in mass activity compared to the activity of a commercial Pt/C catalyst.The downshift of the d-band center due to a negative charge transfer from W to Pd intrinsically accounts for such improvement in activity by weakening the adsorption of reaction intermediates.Also,the 1.2%W-doped Pd nanocubes/C showed superior catalytic properties for the ethanol oxidation reaction,showing great potential for serving as a bifunctional electrocatalyst in fuel cells.

Preparation and Characterization of Macroporous Resin Immobilized Pd－Cu Bimetallic Cluster Catalysts

The Solvated Metal Atom Impregnation (SMAI) technique was employed to prepare macroporous resin immobilized Pd--Cu bimetallic cluster catalysts. The X--ray diffraction (XRD) and transmission electron micrograph (TEM) showed that Pd--Cu alloy was formed and the particle sizes of Pd--Cu clusters were very small, with average diameters <3nm. X--ray photoelectron spectroscopy indicated that both Pd and Cu were in zero--valent state. The catalytic activities of the macroporous resin immobilized Pd--Cu catalysts in hydrogenation of 4--methyl--3--penten--2--one were much greater than that of the carbon supported Pd--Cu catalysts.

Bimetallic Pd-Ni core-shell nanoparticles catalysts for the Suzuki reaction

A simple and efficient solution-based method for the synthesis of Pd-Ni bimetallic nanoparticles （NPs） has been developed. A series of Pd-Ni bimetallic NPs were readily achieved by reduction of PdC12 and Ni（acac）2 （acac = acetyl- acetonate） in the presence of oleylamine （OAm）, oleic acid （OA） and benzyl alcohol. Furthermore, by using high-resolution transmission electron microscopy （HRTEM）, energy-dispersive spectrometry （EDS） mapping and X-ray diffraction （XRD）, we demonstrate that the as-prepared Pd-Ni bimetallic NPs have core-shell structures with a Pd-rich core and a Ni-rich shell. In addition, the as-obtained Pd-Ni bimetallic NPs with varying compositions show excellent catalytic activities in the Miyaura-Suzuki reaction. When the nickel molar percentage was 0.23 to 0.65, the conversion with the as-obtained Pd-Ni bimetallic catalysts was above 90%. It is believed that this strategy can be employed to produce a variety of other well-defined core-shell type multimetallic nanostructures.

A disubstituted-norbornene-based comonomer strategy to address polar monomer problem

The transition-metal-catalyzed copolymerization of olefins with polar comonomers is a direct strategy to access polar-functionalized polyolefins in an economical manner.Due to the intrinsic poisoning effect of polar groups towards Lewis acidic metal centers and the drastic reactivity differences of polar comonomers versus non-polar olefins,it is challenging to develop catalysts that provide the desired polymer molecular weight,comonomer incorporation,and activity.In this contribution,we tackle this issue from a comonomer perspective using 5,6-disubstituted norbornenes,which are highly versatile,easily accessible,inexpensive,and capable of introducing two functional groups in a single insertion.More importantly,they are only mildly poisoning due to the presence of long spacers between double bonds and polar groups,and are not prone to b-hydride elimination due to their cyclic structures.As strong pdonors,they can competitively bind to metal centers versus olefins.Indeed,phosphine-sulfonate palladium catalysts can catalyze the copolymerization of ethylene with 5,6-disubstituted norbornenes and simultaneously achieve a high polymerization activity,copolymer molecular weight,and comonomer incorporation.The practicality of this system was demonstrated by studying the properties of the resulting polymers,copolymerization in hydrocarbon solvents or in bulk,recovery/utilization of unreacted comonomer,molecular weight modulation,and large-scale synthesis.

PdPb bimetallic nanowires as electrocatalysts for enhanced ethanol electrooxidation

Less-expensive but efficient electrocatalysts are essential to accelerate the commercialization of fuel cells.Herein,ultrathin PdPb nanowires(PdPb NWs)with a diameter of around 3.5 nm were prepared by using a one-step hydrothermal method.The introduction of Pb in Pd-based bimetallic nanostructures produced high differences in the morphology from Pd nanoparticles(NPs)to various PdPb NWs.All the as-prepared PdPb NWs exhibited better electrocatalytic activity and durability than Pd NPs due to the synergistic effect.Especially,Pd65Pb35 possessed the highest current density of about 3460 mA mgPd^−1 for the ethanol electrooxidation which was around 6.3 times higher than commercial Pd/C.The high-performance of Pd65Pb35 is attributed to the defect-rich and stable nanowire structure with optimized surface atomic arrangement,as evidenced by high resolution transmission electron microscopy measurements and long-time treatment in an acidic media.The differences in the morphologies and electrocatalytic activities of PdPb NWs with varied Pb contents have also been discussed and analyzed.