磁性纳米粒子负载亚胺吡啶钯催化Suzuki反应研究

以硅胶包裹的纳米四氧化三铁为磁性载体,经硅烷化亚胺吡啶配体化学改性后与钯盐配位,制备一种新型磁性钯催化剂,采用元素分析、红外光谱、透射电镜、X射线光电子能谱以及电感耦合等离子发射光谱等手段对催化剂进行了表征,并将其应用于水溶液相Suzuki反应.结果表明,这种新颖的磁性纳米粒子负载钯催化剂在空气氛围和较低的钯催化量下即可有效地催化多种溴代芳烃和芳基硼酸的Suzuki反应,产率达83%~98%.此外,该催化剂通过磁分离来高效回收,可循环使用5次且催化活性无明显下降.     

四乙烯五胺功能化纤维素负载纳米钯催化剂的制备及其对Suzuki反应催化性能的研究

利用四乙烯五胺对环氧化纤维素进行功能化改性,并以其为载体在95％乙醇溶液中现场还原氯化钯制备出四乙烯五胺功能化纤维素负载的纳米钯催化剂.利用IR,XRD,SEM,TEM等分析方法对其进行了表征并用于催化Suzuki交叉偶联反应.实验表明,该催化剂在温和条件下能有效催化卤代芳烃与芳基硼酸的Suzuki交叉偶联反应,该催化剂经回收重复利用5次后,仍具有较高的催化活性.     

负载钯催化的Suzuki偶联反应研究进展

负载钯催化的Suzuki偶联反应,由于产物易分离、催化剂可重复使用,已引起人们的广泛关注.综述了近年来负载钯催化的Suzuki偶联反应研究进展,载体包括活性碳、金属氧化物、硅铝酸盐微孔分子筛、二氧化硅材料、活性粘土和聚合物等.     

磁性微孔聚1,1'-联二萘酚负载钯催化的Suzuki偶联反应

为了解决均相钯催化剂难分离回收的问题,通过两步反应合成了易磁分离回收的微孔聚1,1'-联二萘酚(BINOL)包覆磁性纳米Fe3O4负载钯催化剂Fe3O4@MOPB-Pd,该催化剂可在空气氛围下高效催化不同卤代芳香烃与苯硼酸衍生物的Suzuki偶联反应.反应结束后,在外加磁场作用下,Fe3O4@MOPB-Pd可由反应体系中快速分离回收,而且在碘苯与苯硼酸的Suzuki偶联反应中该负载钯催化剂循环使用到7次时,依然保持高的催化活性.     

纳米钯催化芳基重氮盐的Suzuki和Heck偶联反应

开发了一种使用纳米Al2O3作载体,由四三苯基膦钯衍生的纳米钯催化剂催化的使用芳基重氮盐作原料的高效绿色Suzuki和Heck偶联反应来制备联苯类和芳基烯类化合物的方法.该反应体系以乙醇作反应溶剂,在空气中于25℃下,催化剂可高效催化芳基重氮盐分别与芳基硼酸和烯烃的Suzuki和Heck偶联反应,各类考察的反应底物都给出较高的收率,而且催化剂循环利用4次后,其催化活性和反应收率都没有明显降低.     

纳米钯催化的高效Suzuki偶联反应

开发了一种使用Al2O3作载体,由四三苯基膦钯制备的纳米钯催化剂催化的高效绿色Suzuki反应来合成联苯类化合物的方法.该反应体系以DMF和H2O的混合体系作反应溶剂,在空气中于25~90℃下,催化剂可高效催化卤代芳烃与芳基硼酸的Suzuki偶联反应,所有考察的反应底物都给出很高的收率,并且催化剂循环利用6次后,其催化活性和反应收率都没有明显降低.     

氧化石墨烯负载席夫碱钯催化剂的合成、表征及对Suzuki反应催化性能的研究

以修饰的Hummers法制备的氧化石墨烯为载体,席夫碱为配体制备了一种新型的负载型钯催化剂,采用红外光谱仪、透射电镜、X射线光电子能谱仪、热重分析仪和X射线衍射仪等手段对负载型催化剂进行了表征,并评价了其对水相Suzuki反应的催化活性.结果表明,该催化剂在较温和的实验条件下即可高效催化水相芳基卤与芳基硼酸的Suzuki反应,催化剂重复使用5次后,活性基本不变.     

Merrifield树脂负载的膦钯催化剂制备及其在Suzuki反应中的应用

合成了一种Merrifield树脂负载的芳基膦钯催化剂, 并将其应用于催化Suzuki反应. 结果表明, 该催化剂对碘代芳烃和溴代芳烃与苯硼酸的Suzuki反应显示出较好的催化效果, 得到相应的联苯. 催化剂循环使用五次, 活性无显著下降.     

多孔网状聚苯胺包覆磁性纳米Fe_3O_4负载钯催化的Suzuki及Heck偶联反应

为解决均相钯催化剂难于分离回收及循环使用问题,发展了一种廉价易行的方法合成易于原位磁分离回收的磁性纳米粒子(MNPs)负载钯催化剂Fe3O4@MOPPA-Pd.该催化剂可高效催化卤代苯的Suzuki反应及Heck反应,且对Suzuki偶联反应具有尤其高的催化活性,在温和条件下,10 mg Fe3O4@MOPPA-Pd可催化300 mmol溴苯与苯硼酸的偶联反应,联苯的分离收率达98%,转化数(TON)及转化率(TOF)分别高达77052和51368 h-1.此外,Fe3O4@MOPPA-Pd可在外加磁场存在下由反应体系中方便分离回收,循环使用4次以上催化活性无明显降低.     

无配体钯催化乙醇水溶液中芳基三氟硼酸钾的Suzuki反应

发展了一个无配体钯催化芳基三氟硼酸钾的Suzuki反应体系.该体系在空气条件下,以醋酸钯为催化剂,1equiv.的无水碳酸钾为碱,在乙醇水溶液中可高效催化卤代芳烃或杂环卤代芳烃与芳基三氟硼酸钾的Suzuki反应,周转频率(TOF)值最高达4656 h~(-1),且该体系还适用于三苯胺衍生物的合成.透射电镜分析结果及汞中毒实验证明该体系的实际催化物质为原位生成的纳米钯粒子.     

Palladium Nanoparticles Embedded into Graphene Nanosheets: Preparation,Characterization, and Nonenzymatic Electrochemical Detection of H2O2

A novel nonenzymatic H₂O₂ sensor based on a palladium nanoparticles/graphene (Pd‐NPs/GN) hybrid nanostructures composite film modified glassy carbon electrode (GCE) was reported. The composites of graphene (GN) decorated with Pd nanoparticles have been prepared by simultaneously reducing graphite oxide (GO) and K₂PdCl₄ in one pot. The Pd‐NPs were intended to enlarge the interplanar spacing of graphene nanosheets and were well dispersed on the surface or completely embedded into few‐layer GN, which maintain their high surface area and prevent GN from aggregating. XPS analysis indicated that the surface Pd atoms are negatively charged, favoring the reduction process of H₂O₂. Moreover, the Pd‐NPs/GN/GCE could remarkably decrease the overpotential and enhance the electron‐transfer rate due to the good contact between Pd‐NPs and GN sheets, and Pd‐NPs have high catalytical effect for H₂O₂ reduction. Amperometric measurements allow observation of the electrochemical reduction of H₂O₂ at 0.5 V (vs. Ag/AgCl). The H₂O₂ reduction current is linear to its concentration in the range from 1×10^?9 to 2×10^?3 M, and the detection limit was found to be 2×10^?10 M (S/N=3). The as‐prepared nonenzymatic H₂O₂ sensor exhibits excellent repeatability, selectivity and long‐term stability.     

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.     

Low‐Coordinated Edge Sites on Ultrathin Palladium Nanosheets Boost Carbon Dioxide Electroreduction Performance

Electrochemical conversion of carbon dioxide (CO₂) to value‐added products is a possible way to decrease the problems resulting from CO₂ emission. Thanks to the eminent conductivity and proper adsorption to intermediates, Pd has become a promising candidate for CO₂ electroreduction (CO₂ER). However, Pd‐based nanocatalysts generally need a large overpotential. Herein we describe that ultrathin Pd nanosheets effectively reduce the onset potential for CO by exposing abundant atoms with comparatively low generalized coordination number. Hexagonal Pd nanosheets with 5 atomic thickness and 5.1 nm edge length reached CO faradaic efficiency of 94 % at ?0.5 V, without any decay after a stability test of 8 h. It appears to be the most efficient among all of Pd‐based catalysts toward CO₂ER. Uniform hexagonal morphology made it reasonable to build models and take DFT calculations. The enhanced activity originates from mainly edge sites on palladium nanosheets.     

Pd Nanoparticles Supported on Triangle-Shaped La2O2CO3 Nanosheets: A New Highly Efficient and Durable Catalyst for Selective Hydrogenation of Cinnamaldehyde to Hydrocinnamaldehyde

A catalyst in which Pd nanoparticles are supported on triangle-shaped La₂O₂CO₃ nanosheets exposing predominantly the (001) planes (Pd/La₂O₂CO₃-TNS; where TNS denotes triangular nanosheets) was prepared by a facile solvothermal method. The Pd/La₂O₂CO₃-TNS catalysts exhibited excellent catalytic activity and recycling stability for hydrogenation of cinnamaldehyde to hydrocinnamaldehyde with turnover frequency of up to 41 238 h⁻¹. This enhanced activity of Pd/La₂O₂CO₃-TNS results from strong metal–support interactions. Structure analysis and characterization demonstrated that surface-oxygen-enriched La₂O₂CO₃-TNS supports exposing (001) planes are beneficial to charge transfer between the Pd nanoparticles and triangle-shaped La₂O₂CO₃ nanosheets and increase the electron density of Pd. Moreover, the modulated electronic states of the Pd/La₂O₂CO₃-TNS catalysts can enhance the adsorption and activation of hydrogen to enhance the hydrogenation activity.     

Enhanced oxidase-like activity of g-C3N4 nanosheets supported Pd nanosheets for ratiometric fluorescence detection of acetylcholinesterase activity and its inhibitor

The undesirable enzymatic activity of nanozymes under near neutral p H condition and the traditional single signal output always restrict the analytical application of nanozyme-based biosensors.Herein,graphitic carbon nitride nanosheets supported palladium nanosheets composite （Pd/g-C₃N₄） with both oxidase-like activity and fluorescent property is synthesized.Notably,Pd/g-C₃N₄exhibits enhanced oxidase-like activity compared to Pd NSs under p H 7.4.By c...     

Hydrodechlorination of 4-Chlorophenol on Pd-Fe Catalysts on Mesoporous ZrO2SiO2 Support

A mesoporous support based on silica and zirconia (ZS) was used to prepare monometallic 1 wt% Pd/ZS, 10 wt% Fe/ZS, and bimetallic FePd/ZS catalysts. The catalysts were characterized by TPR-H₂, XRD, SEM-EDS, TEM, AAS, and DRIFT spectroscopy of adsorbed CO after H₂ reduction in situ and tested in hydrodechlorination of environmental pollutant 4-chlorophelol in aqueous solution at 30 °C. The bimetallic catalyst demonstrated an excellent activity, selectivity to phenol and stability in 10 consecutive runs. FePd/ZS has exceptional reducibility due to the high dispersion of palladium and strong interaction between FeOx and palladium, confirmed by TPR-H₂, DRIFT spectroscopy, XRD, and TEM. Its reduction occurs during short-time treatment with hydrogen in an aqueous solution at RT. The Pd/ZS was more resistant to reduction but can be activated by aqueous phenol solution and H₂. The study by DRIFT spectroscopy of CO adsorbed on Pd/ZS reduced in harsh (H₂, 330 °C), medium (H₂, 200 °C) and mild conditions (H₂ + aqueous solution of phenol) helped to identify the reasons of the reducing action of phenol solution. It was found that phenol provided fast transformation of Pd⁺ to Pd⁰. Pd/ZS also can serve as an active and stable catalyst for 4-PhCl transformation to phenol after proper reduction.     

Impact of palladium silicide formation on the catalytic properties of Pd/SiO2 catalysts in liquid-phase semihydrogenation of phenylacetylene

In this study, palladium silicide was formed on the sol–gel derived SiO₂ supported Pd catalysts when they were prepared by ion-exchange method using Pd(NH₃)₄Cl₂ as a palladium precursor. No other palladium phases (PdO or Pd⁰) were evident after calcinations at 450 °C for 3 h. The Pd/SiO₂ catalysts with Pd silicide formation were found to exhibit superior performance than commercial SiO₂ supported ones in liquid-phase semihydrogenation of phenylacetylene. From XPS results, the binding energy of Pd 3d of palladium silicide on the Pd/SiO₂ catalyst shifted toward larger binging energy, indicating that Pd is electron deficient. This could probably result in an inhibition of a product styrene on the Pd surface and hence high styrene selectivities were obtained at high phenylacetylene conversions. The formation of Pd silicide, however, did not have much impact on specific activity of the Pd catalysts since the TOFs were quite similar among the various catalysts with or without palladium silicides if their average particle sizes were large enough. The TOFs decreased by an order of magnitude when palladium dispersion was very high and their average particle sizes were smaller than 3–5 nm.     

Polyacrylonitrile fiber mat‐supported palladium catalyst for Mizoroki–Heck reaction in aqueous solution

A novel palladium catalyst immobilized on polyacrylonitrile fiber mats (Pd/PAN) was prepared by electrospinning. The catalytic activity and recyclability of the microwave‐assisted Pd/PAN fiber mats were examined for the Mizoroki–Heck cross‐coupling of aryl iodides with three different acrylates in aqueous solution. The morphology of the prepared Pd/PAN fiber mats was characterized by scanning electron microscopy. The large size of the PAN fiber mat‐supported palladium catalyst enables much easier separation from the reaction mixture by simple filtration. Density functional theory calculation indicates that the chelation energy of palladium chloride (PdCl₂) with propionitrile (model of PAN) is considerable smaller than that of PdCl₂ with water, suggesting that the stability and reactivity of the Pd/PAN fiber mats catalyst could be improved through the surface derivatization with polar functional groups. Copyright © 2011 John Wiley & Sons, Ltd.     

SBA-15负载Pd催化剂的制备及其在Heck反应中的应用研究

利用水热反应制备了表面离子液体功能化的SBA-15介孔材料,在丙酮溶液中与氯化钯反应,然后使用水合肼在乙醇中还原.测试了这种催化剂在Mizoroki-Heck反应中的催化活性.与直接负载在SBA-15上的钯催化剂相比,这种表面修饰的介孔SBA-15负载催化剂表现出更高的催化活性、可回收性和反应稳定性.氮气吸脱附实验和小角XRD衍射实验表明,在合成中,材料的介孔性能并没有被破坏.透视电镜也表征了该材料的表面形貌.最后,Mizoroki-Heck反应表明该催化剂具有很高的催化活性,且循环五次后,其催化活性降低并不明显.     

The Measurement of the Dispersion of Pd/C Catalysts

A 10 w/o Pd/C catalyst from Johnson Matthey has been examined by three different techniques: chemisorption, line broadening of X-ray diffraction, and TEM (transmission electron microscopy) to investigate the size of the palladium crystallites. The dispersion of this catalyst was determined to be 20%. Among these techniques, the X-ray diffraction was found to be the most convenient method. Through this method, the dispersion of Pd was found to decrease on catalyzing hydroxylamine reactions at 330 K. The deactivation of Pd/C for these reactions was correlated to the sintering of palladium. H₂ chemisorption at 373 K was found to be a good way to accurately measure the number of active palladium sites in the Pd/C catalysts.