纳米级Pd/Fe双金属体系对水中2,4-二氯苯酚脱氯的催化作用

 利用化学沉淀法制备了纳米级Fe和纳米级Pd/Fe双金属催化剂,研究了它们对2,4-二氯苯酚(2,4-DCP)还原脱氯的催化性能. 结果表明,纳米级颗粒具有较高的比表面积和表面反应活性,其BET比表面积可达12.4 m2/g,当Pd/Fe用量为6 g/L时,2,4-DCP脱氯率达到90%以上. 脱氯效率与pH值、温度、钯含量和Pd/Fe投加量等因素有关. 2,4-DCP在脱氯过程中先生成2-氯苯酚和4-氯苯酚,最终生成苯酚,而少量的2,4-DCP可直接降解成苯酚.     

Kinetics and Mechanism of Dechlorination of o-Chlorophenol by Nanoscale Pd／Fe

IntroductionTherehasbeenagrowinginterestintheuseofzero valentironforthetreatmentofchlorinatedor ganiccompounds(COCs)inwaterandgroundwater .Thestudieshavebeenfocusedonsuchcompoundsascarbontetrachloride ,trichloroethene ,pesticidesandtherelatedcompounds[1— 7] .Whenironisincontactwithalessreductivemetalsuchaspalladiumwhosecomplexhasbeenusedtohydrogenatenitroben zene[8] ,themetalcouplecanformgalvaniccells .ThisledtothediscoveryofaPd/Febimetalliccomplexofwhichpalladiumservesasacatalystandironasa…     

Catalytic Dechlorination of Chlorobenzene in Water by Pd／Fe System

Chlorobenzene was dechlorinated by Pd/Fe bimetallic system in water through catalytic reduction. The dechlorination rate increases with increase of bulk loading of Pd due to the increase of both the surface loading of the Pd and the total surface area. For conditions with 0.005% Pd/Fe, 45% dechlorination efficiency was achieved within 5 h. The dechlorinated reaction is believed to take place on the bimetal surface in a pseudo-first-order reaction, with the rate constant being 0.0043 min^-1.     

Green Synthesis of Fe and Fe/Pd Bimetallic Nanoparticles in Membranes for Reductive Degradation of Chlorinated Organics

Membranes containing reactive nanoparticles (Fe and Fe/Pd) immobilized in a polymer film (polyacrylic acid, PAA-coated polyvinylidene fluoride, PVDF membrane) are prepared by a new method. In the present work a biodegradable, non-toxic -"green" reducing agent, green tea extract was used for nanoparticle (NP) synthesis, instead of the well-known sodium borohydride. Green tea extract contains a number of polyphenols that can act as both chelating/reducing and capping agents for the nanoparticles. Therefore, the particles are protected from oxidation and aggregation, which increases their stability and longevity. The membrane supported NPs were successfully used for the degradation of a common and highly important pollutant, trichloroethylene (TCE). The rate of TCE degradation was found to increase linearly with the amount of Fe immobilized on the membrane, the surface normalized rate constant (k(SA)) being 0.005 L/m(2)h. The addition of a second catalytic metal, Pd, to form bimetallic Fe/Pd increased the k(SA) value to 0.008 L/m(2)h. For comparison purposes, Fe and Fe/Pd nanoparticles were synthesized in membranes using sodium borohydride as a reducing agent. Although the initial k(SA) values for this case (for Fe) are one order of magnitude higher than the tea extract synthesized NPs, the rapid oxidation reduced their reactivity to less than 20 % within 4 cycles. For the green tea extract NPs, the initial reactivity in the membrane domain was preserved even after 3 months of repeated use. The reactivity of TCE was verified with "real" water system.     

Ionic Liquid Assisted Synthesis of Au–Pd Bimetallic Particles with Enhanced Electrocatalytic Activity

Morphology‐ and composition‐controlled synthesis of Au–Pd bimetallic particles was realized by a facile ionic liquid assisted route at room temperature. The morphologies of the synthesized particles, such as nanoflake‐constructed spheres with a core–shell structure, nanoparticle‐constructed spheres, and nanoparticle‐constructed dendrites, could be well controlled by the present route. The ionic liquid was found to play a key role in the formation of these interesting particles. Moreover, the composition (Au:Pd) of the particles could be modulated by means of the molar ratio of the metal precursors in the feeding solutions. The Au–Pd bimetallic particles exhibit high electrocatalytic activity toward oxidation of ethanol and formic acid. Furthermore, cyclic voltammetric studies on the as‐prepared Au–Pd bimetallic particles revealed good electroactivity for H₂O₂, which results in an effective amperometric H₂O₂ sensor.     

Analysis of Polychlorinated Biphenyl Residues in Waste Oils by High-Performance Liquid Chromatography

Abstract

The qualitative analysis of polychlorinated biphenyl residues (PCBs) in waste mineral oils can be rapidly and accurately carried out by high-performance reverse phase liquid chromatography (HPLC) using a 25 cm HC-ODS Sil-X (Perkin-Elmer) column and a gradient elution system consisting of water-acetonitrile where the latter increases with linear program from 50 to 77% over 9 minutes.     

Simultaneous determination of total polychlorinated biphenyl and dichlorodiphenyltrichloroethane (DDT) by dechlorination with Fe/Pd and Mg/Pd bimetallic particles and flame ionization detection gas chromatography

Simultaneous measurement of total dichlorodiphenyltrichloroethane (DDT, technical mixture) and polychlorinated biphenyl (PCB-Aroclors 1248 and 1260) is facilitated by quantitative dechlorination to diphenylethane and biphenyl. The two-stage dechlorination reaction utilizes a palladium catalyst deposited onto iron and magnesium particles. The treatment has the advantage of converting the complex chromatographic pattern that arises from the multiple congeners and degradation products of PCB and DDT into peaks corresponding to their representative hydrocarbon skeletons. The limit for quantitative measurement (LOQ) using this treatment and GC-FID analysis is 40 parts-per-billion (ppb, μg/l) for Aroclor 1260 and 100 ppb for DDT with a linear response extending to 100 times the LOQ. The calibration was successfully tested with triplicate water samples fortified at 15 (DDT) and 10 (Aroclor 1260) times the LOQ. Accuracy (mean percent) and precision (percent relative standard deviation) were 92% and 6.2% for DDT and 96% and 5.2% for Aroclor 1260. Accuracy and RSD for 35 ppm triplicate spiked soil samples were 76% and 18% for Aroclor 1260 and 68% and 26% for DDT. These results are comparable to the published single laboratory results for EPA method 8082 ‘Polychlorinated Biphenyls by Gas Chromatography’. However, the single laboratory results for EPA method 8081A ‘Organohalide Pesticides by Gas Chromatography,’ failed to resolve DDT and therefore could not be compared with this method.     

Enhanced Photoactivated Luminescence of Selected Polychlorinated Biphenyl Congeners and Aroclor Mixtures

Fluorescence studies of selected polychlorinated biphenyl (PCB) congeners and Aroclor mixtures were conducted using enhanced photoactivated luminescence. Diphenylamine (DPA) was used as a photoactivator. DPA reacts with PCBs to form a fluorescent photoproduct under UV activation. The sensitivities of fluorescence detection using three different solid substrates were compared. Background studies of the substrates and DPA blanks were also conducted to determine the substrate with the best detection characteristics for enhanced photoactivated fluorescence. It was found that the Envi disk with a glass-fiber mesh and C-18-modified silica provides more analyte access for fluorescence detection, thereby providing best sensitivity. By comparison of the fluorescence from pure PCB congener–DPA complexes, the more coplanar congeners exhibited a red shift in excitation and emission as compared with theortho-substituted nonplanar congeners. These studies may prove useful in determining trends relating fluorescence intensity and toxicity factors.     

Isolation of Biphenyl and Polychlorinated Biphenyl-Degrading Bacteria and Their Degradation Pathway

Four strains of biphenyl-degrading bacteria were isolated from a sewage and identified from the Rhodococcus genus (SK-1, SK-3, and SK-4) and Aquamicrobium genus (SK-2) by 16S rRNA sequence. Among these strains, strain SK-2 was most suitable for biphenyl degradation. When 0.65, 1.3, 2.6, or 3.9 mM of biphenyl was used, the biphenyl was completely degraded within 24 and 96 h of culture, respectively. However, in the case of 6.5 and 9.75 mM of biphenyl, the biphenyl degradation yields were about 80 % and 46.7 % after 120 h of culture, respectively. The isolated strains could degrade a broad spectrum of aromatic compounds including high-chlorinated polychlorinated biphenyl (PCB) congeners in the presence of biphenyl. In addition, strain SK-2 could utilize PCB congeners containing one to six chlorine substituents such as 2,2′,4,4′,5,5′-hexachlorobiphenyl. The PCB utilization rate by the strain SK-2 was increased compared to that of other PCB congener-utilizing bacteria. The four isolates metabolized 4-chlorobiphenyl to 4-chlorobenzoic acid and 2-hydroxy-6-oxo-6-(4′-chlorophenyl)-hexa-2,4-dienoic acid. These results suggest the isolated strains might be good candidates for the bioremediation of PCB-contaminated soil, especially high-saline soils.     

Au/Pd(111)双金属表面催化噻吩加氢脱硫的反应机理

采用密度泛函理论(DFT)计算了Pd(111)表面含有N(N=1-4)个Au原子数目时的表面形成能,选取最优构型进一步研究了噻吩在Au/Pd(111)双金属表面的吸附模式及加氢脱硫反应过程.结果表明:当Pd(111)表面含有1个Au原子时,其形成能最低.在Au/Pd(111)双金属表面噻吩初始吸附于Pd-Hcp-30°位时,其构型最稳定.在各加氢脱硫过程中,反应总体均放出热量.对于直接脱硫机理,其所需活化能较低,但脱硫产物较难控制;对于间接脱硫机理,反应最有可能按照顺式加氢方式进行,C―S键断裂开环时所需活化能最高,是反应的限速步骤.此外,与单一Au(111)面及Pd(111)面相比,Au/Pd(111)双金属表面限速步骤的反应能垒最低,表明AuPd双金属催化剂比Au、Pd单金属催化剂更有利于噻吩加氢脱硫反应的进行.     

Au/Pd(111)双金属表面催化噻吩加氢脱硫的反应机理

采用密度泛函理论（DFT）计算了Pd（111）表面含有N（N=1-4）个Au原子数目时的表面形成能,选取最优构型进一步研究了噻吩在Au/Pd（111）双金属表面的吸附模式及加氢脱硫反应过程. 结果表明：当Pd（111）表面含有1个Au原子时,其形成能最低. 在Au/Pd（111）双金属表面噻吩初始吸附于Pd-Hcp-30°位时,其构型最稳定. 在各加氢脱硫过程中,反应总体均放出热量. 对于直接脱硫机理,其所需活化能较低,但脱硫产物较难控制;对于间接脱硫机理,反应最有可能按照顺式加氢方式进行,C―S键断裂开环时所需活化能最高,是反应的限速步骤. 此外,与单一Au（111）面及Pd（111）面相比,Au/Pd（111）双金属表面限速步骤的反应能垒最低,表明AuPd双金属催化剂比Au、Pd单金属催化剂更有利于噻吩加氢脱硫反应的进行.     

单层分散型Pd/Ni双金属催化剂的制备及其催化加氢性能

通过置换反应制备了Pd/Ni双金属催化剂,利用X射线衍射、CO化学吸附和吸附H2的程序升温脱附对其进行了表征,并测定了该催化剂对环己烯、苯乙烯和丙酮气相加氢反应的催化性能.结果发现,在这种催化剂中Pd原子单层分散在金属Ni的表面,因而该催化剂表现出比浸渍法制备的相同Pd含量的Pd/Ni-im和Pd/-γAl2O3催化剂更高的催化加氢活性.     

Analysis of Affinity Energy Between Biphenyl Dioxygenase and Polychlorinated Biphenyls Using Molecular Docking

Molecular docking was used to calculate the affinity energy between biphenyl dioxygenases(BphA),including 1ULJ,1WQL,2YFJ,2YFL,2GBX,2XSH,2B4P,3GZX,and 3GZY(selected from the Protein Data Bank)and 209 polychlorinated biphenyl(PCB)congeners.The relationships between the calculated affinity energy and the persistent organic pollutant characteristics(migration,octanol-air partition coefficients,lgKOA;persistence,half-life,lgt1/2;toxicity,half-maximal inhibitory concentration,IgIC50;bioaccumulation,bioconcentration factor,lgBCF)of the PCBs were studied to mderstand the BphA mediated degradation of PCBs.The effect of substituent characteristics on the affinity energy was explored through full factorial experimental design.The affinities of nine kinds of BphA proteins on PCBs ranked as follows:2GBX>2YFJ>2YFL>3GZX>2XSH>3GZY>2E4P>1 WQL>1ULJ.The relationships between the calculated affinity energy and the molecular weight,lgKOA,lgBCF,and lgt1/2 of the PCBs were statistically signiflcant(p<0.01),whereas the relationship with the lgIC50 of PCBs was not statistically significant(p>0.05).PCBs were more difficult to degrade following an increase in the free energy of binding.Correlation analysis showed that the average affinity energy values of PCBs gradually increased as the number of chlorine atoms increased,regardless of the substituent position.The substituents at the ortho-positions interacted mainly through a second-order interaction,whereas those at the para-positions did not participate via a second-order interaction.     

Pt/Fe双金属Fischer-Tropsch催化剂的设计、合成及表征

利用强静电吸附(SEA)理论,根据Fe2O3与SiO2表面不同的零电荷点(PZC),将铂盐溶液pH值调控后浸渍在Fe2O3/SiO2的载体上,制备出Pt/Fe双金属Fischer-Tropsch(F-T)催化剂,通过N2吸脱附技术、X射线衍射(XRD)、扫描投射电镜(STEM)和X射线能量散射谱(EDS)对催化剂的结构、形貌及组成进行表征.结果表明浸渍过程中PtCl62-离子定向选择性地吸附在Fe2O3表面,而非SiO2表面.与传统浸渍(IW)法制备的催化剂比较,Pt与Fe紧密结合在一起,还原后形成高度分散均一的纳米颗粒,粒径尺寸在2 nm左右.以F-T合成反应作为模型反应对催化活性进行表征,强静电吸附法合成的催化剂表现出优异的催化性能,反应进行150 h后CO转化率仍保持在51%以上.     

Pd/Pt二元合金电极的制备及氧还原性能

本文利用欠电位沉积亚单层的Cu及Pt置换取代Cu的方法, 制备了具有不同表面元素组成的Pd/Pt二元合金电极(用Pd/Ptx表示, x指欠电位沉积Cu-Pt置换取代Cu过程的次数),并对其表面元素组成、氧还原性能进行了表征. 在控制欠电位沉积Cu的下限电位恒定(0.34 V)的前提下, 表面Pt/Pd的元素组成比通过重复欠电位沉积Cu及Pt置换取代Cu的次数(1~5次)来可控地调变. 光电子能谱(XPS) 以及红外光谱实验表明,Pd/Ptx电极表层区的Pt：Pd元素组成比随着Pt沉积次数增加而增加, 对Pd/Pt4电极, 在电极表层区约2~3 nm内的Pt/Pd的原子比大约是1:4,而最表层裸露Pd原子的比例仍在20%以上。循环伏安结果显示, 随着Pt沉积次数的增加(1-5次), Pd/Ptx电极表面越不易被氧化。氧还原测试结果显示随着Pt沉积次数的增加(1~4次), Pd/Ptx二元金属电极的氧还原活性依次增加, 经过第3次沉积后其氧还原活性已优于纯Pt,而经4次以上沉积,其氧还原活性基本不变。在其它反应条件相同条件的前提下, Pd/Pt4电极上氧还原的半波电位与纯Pt相比右移约25 mV。结合本文与文献的实验结果,我们初步认为Pd/Ptx二元金属体系氧还原性能改善主要源自表层Pd原子导致其邻近的Pt原子上含氧物种吸附能的降低.     

间氯苯甲酸在Pd/Ti电极上的电化学脱氯反应

以Ti为基底电极, 在PdCl₂溶液中电沉积制备了Pd/Ti电极, 采用SEM和XPS进行表征. 采用循环伏安法研究了Cu, Ag, Ti和Pd/Ti电极对间氯苯甲酸(3-CBA)的电还原特性, 与Cu, Ag和Ti电极相比, Pd/Ti电极对3-CBA有较好的电化学还原活性. 同时采用电化学原位红外反射光谱对3-CBA在Pd/Ti电极上的电还原反应机理进行了系统分析, 结果表明3-CBA在Pd/Ti电极上的电化学脱氯反应是一个脱氯加氢过程, 3-CBA首先得到一个电子形成阴离子自由基中间体, 随后释放一个氯离子, 产生苯甲酸盐的自由基, 最后该自由基得到一个电子并夺取一个氢质子, 在电极表面脱去氯得到最终产物苯甲酸.     

Bimetallic Pd/Sn-based Nanoparticles and their Catalytic Properties in the Semihydrogenation of Diphenylacetylene

Multimetallic nanoparticles often enhance the catalytic performance of their monometallic counterparts by increasing reaction rates, catalyst selectivity, and/or stability. A prerequisite for understanding structure- and composition-associated properties, however, is the careful design of multimetallic nanoparticles with various structures and compositions. Here, bimetallic Pd/Sn-based nanoparticles are prepared with a tunable composition and structure exploiting ionic liquids (ILs) as reaction medium (i. e., methyltrioctylammonium bis(trifluoromethylsulfonyl)imide). The nanoparticles are obtained in a one-pot synthetic procedure by reducing the metal salt precursors with triethylborohydride in the IL. The results show that the reaction parameters, in particular the nature and ratio of the Pd²⁺/Sn²⁺ precursors as well as the reaction temperature, influence NP formation and composition. X-ray diffraction with Rietveld analysis and transmission electron microscopy are employed to determine NP size and phase composition. Under optimized reaction conditions Pd₂Sn or PdSn nanocrystals are formed as single-phase products after introducing an additional annealing step at 200 °C. Nanocrystals with intermetallic composition reveal enhanced catalytic properties in the semihydrogenation of diphenylacetylene which was used as a model reaction.