Investigation of surface structure and composition of in situ annealed Fe–Mn binary alloy samples using RHEED and electron spectroscopy

The formation of oxides at the surface of Fe–1.5%Mn and Fe–0.6%Mn binary alloys was investigated as a function of the conditions of the heat treatments. Both the influence of temperature and the atmosphere under which the experiments were performed were studied. The range of annealing temperatures was adjusted to 800°C. The atmosphere consisted of a mixture of N₂–5%H₂ and traces of water vapour, with different fixed dew points ranging from −10°C to −30°C. The state of the annealed surfaces was determined using in situ analytical devices attached to the annealing reactor in order to avoid surface contamination or the formation of native oxides after the experiments due to contact with air. The structure and composition of the surfaces were determined by reflection high-energy electron diffraction (RHEED) and electron spectroscopy (XPS, AES). Copyright © 2002 John Wiley & Sons, Ltd.     

CO偶联临氢反应Pd-Fe/Al2O3催化剂的XPS研究

 利用XPS及氩离子溅射等技术对CO偶联和临氢反应中所用催化剂\r\n表面活性组分和助剂的含量及其化学状态进行了分析，并通过测定氢在\r\n催化剂表面的化学吸附，以及氢浓度对催化剂活性的影响，探讨了CO偶\r\n联反应中催化剂临氢失活的主要原因．XPS表征结果表明，CO偶联反应\r\n中催化剂活性组分以Pd0和Pd2＋形式共存；而临氢反应后仅以Pd0形式\r\n存在，助剂FeO从催化剂的内部向表面迁移且有少量Fe2＋转变为Fe3＋\r\n．催化剂临氢失活的主要原因是H2在活性组分Pd及助剂Fe（主要是FeO\r\n）表面均可形成解离吸附，形成的金属氢化物可在低活化能条件下发生\r\n迁移．这种迁移有利于副产物乙醇的生成，从而削弱了CO偶联主反应，\r\n催化剂表面活性组分Pd的相对含量减少，并几乎处于钝化状态，导致临\r\n氢反应中CO转化率、草酸二乙酯选择性及空时收率均下降．停止通入H\r\n2后，催化剂的活性可恢复至正常状态．     

Characterization of molybdenum carbide nanoparticles formed on Au(111) using reactive-layer assisted deposition

Temperature programmed desorption (TPD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM) have been used to characterize molybdenum carbide nanoparticles prepared on a Au(111) substrate. The MoC(x) nanoparticles were formed by Mo metal deposition onto a reactive multilayer of ethylene, which was physisorbed on a Au(111) substrate at low temperatures (<100 K). The resulting clusters have an average diameter of approximately 1.5 nm and aggregate in the fcc troughs located on either side of the elbows of the reconstructed Au(111) surface. Core level XPS shows that the electronic environment of the Mo and C atoms in the nanoparticles is similar to that found in Mo(2)C(0001) single crystals and carburized Mo metal surfaces. Peak intensities in XPS and AES spectra were used to estimate an average Mo/C atomic ratio of 1.2 +/- 0.3 for nanoparticles annealed above 600 K.     

Surface and subsurface oxidation of Mo2C/Mo(100): low-energy ion-scattering, auger electron, angle-resolved X-ray photoelectron, and mass spectroscopy studies

The interaction of oxygen with a carburized Mo(100) surface was investigated at different temperatures (300-1000 K). The different information depths of low-energy ion-scattering (LEIS) spectroscopy, with topmost layer sensitivity, Auger electron spectroscopy (AES), and angle-resolved X-ray photoelectron spectroscopy (ARXPS) allowed us to discriminate between reactions on the topmost layer and subsurface transformations. According to ARXPS measurements, a carbide overlayer was prepared by the high-temperature decomposition of C(2)H(4) on Mo(100), and the carbon distribution proved to be homogeneous with a Mo(2)C stoichiometry down to the information depth of XPS. O(2) adsorbs dissociatively on the carbide layer at room temperature. One part of the chemisorbed oxygen is bound to both C and Mo sites, indicated by LEIS. Another fraction of oxygen atoms probably resides in the hollow sites not occupied by C. The removal of C from the outermost layer by O(2), in the form of CO, detected by mass spectroscopy (MS), was observed at 500-600 K. The carbon-depleted first layer is able to adsorb more oxygen compared to the Mo(2)C/Mo(100) surface. Applying higher doses of O(2) at 800 K results in the inward diffusion of O and the partial oxidation of Mo atoms. This process, however, is not accompanied by the removal of C from subsurface sites. The depletion of C from the bulk starts only at 900 K (as shown by MS, AES, and XPS), very probably by the diffusion of C to the surface followed by its reaction with oxygen. At T(ads) = 1000 K, the carbon content of the sample, down to the information depth of XPS, decreased further, accompanied by the attenuation of the C concentration gradient and a substantially decreased amount of oxygen.     

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.     

STUDY ON XPS OF IRON CATALYSTS

IntroduCtioniron-basedcatalystSareactiveinformingliquidfuelsfromthehydrogenationofCO[l~6].However,itiswellknownthatthepoisoningofironcatalystsespeciallythesulfurandoXygenisoneofthemostseriousdeactivationproblemsincommercialproduCtionofsubstitUtenatUralgas…     

Surface characterisation of laser irradiated SiC ceramics by AES and XPS

Samples of sintered silicon carbide (SSiC) were irradiated with a KrF excimer laser (λ = 248 nm) at energy densities of 10, 15 and 25 J/cm² in He atmosphere. The composition of the near surface region was investigated by Auger electron spectroscopy (AES) and photoelectron spectroscopy (XPS) after lapping, laser irradiation and tribological treatment, respectively. By laser irradiation a surface layer is formed which contains about 30% oxygen. The existence of different bonding states of Si, C and O was established by factor analysis of the AES depth profiles and by XPS. By laser irradiation SiC is decomposed and a siliconoxycarbide with the average composition SiC_3.5O_1.5 is formed. Beneath the oxidised surface layer the nominal elemental composition SiC is found but the sample represents a mixture of Si, graphite and siliconoxycarbide with a small amount of SiC only. Obviously, the decomposition zone exceeds in a depth > 300 nm.     

Fe-K/AC催化氧化脱硫剂制备及反应机理研究

采用正交实验法制备了负载铁、钾的活性炭(Fe-K/AC)热煤气催化氧化脱硫剂,考察了活性组分铁、钾含量、二价铁和三价铁比例、煅烧温度对催化氧化脱硫反应活性的影响。由正交实验极差分析可知,各因素影响程度依次为:钾含量>铁含量>煅烧温度> Fe²⁺/Fe³⁺,最优制备条件为,铁含量0.5%、钾含量5.0%、煅烧温度600 ℃、Fe²⁺/Fe³⁺比0.5。通过对脱硫剂的孔隙结构和表面形貌分析可知,活性炭表面负载的铁金属氧化物具有催化氧化硫化氢生成单质硫的活性,碱金属氧化物具有协同作用,可以改变表面酸碱性,促进硫化氢的催化转化,但过高的金属氧化物负载量会阻塞孔道,减小反应比表面积,从而降低脱硫剂的反应活性。     

Modifying metal nanoparticle placement on carbon supports using an aerosol-based process, with application to the environmental remediation of chlorinated hydrocarbons

A facile aerosol-based process (ABP) is developed to vary the placement of iron nanoparticles on the external surface of carbon microspheres or within the interior. This is accomplished through the competitive mechanisms of sucrose carbonization and the precipitation of soluble iron salts, in an aerosol droplet passing through a high temperature heating zone. At lower aerosolization temperatures, carbonization occurs first leading to iron salt precipitation on the external surface, while at higher temperatures interior placement occurs through concurrent iron salt precipitation and sucrose carbonization. The resulting composites are highly conducive to the reductive dechlorination of compounds such as trichloroethylene (TCE) as the carbon support is a strong adsorbent, and zerovalent iron effectively reduces TCE to innocuous gases such as ethane. Since both iron and carbon are widely used catalysts and catalyst supports, the simple process of modifying iron placement has significant potential applications in heterogeneous catalysis.     

Mechanism and influence factors of 2,4-D dechlorination by sodium citrate-activated bimetallic palladium-zero valent iron nanoparticles

Nanoscale zero-valent iron (nZVI) has high removal efficiency and strong reductive ability to organic contaminants, but this reactivity soon ceases and is attributed to rapid passivation of the nZVI surface due to the formation of iron oxides. In the present study, bimetallic palladium-zero valent iron nanoparticles were activated with sodium citrate (SC-nPd/Fe) to enhance 2,4-D dechlorination from aqueous solutions. FTIR and XRD analyses showed that there was no passivation layer on the surface of nZVI after the addition of SC, and XPS analysis confirmed the nZVI after the reaction still maintained high reactivity and surface Pd ratio. The existence of SC facilitated the transfer of electrons from Fe⁰ to contaminants, thus accelerating the reductive dechlorination of 2,4-D. The dechlorination efficiency of 2,4-D on nPd/Fe was only 56.4% in 210 min, while complete dechlorination could be achieved on SC-nPd/Fe under the same conditions, and simultaneously 97.1% of phenoxyacetic acid (PA) was generated. Moreover, the effect of reaction conditions on the dechlorination such as Pd ratio, SC dosage, initial pH and temperature was also investigated, and it was well described by pseudo-first-order kinetic model. In particular, The chelating abilities of SC is similar to EDTA, but it is an environmentally-friendly chelating agent. Findings from the present study suggested that the SC could be a promising substitute for application in the remediation of 2,4-D contained water.     

Metallorganic routes to nanoscale iron and titanium oxide particles encapsulated in mesoporous alumina: formation, physical properties, and chemical reactivity

Iron and titanium oxide nanoparticles have been synthesized in parallel mesopores of alumina by a novel organometallic "chimie douce" approach that uses bis(toluene)iron(0) (1) and bis(toluene)titanium(0) (2) as precursors. These complexes are molecular sources of iron and titanium in a zerovalent atomic state. In the case of 1, core shell iron/iron oxide particles with a strong magnetic coupling between both components, as revealed by magnetic measurements, are formed. M?ssbauer data reveal superparamagnetic particle behavior with a distinct particle size distribution that confirms the magnetic measurements. The dependence of the M?ssbauer spectra on temperature and particle size is explained by the influence of superparamagnetic relaxation effects. The coexistence of a paramagnetic doublet and a magnetically split component in the spectra is further explained by a distribution in particle size. From M?ssbauer parameters the oxide phase can be identified as low-crystallinity ferrihydrite oxide. In agreement with quantum size effects observed in UV-visible studies, TEM measurements determine the size of the particles in the range 5-8 nm. The particles are mainly arranged alongside the pore walls of the alumina template. TiO2 nanoparticles are formed by depositing 2 in mesoporous alumina template. This produces metallic Ti, which is subsequently oxidized to TiO2 (anatase) within the alumina pores. UV-visible studies show a strong quantum confinement effect for these particles. From UV-visible investigations the particle size is determined to be around 2 nm. XPS analysis of the iron- and titania- embedded nanoparticles reveal the presence of Fe2O3 and TiO2 according to experimental binding energies and the experimental line shapes. Ti4+ and Fe3+ are the only oxidation states of the particles which can be determined by this technique. Hydrogen reduction of the iron/iron-oxide nanoparticles at 500 degrees C under flowing H2/N2 produces a catalyst, which is active towards formation of carbon nanotubes by a CVD process. Depending on the reaction conditions, the formation of smaller carbon nanotubes inside the interior of larger carbon nanotubes within the alumina pores can be achieved. This behavior can be understood by means of selectively turning on and off the iron catalyst by adjusting the flow rate of the gaseous carbon precursor in the CVD process.     

Surface characterization of functional iron–gallium alloys annealed under different conditions

Fe–Ga alloys are functional magnetostrictive materials, which are promising for application in actuators and sensors. Because surface properties of these alloys such as corrosion resistance are important in technological applications, it is required to characterize the chemical composition and state of the surface of these alloys, which depend on annealing conditions. In this study, X-ray absorption spectroscopy (XAS) and secondary ion mass spectrometry (SIMS) were used to characterize surface layers formed on the Fe–Ga alloys annealed under different atmospheric conditions. The XAS spectra of the annealed sample showed that the amount of gallium in the surface layers increased due to annealing, whereas the XAS spectra of the as-polished alloys revealed that the amounts of iron and gallium arise from the bulk composition. The XAS spectra of the alloys annealed in argon–hydrogen with residual oxygen showed that gallium is increased for its preferential oxidation. SIMS depth profile also showed the enrichment of gallium on the surface and the inhomogeneous distribution of iron on the surface layers.     

Cyclodextrins for remediation of soils contaminated with chlorinated organics

The effect of random methylated ??CD (RAMEB) on the efficiency of various remediation technologies was studied in lab-scale model-experiments applying soil and groundwater originating from a site contaminated with trichloroethylene (TCE). The solubility of TCE was enhanced to tenfold in 10% solution of RAMEB compared to that in water. This solubilizing effect was utilized for remediation of the TCE contaminated soil using enhanced groundwater extraction and in situ TCE oxidation by ISCO (= in situ chemical oxidation). The effect of CD on TCE extraction from soil was studied using two technologies: ground-water extraction followed by air stripping or UV irradiation. The RAMEB-enhanced ISCO was applied directly to the water-saturated soil without water extraction or separation. The efficiency of air stripping of TCE (removal by bubbling air through the contaminated ground-water obtained by extraction) was decreased in the presence of RAMEB due to the volatility decreasing effect of complexation. The efficiency of the entire technology (extraction and air stripping together) was, however, enhanced as three times more TCE was dissolved, and more than twice as much could be removed when 5% RAMEB solution was applied instead of water. Similar results were obtained by UV irradiation. Although the complexation has a protective effect against degradation caused by irradiation, the efficiency of the technology (extraction and subsequent UV irradiation) is enhanced to approximately threefold, because more than 10 times higher TCE concentration was found in the extract using 20% RAMEB concentration. ISCO is based on Fe-catalyzed oxidation using hydrogen peroxide. The catalytic effect of RAMEB was observed only when it was applied together with Fe(II) salts. Without Fe(II) the effect of complex formation dominated. When hydrogen peroxide and FeSO₄ were applied with RAMEB, over five times enhancement in TCE removal was obtained compared to the technology based on the addition of hydrogen peroxide and Fe(II) salts without RAMEB. This effect shows that the solubilizing effect on iron catalyst is at least as much or even more important than the solubilizing effect on TCE. The ternary complex formation with ferrous/ferric ion and TCE seems to be responsible for the enhanced efficacy.     

Single crystal RuO2 (110): Surface structure

The surface structure of RuO₂ (110) has been studied with LEED, AES and XPS. The “as-grown” surface shows no LEED patterns and both AES and XPS indicate that the surface is depleted in oxygen in high vacuum. After extensive annealing in an O₂ atmosphere reproducible LEED patterns characteristic of the (110) surface were obtained. For the well-ordered surface the oxygen XPS results revealed oxygen associated with the bulk RuO₂, the presence of RuO₃ and oxygen bound to surface atoms.     

Iron nanoparticles catalyzing the asymmetric transfer hydrogenation of ketones

Investigation into the mechanism of transfer hydrogenation using trans-[Fe(NCMe)CO(PPh(2)C(6)H(4)CH═NCHR-)(2)][BF(4)](2), where R = H (1) or R = Ph (2) (from R,R-dpen), has led to strong evidence that the active species in catalysis are iron(0) nanoparticles (Fe NPs) functionalized with achiral (with 1) and chiral (with 2) PNNP-type tetradentate ligands. Support for this proposition is given in terms of in operando techniques such as a kinetic investigation of the induction period during catalysis as well as poisoning experiments using substoichiometric amounts of various poisoning agents. Further support for the presence of Fe(0) NPs includes STEM microscopy imaging with EDX analysis, XPS analysis, and SQUID magnetometry analysis of catalytic solutions. Further evidence of Fe NPs acting as the active catalyst is given in terms of a polymer-supported substrate experiment whereby the NPs are too large to permeate the pores of a functionalized polymer. Final support is given in terms of a combined poisoning/STEM/EDX experiment whereby the poisoning agent is shown to be bound to the Fe NPs. This paper provides evidence of a rare example of asymmetric catalysis with nonprecious metal, zerovalent nanoparticles.     

Spectroscopic study on sorption of hydrogen sulfide by means of red soil

This paper reports the results of the characterization of red soils in relation to the sorption of H2S from coal gas at 500 degrees C by spectroscopic techniques in order to provide more information on red soils' structural change both before and after reaction. In addition, by-products analysis has also been studied using Fourier transform infrared (FTIR) spectroscopy. Before and after the experiments the red soils were characterized with X-ray powder diffraction (XRPD), energy dispersion spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and FTIR spectroscopy. XRPD results indicate that iron oxide species disappear from the original to reacted red soil. EDS analysis shows that a significant amount of sulfur is present in the reacted red soil, which is in agreement with the results of the elemental analysis and the calculated value based on breakthrough curve. XPS regression fitting results further indicate that sulfur retention may be associated with the iron oxides. S 2p XPS fittings point out that the major sulfur species present in the reacted red soil are composed of S(-2), elemental sulfur, polysulfide, sulfite and sulfate. Additionally, the binding energy of iron shifts to a lower position for the reacted red soil, which indicates that iron oxides in the original red soil have been converted into iron sulfide. Appreciable amounts of the by-products CO2, SO2 and COS are detected by on-line FTIR spectroscopy during the initial and later stages of the sorption process. The formation of CO2 is related to the water-shift reaction, and SO2 is probably attributable to the reaction of organic matters and H2S. The concentration of COS is quantified by GC/FPD and found it to be about 350 ppm, which is close to the equilibrium concentration of the reaction of inlet CO and H2S at a temperature of 500 degrees C.     

Degradation of trichloroethylene in aqueous solution by persulfate activated with Fe(III)–EDDS complex

In this study, an environmentally friendly complexing agent, S,S′-ethylenediamine-N,N′-disuccinic acid (EDDS), was applied in Fe(III)-mediated activation of persulfate (PS), and the degradation performance of trichloroethylene (TCE) was investigated. The effects of PS concentration, Fe(III)/EDDS molar ratio, and inorganic anions on TCE degradation were evaluated, and the generated reactive oxygen species responsible for TCE removal were identified. The results showed that nearly complete TCE degradation was achieved with PS of 15.0 mM and a molar ratio of Fe(III)/EDDS of 4:1. An increase in PS concentration or Fe(III)/EDDS molar ratio to a certain value resulted in enhanced TCE degradation. All of the anions (Cl^?, HCO₃ ^?, SO₄ ^2?, and NO ₃ ^? ) at tested concentrations had negative effects on TCE removal. In addition, investigations using radical probe compounds and radical scavengers revealed that sulfate radicals (SO ₄ ^·? ), hydroxyl radicals (^·OH), and superoxide radical anions (O ₂ ^·? ) were all generated in the Fe(III)–EDDS/PS system, and ^·OH was the primary radical responsible for TCE degradation. In conclusion, the Fe(III)–EDDS-activated PS process is a promising technique for TCE-contaminated groundwater remediation.     

Evaluation of mutual connections between zero-valent iron reactivity and groundwater composition in trichloroethylene degradation

Zero-valent iron Permeable Reactive Barriers (PRBs) are an efficient and relatively low cost in situ technology for the remediation of aquifers polluted by chlorinated solvents. The groundwater composition and the zero-valent iron reactive material are linked by mutual connections. The groundwater, to a certain extent depending on its composition, is able to oxidize the metallic iron, thus decreasing its reactivity; on the other hand, the dechlorination process and the leaching of chemical species from the reactive substrate may deeply modify groundwater composition. In this study the results of some batch and leaching column tests, performed by means of Connelly iron (Environmental Technologies Inc., Canada) and different aqueous phases (distilled water and an artificial groundwater) are compared, to evaluate the influence of groundwater composition on the reactivity of the iron material for trichloroethylene (TCE) remediation. The degradation mechanisms of the pollutant are discussed. On the grounds of the gathered results the aqueous phase composition shows a strong influence on TCE degradation kinetics obtained by means of Connelly iron; in fact the presence of dissolved substances accelerates TCE degradation.     

IR laser photodeposition of a-Fe/Si films developing nanograins of ferrisilicate, iron disilicide and rare hexagonal iron upon annealing

IR laser-induced gas-phase photolysis of Fe(CO)(5)-SiH(4) mixtures occurs as SiH(4)-photosensitized decomposition of Fe(CO)(5) is accelerated by products of this decomposition and it results in deposition of amorphous Si/Fe nanocomposite films. Analyses of the deposited and subsequently annealed solid films were made by FTIR, Raman and X-ray photoelectron spectroscopy, X-ray diffraction and electron microscopy. The deposited films are amorphous, contain crystalline nanostructures of iron silicide FeSi(2) and undergo atmospheric oxidation in topmost layers to iron oxide and hydrogenated silicon oxide. Upon annealing they develop nanocrystalline structures of ferrisilicate, Fe(1.6)SiO(4), carbon-encaged iron disilicide, FeSi(2), and very rare hexagonal (high-pressure) Fe surviving at ambient conditions. The mechanism of formation of these nanostructures is discussed in terms of gas-phase and solid-phase reactions.     

非晶Fe~90Zr~10合金氨合成催化剂的活化行为

在氨合成气氨中对非晶Fe~90Zr~10合金条带进行了活化。采用AES, XPS, SAM,SEM等分析方法, 并结合氩离子原位轰击剥层研究了非晶Fe~90Zr~10合金条带活化前后自由侧及贴辊侧的表层成分分布, 元素化学状态及表面形貌, 结果表明, 原始条带自由侧表层存在差显著的Zr偏聚, 而贴辊侧表层则存在着Fe的偏聚和Zr的贫集。贴辊侧和自由侧表面Fe氧化物分别为Fe~3O~4和Fe~2O~3。活化后, 自由侧表面Zr浓度下降,而贴辊侧表面Zr浓度增加, 贴辊侧Fe氧化物得到了全部还原, 活化后条带体结构发生了晶化, 表面形成了蜂窝状结构及许多环状裂纹, 对活化机理进行了讨论。