Highly unsaturated binuclear butadiene iron carbonyls: quintet spin States, perpendicular structures, agostic hydrogen atoms, and iron-iron multiple bonds

The highly unsaturated binuclear butadiene iron carbonyls (C₄H₆)₂Fe₂(CO)_n (n = 2, 1) have been examined using density functional theory. For (C₄H₆)₂Fe₂(CO)_n (n = 2, 1), both coaxial and perpendicular structures are found. The global minima of (C₄H₆)₂Fe₂(CO)_n (n = 2, 1) are the perpendicular structures 2Q-1 and 1Q-1, respectively, with 17- and 15-electron configurations for the iron atoms leading to quintet spin states. The Fe=Fe distance of 2.361 Å (M06-L) in the (C₄H₆)₂Fe₂(CO)₂ structure 2Q-1 suggests a formal double bond. The Fe≡Fe bond distance in the (C₄H₆)₂Fe₂(CO) structure 1Q-1 is even shorter at 2.273 Å (M06-L), suggesting a triple bond. Higher energy (C₄H₆)₂Fe₂(CO)_n (n = 2, 1) structures include structures in which a bridging butadiene ligand is bonded to one of the iron atoms as a tetrahapto ligand and to the other iron atom through two agostic hydrogen atoms from the end CH₂ groups. Singlet (C₄H₆)₂Fe₂(CO) structures with formal Fe–Fe quadruple bonds of lengths ∼2.05 Å were also found but at very high energies (∼47 kcal/mol) relative to the global minimum.     

Impact of Fe Content in Laboratory-Produced Soot Aerosol on its Composition,Structure, and Thermo-Chemical Properties

Soot aerosol, which is a major pollutant in the atmosphere of urban areas, often contains not only carbonaceous matter but also inorganic material. These species, for example, iron compounds, originated from impurities in fuel or lubricating oil, additives or engine wear may change the physico-chemical characteristics of soot and hence its environmental impact. We studied the change of composition, structure, and oxidation reactivity of laboratory-produced soot aerosol with varying iron content. Soot types of various iron contents were generated in a propane/air diffusion flame by adjusting the doping amount of iron pentacarbonyl Fe(CO)₅ to the flame. Scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) was combined with cluster analysis (CA) to separate individual particles into definable groups of similar chemical composition representing the particle types in dependence of the iron content in soot. Raman microspectroscopy (RM) and infrared spectroscopy were applied for the characterization of the graphitic soot structure, hydrocarbons, and iron species. For the analysis of soot reactivity, temperature-programmed oxidation (TPO) was used. It is demonstrated that iron is most dominantly present in the form of amorphous Fe (III) oxide crystallizing to hematite α-Fe₂O₃ upon thermal treatment. Iron contaminations do not change the soot microstructure crucially, but Fe(CO)₅ doping of the flame impacts hydrocarbon composition. Soot oxidation reactivity strongly depends on the iron content, as the temperature of maximum carbon (di)oxide emission T _max follows an exponential decay with increasing iron content in soot. Based on the results of the thermo-chemical characterization of laboratory-produced internally mixed iron-containing soot, we can conclude that iron-containing combustion aerosol samples cannot be characterized unambiguously by current thermo-optical analysis protocols.

Copyright 2012 American Association for Aerosol Research     

Hydroliquefaction of low-sulfur coals using iron carbonyl complexes—Sulfur as catalysts

Hydroliquefaction of low-sulfur Australian coals (Wandoan and Yallourn) was studied using iron carbonyl complexes as catalyst. The addition of Fe(CO)₅ (2.8 wt% Fe of coal) increased coal conversion from 48.6 to 85.2% for Wandoan coal, and from 36.7 to 69.7% for Yallourn coal in 1-methylnaphthalene at 425°C under an initial hydrogen pressure of 50 kg cm^?2. When molecular sulfur was added to iron carbonyls (Fe(CO)₅, Fe₂(CO)₉ and Fe₃(CO)₁₂), higher coal converions ( > 92%) and higher oil yields (>46%) were obtained, along with an increase in the amount of hydrogen transferred to coal from the gas phase (0.2 to 2.8%, d.a.f. coal basis). In the liquefaction studies using a hydrogen donor solvent, tetralin, Fe(CO)₅S catalyst increased the amount of hydrogen absorbed from the gaseous phase and decreased the amount of naphthalene dehydrogenated from tetralin. The direct hydrogen transfer reaction from molecular hydrogen to coal fragment radicals seems to be a major reaction pathway. Organic sulfur compounds, dimethyldisulfide and benzothiophene, and inorganic FeS₂ and NiS were found to be good sulfur sources to Fe(CO)₅. From X-ray diffraction analyses of liquefaction residues, it is concluded that Fe(CO)₅ was converted into pyrrhotite (Fe_1?xS) when sulfur was present, but into Fe₃O₄ in the absence of sulfur.     

The use of various metal carbonyls as catalyst precursors for coal hydroliquefaction

The catalytic activity of metal carbonyl complexes of chromium, molybdenum, tungsten, manganese, iron, cobalt, and nickel in the liquefaction of coal (Illinois No. 6, Wandoan and Mi-ike) was investigated. The carbonyl compounds of molybdenum, tungsten, iron, cobalt, and nickel acted as highly active catalysts for the liquefaction of Illinois No. 6 coal, resulting in high coal conversion (>90%) and high oil yield (>32%), under hydrogen pressure of 50 kg cm^?1 in a nonhydrogen-donating solvent at 425°C for 60 min. Among the catalysts surveyed, Mo(CO)₆ gave the highest oil yield (57.7%) and the largest amount of hydrogen transferred to coal (3.1 wt.% of d.a.f. coal). However, the molybdenum and tungsten carbonyls did not exhibit high catalytic activity for low sulfur Wandoan coal in the absence of added sulfur. On the other hand, cobalt and nickel carbonyls showed high catalytic activity irrespective of the amount of sulfur in the reaction system. Fe(CO)₅Mo(CO)₆ binary catalyst promoted hydroliquefaction of Wandoan coal, resulting in increases in oil yield and transfer of hydrogen to coal in the presence of sulfur.     

Preparation of Fe-Si Nanoparticles in Furnace Aerosol Reactor

Crystalline Fe-Si alloy particles ranging from 37 to 150 nm in diameter were produced by thermal decomposition of a mixture of Fe(CO)₅ and SiH₄ in a furnace aerosol reactor. The reactor was made of alumina, 2.4 cm in diameter and 100 cm in length. The operating variables were reactor temperature (800–1400°C), the Fe(CO)₅ concentration (2.5 × 10^?5 to 1.5 × 10^?4 moI/I), the molar ratio of Fe(CO)₅ to SiH₄ (100:0 to 50:50), and the residence time (2.5–10s). The primary particle size increased with reactor temperature increase and decreased when the Si content of the precursor was increased. The sintering of the particles within the agglomerates was an important factor in determining the primary particle size, and the sintering was inhibited by the silicon. The spatial variation of particle morphology was observed by in situ deposition of particles on a TEM grid. At 7 cm from the reactor inlet, nonagglomerated spherical particles encapsulating several smaller iron particles were found. The spherical structure were destroyed downstream to form agglomerates.     

Chemically bonded iron carbonyl for magnetic composites based on phthalonitrile polymers

Dicarboxylic acid‐containing 1,3‐benzoxazine was synthesized and chemically bonded on iron carbonyl particles using a post‐coating method. Novel organic–inorganic hybrid magnetic composites were prepared via the interfacial reaction between magnetic phthalonitrile prepolymers and the benzoxazine functional coatings that chemically modified the iron carbonyl particles. The results showed that, compared with pure iron carbonyl particles, the modified particles could cure the phthalonitrile prepolymers efficiently and improve the interfacial compatibility of the functional composites. The magnetic composites with chemically modified particles exhibited stronger magnetism in comparison to composites containing bare particles: the saturation magnetization of the magnetic composites with equal concentration (5 wt%) of Fe(CO)₅ increased from 41.12 to 48.82 emu g^?1. Also, the magnetic composites obtained demonstrated excellent thermal stability up to 500 °C. Copyright © 2010 Society of Chemical Industry     

Removal of Fe(CO)5 from CO Gas as Detected by FTIR Spectroscopy

FTIR spectroscopy has been used to detect iron pentacarbonyl, Fe(CO)₅, in carbon monoxide gas. The capability of PbO/γ-Al₂O₃ as a compound to remove Fe(CO)₅ in CO gas was investigated using FTIR spectroscopy. The amount of iron pentacarbonyl in the CO gas was determined by spectroscopic means and by a complimentary technique based on the analysis of the iron content of spent PbO/γ-Al₂O₃ particles.     

Conjugation of soybean oil by decomposition of its iron tricarbonyl complex with carbon monoxide

Soybean and other vegetable oils are conjugated by decomposing their iron tricarbonyl complexes with carbon monoxide at elevated pressures. This procedure converts the iron tricarbonyl moiety of the complex into iron pentacarbonyl, which is recovered for reuse. When iron carbonyl-complexed soybean oil is heated at 180–200C at CO pressures of 1090–3750 psi, 90–97% of the complex is decomposed into Fe(CO)₅ and conjugated soybean oil. At 180C and 3600 psi CO, 84% of the Fe(CO)₅ is recovered, and 82% of the polyunsaturates in the oil is conjugated. At 200C and 1090 psi CO, 98% of the Fe(CO)₅ is recovered, but the oil is less conjugated (75%). The studies point the way to a possibly economical process for conjugating vegetable oils by consecutive reactions with Fe(CO)₅ and CO.     

Analysis of iron particle growth in aerosol reactor by a discrete-sectional model

The growth of iron particles by thermal decomposition of Fe(CO)₅ in a tubular reactor was analyzed by using a one dimensional discrete-sectional model with the coalescence by sintering of neighboring particles incorporated in. A thermal decomposition of Fe(CO)₅ vapor to produce iron particles was carried out at reactor temperatures varying from 300 to 1,000°C, and the effect of reactor temperature on particle size was compared with model prediction. The prediction exhibited good agreement with experimental observation that the primary particle size of iron was the largest at an intermediate temperature of 800°C. Model prediction was also compared with Giesen et al.’s [1] experimental data on iron particle production from Fe(CO)₅. Good agreement was shown in primary particle size, but a considerable deviation was observed in primary particle size distribution. The deviation may be due to an inadequate understanding of the sintering mechanism for the particles within an agglomerate and to the assumption of an ideal plug flow in model reactor in contrast to the non-ideal dispersive flow in actual reactor.     

OPTICAL PROPERTIES OF AEROSOLS

ABSTRACT

The evolution of small aerosol particles accompanying the combustion of straw for energy production is investigated. A sampling equipment specially designed for field measurements is described and characterized. The aerosol is studied by low-pressure cascade impactor and scanning mobility particle sizer, the particle morphology by transmission electron microscopy, and the chemical composition by energy dispersive x-ray analysis. The combustion gas contains 3–500 mg/Nm³ of submicron particles with a mean diameter of approximately 0.3 μm. The particles consist of almost pure potassium chloride and sulphate. The formation mechanism is analyzed by a theoretical simulation of the chemical reactions and the aerosol change during cooling of the flue gas. It is concluded that some sulphation of KC1 occurs in the gas phase although the sulphate concentration is much lower than predicted by an equilibrium assumption. The theoretical simulation proves that the fine mode particles can be formed by homogeneous nucleation of either KCl or K2SO₄ as the first step and further growth occurs by coagulation and diffusive condensation of both KC1 and K₄SO₄ on existing particles.     

Production of Higher Hydrocarbons from CO2 over Nanosized Iron Catalysts

The effects of the particle size of a Fe/Cu/K catalyst on CO and CO₂ hydrogenation reactions as well as the variation of crucial factors such as surface area and basicity, reduction, carburization, and catalytic behavior of precipitated Fe/Cu/K catalysts were evaluated. Hematite nanoparticle catalysts with various surface tensions were produced by homogeneous precipitation in alcohol/water solvents. The basicity of the K‐promoted iron catalyst was higher in iron catalysts with lower particle size. The increase in K‐basic sites at the surface of catalysts with smaller particle size was attributed to their higher surface areas. Elevation of catalyst basicity led to considerably stronger dissociative CO adsorption. Shifting the oxygen removal pattern to lower temperature was the consequence of faster nucleation of FeCx crystallites on promoted surface oxides. CO₂ hydrogenation can occur in two distinct direct and indirect routes via the Fischer‐Tropsch mechanism.     

PEG-modified magnetic hypercrosslinked poly(styrene-co-divinylbenzene) microspheres to minimize sorption of serum proteins

Monodisperse poly(styrene-co-divinylbenzene) [P(St-DVB)] microspheres were prepared by the precipitation polymerization of styrene (St) and divinylbenzene (DVB) in acetonitrile (ACN). Effect of St/DVB ratio and monomer concentration on morphology and particle size was investigated. Monodisperse 4.1 μm P(St-DVB) microspheres were chloromethylated with chloromethyl methyl ether (CMME) and hypercrosslinked using anhydrous FeCl₃ as a catalyst to form a very fine porous structure and to introduce reactive chloromethyl groups in the resulting product denoted as HC-P(St-DVB) particles. The hypercrosslinked microspheres were then functionalized with amino groups to yield HC-P(St-DVB)-NH₂ particles and iron oxide was precipitated within their pores. The obtained microparticles were highly magnetic with iron content ～38 wt% Fe. The surface of the magnetic microspheres was newly hydrophilized with methoxy-poly(ethylene glycol) (methoxy-PEG) which was confirmed by ATR FT-IR spectroscopy. The poly(ethylene glycol) (PEG)-modified magnetic microspheres were investigated in terms of sorption of serum proteins under different conditions and compared with the sorption on neat magnetic HC-P(St-DVB)-NH₂ particles. The surface modification of magnetic microspheres significantly minimized the adsorption of the serum proteins.     

Aerosol Charge Neutralization by a Mixing-Type Bipolar Charger using Corona Discharge at High Pressure

An aerosol neutralizer called the Mixing-type Bipolar Charger using Corona-Discharge at High Pressure (MBCCHP) was developed. In the MBCCHP, a corona discharge (High-Pressure Corona Ionizer; HPC Ionizer) induced by high frequency voltage (>100 Hz) at high pressure (>0.2 MPa) is used to generate bipolar ions at high concentration (1–3 × 10⁹ ions/cm³) that are then mixed with aerosol particles flowing in a charging chamber where no external electric field is present. The charging performance of the MBCCHP was evaluated by comparing the measured and theoretical number ratios of positively and negatively charged particles to the total number of particles, and by comparing those of negatively charged to positively charged particles for an equilibrium charge distribution. The theoretical and measured results agreed well in the particle size range of 5–80 nm. Particle loss in the MBCCHP for the size range of 5–100 nm was less than 15%, and particle generation from the electrode due to spattering or from the carrier gas containing SO_x due to chemical reaction was either negligible or not observed. The MBCCHP can effectively provide aerosol particles in the equilibrium charge state. Advantages include (1) no selective deposition of charged particles by an electric field, (2) no generation of new particles by reactive molecules, such as atmospheric pollution gases contained in a sample aerosol by chemical reactions with active species, such as OH radicals, produced by discharge, and (3) no effect of carrier gases of the sample aerosol on the ion properties.     

UV laser desorption/ionisation mass spectrometry of the triruthenium clusters Ru3(CO)12−n(PPh3)n (n=1, 2 and 3)

The negative ion ultraviolet laser desorption mass spectra of Ru₃(CO)₁₂ and its triphenylphosphine derivatives Ru₃(CO)_12−n(PPh₃)_n (n=1–3) have been recorded using laser desorption/ionisation time-of-flight mass spectrometry (LDI-TOF-MS). The spectra contain peaks in the parent region together with peaks at higher masses due to extensive gas phase reactions. Substitution of one to three carbonyls by the bulky triphenylphosphine ligand has a number of interesting effects on the spectra, most notably, increasing the degree of coordinative unsaturation of the gas phase clusters in the molecular ion region and increasing the intensity of the subsequent high mass reaction products.     

Preparation of some supported metallic catalysts from metallic cluster carbonyls

An examination was made of the adsorption of some metallic cluster carbonyls (MCCs), Co₂Rh₂(CO)₁₂, Co₃Rh(CO)₁₂, Co₄(CO)₁₂, Ir₄(CO)₁₂, Rh₆(CO)₁₆, and Ru₃(CO)₁₂, from nonaqueous solution onto two typical catalyst supports, γ-alumina and Aerosil silica. With two MCCs, Co₂Rh₂(CO)₁₂ and Ir₄(CO)₁₂, dispersed metallic catalysts were generated, and a study was made of how the main experimental conditions affected the metallic dispersion. MCC adsorption was more facile on γ-alumina than on silica and was often assisted by the presence of oxygen. An ir study showed that initial adsorption of Co₂Rh₂(CO)₁₂ on γ-alumina occurred with the loss of bridging carbonyls, the remaining carbonyls being progressively lost at temperatures >300 K, while adsorption of Ir₄(CO)₂ on γ-alumina resulted in progressive carbonyl loss at 320–620 K. Strong adsorption involves carbonyl loss, probably by ligand exchange with a surface anion, and the effect of oxygen is probably oxidative decarbonylation. Catalysts prepared from Co₂Rh₂(CO)₁₂ or Ir₄(CO)₁₂ were relatively highly dispersed (D ≈ 0.4-1 depending on conditions), and Co₂Rh₂(CO)₁₂ gave a much higher dispersion than was obtained by conventional impregnation using aqueous salt solutions. MCC adsorption in the presence of oxygen favored higher dispersions.     

Thermodynamic analysis and experimental verification of interface reactions of iron aluminide/tetragonal zirconia composite

Abstract

This paper described the thermodynamic analysis and experimental verification of interface reactions between iron aluminide intermetallic and tetragonal zirconia. Thermodynamic analysis confirmed that chemical reactions between Fe–Al intermetallic and ZrO₂ (3 mol.–%Y₂O₃ stabilised zirconia) mainly depended on the Al content in Fe–Al intermetallic. For ZrO₂(3Y)/Fe₃Al composite, the interface reactions to form Al₂O₃ and ZrAl₂ would take place when Al content was >40 at-% in Fe–Al intermetallic, while no interface reaction occurred when using Fe₃Al as toughening phase. ZrO₂(3Y)/Fe₃Al composite was synthesised by hot press sintering to further verify the thermodynamic analysis of interface reactions between iron aluminide intermetallic and tetragonal zirconia. The phase composition, morphology and interface structure of ZrO₂(3Y)/Fe₃Al were investigated by X-ray diffraction, SEM and TEM. The results show that Fe₃Al was thermodynamic stable in ZrO₂(3Y) matrix, which was in good agreement with thermodynamically analysis.     

Fe-ZSM-5 Catalysts: Preparation in Organic Media, Fe-particle Morphology and NO x Reduction Activity

Fe-ZSM5 catalysts were prepared at room temperature. Iron was incorporated into H-ZSM5 in organic media (toluene) using iron acetyl acetonate. In order to elucidate the catalytic performance of this Fe-ZSM5, reference catalysts were prepared by chemical vapour deposition (CVD) and impregnation in aqueous media (IMW). The various catalysts were characterized structurally and morphologically. Materials prepared in organic media and CVD showed fibrous iron particles, with radius between 10 and 40 Å, highly dispersed on the external zeolite surface. Fractal dimension values suggest that iron particles grow dendritically when iron is incorporated into zeolite by impregnation in organic media. Nuclear magnetic resonance of ¹²⁹Xe adsorbed on catalysts shows that dendrites can penetrate into the zeolite channels. The dispersion of the iron species on the external surface of the zeolite and the presence of iron inside the channels explain the good catalytic performance in the Selective Catalytic Reduction (SCR) of NO. Ammonia and n-decane were employed as reducing agents. The highest NO to N₂ conversion (≈100% at 430 °C) was obtained when ammonia was used. In contrast, n-decane is unable to reach Fe species in channels, and the inner active surface is thus lost.     

Preparation of Si–C–N–Fe magnetic ceramic derived from iron-modified polysilazane

In this paper, Si–C–N–Fe magnetoceramics were obtained by pyrolysis of iron-modified polysilazane (PFSZ) precursors which were synthesized by using polysilazane (PSZ) and iron (III) acetylacetonate (Fe(acac)₃) as starting materials. The as-synthesized PFSZ precursors were characterized by Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography. The polymer-to-ceramic conversion of the PFSZ was studied by FT-IR and thermal gravimetric analysis. It is found that the ceramic yield of the PFSZ precursor is ca. 25% higher than that of the original PSZ. The crystallization behavior, microstructures and magnetic properties of the PFSZ-derived Si–C–N–Fe magnetoceramics were studied by techniques such as X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The results indicate that the formed α-Fe nanoparticles are uniformly dispersed in amorphous Si–C–N(O) matrix, leading to the soft magnetization of the resultant Si–C–N–Fe ceramics. Moreover, the iron content and the magnetic properties of the Si–C–N–Fe ceramic could be easily controlled by the amount of Fe(acac)₃ in the precursor.     

Study of Gold Species in Iron-Oxide-Supported Gold Catalysts Derived from Gold-Phosphine Complex Au(PPh3)(NO3) and As-Precipitated Wet Fe(OH)3*

Iron-oxide-supported gold catalysts were prepared by supporting a Au phosphine complex Au(PPh₃)(NO₃) on as-precipitated wet iron hydroxide Fe(OH)₃^*, followed by temperature-programmed calcination. The Au/Fe(OH)₃^*catalysts calcined at the temperatures 573–773 K showed extremely high catalytic performance for CO oxidation at temperatures as low as 203–253 K. Interaction of the Au(PPh₃)(NO₃) gold precursor with the Fe(OH)₃^*upon supporting, transformation of the precursor during the heat treatments, and state of the gold in the catalysts were studied by FT-IR, XRD, TEM, XPS, and EXAFS. The gold precursor dissociated on the Fe(OH)₃^*surface to produce [Au(PPh₃)]⁺species which partially decomposed at 473 K and was transformed to small gold metallic particles with coordination numbers of 7.4–8.0 for Au-Au bond at calcination temperatures ≥573 K. In contrast, decomposition of the gold complex over crystalline Fe₂O₃^*resulted in large gold particles. The Au/Fe₂O₃^*sample was inactive at 203–253 K and exhibited very low activity for CO oxidation at room temperature. The efficiency of the as-precipitated wet Fe(OH)₃^*as a support is explained in terms of a higher stability of [Au(PPh₃)]⁺on the Fe(OH)₃^*as compared to the Fe₂O₃^*due to more effective interaction of the Au species with OH groups and defects of the amorphous Fe(OH)₃^*surface. The results demonstrate the importance of support–metal precursor interactions, both upon supporting and during calcination, in the formation of highly active catalysts with small Au particles for low-temperature CO oxidation.     

Effect of different iron precursors on the synthesis and photocatalytic activity of Fe–TiO2 nanotubes under visible light

Fe–TiO₂ nanotubes (Fe-TNTs) were developed to entitled photocatalytic reactions using a visible range of the solar spectrum. This work reports on the effect of different Fe precursors on the synthesis, characterization, kinetic study, material and photocatalytic properties of Fe-TNTs prepared by electrochemical method using three different Fe precursors i.e. (iron nitrate [Fe(NO₃)₃⋅9H₂O], iron sulfate [FeSO₄⋅7H₂O], and potassium iron ferricyanide [K₃Fe(CN)₆]). X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy are used to examine the influence of the Fe precursor on the Fe-TNTs material characterization. Different Fe-TNT properties, such as enhanced photoactivity, good crystallization, and composition of titania structures (anatase and rutile) could be acquired from different iron precursors. Among the three iron precursors, Fe(NO₃)₃ provided with the only anatase phase, yields the highest photocatalytic activity. Congo red is used as a model compound to check the photocatalytic efficiency of synthesized materials because it has a complex aromatic structure which makes it difficult to be biodegraded or oxidized with the aid of chemicals. The photocatalytic efficiency of all Fe-TNT can be arranged in the following order: TNT-FeN > TNT-FeS > TNT-FeK > TNT. The kinetic rate constant of congo red degradation using the Fe-TNT with Fe(NO₃)₃ was 0.44 h⁻¹ with a half-life of 1.57 h⁻¹