Distribution Of Iron Species Research Articles

Molecular modelling and experimental studies on steam gasification of low-rank coals catalysed by iron species

Pyrolysis and catalytic steam gasification of brown coal containing iron hydroxyl complexes have been investigated experimentally and with semi-empirical and density functional theory molecular modelling. Pyrolysis yielded mainly CO2, CO, and reduced iron species. Catalytic steam gasification at 900 °C after 15 min, consumed 20 wt.% additional char and a higher than expected yield of H2 due to post-gasification reactions; inorganic and organic oxygen in char increased compared to pyrolysis. Apparent turnover numbers for catalytic gasification were 12–22 mole of carbon per mole of iron. The distribution of iron species in brown coal indicated small iron clusters are likely to form on heating; pyrolysis was thus modelled using molecules of char with [Fe3], [Fe5] and [Fe3O], and the active site for gasification was shown to be [Fe–C]. The mechanism of catalytic gasification involved H2O chemi-adsorbed on [Fe–C], formation of the [Fe ← OH2] coordination bond, with H2 produced via iron hydride complexes. Formation of CO was via oxygen insertion into [Fe–C] to form [Fe–O–C] that decomposed into CO and another [Fe–C] site. Lower activation barriers were obtained for concerted chemistry involving iron-hydrides. Active sites in char were accessible to H2O as pores had developed around iron species; large sized iron species were not catalytically active but caused large pores to form in char.

Iron speciation of sediments from Kuhai Lake in China by Mössbauer spectroscopy

The vertical distribution of iron species in the sediments collected from Kuhai Lake was investigated in this study. Their Mossbauer spectra were composed of one sextet and four doublets ascribable to one paramagnetic high-spin Fe3+, two paramagnetic high-spin Fe2+ with different quadrupole splittings, and one diamagnetic low-spin Fe2+ that corresponds to pyrite (FeS2). The distribution of pyrite was considered to reflect the climatic change during the past 2,000 years. Mossbauer spectroscopy was successfully applied to the analysis of the Kuhai Lake sediments so as to reconstruct the history of the past climate.

Preparation and Pretreatment Temperature Influence on Iron Species Distribution and N2O Decomposition in Fe–ZSM-5

Fe–ZSM-5 catalysts are prepared by FeCl3 sublimation between 320 and 850 °C. The catalysts are characterised by XRD, H2–TPR, NH3–TPD, NO adsorption by DRIFTs, and catalytic activity is evaluated for N2O decomposition. The influence of high temperature (850 °C) and pretreatment environment (air, He, He+H2O and H2) on the nature of iron species in Fe–ZSM-5 is further investigated by DRIFTs. High temperature FeCl3 sublimation results in decreased FeOx formation, easily reducible and narrow distribution of iron species in close proximity to alumina in Fe–ZSM-5. High temperature FeCl3 sublimation or pretreatment results in isolated hydroxylated iron species, –Fe(OH)2, which are not significant in Fe–ZSM-5 prepared by 320 °C FeCl3 sublimation followed by calcination below 600 °C. Fe–ZSM-5 prepared by high temperature FeCl3 sublimation show high N2O decomposition activity and the improved performance can be correlated to –Fe(OH)2 species in close proximity to alumina.

Chemistry of N 2O decomposition on active sites with different nature: Effect of high-temperature treatment of Fe/ZSM-5

Nitrous oxide decomposition on Fe/ZSM-5 catalysts, prepared by solid-state ion exchange followed by calcination in O 2 at 823 K or high-temperature treatment in He at 1173 K, was studied by steady-state reaction and transient-response techniques. High-temperature treatment induces profound changes in the distribution of iron species, most notably a substantial fraction of oligonuclear and cationic Fe species are converted to Fe species stabilized by extra-framework Al (Fe O Al species) in zeolite micropores. Nitrous oxide decomposition is much slower over calcined Fe/ZSM-5 than over its high-temperature-treated counterpart. Only over the latter catalysts is inhibition of N 2O conversion by molecular oxygen observed. Transient response experiments show that molecular oxygen and nitrogen evolve simultaneously for calcined Fe/ZSM-5. It is proposed that the reaction proceeds over isolated Fe 3+ sites in cationic species or oligonuclear Fe oxide species via a scavenging mechanism in which adsorbed oxygen species react with gaseous nitrous oxide to give molecular nitrogen and oxygen. In contrast, transient-response experiments for the high-temperature-treated catalyst show slow oxygen desorption compared with nitrogen formation, pointing to recombinative oxygen desorption being rate-limiting. This agrees with the finding that the rate is inhibited by molecular oxygen. It is proposed that ferrous ions in the high-temperature-treated catalyst show a much higher reactivity in nitrous oxide decomposition than Fe 3+ sites. The Fe 2+ species are most likely associated with the mixed iron and aluminium species formed upon high-temperature treatment.

金属還元剤の表面特性と塩素化炭化水素の脱塩素反応速度定数

Chlorinated aliphatic compounds such as trichloroethylene are main contaminants of groundwater, and the dechlorination technique using iron powder as metallic reduction agents was investigated as a remediation technology for such contaminations. As for the iron powder obtained from industrial processes or waste, as well as the dechlorination rate constants of chlorinated aliphatics could be obtained through laboratory experiments, as well as the data on specific surface area and iron content. Furthermore, X-ray photoelectron spectroscopy (XPS) was used for measuring the fraction of zero-valent iron, divalent iron, and trivalent iron at the surface of iron powder, and for measuring the distribution of iron species along the depth direction by XPS after each etching time. The rate constant of a pseudo-first-ordered reaction can be ranked using the index of reaction area, which is determined by multiplying specific surface area by the mean zero-valent iron fraction measured by XPS.

Reduction of N 2O with CO over FeMFI zeolites: influence of the preparation method on the iron species and catalytic behavior

The reduction of N 2O by CO was investigated over FeMFI zeolites prepared by different methods including sublimation, liquid ion exchange, and hydrothermal synthesis followed by steam activation. This leads to catalysts with different nature and distribution of iron species, as characterized by HRTEM, UV/vis, and EPR techniques. A common denominator in the FeZSM-5 samples is the heterogeneous iron constitution, with a significant degree of clustering in the form of iron oxide particles. Iron clustering was suppressed in steam-activated Fe-silicalite, presenting a remarkable uniform distribution of isolated iron species. In the presence of CO, the conversion of N 2O over the catalysts is strongly accelerated with respect to direct N 2O decomposition. The reaction rate increases linearly with the molar CO/N 2O feed ratio and strongly depends on the preparation method applied. A correlation was found between the fraction of isolated Fe(III) species in the as-prepared catalysts and the activity for N 2O reduction with CO. Steam-activated Fe-silicalite, containing mostly isolated iron ions in extraframework positions, shows the highest activity per mole of iron, while the highly clustered liquid-ion-exchanged catalyst presents the lowest activity. In situ UV/vis and EPR studies evidence the participation of mononuclear iron ions in the N 2O–CO reaction, and also support the involvement of oligonuclear Fe x O y species. The reaction mechanism is iron site dependent. Over isolated sites, the reduction of N 2O with CO occurs via coordinated CO species on Fe 3+ ions. The reaction over oligonuclear sites proceeds via a redox Fe 3+/Fe 2+ process with intermediate formation of O − radicals.

Chemical Model of the FeCl<SUB>3</SUB>-HCl-H<SUB>2</SUB>O Solutions at 25°C

A chemical model was developed to calculate the equilibrium concentrations of chemical species in the FeCl 3 -HCl-H 2 O system at 25°C by using chemical equilibria, mass and charge balance equations. The activity coefficients of solutes and the activity of water were calculated with the Bromley equation. The interaction parameters for the individual chemical complexes, which were necessary to calculate the activity coefficients, were obtained from the reported interaction parameters between ions. By applying this model, the distribution of iron species with the electrolyte concentrations was obtained. In the experimental ranges of the ionic strength of solution up to 7.28 m, the experimental pH values were in good agreement with the predicted pH values.

A study on vertical distribution of elements and their chemical states in Yatsu tideland sediments

We have clarified vertical distribution of thirty and more elements in the Yatsu tideland sediment by instrumental neutron activation analysis (INAA) and prompt g-ray analysis (PGA). The distributions of elements were categorized into three groups according the tendency of each vertical distribution. Chemical states of iron in the sediments were investigated by Mossbauer spectroscopy. In the distribution of iron species, maximum pyrite distribution was found in the middle layer. Paramagnetic high-spin Fe2+ distributed complementarily to pyrite, suggesting that the Fe2+ was used for pyrite formation.

Characterization of ultramafic rocks from the Jinchuan nickel deposit in China by 57Fe Mössbauer spectroscopy

57Fe Mossbauer spectroscopy has been applied to the ultramafic rocks collected from the Jinchuan nickel deposit in China to elucidate their mineralization process. Their Mossbauer spectra consisted of two sextets ascribable to magnetite, two doublets ascribable to Fe2+ and Fe3+ in chromite, and one doublet ascribable to olivine. The closest sample to the ore body did not contain chromite and contained a doublet ascribable to pyrite and a sextet ascribable to pyrrhotite. The valence and site distribution of iron species suggested low oxygen fugacity for the formation of the Jinchuan nickel deposit.

Catalysis of HSO3–/SO32– Oxidation by Manganese Ions

Among transition metal ions, Mn(II) ions are considered to be the most active catalysts of HSO3–/SO32– oxidation. All published data on the kinetics of the catalytic oxidation of HSO3–/SO32– by manganese ions are analyzed in this review. In addition to primary experimental data, information on the rate constants of the reactions of \({\text{SO}}_{3 - 5}^{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{ \cdot } }\) and HSO5– with Mn(II)/Mn(III) or Fe(II)/Fe(III) ions was also engaged in this analysis. Unavoidable impurities of iron ions in aqueous solutions were found to be responsible for the observed catalytic activity of manganese ions. Manganese ions are highly efficient activators of iron ions. Manganese ions are catalytically inert in the absence of iron ions. These metal ions form a synergistic pair in which Mn(II) ions increase the catalytic properties of iron ions many times. This effect results from the catalysis of a rate-limiting step of chain propagation in sulfite oxidation and from a shift in the distribution of iron species toward Fe(III), which participates in a step of chain initiation.

Mössbauer Spectroscopic Study on Vertical Distribution of Iron Species in Sediments from Qinghai Lake, China

In this study, 57Fe Mossbauer spectroscopy has been applied to sediments collected from Qinghai Lake in Qinghai Province, China, to investigate the vertical distribution of iron species. Their Mossbauer spectra consisted of four doublets ascribable to one paramagnetic high-spin Fe3+, two paramagnetic high-spin Fe2+ with different quadrupole splittings, and one diamagnetic low-spin Fe2+ that corresponds to pyrite (FeS2). The distribution of pyrite suggested climatic changes during the past nine thousand years. It was demonstrated that the iron speciation in the salt lake sediments by Mossbauer spectroscopy can be used to reconstruct the past environment.

Veränderungen der Eisenspezies während des Verarbeitungsprozesses von Sojabohnen zum fermentierten Produkt Tempeh

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Ferrolysis in Arundian alluvial palaeosols: evidence of a shift in the early Carboniferous monsoonal system

An unusual clay mineral assemblage from early Carboniferous (Arundian) palaeosols in South Wales contains a three component kaolinite/(chlorite-like material)/smectite mixed-layer clay. This is interpreted as the product of ferrolysis, a complex process involving dissolution of clays a d the subsequent production of interlayered varieties from the repetitive reduction and reoxidation of iron compounds in seasonally waterlogged, surface-water grey soils. Support for this interpretation comes from the distribution of iron species, iron concretions and vertic features in the palaeosol profile, which indicate formation under strongly seasonal, dry/hydromorphic conditions. The appearance of the ferrolytic pa- Iaeosol indicates a shi from a ‘dry’ to a ‘wet-type’ monsoonal regime in late Arundian times.

Mössbauer study of iron phthalocyanines as catalysts of cumene oxidation

Mössbauer spectra of mixed Cu–Fe poly(phthalocyanine) catalysts show that the presence of copper ions in the poly(phthalocyanine) core influences the distribution of iron species and their ability to undergo oxidative destruction to iron oxides. The distribution of the two main species is dependent on the Cu/Fe ratio in the catalysts and corresponds to the catalytic activity.

Distribution of iron species in some “oil shales” of the Judea Desert, Israel

Iron-bearing minerals in “oil shales” of the Ghareb Formation have been investigated by Mössbauer and infrared spectroscopy and their chemical compositions have been determined. The minerals studied are: pyrite, kaolinite, iron oxides and iron hydroxides. Pyrite of two types is present, i.e. a framboidal or dispersed microcrystalline type and a very finely crystalline variety detected only by Mössbauer spectroscopy. These occurrences are probably related to differences in hydrophobic—hydrophilic properties of the associated organic matter. The distribution of Fe among oxides, hydroxides, silicates and pyrite in adjacent bituminous and non-bituminous samples indicates that only Fe from oxides and hydroxides has been available for pyrite formation. Fe was not detected in any organically bonded form.