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1.
[Fe]‐Hydrogenase (Hmd) catalyzes reversible hydride transfer from H 2. It harbors an iron‐guanylylpyridinol as a cofactor with an Fe II that is ligated to one thiolate, two COs, one acyl‐C, one pyridinol‐N, and solvent. Here, we report that Cu I and H 2O 2 inactivate Hmd (half‐maximal rates at 1 μM Cu I and 20 μM H 2O 2) and that Fe II inhibits the enzyme with very high affinity ( Ki=40 nM ). Infrared and EPR studies together with competitive inhibition studies with isocyanide indicated that Cu I exerts its inhibitory effect most probably by binding to the active site iron‐thiolate ligand. Using the same methods, it was found that H 2O 2 binds to the active‐site iron at the solvent‐binding site and oxidizes Fe II to Fe III. Also it was shown that Fe II reversibly binds away from the active site iron, with binding being competitive to the organic hydride acceptor; this inhibition is specific for Fe II and is reminiscent of that for the [FeFe]‐hydrogenase second iron, which specifically interacts with H 2. 相似文献
2.
Starting from the mononuclear iron(II) complex [Fe(MeCPy 2Phen)(MeCN) 2] 2+, a non-heme Fe(IV)oxo complex [Fe IV(MeCPy 2Phen)O] 2+ was synthesized via oxidation with meta-chloroperoxybenzoic acid (mCPBA). The Fe(IV)oxo complex was characterized using UV/Vis spectroscopy, Mößbauer spectroscopy and CSI mass spectrometry. The ability of this species to oxidize C−H bonds was tested with cyclohexane and adamantane as model substrates. For cyclohexane, an alcohol-to-ketone ratio ( A/ K) of 6.1 and efficiencies up to 55 were obtained. In case of adamantane, the ratio of tertiary over secondary products (3°/2°) is 38. In combination, this indicates the iron(IV)oxo complex being the catalytically active species. 相似文献
3.
Zeolites having MFI, FER and *BEA topology were loaded with iron using solid state cation exchange method. The Fe:Al atomic ratio was 1:4. The zeolites were characterized using nitrogen adsorption, FTIR and DR UV–Vis–NIR spectroscopy. The catalytic activity in NO oxidation and the occurrence of NO
x
adsorption was determined in a fixed-bed mini reactor using gas mixtures containing oxygen and water in addition to NO and NO 2 and temperatures of 200–350 °C. Under these reaction conditions, the NO
x
adsorption capacity of these iron zeolites was negligible. The kinetic data could be fitted with a LHHW rate expression assuming a surface reaction between adsorbed NO and adsorbed O 2. The kinetic analysis revealed the occurrence of strong reaction inhibition by adsorbed NO 2. FER and MFI zeolites were more active than *BEA type zeolite. MFI zeolite is most active but suffers most from NO 2 inhibition of the reaction rate. FTIR and UV–Vis spectra suggest that isolated Fe 3+ cations and binuclear Fe 3+ complexes are active NO oxidation sites. Compared to the isolated Fe 3+ species, the binuclear complexes abundantly present in the MFI zeolite seem to be most sensitive to poisoning by NO 2. 相似文献
4.
Zero-valent iron (ZVI) aerogels have been synthesized by sol-gel method and supercritical CO 2 drying, followed by H 2 reduction in the temperature range of 350–500 °C. When applied to trichloroethylene (TCE) dechlorination, the ZVI aerogel
reduced at 370 °C showed the highest performance in the conditions employed in this study. Thus, the effect of reduction temperature
in preparing ZVI aerogels has been investigated by several characterizations such as BET, XRD, TPR, and TEM analyses. As the
reduction temperature decreased from 500 to 350 °C, the BET surface area of the resulting aerogels increased from 6 to 30
m 2/g, whereas their Fe 0 content decreased up to 64%. It was also found that H 2 reduction at low temperatures such as 350 and 370 °C leads to the formation of ZVI aerogel particles consisting of both Fe 0 and FeO
x
in the particle cores with a different amount ratio, where FeO
x
is a mixture of maghemite and magnetite. It is, therefore, suggested that reduction at 370 °C for ZVI aerogel preparation
yielded particles homogeneously composed of Fe 0 and FeO
x
in the amount ratio of 87/13, resulting in high TCE dechlorination rate. On the other hand, when Pd- and Ni-ZVI aerogels
were prepared via cogellation and then applied for TCE dechlorination, we also observed a similar effect of reduction temperature.
However, the reduction at 350 or 370 °C produced Pd- or Ni-ZVI aerogel particles in which Fe 0 and Fe 3O 4 co-exist homogeneously. Since both Fe 0 and Fe 3O 4 are advantageous in TCE dechlorination, the activities of Pd- and Ni-ZVI aerogels reduced at 350 °C were comparable to those
of both aerogels reduced at 370 °C, although the former aerogels have less Fe 0 content. 相似文献
5.
La (1−x)Sr xCo (1−y)Fe yO 3 samples have been prepared by sol–gel method using EDTA and citric acid as complexing agents. For the first time, Raman mappings were achieved on this type of samples especially to look for traces of Co 3O 4 that can be present as additional phase and not detect by XRD. The prepared samples were pure perovskites with good structural homogeneity. All these perovskites were very active for total oxidation of toluene above 200 °C. The ageing procedure used indicated good thermal stability of the samples. A strong improvement of catalytic properties was obtained substituting 30% of La 3+ by Sr 2+ cations and a slight additional improvement was observed substituting 20% of cobalt by iron. Hence, the optimized composition was La 0.7Sr 0.3Co 0.8Fe 0.2O 3. The samples were also characterized by BET measurements, SEM and XRD techniques. Iron oxidation states were determined by Mössbauer spectroscopy. Cobalt oxidation states and the amount of O − electrophilic species were analyzed from XPS achieved after treatment without re-exposition to ambient air. Textural characterization revealed a strong increase in the specific surface area and a complete change of the shape of primary particles substituting La 3+ by Sr 2+. The strong lowering of the temperature at conversion 20% for the La 0.7Sr 0.3Co (1−y)Fe yO 3 samples can be explained by these changes. X photoelectron spectra obtained with our procedure evidenced very high amount of O − electrophilic species for the La 0.7Sr 0.3Co (1−y)Fe yO 3 samples. These species able to activate hydrocarbons could be the active sites. The partial substitution of cobalt by iron has only a limited effect on the textural properties and the amount of O − species. However, Raman spectroscopy revealed a strong dynamic structural distortion by Jahn–Teller effect and Mössbauer spectroscopy evidenced the presence of Fe 4+ cations in the iron containing samples. These structural modifications could improve the reactivity of the active sites explaining the better specific activity rate of the La 0.7Sr 0.3Co 0.8Fe 0.2O 3 sample. Finally, an additional improvement of catalytic properties was obtained by the addition of 5% of cobalt cations in the solution of preparation. As evidenced by Raman mappings and TEM images, this method of preparation allowed to well-dispersed small Co 3O 4 particles that are very efficient for total oxidation of toluene with good thermal stability contrary to bulk Co 3O 4. 相似文献
6.
The aim of this study is to develop a process for the removal of Hg 0 using H 2S over iron oxides sorbents, which will be located just before the wet desulfurization unit and catalytic COS converter of a coal gasification system. It is necessary to understand the reactions between the iron oxide sorbent and other components of the fuel gas such as H 2S, CO, H 2, H 2O, etc. In this study, the sulfidation behavior and activity for COS formation during Hg 0 removal from coal derived fuel gas over iron oxides prepared by precipitation and supported iron oxide (1 wt% Fe 2O 3/TiO 2) prepared by conventional impregnation were investigated. The iron oxide samples were dried at 110 °C (designated as Fe 2O 3-110) and calcined at 300 and 550 °C (Fe 2O 3-300 and Fe 2O 3-550). The sulfidation behavior of iron oxide sorbents in coal derived fuel gas was investigated by thermo-gravimetric analysis (TGA). COS formation during Hg 0 removal over iron oxide sorbents was also investigated using a laboratory-scale fixed-bed reactor. It was seen that the Hg 0 removal activity of the sorbents increased with the decrease of calcinations temperature of iron oxide and extent of sulfidation of the sorbents also increased with the decrease of calcination temperature. The presence of CO suppressed the weight gain of iron oxide due to sulfidation. COS was formed during the Hg 0 removal experiments over Fe 2O 3-110. However, in the cases of calcined iron oxides (Fe 2O 3-300, Fe 2O 3-550) and 1 wt% Fe 2O 3/TiO 2, formation of COS was not observed but the Hg 0 removal activity of 1 wt% Fe 2O 3/TiO 2 was high. Both FeS and FeS 2 were active for Hg 0 removal in coal derived fuel gas without forming any COS. 相似文献
7.
Using Fusarium oxysporum species (F. oxysporum), a green synthesis of super-paramagnet iron oxide @silver@ Chitosan (SPION@Ag@Cs) was achieved. The physico-chemical characteristics of the SPION@Ag@Cs nanocomposite revealed the development of superparamagnetic phases of iron oxide (Fe2O3), as well as fluorescence, Raman absorption, and biocompatibility. Drug and gene delivery, and diagnosis, are all possibilities for the nanocomposite. The uptake of nitric oxide by HT-29 colorectal cell lines is examined in this article, for up to 72 h, the cytotoxicity of the HCT116 cell line was investigated. These characteristics were compared to Streptomyces griseus fungal species (S. griseus) which develops Fe3O4 under the same preparation conditions. 相似文献
8.
In this paper, Fe 3O 4 powder was prepared by the chemical precipitation method using impinging stream technology. The influences of feed flow rate, L/ D, reactant concentration, ratio of iron ion concentration, reaction temperature, and impact time on the size and distribution of particles were investigated by the orthogonal experiment method. The microstructure and morphology of Fe 3O 4 powders were characterized by scanning electron microscopy, X-ray diffractometer, and granulometer. The results showed that when ratio of iron ion concentration c(Fe 2+): c(Fe 3+) = 0.75, reactant concentration c(Fe 3+) = 0.4 mol · L −1, feed flow rate Q = 800 L · h −1, L/ D = 3, reaction temperature T = 20°C, impact time t = 50 min, the prepared Fe 3O 4 had an average particle size of 1.815 μm and the most uniform distribution. The influence of ultrasonic enhancement on the mixing process and powder preparation in an impinging stream reactor was investigated. The size and distribution of the powders were significantly affected by ultrasonic enhancement. With the increase in ultrasonic power, the particle size of the powders decreased and the distribution became narrower. The particle size was reduced by 68.78%, and the particle distribution range was narrowed by 84.34% under ultrasound enhancement. This study promised the effective utilization of ultrasonic cavitation in the optimization of experimental equipment and the preparation of ultrafine powder, which provides a basis for process optimization of powder preparation. 相似文献
9.
ZSM-5 and Y zeolites were modified with iron by an ion-exchange method and then calcined at 773, 873, 973 and 1,073 K. The obtained materials were characterized with respect to textural parameters (low-temperature N 2 sorption), structure (X-ray diffraction, UV–vis–DRS), redox properties (H 2-temperature programmed desorption, TPD) and surface acidity (NH 3-TPD). The obtained results have shown that the structure of zeolites influenced form, aggregation and content of the introduced iron species. In case of the FAU type structure characterized by wide pores (max. ring size, T-atoms—12) mainly iron in form of mononuclear Fe 3+ cations and Fe x 3+ O y oligonuclear clustered species was found. On the other hand for the MFI type structure characterized by smaller pores (max. ring size, T-atoms—10) significant contribution of iron in the form of bulky Fe 2O 3 clusters located possibly on the outer surface of ZSM-5 was detected. Such significant differences in distribution of iron species is probably related to various mobility of iron species in the pore systems of both zeolites. The obtained materials were tested as catalysts in the process of N 2O decomposition. Calcination of zeolites at different temperatures influenced neither the properties nor the activity of the obtained catalysts. 相似文献
10.
The electrochemistry of water-soluble iron porphyrins (Fe( n-TMPyP)) (where n=2 and 4) was studied as an electrochemically active film on DNA modified glassy carbon, gold, platinum, and transparent semiconductor tin oxide electrodes in solutions of various pH values. The two layers of the modified electrode containing the iron porphyrin and the DNA film were prepared by depositing the iron porphyrin on a DNA film modified electrode. The Fe(4-TMPyP)/DNA film was electrocatalytic reductive for p-nitrobenzoic acid in a weak acidic, or neutral aqueous solution through an Fe II species, and the electrocatalytic reduction peak potential became more negative than the cathodic peak of the Fe III/II redox couple. The electrocatalytic reduction properties by the Fe(2-TMPyP)/DNA film as catalysts for nitrite reduction have also been determined, and shown to be active through an Fe I species and to be pH-dependent. The electrocatalytic oxidation properties of nitrite by Fe( n-TMPyP)/DNA (for n=2 and 4) film have also been determined and shown to be active through an Fe IV species with the electrocatalytic oxidation efficiency of NO 2− with Fe IV(O)( n-TMPyP) being higher than with (HO)Fe IV(O)( n-TMPyP). The electrocatalytic oxidation efficiency of NO 2− by iron porphyrin is pH-dependent. The electrocatalytic reduction of p-nitrophenol by Fe(2-TMPyP)/DNA film are also discussed. 相似文献
11.
The incorporation of electrolyte-phobic material into gas diffusion electrodes enhances their performance. The principles governing the choice of electrolyte-phobic materials in molten carbonate electrolyte are discussed. Contact angle measurements of molten NaLiCO 3 on materials which have hexagonal layer-like structures confirmed that provided
LV
SV, the contact angle will be greater than 90°. Of the materials tested (C, BN, BaO.6.Fe 2O 3, PbO.6Fe 2O 3), only C possessed adequate corrosion resistance. Electrolyte-phobic anodes, prepared by incorporation of graphite fibres into the electrocatalyst mixture, significantly reduced concentration polarization and paste electrolyte cells using such electrodes gave 160 mA/cm 2 at 0.6 V on 80% H 2/20% CO 2 fuel at 600°C, as opposed to 80 mA/cm 2 for conventional cells. 相似文献
12.
The behaviour of the iron-sulphur system in the presence of water and hydrogen under coal liquefaction conditions has been investigated by using a high-pressure differential thermal analysis technique. The iron compounds used were Fe 2O 3, Fe 3O 4 and FeS 2. DTA was performed under 10.1 MPa (initial pressure) N 2 or H 2, heating to 450 °C (2.5 °C min −1). Sulphate ions were detected by BaCl 2 addition to the product aqueous solution; sulphides were formed as gaseous and solid products. The results suggest that the catalytic behaviour of the sulphate and sulphides formed under the conditions employed must be considered for the iron-sulphur system in coal liquefaction. 相似文献
13.
A hybrid sorbent material for removal of hydrogen sulfide from air was developed. The material is based on activated carbon and iron compounds obtained from waste iron(II) sulfate(VI) heptahydrate. The iron salt is deposited on the carbonaceous support and subjected to oxidation (Fe 2+ to Fe 3+) using atmospheric oxygen under alkaline conditions. An effect of H 2O 2 addition to the process on the composition of the resultant material was also examined. X-ray diffraction (XRD) analyses confirmed easy conversion of waste FeSO 4·7H 2O to iron oxides Fe 3O 4 and FeOOH. The activated carbon supporting iron oxides revealed a higher efficiency in H 2S elimination from air compared to the commercial activated carbon, without any modification. 相似文献
14.
The catalytic ammonia decomposition over iron and iron nitride, Fe 4N, under the atmosphere of ammonia–hydrogen mixtures of different amounts of ammonia in the temperature range of 400–550 °C by means of thermogravimetry has been studied. A differential tubular reactor with mixing has been used. The ammonia concentration in the gas phase during all the process was analysed. The balance between the inlet and outlet ammonia quantity has been used to determine a degree of ammonia conversion and the values of decomposition reaction rate. The activation energy of ammonia decomposition reaction over Fe and Fe 4N was found to be 68 and 143 kJ/mol, respectively. 相似文献
15.
Developing effective iron-incorporated zeolites and determining their active centers for the direct oxidation of CH 4 to oxygenates have remained challenging topics so far. In this paper, we successfully prepare the highly-dispersed iron supported Y zeolites by a facile solid-state ion-exchange method with ferrocene, which was conducted under water-free conditions followed by a series of calcination. Moreover, extra-framework dinuclear Fe 2 + complexes are identified as so-called active α-iron sites on zeolites. ICP-OES, N 2 adsorption–desorption test, X-ray diffraction, solid-state 27Al NMR, N 2O titration, TEM, EPR and 57Fe Mössbauer spectra were carried out to characterize properties of sample structure, acid sites, as well as the supported iron species. Characterization results indicate that high-temperature treatments have no effect on the typical structure feature of zeolites. Compared with catalysts synthesized by conventional impregnation, the samples prepared by the facile approach possess abundant dinuclear Fe 2 + complexes but no Fe 2O 3 bulks and show weak acidity. These lead to a higher oxygenate selectivity in CH 4 oxidation to oxygenates. Remarkably, the oxygenate (HCHO and CH 3OH) selectivity of 6.5% at 375°C can be eventually obtained. 相似文献
16.
Cyclic voltammetric experiments were carried out on platinum in acidic solution (pH 3) containing ferrous sulfate, nickel sulfate and ethylamines (EtNH 2, Et 2NH, Et 3N). Spectral ultraviolet absorption studies indicate the complexation of both Fe 2+ and Ni 2+ ions with ethylamines. The results under transient polarisation conditions indicate the reduction of Fe 2+ ions through the intermediate species FeOH +, with second electron transfer as a slow step. The higher charge transfer rate of FeOH + over NiOH + reduction causes the anomalous codeposition of Fe–Ni alloy film. Among the ethylamines, Et 3N considerably assists the alloy deposition process. A gradual variation in free energy of alloy formation with Fe 2+:Ni 2+ (mol:mol) in the bath suggests the formation of an alloy intermediate phase rich in iron. Stripping voltammetric curves indicate the preferential dissolution of iron from iron rich alloy intermediate phase. X-ray diffraction studies further confirm the phase to be b.c.c. Fe–Ni alloy. The extent of corrosion of the Fe–Ni alloy film in the presence of ethylamines is in the following order: Et 3N > Et 2NH > EtNH 2. 相似文献
17.
Iron-carbon composites have been prepared by adding Fe 2O 3 hematite to a petroleum vacuum residue as a carbon precursor. Iron contents and other synthesis parameters were varied to evaluate the evolution of the observed iron phases. XRD patterns and 57Fe Mössbauer spectroscopy was used to monitor the reduction of the initial iron oxide to pyrrhotite (Fe 7S 8) intermediate, austenite (Fe xC) and metallic iron as final reaction product when annealing temperature and time were high. Pyrrhotite has demonstrated to be electrochemically active and beneficial for the capacity retention in lithium test cells. Those samples with the higher pyrrhotite contribution have a good capacity retention achieving values close to 350 mAh/g after 30 cycles. AC measurements evidenced that iron species inhibit the increase of both the charge transfer resistance and the surface film resistance upon cycling. 相似文献
18.
The instability of the premise of direct quantitative contaminant reduction by elemental iron (Fe 0) materials in Fe 0/H 2O systems is pointed out. Basic knowledge of aqueous iron corrosion shows that the Fe 0 surface is not available for decontamination in nature. A comparison of the reactivity of Fe 0 and Zn 0 shows that the effectiveness of Fe 0 materials for environmental remediation is due to the formation of a non-adhesive, porous oxide scale on Fe 0. Contaminants are enmeshed within the scale and possibly reduced by Fe II and H/H 2. An evaluation of current experimental conditions shows that well-mixed batch systems have disturbed the process of scale formation. Therefore, the majority of published works have operatively created conditions for contaminant reduction that are not likely to occur in nature. Since working under such unrealistic conditions has mediated the above-mentioned premise, interactions in Fe 0/H 2O systems yielding contaminant removal should be revisited. 相似文献
19.
The sulphur derivatives of iron rust and a mixed iron oxide from the co-precipitation of Fe II-Fe III chlorides in 6M NaOH have been found to posses high hydrogen evolution in sodium chloride solution. The enhanced performance of these suphides for hydrogen evolution is observed to depend on the sulphide constituents, prepared by the combinations of Fe 1-x), α-Fe 2O 3 and Fe 3O 4 oxide mixtures, and reduced by hydrogen gas. Pyrite, prepared from iron rust-H 2S with optimum sulphide mixture, has the best performance for hydrogen evolution reaction (h.e.r.) of 100 MA/cm 2, -270mV vs scein 3.5% sodium chloride solution at 25°C after ohmic corrections. 相似文献
20.
The denitridation behaviour of binary iron, cobalt and rehnium nitrides under H 2 /Ar has been investigated. The iron nitride was found to lose over 70 % of its as prepared nitrogen content at 400 °C. The cobalt nitride was completely denitrided at 250 °C. Rhenium nitride lost close to 90 % of its nitrogen at 350 °C. In addition, Co-Re 4 prepared by ammonolyis was investigated, whilst only traces of NH 3 were lost from this material under H 2/Ar at 400 °C, with H 2/N 2 it proved to be an active ambient pressure ammonia synthesis catalyst in accordance with previous literature. 相似文献
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