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Density functional theory is used to investigate geometric structures and mechanisms for hydroxylation and epoxidation from propene for four non-heme iron complexes, [Fe(IV)(L(ax))(TMC)(O)](n+), which are the inverted isomers of [Fe(IV)(O)(TMC)(Lax)](n+) (Lax = acetonitrile (AN), monoanionic trifluoroacetate (TF), azide (N3), thiolate (SR)). The Fe(IV)O unit is found to be sterically less hindered in [Fe(IV)(L(ax))(TMC)(O)](n+) than that in [Fe(IV)(O)(TMC)(L(ax))](n+). Becke, three-parameter, Lee-Yang-Parr (B3LYP) calculations show that hydroxylation and epoxidation proceed via a two-state-reactivity on competing triplet and quintet spin surfaces; and the reactions have been invariably mediated by the S = 2 state. The reaction pathways computed reveal that 2-AN is the most reactive in the four [Fe(IV)(L(ax))(TMC)(O)](n+) complexes; along the reaction pathway, the axial ligand moves away from the iron center, and thus, the energy of the LUMO decreases. The anionic axial ligand, which is more electron releasing than neutral AN, shows a strong overlap of iron orbitals. Thus, the anionic ligand does not move away from the iron center. The H-abstraction is affected by the tunneling contribution, the more electron donation power of the axial ligand, the more effect of the tunneling contribution. Adding the tunneling correction, the relative reactivity of the hydroxylation follows the trend: 2-AN > 2-SR ≈ 2-N3 > 2-TF. However, for the epoxidation, the reactivity is in the following order of 2-AN > 2-TF > 2-N3 > 2-SR. Except for 2-AN, 2-X (L(ax) = TF, N3, SR) complexes chemoselectively hydroxylate even in the presence of a C=C double bond.

Spin-polarized density functional theory computations have been carried out to study the stable adsorption configurations of Cun (n = 1-7, 13) on Fe and Fe3C surfaces for understanding the initial stages of copper promotion in catalysis. At low coverage, two-dimensional aggregation is more preferred over dispersion and three-dimensional aggregation on the Fe(110) and Fe(100) surfaces as well as the metallic Fe3C(010) surfaces, while dispersion is more favorable over aggregation on the Fe(111) surface. On the Fe3C(001) and Fe3C(100) surfaces with exposed iron and carbon atoms, the adsorbed Cu atoms prefer dispersion at low coverage, while aggregation along the iron regions at high coverage. On the iron surfaces, the adsorption energies of Cun (n = 2-7) are highest on Fe(111), medium on Fe(100) and lowest on Fe(110). On the Fe3C surfaces, the adsorption energies of Cun (n = 1-3) are highest on Fe3C(100), medium on Fe3C(010) and lowest on Fe3C(001), while, for n = 4-7 and 13, Fe3C(010) has stronger adsorption than Fe3C(100). On the basis of their differences in electronegativity, the adsorbed Cu atoms can oxidize the metallic Fe(110), Fe(100) and Fe3C(010) surfaces and become negatively charged. On the Fe3C(001) and Fe3C(100) surfaces with exposed iron and carbon atoms, the adsorbed Cu atoms interacting with surface carbon atoms are oxidized and positively charged. Unlike the most stable Fe(110) and Fe3C(001) surfaces, where the Fe(110) surface has stronger Cu affinity than the Fe3C(001) surface, which is in agreement with the experimental finding, the less and least stable Fe3C(010) and Fe3C(100) surfaces have stronger Cu affinities than the Fe(110) and Fe(100) surfaces. Since less stable facets are not preferably formed thermodynamically, it is crucial to prepare such surfaces to explore Cu adsorption and promotion, and this provides challenges to surface sciences.

The structures and energies of the electronic ground states of the FeS(0/-), FeS2(0/-), Fe2S2(0/-), Fe3S4(0/-), and Fe4S4(0/-) neutral and anionic clusters have been computed systematically with nine computational methods in combination with seven basis sets. The computed adiabatic electronic affinities (AEA) have been compared with available experimental data. Most reasonable agreements between theory and experiment have been found for both hybrid B3LYP and B3PW91 functionals in conjugation with 6-311+G* and QZVP basis sets. Detailed comparisons between the available experimental and computed AEA data at the B3LYP/6-311+G* level identified the electronic ground state of (5)Δ for FeS, (4)Δ for FeS(-), (5)B2 for FeS2, (6)A1 for FeS2(-), (1)A1 for Fe2S2, (8)A' for Fe2S2(-), (5)A'' for Fe3S4, (6)A'' for Fe3S4(-), (1)A1 for Fe4S4, and (1)A2 for Fe4S4(-). In addition, Fe2S2, Fe3S4, Fe3S4(-), Fe4S4, and Fe4S4(-) are antiferromagnetic at the B3LYP/6-311+G* level. The magnetic properties are discussed on the basis of natural bond orbital analysis., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Spin-polarized density functional theory calculations have been performed to investigate the carbon pathways and hydrogenation mechanism for CH(4) formation on Fe(2)C(011), Fe(5)C(2)(010), Fe(3)C(001), and Fe(4)C(100). We find that the surface C atom occupied sites are more active toward CH(4) formation. In Fischer-Tropsch synthesis (FTS), CO direct dissociation is very difficult on perfect Fe(x)C(y) surfaces, while surface C atom hydrogenation could occur easily. With the formation of vacancy sites by C atoms escaping from the Fe(x)C(y) surface, the CO dissociation barrier decreases largely. As a consequence, the active carburized surface is maintained. Based on the calculated reaction energies and effective barriers, CH(4) formation is more favorable on Fe(5)C(2)(010) and Fe(2)C(011), while Fe(4)C(100) and Fe(3)C(001) are inactive toward CH(4) formation. More importantly, it is revealed that the reaction energy and effective barrier of CH(4) formation have a linear relationship with the charge of the surface C atom and the d-band center of the surface, respectively. On the basis of these correlations, one can predict the reactivity of all active surfaces by analyzing their surface properties and further give guides for catalyst design in FTS.

A simple 1,2-squaraine based chemosensor material (SQ) has been reported to show dual sensing performance for colorimetric detection of Fe3+ and Hg2+ ions. Compared to common instrumental analysis, this method could provide fast and direct detection though colorimetric changes by the naked eye. The sensor has shown excellent selectivity over the other metal ions by tuning different solvent environments. The detection limit for Fe3+ could reach to 0.538 μM, which was lower than that in the environmental agency guideline (U.S. Environmental Protection Agency, U.S. EPA) in drinking water. And for Hg2+ detection, the limit was calculated as 1.689 μM in our case. A 1:1 binding mode between SQ–Fe3+ and SQ–Hg2+ ion were evidenced by Job’s plot measurement and IR analysis. The proposed different binding mechanisms were also supported by Density Function Theory (DFT) calculation. All these findings provide a unique material and a simple, facile, and low cost colorimetric method for dual metal ions analysis and have shown preliminary analytical applications in industrial water sample analysis.

The cytochromes P450 are drug metabolizing enzymes in the body that typically react with substrates through a monoxygenation reaction. During the catalytic cycle two reduction and protonation steps generate a high-valent iron (IV)-oxo heme cation radical species called Compound I. However, with sufficient reduction equivalents present, the catalytic cycle should be able to continue to the reduced species of Compound I, called Compound II, rather than a reaction of Compound I with substrate. In particular, since electron transfer is usually on faster timescales than atom transfer, we considered this process feasible and decided to investigate the reaction computationally. In this work we present a computational study using density functional theory methods on active site model complexes alongside quantum mechanics/molecular mechanics calculations on full enzyme structures of cytochrome P450 enzymes. Specifically, we focus on the relative reactivity of Compound I and II with a model substrate for O–H bond activation. We show that generally the barrier heights for hydrogen atom abstraction are higher in energy for Compound II than Compound I for O–H bond activation. Nevertheless, for the activation of such bonds, Compound II should still be an active oxidant under enzymatic conditions. As such, our computational modelling predicts that under high-reduction environments the cytochromes P450 can react with substrates via Compound II but the rates will be much slower.

Earth’s inner core is predominantly composed of solid iron (Fe) and displays intriguing properties such as strong shear softening and an ultrahigh Poisson’s ratio. Insofar, physical mechanisms to explain these features coherently remain highly debated. Here, we have studied longitudinal and shear wave velocities of hcp-Fe (hexagonal close-packed iron) at relevant pressure–temperature conditions of the inner core using in situ shock experiments and machine learning molecular dynamics (MLMD) simulations. Our results demonstrate that the shear wave velocity of hcp-Fe along the Hugoniot in the premelting condition, defined as T/Tm (Tm: melting temperature of iron) above 0.96, is significantly reduced by ~30%, while Poisson’s ratio jumps to approximately 0.44. MLMD simulations at 230 to 330 GPa indicate that collective motion with fast diffusive atomic migration occurs in premelting hcp-Fe primarily along [100] or [010] crystallographic direction, contributing to its elastic softening and enhanced Poisson’s ratio. Our study reveals that hcp-Fe atoms can diffusively migrate to neighboring positions, forming open-loop and close-loop clusters in the inner core conditions. Hcp-Fe with collective motion at the inner core conditions is thus not an ideal solid previously believed. The premelting hcp-Fe with collective motion behaves like an extremely soft solid with an ultralow shear modulus and an ultrahigh Poisson’s ratio that are consistent with seismic observations of the region. Our findings indicate that premelting hcp-Fe with fast diffusive motion represents the underlying physical mechanism to help explain the unique seismic and geodynamic features of the inner core. [ABSTRACT FROM AUTHOR]

A novel synthetic protocol for the direct oxidation of alkanes, including cyclic and linear ones, to give ketones and alcohols using hydrogen peroxide as terminal oxidant under ambient conditions is presented. The active catalyst for this challenging transformation is conveniently generated by combination of simple Fe salts with N‐methyl bis(picolylamine) (Me‐bpa). Utilizing picolinic acid as additive leads to improved yields of ketones and alcohols (32‐57 %). The reaction can be conveniently scaled up to multi‐g scale. [ABSTRACT FROM AUTHOR]

The combination of Fe(OTf)2 with N‐methyl bis(picolylamine) (Me‐bpa) L7 enables epoxidation of linear olefins including terminal, internal, and cyclic ones, using hydrogen peroxide as terminal oxidant under mild conditions. In the presence of picolinic acid as additive improved yields of epoxides up to 75 % have been achieved. [ABSTRACT FROM AUTHOR]

Spin-polarized density functional theory calculations have been performed to investigate the carbon pathways and hydrogenation mechanism for CH4 formation on Fe2C(011), Fe5C2(010), Fe3C(001), and Fe4C(100). We find that the surface C atom occupied sites are more active toward CH4 formation. In Fischer-Tropsch synthesis (FTS), CO direct dissociation is very difficult on perfect FexCy surfaces, while surface C atom hydrogenation could occur easily. With the formation of vacancy sites by C atoms escaping from the FexCy surface, the CO dissociation barrier decreases largely. As a consequence, the active carburized surface is maintained. Based on the calculated reaction energies and effective barriers, CH4 formation is more favorable on Fe5C2(010) and Fe2C(011), while Fe4C(100) and Fe3C(001) are inactive toward CH4 formation. More importantly, it is revealed that the reaction energy and effective barrier of CH4 formation have a linear relationship with the charge of the surface C atom and the d-band center of the surface, respectively. On the basis of these correlations, one can predict the reactivity of all active surfaces by analyzing their surface properties and further give guides for catalyst design in FTS. [ABSTRACT FROM AUTHOR]

A novel and efficient synthesis of pyrido[1 ,2-a]benzimidazoles through direct intramolecular aromatic C-H amination of N-aryl-2-aminopyridines has been developed. The reaction, cocatalyzed by Cu(OAc)2 and Fe(NO3)3∙9H2O, is carried out in DMF under a dioxygen atmosphere. Diversified pyrido[1 2- a]benzimidazoles containing various substitution patterns are obtained in moderate to excellent yields by using this procedure. The results of mechanistic studies suggest that a Cu(III)-catalyzed electrophilic aromatic substitution (SEAr) pathway is operating in this process. The unique role of iron(III) is believed to lie in its ability to facilitate formation of the more electrophilic Cu(III) species. In the absence of iron(III), a much less efficient and reversible Cu(II)-mediated SEAr process takes place. [ABSTRACT FROM AUTHOR]

In this study, we report the growth of metallic tungsten nanowires induced by alloy catalysts (Fe-Ni) at a temperature of 850 °C. The synthesized tungsten nanowires have bottom diameters of 100 to 400 nm and tip diameters of < 80 nm, and show a well-defined single-crystalline structure. The formation of the (Fe, Ni)-catalyzed W nanowires should be controlled by the vapor-solid-solid mechanism, rather than the traditional vapor-liquid-solid mechanism, because the growth temperature is significantly below the lowest eutectic temperature (1455 °C) of the Fe-Ni-W ternary system. Our study demonstrates the feasibility of synthesizing metallic nanowires via metal-catalyzed methods, which may be extended to the synthesis of some other metallic nanowires. [ABSTRACT FROM AUTHOR]

Abstract: Spin-polarized density functional theory calculations have been performed to investigate carbon deposition and carbide formation on Fe(100) and Fe(110) at different carbon coverage. On Fe(100) with increasing carbon coverage, the most stable carbon adsorption configuration changes from surface carbon adsorption to surface carbon diffusion into subsurface, and surface carbon clustering is not favored thermodynamically. However, surface carbon clustering is more favored kinetically than carbon diffusion; and carbon diffusion into subsurface and surface carbon clustering become competitive. On Fe(110) with increasing surface carbon coverage, the most stable adsorption configuration changes from surface carbon adsorption to surface carbon diffusion into subsurface, and this process is favored both kinetically and thermodynamically, and surface carbon clustering is neither favored nor competitive. Surface carbon deposition might form on Fe(100), while carbide formation might be found on Fe(110). [Copyright &y& Elsevier]

[Display omitted] • Real space evidence of p4g(2 × 2) Fe 2 C and Co 2 C surface carbides. • Tip-sample distance dependent STM imaging of Fe 2 C. • Fe 2 X (X = B, C, N, O) with increasing electrons the reconstruction becomes less favourable. Thin FCC (1 0 0) iron and cobalt carbide films were prepared on Cu(1 0 0) to study the connection between their structure, electronic properties and stability. We present the first detailed, real space experimental confirmation of the C-induced clock reconstruction on the FCC(1 0 0) surfaces of iron and cobalt. Both Fe and Co surface carbides show p4g (2 × 2) surface reconstruction with tetracoordinated square planar carbon and pure FCC (1 0 0) metal layers underneath. Combining tip-sample distance dependent STM imaging with theoretical calculations we present different imaging modes of Fe 2 C. Using a combination of angle-resolved x-ray photoelectron spectroscopy (AR-XPS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and theoretical calculations we provide detailed electronic and structural models for Fe 2 C and Co 2 C p4g (2 × 2) surface carbides and other 2D Fe 2 X interstitial compound systems. In various Fe 2 X (X = B, C, N, O) surface compounds moving to the right in the periodic table with increasing electrons the reconstruction becomes less favorable, while iron carbide shows the highest stability. [ABSTRACT FROM AUTHOR]

Spin-polarized density functional theory computations have been performed to investigate n CO + m H 2 co-adsorption and mutual interaction on the Fe(1 1 0) and Fe(1 1 1) surfaces. It is found that CO pre-coverage affects hydrogen adsorption strongly, while H pre-coverage hardly affects CO adsorption. It is possible to have CO + H 2 co-adsorption on Fe(1 1 0), while very strong preference of CO pre-coverage on Fe(1 1 1) has been found. On Fe(1 1 1), it is also found that each CO molecule blocks on average 2H adsorption sites at all CO pre-coverage. All these findings are consistent with available experimental results. Compared with CO/H 2 ratios in gas phase, CO/H 2 surface ratios are very different and much more sensitive to temperature than pressure. Our results provide the basis for exploring the mechanisms of iron-catalyzed conversion of synthesis gas. [ABSTRACT FROM AUTHOR]

A series of Fe-substituted ZSM-22 zeolites were synthesized via an organic structure-directing agent-free route with a small amount of precursor suspension. Characterizations by XRD, SEM, TEM, N 2 adsorption, UV–vis, FT-IR, and XPS confirm the high crystallinity, uniform morphology, and smaller crystal size of the as-synthesized zeolites and the presence of Fe 3+ in the framework of the zeolites. The acidity, especially the Brønsted acidity, decreases significantly due to the low acidity of Si–OH–Fe bridge hydroxyls compared with that of Si–OH–Al. Moreover, in the Fe-containing catalysts, Pt can easily be reduced and its dispersion slightly increases, as confirmed by H 2 TPR and CO chemisorption. As a result, the Pt/[Al,Fe]-ZSM-22 catalysts exhibit superior selectivity in n -dodecane isomerization compared with the Pt/ZSM-22 catalyst. The higher monobranched isomer selectivity of the catalyst using Fe-substituted ZSM-22 zeolites may be due to more balanced bifunctionality between acid sites and metal sites and decreased crystallite size of the Fe-containing zeolites, which improves the diffusion of intermediates and prevents the products from further cracking. It is also observed that more dibranched isomers were formed with more Fe replacement even at higher temperatures due to reduced strong acidity by Fe replacement, which significantly suppressed the cracking and improved the selectivity to deeper isomerization. [ABSTRACT FROM AUTHOR]

Abstract: Spin-polarized density functional theory has been used to characterize hydrogen adsorption on the Fe3C(100), Fe3C(001) and Fe3C(010) surfaces. It is found that hydrogen adsorbs dissociatively on the three surfaces. On the Fe3C(100) surface, the most stable surface species is CH at 1/3 or 2/3 monolayer, and CH4 at 1 monolayer; in contrast on the Fe3C(001) surface the most stable surface intermediates are 3-fold H at 1/3 monolayer, and CH at 2/3 monolayer, and CH4 at 1 monolayer. On the metallic Fe3C(010) surface, hydrogen adsorbs at 2-fold or 3-fold sites. The computed energetic order of hydrogen adsorption is Fe3C(100)>Fe3C(010)>Fe3C(001), and this differs from that of CO adsorption (Fe3C(010)>Fe3C(100)>Fe3C(001)). [Copyright &y& Elsevier]

Abstract: The effect of co-feeding CO2 on the catalytic properties of an Fe–Mn catalyst during Fischer–Tropsch synthesis (FTS) was investigated in a spinning basket reactor by varying added CO2 partial pressure in the feed gas. It was found that co-feeding CO2 to syngas did not decrease the activity of the catalyst, on the contrary, a dramatic increase of the activity and an increase of methane selectivity were observed over the catalyst after removal of CO2 from the feed gas. The addition of CO2 led to an increase in olefin/paraffin ratios of low carbon hydrocarbons and a slight decrease in C19 + selectivity. It also slightly decreased CO2 formation rate on the catalyst by increasing the rate of reverse step of the water–gas shift (WGS) reaction and pushing the reaction towards equilibrium, and did not remarkably influence the hydrocarbon formation rate. However, the co-feeding CO2 can significantly increase the water formation rate and the overall oxygenate formation rate under these reaction conditions. [Copyright &y& Elsevier]