Nitrogen reduction reaction on small iron clusters supported by N-doped graphene:A theoretical study of the atomically precise active-site mechanism

Nonprecious metal catalysts are known of significance for electrochemical N2 reduction reaction(NRR)of which the mechanism has been illustrated by ongoing investigations of single atom catalysis.However,it remains challenging to fully understand the size-dependent synergistic effect of active sites inherited in substantial nanocatalysts.In this work,four types of small iron clusters Fen(n=1–4)supported on nitrogen-doped graphene sheets are constructed to figure out the size dependence and synergistic effect of active sites for NRR catalytic activities.It is revealed that Fe3 and Fe4 clusters on N4G supports exhibit higher NRR activity than single-iron atom and iron dimer clusters,showing lowered limiting potential and restricted hydrogen evolution reaction(HER)which is a competitive reaction channel.In particular,the Fe4-N4G displays outstanding NRR performance for“side-on”adsorption of N2 with a small limiting potential(−0.45 V).Besides the specific structure and strong interface interaction within the Fe4-N4G itself,the high NRR activity is associated with the unique bonding/antibonding orbital interactions of N-N and N-Fe for the adsorptive N2 and NNH intermediates,as well as relatively large charge transfer between N2 and the cluster Fe4-N4G.

The Major Ore Clusters of Super-Large Iron Deposits in the World, Present Situation of Iron Resources in China, and Prospect

The metamorphosed sedimentary type of iron deposits（BIF） is the most important type of iron deposits in the world, and super-large iron ore clusters of this type include the Quadrilatero Ferrifero district and Carajas in Brazil, Hamersley in Australia, Kursk in Russia, Central Province of India and Anshan-Benxi in China. Subordinated types of iron deposits are magmatic, volcanic-hosted and sedimentary ones. This paper briefly introduces the geological characteristics of major super-large iron ore clusters in the world. The proven reserves of iron ores in China are relatively abundant, but they are mainly low-grade ores. Moreover, a considerate part of iron ores are difficult to utilize for their difficult ore dressing, deep burial or other reasons. Iron ore deposits are relatively concentrated in 11 metallogenic provinces（belts）, such as the Anshan-Benxi, eastern Hebei, Xichang-Central Yunnan Province and middle-lower reaches of Yangtze River. The main minerogenetic epoches vary widely from the Archean to Quaternary, and are mainly the Late Archean to Middle Proterozoic, Variscan, and Yanshanian periods. The main 7 genetic types of iron deposits in China are metamorphosed sedimentary type（BIF）, magmatic type, volcanic-hosted type, skarn type, hydrothermal type, sedimentary type and weathered leaching type. The iron-rich ores occur predominantly in the skarn and marine volcanic-hosted iron deposits, locally in the metamorphosed sedimentary type（BIF） as hydrothermal reformation products. The theory of minerogenetic series of mineral deposits and minerogenic models has applied in investigation and prospecting of iron ore deposits. A combination of deep analyses of aeromagnetic anomalies and geomagnetic anomalies, with gravity anomalies are an effective method to seeking large and deep-buried iron deposits. China has a relatively great oresearching potential of iron ores, especially for metamorphosed sedimentary, skarn, and marine volcanic-hosted iron deposits. For the lower guarantee degree of iron and steel industry, China should give a trading and open the foreign mining markets.

Role of Ga-doping in iron-gallium alloy clusters

The structural and magnetic properties of Fen-mCam （n = 3 - 6, m = 0 - 2; n = 13, m = 0 - 3） alloy clusters have been studied using density functional theory. The substitutional doping is favourable for small clusters with up to six atoms at low Ga concentration and substitutional Ga atoms in 13-atom clusters prefer surface sites. The Ca-doping generally could reduce the energetic stability but enhance the electronic stability of Fe clusters, along with a decrease of the local magnetic moments of Fe atoms around Ca dopants. These findings provide a microscopic insight into Fe-Ga alloys which are well：known magnetostriction materials.

Preparation of Nano-Sized γ-Al_2O_3 Supported Iron Catalyst for Fischer-Tropsch Synthesis by Solvated Metal Atom Impregnation Methods

Two types of small iron clusters supported on γ-Al2O3-RT（dehydroxylated at room temperature） and γ-Al2O3-800 （dehydroxylated at 800 ℃） were prepared by solvated metal atom impregnation （SMAI） techniques. The iron atom precursor complex, bis（toluene）iron（0） formed in the metal atom reactor, was impregnated into γ-Al2O3 having different concentrations of surface hydroxyl groups to study the effect of surface hydroxylation on the crucial stage of iron cluster formation. Catalysts prepared in this way were characterized by TEM, Mǒssbauer, and chemisorption measurements, and the results show that higher concentration of surface hydroxyl groups of γ-Al2O3-RT favors the formation of more positively charged supported iron cluster Fen/γ-Al2O3-RT, and the lower concentration of surface hydroxyl groups of γ-Al2O3-800 favors the formation of basically neutral supported iron cluster Fen/γ-Al2O3-800. The measured results also indicate that the higher concentration of surface hydroxyl groups causes the rapid decomposition of precursor complex, bis（toluene）iron（0）, and favors the formation of relatively large iron cluster. Consequently, these two types of catalysts show different catalytic properties in Fischer-Tropsch reaction. The catalytic pattern of Fen/γ-Al2O3-RT in F-T reaction is similar to that of the unreduced γ-Fe2O3 and that of Fen/γ-Al2O3-800 is similar to that of the reduced α-Fe2O3.

Preparation of Highly Dispersed Supported Metal Catalysts via Solvated Metal Atom Impregnation ( V) --The Effects of Hydroxyl Group on the Surface Concentrations of SiO2 on the Properties of Supported Fe Clusters

Two kinds of small iron clusters supported on SiO2-200 (dehydroxylated at 200℃ and SiO2-600 (de-hydroxylated at 600℃) were prepared by Solvated Metal Atom Impregnation (SMAI) techniques. The iron atom precursor complex, bis (toluene) iron(0) formed in the metal atom reactor, was impregnated into SiO2 having different concentrations of surface hydroxyl groups to study the effect of surface hydroxylation on the crucial stage of iron cluster formation. Catalysts prepared in this way were characterized by THM, Mosbauer and chemisorption measurements, and the resules show that higher concentration of surface hydroxyl groups of SiO2-200 favours the formation of more positively charged support iron cluster Fen/SiO2-200 and the lower concentration of surface hydroxyl groups of SiO2-600 favours the formation of basically neutral supported iron cluster Fe2/SiO2-600. The measured results also indicate that the higher concentration of surface hydroxyl groups causes the precursor complex,bis(toluene) fron(0), to decompose more rapidly, and favours the formation of relatively large iron cluster. As a consequence, these two kinds of catalysts show different catalytic properties in Fischer-Tropsch reaction. The catalytic pattern of Fe/SiO2-200 in F-T reaction is similar to that of the unreduced a-Fe2O2, while Fe2/SiO2 -600 is similar to that of reduced α-Fe2O2.

Expansion Reaction of μ-FcCCHCo_2(CO)_6 with Benzylideneacetonetricarbonyliron, and Molecular Structure of μ_3-FcCHCFeCo_2(CO)_9

The vinylidene-bridged cluster μ_3-FcCHCFeCo_2(CO)_9 2 was prepared by the expansionreaction of ferrocenyl-acetylene dicobalt complex μ-FcCCHCo_2(CO)_6 1. Benzylideneacetone-tricarbonyliron [(BDA)Fe(CO)_3] was used as the source of Fe(CO)_3. The molecular structure of thecluster 2 was detendned by x-ray structural analysis.

In situ Preparation of Tri-Fe(Ⅲ) and Bi-Cu(Ⅱ) Clusters from Benzoyl Peroxide Reacting with Metal Powders

Three crystal architectures, including one organic compound of benzoyl peroxide（Ⅰ） and two clusters of tri-iron（Ⅲ） and bi-cupper（Ⅱ） with benzoic ligands（2 and 3）, were self-assembled by an in situ redox way of benzoyl peroxide oxidants reacting with Mo, Fe and Cu powders, respectively. X-ray crystallographic results show that both the asymmetry tri-iron（Ⅲ） cluster and the benzoylperoxide crystal architecture（2 and 1） with complicated 3D networks were constructed by intermolecular hydrogen-bonding interactions. Contrarily, the symmetrical bi-copper（Ⅱ） cluster crystal architecture（3）, only with π-π stacking between paralleled phenyl groups and without any intermolecular hydrogen-bonding interactions, only presented an 1D zigzag chain along the a-axis.

Study on the Magnetic Properties of MoFe_3S_4 Single Cubane-like Clusters Containing R_2dtc Ligands

Both cubane-like clusters MoFe_3S_4 (Me_2dtc)_5·2CH_2Cl_2 (1) and MoFe_3S_4(C_4H_8dtc)_5·2EtCN (2) were used to study the temperature-dependent behavior of the molar magnetic susceptibility. A spin coupling model was suggested and the fitting results agree with the model and structural and spectroscopic parameters.

GAG-containing nucleotides as mediators of DNA-silver clusters and iron-DNA interplay

New types of fluorescence DNA-based silver nanoclusters（DNAn-Ag NCs, n = 1, 2, 3c, 4c, 5c） were synthesized by C3T-rich nucleotides as templates. It is found that the assembly of DNAn-Ag NCs with nucleotides containing GAG sequences produce silver clusters with an enhanced red emission. Results indicate that GAG is the good enhancer of DNAn-Ag NCs constructed by C3T-rich nucleotides. The fluorescence titration reveals that enhanced red emission is sensitive to Fe（Ⅲ/Ⅱ） ions with the formation of non-emission nanoclusters. Thus, the GAG-containing nucleotide can be an enhancer for the emission of silver clusters with C3T-rich nucleotide and a mediator of the iron-cluster interplay.

Development of slope mass rating system using K-means and fuzzy c-means clustering algorithms

Classification systems such as Slope Mass Rating(SMR) are currently being used to undertake slope stability analysis. In SMR classification system, data is allocated to certain classes based on linguistic and experience-based criteria. In order to eliminate linguistic criteria resulted from experience-based judgments and account for uncertainties in determining class boundaries developed by SMR system,the system classification results were corrected using two clustering algorithms, namely K-means and fuzzy c-means(FCM), for the ratings obtained via continuous and discrete functions. By applying clustering algorithms in SMR classification system, no in-advance experience-based judgment was made on the number of extracted classes in this system, and it was only after all steps of the clustering algorithms were accomplished that new classification scheme was proposed for SMR system under different failure modes based on the ratings obtained via continuous and discrete functions. The results of this study showed that, engineers can achieve more reliable and objective evaluations over slope stability by using SMR system based on the ratings calculated via continuous and discrete functions.

Crystal Structure of Complex(Et4N)[VFe3S4Cl3(CH3CN)3]

Complex (Et4N) [VFe3S4Cl3 (CH3CN)(3)] (1) has been obtained from (NH4)(3) VS4/FeCl2/NaHS/Et-4 NCl reaction system in CH3CN solvent and structurally characterized by X-ray diffraction analysis. It crystallizes in orthorhombic space group Pnma (No. 62) with a = 8.851(2), b =16.447(3), c = 19.448(4) Angstrom, V = 2865.6(10) Angstrom (3), Z = 4, M-r = 706.49, D-c =1.638g/cm(3), F(000)=1428, mu (MoK alpha)=2.385 cm(-1) and T = 293(2)K. With use of 1467 observed reflections (I >2 sigma (I)) the structure was refined to R = 0.0874 and wR = 0.2065. Complex 1 contains a VFe3S4 cuboidal core with average V - Fe distance of 2.759(4) Angstrom, which is a little longer than Fe - Fe of 2.716(3) Angstrom,. Around the core, each Fe atom is coordinated by one Cl atom and V atom by three N atoms of CH3CN ligands.

Dipolar Interaction and Magnetic Ordering Ground State in Mn12 Molecular Magnet

Here a direct calculation of the dipolar interaction in a single crystal Mn12, with all of Mn ions summed, shows that a transition between ferromagnetic and antiferromagnetic ground states takes place where the dimension along the α（b） axis versus the dimension along the c axis reaches a certain critical value. It is shown that the w ~ ~ ground state is dependent upon the shape of the specimen. The reason of the shape dependence of ordering is that dipolar interaction is of long-range nature and the sign of dipolar interaction is dependent on the direction.

Synthesis and Structural Characterization of [(h^5-C_5Me_5)_2Mo_2Fe_2S_4Br_2]

The reactions of [(h5-C5Me5)Mo(StBu)3] with equimolar FeBr3 in THF afforded a neutral tetranuclear cluster [(h5-C5Me5)2Mo2Fe2S4Br2] 1. The structure of 1 was determined by single-crystal X-ray diffraction analysis. 1 crystallizes in the monoclinic space group P21/n (No. 14) with a = 9.691(2), b = 15.204(2), c = 18.850(2) ? b = 96.44(1), V = 2759.8(7) ?, Z = 4, Mr = 862.08, Dc = 2.075 g/cm3, F(000) = 1680, m (MoKa) = 51.31 cm-1 and T = 296.2 K. With the use of 3667 observed reflections (I > 3.0s(I)), the structure was refined to R = 0.041 and Rw = 0.051. 1 is composed of a distorted Mo2Fe2S4 cubane core with two Br atoms and two h5-C5Me5 groups coordinating at the Fe and Mo sites, respectively. The lengths of MoMo and FeFe bonds are 2.826 and 2.773 ? respectively the mean length of MoFe bond is 2.751 ?

Synthesis and Crystal Structure of Novel Fe_3 Cluster Compound

The title compound Fe_3 (CO)_8(CN)S_2 was synthesized by the reaction of C_6H_5NCS cleaving fragments with Fe_3 (CO)_(12) at room temperature. Crystal data: C_9Fe_3NO_8S_2, Mr=481. 76, triclinic , space group P1,a= 9. 436 (3), b=10. 210(2), c=9. 14l(3) A, a =90. 63(2), β=117. 55(3), γ=96. 66(2)°, V=773. 5(4) A￣3 , Z=2, D_c= 2. 068 g/cm￣3, μ(MoKa)=30. 78 cm￣(-1), F(000)=470 .T= 293K , final R=0. 030 and R_w=0. 041 for 2314 observed reflections with I>3. 00 σ(I).The monosubstituted ligand(CN)in Fe_3 (CO)_8 (CN)S_2 is linked to basal Fe (3) atom of the distorted tetragonal pyramid Fe_3S_2 framework.

Synthesis and characterization of tris(η~5-cyclopentadienyl-μ-carbonyliron)-μ_3-nitrosyl cluster:X-ray structure of[(η~5-C_5H_5)(μ-CO)Fe]_3(μ3-NO).C_4H_8O

Tris)(η 5-cyclopentadienyl-μ-carbonyl-iron)-μ3-nitrosyl cluster was obtained from the reaction of cyclopentadienyl dicarbonyliron dimer with nitrogen monoxide in xylene. The cluster was characterized by elemental analyses, IR, MS and 1H NMR. The crystal structure of [(η5-C5H5)(μ-CO)Fe]3(μ3-NO).C4H8O was determined by X-ray diffraction analysis. It crystallizes in the orthorhombic space group Pnma, a=9.053(2), 6=10.545(2), c=22.525(4) A, V=2150.3(7) A3, Z=4,Dc=1.68 g.cm-3; structure solution and refinement based on 1141 reflections with I > 3.0 (I) (MoKa, A=0.71073 A) converged at R=0.0540. The infrared absorption band at 1325 cm-1 of the μ3-NO in the cluster, which is red shifted, shows that μ3-NO is activated.