Electron availability and the surface fermi level local density of states: an alternative way to see catalytic activity of metals

Tong, YuYe J.; Renouprez, A.J.; Martin, G.; Klink, J. J. van der

doi:10.1016/s0167-2991(96)80301-6

Cited by 17 publications

(9 citation statements)

References 36 publications

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“…The electron near the Fermi lever showed the strongest activity; therefore the density of states (DOS) of electrons near the Fermi energy can be observed to judge the reactivity of surface atoms in chemical adsorption [34,35]. The DOSes of electrons in these two minerals surface were calculated, and the results are presented in Figures 6 and 7, respectively.…”

Section: Electronic Structure and Properties Of Mineral Surfacementioning

confidence: 99%

Surface Properties and Floatability Comparison of Aegirite and Specularite by Density Functional Theory Study and Experiment

Gao

et al. 2019

Minerals

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Understanding the differences in surface properties between aegirite and specularite is of great significance to study their separation. In this work, the surface properties of aegirite and specularite, as well as their relationships to floatability, have been explored by first principle calculation, flotation, and Zeta potential measurement. The surface relaxation indicated that the specularite (001) surface appeared to show more surface reconstruction. The unsatisfied bond properties, Mulliken bond population, and surface charge showed that the floatability of specularite was superior to that of aegirite. The flotation results showed that the hydrophobicity of specularite was higher than that of aegirite with dodecylamine (DDA) as the collector. It is infeasible to separate specularite from aegirite by flotation using starch as the depressant, and research of effective reagents with high affinity to the element Si is the subclinical breakthrough point of specularite/aegirite separation.Minerals 2019, 9, 782 2 of 15 flotation with amines. They also found that starch was not a selective depressant for magnetite in the process of the reverse cationic flotation of iron ores when iron-containing silicates as amphiboles are present in the flotation system [8]. Carboxymethyl cellulose, an effective depressant for iron oxide, was also found to be a depressant for chlorite [14].The novel high-efficiency depressants or collectors are considered to be an effective method to solve the unsatisfactory separation problems [15,16]. These depressants and collectors are targeted for making a sufficient hydrophilic and hydrophobic state of the mineral and gangue surface, respectively. Therefore, they are profoundly inseparable from understanding the surface properties of the minerals in the novel depressant or collector molecule design and their adsorption mechanism on the mineral surface.In recent years, with the rapid developments of theoretical and computational chemistry, a density functional theory (DFT) calculation can be adopted to visually investigate the surface properties and floatability of minerals and to predict possible novel reagents [4,17]. The wettability of the mineral surface and its regulation have always been the core issues of the flotation process [18][19][20]. Thus, further research of the nature of the cleavage surface, especially of the main cleavage surface, is of great significance for investigating the floatability of the minerals. For example, Han et al. [21] calculated the surface properties of the hemimorphite (110) surface and the simthsointe (101) surface by the first-principle calculation method to investigate their relationships to the mineral floatability, which implied that hemimorphite (110) surface is more readily wetted by water, while the O atoms on hemimorphite (110) surface are more impeding of collector molecules. He et al. [22] calculated the properties of spodumene and revealed that the O atoms in spodumene are the most active, while the Li atoms are inactive, so an activator is nece...

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Section: Electronic Structure and Properties Of Mineral Surfacementioning

confidence: 99%

Surface Properties and Floatability Comparison of Aegirite and Specularite by Density Functional Theory Study and Experiment

Gao

et al. 2019

Minerals

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“…The weak-overlap covalent interaction that is characteristic of both types of bonds suggests that inclusion of redox-active ligands on cluster compounds will approximate the distributed electronic structures of higher nuclearity cluster complexes. These unique bonding scenarios can yield compact valence manifolds that model the high state densities of catalytically active metallic surfaces . The presence of redox-active ligands further raises questions about the interplay between M–M bonding and the presence of electron density on the redox-active motif.…”

Section: Introductionmentioning

confidence: 99%

“…These unique bonding scenarios can yield compact valence manifolds that model the high state densities of catalytically active metallic surfaces. 33 The presence of redoxactive ligands further raises questions about the interplay between M−M bonding and the presence of electron density on the redox-active motif. The admixture of redox-active fragment orbitals into M−M bonded cluster cores may be envisioned to impact the extent of ligand-based reduction, the degree of M−M bonding, and the physical oxidation states of the metal centers (Figure 2).…”

Section: ■ Introductionmentioning

confidence: 99%

Interdependent Metal–Metal Bonding and Ligand Redox-Activity in a Series of Dinuclear Macrocyclic Complexes of Iron, Cobalt, and Nickel

et al. 2019

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This report describes an isostructural series of dinuclear iron, cobalt, and nickel complexes bound by a redox-active macrocyclic ligand. The series spans five redox levels (34–38 e–/cluster core), allowing for a detailed investigation into both the degree of metal–metal interaction and the extent of ligand-based redox-activity. Magnetometry, electrochemistry, UV–vis–NIR absorption spectroscopy, and crystallography were used in conjunction with DFT computational analyses to extract the electronic structures of the six homodinuclear complexes. The isoelectronic, 34 e– species [(3PDI2)Fe2(PMe3)2(μ-Cl)](OTf) and [(3PDI2)Co2(PMe3)2(μ-Cl)](OTf)3 exhibit metal–metal single bonds, with varying amounts of electron density delocalization into the ligand as a function of the effective nuclear charge of the metal ions. One- and two-electron reductions of [(3PDI2)Co2(PMe3)2(μ-Cl)](OTf)3 lead to isolable products, which show successive increases in both the Co–Co distances and the extent of reduction of the ligand manifold. This trend results from reduction of a Co–Co σ* orbital, which was found to be heavily mixed with the redox-active manifold of the 3PDI2 ligand. A similar trend was observed in the 37 and 38 e– dinickel complexes [(3PDI2)Ni2(PMe3)2(μ-Cl)](OTf)2 and [(3PDI2)Ni2(PMe3)2(μ-Cl)](OTf); however, their higher electron counts lead to high-spin ground states that result from occupation of a high-lying δ/δ* manifold with significant Ni–NPDI σ* character. This change in ground state configuration reforms a M–M bonding interaction in the 37 e– complex, but formation of the 38 e– species again disrupts the M–M bond alongside the transfer of electron density to the ligand.

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“…This agrees with the results from UPS, which show that the two Fe complexes differ in the Fe-related contributions to the DOS around the Fermi energy. Considering that the DOS of the d-electrons around the Fermi energy is known to correlate with the chemical reactivity and the catalytic activity of a surface, , it is expected that the observed differences in the electronic structure also lead to different chemical properties of the corresponding monolayers.…”

Section: Results and Discussionmentioning

confidence: 99%

On-Surface Synthesis and Characterization of an Iron Corrole

et al. 2018

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To explore the possibility of tuning the oxidation state of a coordinated metal ion in an adsorbed tetrapyrrole complex by a minor modification of the ligand structure, multilayers and monolayers of 3H-hexaethyl-dimethyl-corrole (3H-HEDMC) on Ag(111) were in situ metalated under ultrahigh vacuum (UHV) conditions and subsequently analyzed with spectroscopic and microscopic methods. The metalation reaction leads to the formation of Fe(III)-hexaethyl-dimethylcorrole (Fe-HEDMC). The results were compared with those for Fe-octaethyl-porphyrin (Fe-OEP), in which the Fe metal center has a formal Fe(+II) character. The analysis of the nearly unperturbed iron-corrole in the multilayer regime with X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy shows that the electronic structure of the corrole-coordinated iron is consistent with an Fe(+III) state in Fe-HEDMC. In the monolayers, the Fe centers in Fe-HEDMC and Fe-OEP interact similarly with the Ag(111) surface, as indicated by contributions to the Fe 2p signals at a typical Fe(0) position. Nevertheless, a closer investigation of the Fe-HEDMC and Fe-OEP monolayers with NEXAFS, UV photoelectron spectroscopy (UPS), and scanning tunneling microscopy (STM) reveal significant differences between electronic states of the Fe centers, depending on the type of ligand. Apparently, the interfacial interactions between the coordinated metal centers and the surface modify the electronic state of Fe but do not fully equalize the differences induced by the corrole and porphyrin ligand structures. Thus, the experiments show that it is not only possible to perform a direct in situ metalation of corroles with iron atoms under UHV conditions but also that the differences in the electronic structures between Fe-corroles and Fe-porphyrins persist even in the presence of interfacial interactions with Ag(111). Especially, the differences in the Fe-related density of states around the Fermi energy are expected to result in different chemical reactivities and potential catalytic activities of the two supported Fe complexes.

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Electron availability and the surface fermi level local density of states: an alternative way to see catalytic activity of metals

Cited by 17 publications

References 36 publications

Surface Properties and Floatability Comparison of Aegirite and Specularite by Density Functional Theory Study and Experiment

Surface Properties and Floatability Comparison of Aegirite and Specularite by Density Functional Theory Study and Experiment

Interdependent Metal–Metal Bonding and Ligand Redox-Activity in a Series of Dinuclear Macrocyclic Complexes of Iron, Cobalt, and Nickel

On-Surface Synthesis and Characterization of an Iron Corrole

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