High Coordination Sites Research Articles

Atomically dispersed Fe-N5 sites with optimized electronic structure for sustainable wastewater purification via efficient Fenton-like catalysis

Herein, a single-atom catalyst (SAC) featuring Fe-N5 sites (FeNC) with optimized electronic structures was constructed and applied to activate peroxymonosulfate (PMS) for wastewater purification. The high-coordinated Fe-N5 sites was obtained by creating a high-nitrogen gas environment around fully exposed Fe atomic sites on chitosan surface during pyrolysis. The FeNC/PMS system demonstrated excellent decontamination capability, superior anti-pH interference ability, while also exceptional durability in a continuous-flow catalytic filtration reactor. Experiments and density functional theory calculations unveiled that Fe-N5 site was the active center. Meaningfully, neighboring carbonyl groups narrowed the gap between d-band center of Fe 3d and Fermi level, which increased the adsorption energy of PMS on Fe-N5 sites, thus lowering the energy barrier for singlet oxygen generation. This study brings a vivid electronic structure optimization strategy for enhancing the catalytic activity of Fe SAC as well as guiding the selection of desirable catalysts for wastewater purification by Fenton-like chemistry.

Regulation of oriented NO photooxidation to circumvent NO2 with high-coordinated M–N5 (M = Fe, Co, Mn, Ti) sites and far–carbon defects

The targeted oxidization of trace NO to NO3- instead of toxic NO2via photocatalytic process represents one of the promising protocols for assuring environmental benefits. A novel type of graphite carbon nitride (CN) photocatalysts with high coordination sites (M–N5; M = Fe, Co, Mn, Ti) and far–carbon defects were manufactured by reconstructing the low coordination structure (M–N4). The mingled characterizations and theoretical calculations demonstrated that the reconstructed sites could improve the charge and energy transfer process of the exciton to precisely regulate the activation process of O2, while inhibiting the activation of adsorbed H2O. Superior orientation to form superoxide radical and singlet oxygen, rather than hydroxyl radical, showed excellent NO removal rates (68.6%) and superior NO3- selectivity (about 100%) under visible–light irradiation. This work proposes a unique mechanism via tailored construction of highly coordinated structures for selective NO oxidation to achieve the goal of atmospheric purification.

High-coordinated Fe-N5 sites effectively promoted peroxymonosulfate activation for degradation of 4-chlorophenol

M-Nx single-atom catalysts (SACs) with a higher coordination number (x>4) are effective catalysts for eliminating organic pollutants, while the origin of SACs with high activity still remains elusive. In this...

A unimolecular artificial cation channel based on cascaded hydrated acid groups.

A cation channel possessing cascaded hydrated acid groups has been successfully constructed using pillar[5]arene integrated with dual cyclodextrins. As a proof-of-concept, the secondary side of cyclodextrin substituted by 24 -CO2H groups presents high coordination sites, which helps hydrated cations to quickly dehydrate and accelerates efficient cation transport (Rb+ > Cs+ > K+ > Na+ > Li+). Notably, benefitted by the protonation and deprotonation of -CO2H groups, ion permeation activity of the channel molecules under acidic condition (pH = 6.0) is 2.8 times higher than that under alkaline conditions (pH = 8.0), exhibiting pH-modulated property and promising potential in building intelligent artificial ion channels with customized features.

Remarkable water-mediated proton conductivity of two porous zirconium(IV)/hafnium(IV) metal-organic frameworks bearing porphyrinlcarboxylate ligands

Obtaining crystalline materials with high structural stability as well as super proton conductivity is a challenging task in the field of energy and material chemistry. Therefore, two highly stable metal-organic frameworks (MOFs) with macro-ring structures and carboxylate groups, Zr-TCPP (1) and Hf-TCPP (2) assembled from low-toxicity as well as highly coordination-capable Zr(IV)/Hf(IV) cations and the multifunctional linkage, meso-tetra(4-carboxyphenyl)porphine (TCPP) have attracted our strong interest. Note that TCPP as a large-size rigid ligand with high symmetry and multiple coordination sites contributes to the formation of the two stable MOFs. Moreover, the pores with large sizes in the two MOFs favor the entry of more guest water molecules and thus result in high H2O-assisted proton conductivity. First, their distinguished structural stabilities covering water, thermal and chemical stabilities were verified by various determination approaches. Second, the dependence of the proton conductivity of the two MOFs on temperature and relative humidity (RH) is explored in depth. Impressively, MOFs 1 and 2 demonstrated the optimal proton conductivities of 4.5 × 10−4 and 0.78 × 10−3 S·cm−1 at 100 °C/98 % RH, respectively. Logically, based on the structural information, gas adsorption/desorption features, and activation energy values, their proton conduction mechanism was deduced and highlighted.

Design principles for sodium superionic conductors

Motivated by the high-performance solid-state lithium batteries enabled by lithium superionic conductors, sodium superionic conductor materials have great potential to empower sodium batteries with high energy, low cost, and sustainability. A critical challenge lies in designing and discovering sodium superionic conductors with high ionic conductivities to enable the development of solid-state sodium batteries. Here, by studying the structures and diffusion mechanisms of Li-ion versus Na-ion conducting solids, we reveal the structural feature of face-sharing high-coordination sites for fast sodium-ion conductors. By applying this feature as a design principle, we discover a number of Na-ion conductors in oxides, sulfides, and halides. Notably, we discover a chloride-based family of Na-ion conductors NaxMyCl6 (M = La–Sm) with UCl3-type structure and experimentally validate with the highest reported ionic conductivity. Our findings not only pave the way for the future development of sodium-ion conductors for sodium batteries, but also consolidate design principles of fast ion-conducting materials for a variety of energy applications.

High or Low Coordination: Insight into the Active Site of Pt Nanoparticles toward CO Oxidation.

The catalytic activity of metal nanoparticles (NPs) is highly dependent on the coordination environment of the surface sites. Understanding the role of different sites in reactions is essential for gaining insights into catalytic activity and the precise design of catalysts. Herein, we used first-principles calculation-based kinetic Monte Carlo simulations to investigate correlations between different sites on Pt NPs in CO oxidation reactions. Low-coordinated (LC) sites favor the CO adsorption and reaction, whereas the oxygen mainly adsorbs on high-coordinated (HC) sites and diffuses to LC sites for reaction at low temperatures. Compared with step-dominated and terrace-dominated structures, the step-terrace structures exhibit higher activities. This reveals that the catalytic performance is not simply determined by the sites where the reaction occurs but is dramatically affected by the kinetic synergies between different sites. A proper way to optimize the activity of Pt catalysts is to balance the LC and HC sites.

Molecule Saturation Boosts Acetylene Semihydrogenation Activity and Selectivity on a Core‐Shell Ruthenium@Palladium Catalyst

AbstractIncreasing selectivity without the expense of activity is desired but challenging in heterogeneous catalysis. By revealing the molecule saturation and adsorption sensitivity on overlayer thickness, strain, and coordination of Pd‐based catalysts from first‐principles calculations, we designed a stable Pd monolayer (ML) catalyst on a Ru terrace to boost both activity and selectivity of acetylene semihydrogenation. The least saturated molecule is most sensitive to the change in catalyst electronic and geometric properties. By simultaneously compressing the Pd ML and exposing the high coordination sites, the adsorption of more saturated ethylene is considerably weakened to facilitate the desorption for high selectivity. The even stronger weakening to the least saturated acetylene drives its hydrogenation such that it is more exothermic, thereby boosting the activity. Tailoring the molecule saturation and its sensitivity to structure and composition provides a tool for rational design of efficient catalysts.

Molecule Saturation Boosts Acetylene Semihydrogenation Activity and Selectivity on a Core-Shell Ruthenium@Palladium Catalyst.

Increasing selectivity without the expense of activity is desired but challenging in heterogeneous catalysis. By revealing the molecule saturation and adsorption sensitivity on overlayer thickness, strain, and coordination of Pd-based catalysts from first-principles calculations, we designed a stable Pd monolayer (ML) catalyst on a Ru terrace to boost both activity and selectivity of acetylene semihydrogenation. The least saturated molecule is most sensitive to the change in catalyst electronic and geometric properties. By simultaneously compressing the Pd ML and exposing the high coordination sites, the adsorption of more saturated ethylene is considerably weakened to facilitate the desorption for high selectivity. The even stronger weakening to the least saturated acetylene drives its hydrogenation such that it is more exothermic, thereby boosting the activity. Tailoring the molecule saturation and its sensitivity to structure and composition provides a tool for rational design of efficient catalysts.

Upcycling of nickel iron slags to hierarchical self-assembled flower-like photocatalysts for highly efficient degradation of high-concentration tetracycline

The utilization of large-volume nickel–iron slags is largely limited by the existence of heavy metal chromium, resulting in a sharply increase environment problem. Here we report a viable strategy to fully convert nickel–iron slags into self-assembled flower-like silicate photocatalysts. Intriguingly, these decent 3D hierarchical architectures made from wild wastes are composed of core–shell structured silicates. In the meanwhile, nearly 100% chromium is extracted from the slags. Due to the high specific surface area and effective metal coordination sites (i.e., Na+, Mg2+ and Ca2+), the as-obtained silicate catalysts exhibit the extraordinary photocatalytic degradation rate (81.7 %) and the mineralization rate (27 %) of high-concentration tetracycline (100 mg/L) after 30-min Xe lamp irradiation, which are higher than those in most previous reports in terms of degradation and mineralization rates of the high-concentration tetracycline. This simple yet robust strategy to craft 3D self-assembled hierarchical flower-like silicate photocatalysts pave a novel way to the large-scale and value-added consumption of waste residues.

Engineering high-coordinated cerium single-atom sites on carbon nitride nanosheets for efficient photocatalytic amine oxidation and water splitting into hydrogen

Developing highly-active rare-earth single atom photocatalysts have attracted extensive attention due to their excellent catalytic properties. Herein, we prepared a single-atom Ce-SA-C3N4 catalyst composed of atomically dispersed rare-earth cerium (Ce) on C3N4 nanosheets by the pyrolysis of cerium-incorporated layered precursor. The atomic distribution and high-coordinated environment of Ce sites were disclosed by aberration-corrected scanning transmission electron microscopy, electron energy-loss spectra, X-ray absorption spectroscopy, and theoretical calculations. In Ce-SA-C3N4, Ce single atoms are coordinated by four N atoms and six O atoms (Ce-N4/O6). The cooperation of single-atom Ce-N4/O6 active sites in C3N4 nanosheets tunes the electronic structure and the surface trap states, resulting in accelerated charge transfer/separation and extended lifetime of photoinduced electrons. Meanwhile, the high-coordinated Ce-N4/O6 active sites could promote the production of superoxide radicals (•O2−) and C = N bond, thus, the optimized single-atom Ce-SA-C3N4 photocatalyst exhibits highly efficient photocatalytic oxidation of amines under visible light irradiation. Furthermore, the fabricated single-atom Ce-SA-C3N4 photocatalysts are applied to split water into hydrogen, producing the maximum hydrogen yield of 33.5 mmol h−1 g−1. The apparent quantum efficiency for hydrogen evolution achieves 32.6% at 420 nm. This study provides a guideline for rationally designing efficient high-coordinated rare-earth single-atom active sites for efficient solar energy conversion and utilization.

In situ infrared CO detection using silver loaded EMT zeolite films.

Ag cluster catalyst-based oxidation of CO to CO2 is an important way to remove CO at low temperatures. However, the instability of silver clusters seriously limits the catalytic application. Herein, sub-nanosized EMT zeolite nanoparticles served as Ag cluster carriers with high selectivity, low coordination, and unsaturated atom active sites. The silver clusters with sub-nanometer size can be controlled with different charge states and loading rates. A detection film with 500 nm was further prepared by assembling the Ag-EMT composites with a small amount of Nalco as an adhesive. For CO detection, a completely enclosed gas sensing device based on in situ infrared spectroscopy was employed without air interference. CO was accurately introduced into the detection chamber and catalysed into CO2 by silver loaded EMT zeolite films, and the whole process was accurately recorded by infrared spectroscopy. CO with a detection range of 2-50 ppm was realized, showing great application potential in gas monitoring.

Density Functional Calculations of the Sequential Adsorption of Hydrogen on Single Atom and Small Clusters of Pd and Pt Supported on Au(111)

We have used density functional theory calculations to study the sequential adsorption of hydrogen on Pd and Pt atomic site catalysts such as single-atom alloy catalysts (SAAC), single-atom catalysts (SAC), and single cluster catalysts (SCC) on Au(111). The results show that Pd systems tend to have near-zero free energy of hydrogen adsorption (\(\Delta {G}_{{\mathrm{H}}_{\mathrm{ads}}}\approx 0\)) under various coverage conditions of adsorbed hydrogen. In the case of Pt systems, \(\Delta {G}_{{\mathrm{H}}_{\mathrm{ads}}}\approx 0\) only at high coverage conditions of adsorbed hydrogen. Such differences come from the preference of hydrogen for high-coordination and low-coordination sites on Pd and Pt, respectively. The low coordination of hydrogen results in multiple adsorption sites with \(\Delta {G}_{{\mathrm{H}}_{\mathrm{ads}}}\approx 0\) in SCC of Pt/Au. These results can help to understand the different catalytic properties of Pd/Au and Pt/Au.Graphical Abstract

A computational study of direct CO2 hydrogenation to methanol on Pd surfaces.

The reaction mechanism of direct CO2 hydrogenation to methanol is investigated in detail on Pd (111), (100) and (110) surfaces using density functional theory (DFT), supporting investigations into emergent Pd-based catalysts. Hydrogen adsorption and surface mobility are firstly considered, with high-coordination surface sites having the largest adsorption energy and being connected by diffusion channels with low energy barriers. Surface chemisorption of CO2, forming a partially charged CO2δ-, is weakly endothermic on a Pd (111) whilst slightly exothermic on Pd (100) and (110), with adsorption enthalpies of 0.09, -0.09 and -0.19 eV, respectively; the low stability of CO2δ- on the Pd (111) surface is attributed to negative charge accumulating on the surface Pd atoms that interact directly with the CO2δ- adsorbate. Detailed consideration for sequential hydrogenation of the CO2 shows that HCOOH hydrogenation to H2COOH would be the rate determining step in the conversion to methanol, for all surfaces, with activation barriers of 1.41, 1.51, and 0.84 eV on Pd (111), (100) and (110) facets, respectively. The Pd (110) surface exhibits overall lower activation energies than the most studied Pd (111) and (100) surfaces, and therefore should be considered in more detail in future Pd catalytic studies.

Engineering High-Coordinated Cerium Single-Atom Sites on Carbon Nitride Nanosheetsfor Efficient Photocatalytic Amine Oxidation and Water Splitting into Hydrogen

Engineering High-Coordinated Cerium Single-Atom Sites on Carbon Nitride Nanosheetsfor Efficient Photocatalytic Amine Oxidation and Water Splitting into Hydrogen

Theoretical study on water adsorption and dissociation on the nickel surfaces.

Using density functional theory methods, H2O dissociation was investigated on the Ni(111), Ni(100), and Ni(110) surfaces. H and O atom as well as OH species adsorb stably at the high coordination sites. While on the Ni(110) surface, the OH species prefers at the twofold short bridge site because the adsorption on the fourfold hollow site is less feasible due to the increased distances between the nickel atoms. The amount of charge transfer is related to the adsorption stability. The more charge transfer, the more stable the adsorption. The charge transfer decreases in the order of O > OH > H. H2O molecule adsorbs at the top site in a configuration parallel to the surface. The final products are different for H2O dissociation due to the different mechanisms. On the Ni(111) surface, the final product is the O atom. On the Ni(100) and Ni(110) surfaces, the most abundant species are OH and H, but the reaction mechanisms were different. It is not necessary to linear BEP relationship for a given reaction on different surfaces. These results could provide fundamental insights into water behaviors and a favorable theoretical basis for further understanding and research on the interaction between water and metal surfaces.

High-content Co-Nx sites on carbon nanotubes for effective sulfur catalysis in lithium–sulfur batteries

Multiwall carbon nanotubes (MWCNT) with high content Co-Nx coordination sites uniformly dispersed on the surface are synthesized and used as a high efficiency catalytic material in lithium-sulfur battery cathodes. The improved contents and dispersity of the Co-Nx active sites originate from the utilization of a tetraaminophthalocyanine precursor that is chemically bonded with the MWCNT. This significantly improves the exposure of the Co-Nx active sites to the active sulfur species. Density functional theory calculations reveal that the Co-Nx sites exhibit dual lithiophilic/sulfiphilic binding with polysulfides. Promoted sulfur conversion kinetics were obtained, that enabled significantly improved sulfur utilizations, high-rate capability, and cycling stability. Specific capacities of 1303 and 759 mAh g−1 were achieved at 0.2 and 3 C, respectively. Low capacity decay along cycling was also enabled, with 925 mAh g−1 retained after 500 charge/discharge cycles at 0.5 C.

Modification of geometrical and electronic structures of anionic and neutral silicon clusters by double-doped tantalum atoms

In this work, structural evolution, geometrical and electronic structures of Ta2Sin − and Ta2Sin (n = 3–21) clusters are investigated by joint Crystal structure AnaLYsis by Particle Swarm Optimisation (CALYPSO) global search algorithm and quantum chemical calculations. n = 21 is confirmed as the critical size of forming a Ta2-endohedral silicon cage-like structure for both anionic and neutral Ta2Sin clusters. It is found that the two Ta atoms tend to occupy the high coordination sites and stay close as a whole to bond with the Sin frames, as a result, the global minima of Ta2Sin − /0 (n = 3–21) clusters can be all viewed as a central Ta–Ta bonding axis interacted with the surrounding Si atoms. Ta2Sin − /0 (n = 3−13) clusters are majorly dominated by the bipyramid or prism-based geometries and Ta2Sin − /0 (n = 14−18) clusters are primarily governed by the polyhedral cage-like geometries, whereas Ta2Sin − /0 (n = 19−21) clusters are mainly controlled by the prolate geometries. In particular, Ta2Si3 − has a D 3h symmetric trigonal bipyramid structure, and Ta2Si6 − adopts C 2h symmetric chair-shaped structure and Ta2Si12 − is a C 6v symmetric Ta-face-capped hexagonal antiprism with the other Ta atom at the interior of Si12 cage. The odd-even alternations for the relative stabilities of Ta2Sin − /0 are observed.

Hydrodeoxygenation of anisole over different Rh surfaces

The cleavage of the alkoxy (Ar–O–R) ether bond present in anisole is an interesting hydrodeoxygenation (HDO) reaction, since this asymmetric group contains two different C–O bonds, C aryl –O or C alkyl –O, which could potentially cleave. Recent work on the HDO of anisole over Pt, Ru, and Fe catalysts has shown that a common phenoxy surface intermediate is formed on all three metals. The subsequent reaction path of this intermediate varies from metal to metal, depending on the metal oxophilicity. Over the less oxophilic Pt, phenol is the only primary product. By contrast, on the more oxophilic Fe catalyst, the sole primary product is benzene instead of phenol. On Ru, with intermediate oxophilicity, both benzene and phenol are primary products. In this contribution, we have investigated Rh catalysts of varying surface nanostructures. A combination of experimental measurements and computational calculations was used to explore the effects of varying metal coordination number, an additional parameter that can be used to control the oxophilicity of a metal. The results confirm that metal oxophilicity is a good descriptor for HDO performance of metal catalysts and it can be controlled via selection of metal type and/or metal extent of coordination. Small Rh metal clusters with low coordination metal sites are more active for the deoxygenation pathway but also quickly deactivated while large clusters with high coordination sites are more active toward hydrogenation and more stable. Manipulating the surface coordination of rhodium atoms can greatly affect the metal oxophilicity and in turn control its activity for C–O bond cleavage. In the hydrodeoxygenation of anisole, a step surface favors deoxygenation to benzene while a smooth terrace prefers hydrogenation to phenol.

Some insight on the structure/activity relationship of metal nanoparticles in Cu/SiO2 catalysts

The activity of two Cu/SiO 2 catalysts prepared by the chemisorption hydrolysis technique has been tested in the hydrogenation reaction of 3-methyl-cyclohexanone. Both catalysts were found to be very active at 60 °C and 1 atm of H 2 . Characterization of the materials by FT-IR of adsorbed CO and TEM put in light the presence of well formed Cu cristallites. By assuming a cuboctahedral model we could show that the hydrogenation activity is linked to high coordination sites on the metal particle. A comparison is also reported with a sample prepared by ammonia evaporation that was found to be inactive in the hydrogenation reaction under the same experimental conditions. The activity of Cu/SiO 2 catalysts in the hydrogenation of 3-methyl-cyclohexanone was found to be linked to high coordination sites on the metal Cu particle, whereas acidic sites are represented by defective, low coordination sites.