Regulating the coordination environment of Ru single-atom catalysts and unravelling the reaction path of acetylene hydrochlorination

In this work,DFT calculations were used firstly to simulate the nitrogen coordinated metal single-atom catalysts(M-N_(x)SACs,M=Hg,Cu,Au,and Ru) to predict their catalytic activities in acetylene hydrochlorination.The DFT results showed that Ru-N_(x)SACs had the best catalytic performance among the four catalysts,and Ru-N_(x)SACs could effectively inhibit the reduction of ruthenium cation.To verify the DFT results,Ru-N_(x)SACs were fabricated by pyrolyzing MOFs in-situ spatially confined metal precursors.The N coordination environment could be controlled by changing the pyrolysis temperature.Catalytic performance tests indicated that low N coordination number(Ru-N_(2),Ru-N_(3))exhibited excellent catalytic activity and stability compared to RuCl_(3)catalyst.DFT calculations further revealed that Ru-N_(2)and Ru-N_(3)had a tendency to activate HCl at the first step of reaction,whereas Ru-N4tended to activate C_(2)H_(2).These findings will serve as a reference for the design and control of metal active sites.

Simultaneous regulation on coordination environment and interfacial chemistry via taurine for stabilized Zn metal anode

Aqueous Zn-ion batteries(AZIBs)are the potential options for the next-generation energy storage scenarios due to the cost effectiveness and intrinsic safety.Nevertheless,the industrial application of AZIBs is still impeded by a series of parasitic reactions and dendrites at zinc anodes.In this study,taurine(TAU)is used in electrolyte to simultaneously optimize the coordination condition of the ZnSO4electrolyte and interfacial chemistry at the anode.TAU can preferentially adsorb with the zinc metal and induce an in situ stable and protective interface on the anode,which would avoid the connection between H_(2)O and the zinc metal and promote the even deposition of Zn^(2+).The resulting Zn//Zn batteries achieve more than 3000 hours long cyclic lifespan under 1 mA cm^(-2)and an impressive cumulative capacity at 5 mA cm^(-2).Moreover,Zn//Cu batteries can realize a reversible plating/stripping process over 2,400cycles,with a desirable coulombic efficiency of 99.75%(1 mA cm^(-2)).Additionally,the additive endows Zn//NH_(4)V_(4)O_(10)batteries with more stable cyclic performance and ultrafast rate capability.These capabilities can promote the industrial application of AZIBs.

Strong synergy between physical and chemical properties:Insight into optimization of atomically dispersed oxygen reduction catalysts

Atomically dispersed catalysts exhibit significant influence on facilitating the sluggish oxygen reduction reaction(ORR)kinetics with high atom economy,owing to remarkable attributes including nearly 100%atomic utilization and exceptional catalytic functionality.Furthermore,accurately controlling atomic physical properties including spin,charge,orbital,and lattice degrees of atomically dispersed catalysts can realize the optimized chemical properties including maximum atom utilization efficiency,homogenous active centers,and satisfactory catalytic performance,but remains elusive.Here,through physical and chemical insight,we review and systematically summarize the strategies to optimize atomically dispersed ORR catalysts including adjusting the atomic coordination environment,adjacent electronic orbital and site density,and the choice of dual-atom sites.Then the emphasis is on the fundamental understanding of the correlation between the physical property and the catalytic behavior for atomically dispersed catalysts.Finally,an overview of the existing challenges and prospects to illustrate the current obstacles and potential opportunities for the advancement of atomically dispersed catalysts in the realm of electrocatalytic reactions is offered.

Precise synthesis of dual atom sites for electrocatalysis

Single atom sites are widely applied in various electrocatalytic fields due to high atom utilization, mass activity, and selectivity. They are limited in catalyzing multi-electron reactions due to their intrinsic mono-metal center feature. Dual atom sites (DASs) as promising candidate have received enormous attentions because adjacent active sites can accelerate their catalytic performance via synergistic effect. Herein, the fundamental understandings and intrinsic mechanism underlying DASs and corresponding electrocatalytic applications are systemically summarized. Different synergy dual sites are presented to disclose the structure-performance relationship with engineering the well-defined DASs on the basis of theoretical principle. An overview of the electrocatalytic applications is showed, including oxygen reduction reaction, hydrogen evolution reaction, oxygen evolution reaction, carbon dioxide reduction reaction, and nitrogen reduction reaction. Finally, a conclusion and future prospective are provided to reveal the current challenges for rational designing, synthesizing, and modulating the advanced DASs toward electrocatalytic reactions.

Coordination environment of active sites and their effect on catalytic performance of heterogeneous catalysts

The structural complexity of supported metal catalysts,playing significant role in a wide range of chemical technologies,have prevented us from deeply understanding their catalytic mechanisms at atomic level.A fundamental understanding of the nature of active sites and structure–performance relationship of supported metal catalysts from a comprehensive view will open up numerous new opportunities for the development of advanced catalysts to address the global challenges in energy conversion and environmental protection.This review surveys the effects of multiple factors,including the metal size,shape,support,alloy and ligand modifier,on the coordinated environment of active center and further their influence on the catalytic reactions,aiming to provide guidance for the design of industrialized heterogeneous catalysts with extraordinary performance.Subsequently,the key structure characterization techniques in determining the coordination structure of active metal sites,especially the dynamic coordination structure change under the reaction condition,are well summarized.A brief summary is finally provided together with personal perspectives on the further development in the field of heterogeneous metal catalysts.

CO_(2) reduction reaction pathways on single‐atom Co sites:Impacts of local coordination environment

Single‐atom catalysts have been proposed as promising electrocatalysts for CO_(2) reduction reactions(CO_(2)RR).Co‐N_(4) active sites have attracted wide attention owing to their excellent CO selectivity and activity.However,the effect of the local coordination environment of Co sites on CO_(2) reduction reaction pathways is still unclear.In this study,we investigated the CO_(2) reduction reaction pathways on Co‐N_(4) sites supported on conjugated N_(4)‐macrocyclic ligands with 1,10‐phenanthroline subunits(Co‐N_(4)‐CPY)by density functional theory calculations.The local coordination environment of single‐atom Co sites with N substituted by O(Co‐N_(3)O‐CPY)and C(Co‐N_(3)C‐CPY)was studied for comparison.The calculation results revealed that both C and O coordination break the symmetry of the primary CoN_(4) ligand field and induce charge redistribution of the Co atom.For Co‐N_(4)‐CPY,CO was confirmed to be the main product of CO_(2)RR.HCOOH is the primary product of Co‐N_(3)O‐CPY because of the greatly increased energy barrier of CO_(2) to*COOH.Although the energy barrier of CO_(2) to*COOH is reduced on Co‐N_(3)C‐CPY,the desorption process of*CO becomes more difficult.CH3OH(or CH_(4))are obtained by further*CO hydrogenation reduction when using Co‐N_(3)C‐CPY.This work provides new insight into the effect of the local coordination environment of single‐atom sites on CO_(2) reduction reaction pathways.

Europium Coordination Compound with Highly Improved Luminescent Quantum Yield

The luminescent properties of two Eu3＋ compounds based on quinoline-2-car- boxylic acid （Hqc）, [Na2Eu2（qc）6（CH3COO）2（H2O）4].2DMF （1） and [Eu2（qc）6（H2O）6].3H2O （2）, as well as their syntheses and structures are reported. Both compounds are formed by slow evaporation at room temperature and exhibit zero dimensional dinuclear structures. It is worth mentioning that a 4.5-fold enhancement in luminescent quantum yield is achieved by reducing the nonradiative deactivation, through which the quantum yield increases remarkably to 67.62% for 1 compared with 12.18% for 2.

High-temperature treatment to engineer the single-atom Pt coordination environment towards highly efficient hydrogen evolution

Development of high-performance and cost-effective catalysts for electrocatalytic hydrogen evolution reaction(HER)play crucial role in the growing hydrogen economy.Recently,the atomically dispersed metal catalysts have attracted increasing attention due to their ultimate atom utilization and great potential for highly cost-effective and high-efficiency HER electrocatalyst.Herein,we propose a hightemperature treatment strategy to furtherly improve the HER performance of atomically dispersed Ptbased catalyst.Interestingly,after appropriate high-temperature treatment on the atomically dispersed Pt0.8@CN,the Pt species on the designed N-doped porous carbon substrate with rich defect sites can be re-dispersed to single atom state with new coordination environment.The obtained Pt0.8@CN-1000 shows superior HER performance with overpotential of 13 m V at 10 m A cm^(-2)and mass activity of 11,284 m A/mgPtat-0.1 V,much higher than that of the pristine Pt0.8@CN and commercial Pt/C catalyst.The experimental and theoretical investigations indicate that the high-temperature treatment induces the restructuring of coordination environment and then the optimized Pt electronic state leads to the enhanced HER performances.This work affords new strategy and insights to develop the atomically dispersed high-efficiency catalysts.

Manipulating coupling state and magnetism of Mn-doped ZnO nanocrystals by changing the coordination environment of Mn via hydrogen annealing

Mn-doped ZnO nanocrystals are synthesized by a wet chemical route and treated in H2/Ar atmosphere with different H2/Ar ratios. It is found that hydrogen annealing could change the coordination environment of Mn in ZnO lattice and manipulate the magnetic properties of Mn-doped ZnO. Mn ions initially enter into interstitial sites and a Mn3＋ 06 octahedral coordination is produced in the prepared Mn-doped ZnO sample, in which the nearest neighbor Mn3＋ and 02 ions could form a Mn3＋-O2--Mn3＋ complex. After H2 annealing, interstitial Mn ions can substitute for Zn to generate the Mn2＋O4 tetrahedral coordination in the nanocrystals, in which neighboring Mn2＋ ions and H atoms could form a Mn2＋-O2--Mn2＋ complex and Mn-H-Mn bridge structure. The magnetic measurement of the as-prepared sample shows room temperature paramagnetic behavior due to the Mn3＋-O2--Mn3＋ complex, while the annealed samples exhibit their ferromagnetism, which originates from the Mn-H-Mn bridge structure and the Mn-Mn exchange interaction in the Mn2＋-O2--Mn2＋ complex.

Engineering the Local Coordination Environment of Single-Atom Catalysts and Their Applications in Photocatalytic Water Splitting:A Review

Single-atom catalysts(SACs),with atomically dispersed metal atoms anchored on a typical support,representing the utmost utilization effi ciency of the atoms,have recently emerged as promising catalysts for a variety of catalytic applications.The electronic properties of the active center of SACs are highly dependent on the local environment constituted by the single metal atom and its surrounding coordination elements.Therefore,engineering the coordination environment near single metal sites,from the fi rst coordination shell to the second shell or higher,would be a rational way to design effi cient SACs with optimized electronic structure for catalytic applications.The wide range of coordination confi gurations,guaranteed by the multiple choices of the type and heterogeneity of the coordination element(N,O,P,S,etc.),further off er a large opportunity to rationally design SACs for satisfactory activities and investigate the structure-performance relationship.In this review,the coordination engineering of SACs by varying the type of coordination element was elaborated and the photocatalytic water splitting of SACs was highlighted.Finally,challenging issues related to the coordination engineering of SACs and their photocatalytic applications were discussed to call for more eff orts devoted to the further development of single-atom catalysis.

Single‐atomic Co‐B_(2)N_(2)sites anchored on carbon nanotube arrays promote lithium polysulfide conversion in lithium-sulfur batteries

Due to low cost,high capacity,and high energy density,lithium–sulfur(Li–S)batteries have attracted much attention;however,their cycling performance was largely limited by the poor redox kinetics and low sulfur utilization.Herein,predicted by density functional theory calculations,single‐atomic Co‐B2N2 site‐imbedded boron and nitrogen co‐doped carbon nanotubes(SA‐Co/BNC)were designed to accomplish high sulfur loading,fast kinetic,and long service period Li–S batteries.Experiments proved that Co‐B2N2 atomic sites can effectively catalyze lithium polysulfide conversion.Therefore,the electrodes delivered a specific capacity of 1106 mAh g−1 at 0.2 C after 100 cycles and exhibited an outstanding cycle performance over 1000 cycles at 1 C with a decay rate of 0.032%per cycle.Our study offers a new strategy to couple the combined effect of nanocarriers and single‐atomic catalysts in novel coordination environments for high‐performance Li–S batteries.

Engineering the axial coordination of cobalt single atom catalysts for efficient photocatalytic hydrogen evolution

Improving the catalytic activity of non-noble metal single atom catalysts(SACs)has attracted considerable attention in materials science.Although optimizing the local electronic structure of single atom can greatly improve their catalytic activity,it often involves in-plane modulation and requires high temperatures.Herein,we report a novel strategy to manipulate the local electronic structure of SACs via the modulation of axial Co-S bond anchored onto graphitic carbon nitride(C_(3)N_(4))at room temperature(RT).Each Co atom is bonded to four N atoms and one S atom(Co-(N,S)/C_(3)N_(4)).Owing to the greater electronegativity of S in the Co-S bond,the local electronic structure of the Co atoms is available to be controlled at a relatively moderate level.Consequently,when employed for the photocatalytic hydrogen evolution reaction,the adsorption energy of intermediate hydrogen(H*)on the Co atoms is remarkably low.In the presence of the Co-(N,S)/C_(3)N_(4)SACs,the hydrogen evolution rates reach up to 10 mmol/(g·h),which is nearly 10 and 2.5 times greater than the rates in the presence of previously reported transition metal/C_(3)N_(4)and noble platinum nanoparticles(PtNPs)/C_(3)N_(4)catalysts,respectively.Attributed to the tailorable axial Co-S bond in the SAC,the local electronic structure of the Co atoms can be further optimized for other photocatalytic reactions.This axial coordination engineering strategy is universal in catalyst designing and can be used for a variety of photocatalytic applications.

Tuning the atomic configuration environment of MnN_(4) sites by Co cooperation for efficient oxygen reduction

Carbon-based N-coordinated Mn(Mn-N_(x)/C)single-atom electrocatalysts are considered as one of the most desirable non-precious oxygen reduction reaction(ORR)candidates due to their insignificant Fenton reactivity,high abundance,and intriguing electrocatalytic performance.However,current MnN_(x)/C single-atom electrocatalysts suffer from high overpotentials because of their low intrinsic activity and unsatisfactory chemical stability.Herein,through an in-situ polymerization-assisted pyrolysis,the Co as a second metal is introduced into the Mn-N_(x)/C system to construct Co,Mn-N_(x)dual-metallic sites,which atomically disperse in N-doped 1D carbon nanorods,denoted as Co,Mn-N/CNR and hereafter.Using electron microscopy and X-ray absorption spectroscopy(XAS)techniques,we verify the uniform dispersion of CoN4and MnN4atomic sites and confirm the effect of Co doping on the MnN_(4) electronic structure.Density functional theory(DFT)calculations further elucidate that the energy barrier of ratedetermining step(^(*)OH desorption)decreases over the 2 N-bridged MnCoN_(6) moieties related to the pure MnN_(4).This work provides an effective strategy to modulate the local coordination environment and electronic structure of MnN_(4) active sites for improving their ORR activity and stability.

Controlling of coordination state of Ru_(x)N_(y) clusters for efficient oxygen reduction electrocatalysis

Ruthenium(Ru)is an attractive potential alternative to platinum as an electrocatalyst for the oxygen reduction reaction(ORR),in virtue of its high catalytic selectivity and relatively low price.In this work,a series of well-dispersed nitrogen-coordinated Ru-clusters on carbon black(Ru_(x)N_(y)/C)were prepared by pyrolyzing different Ru-containing sandwich compounds as the Ru sources.The higher thermal stability of these complexed sandwich precursors(bis(1,2,3,4,5-pentamethylcyclopentadienyl)Ru(II)monomer,dichloro(p-cymene)Ru(II)dimer,and chloro(1,2,3,4,5-pentamethylcyclopentadienyl)Ru(II)tetramer)affords the control of coordinated state for the resulting Ru-clusters,in comparison of that derived from ruthenium chlorides.After the pyrolysis treatment,the Ru coordinated state in Ru_(x)N_(y)/C,with the Ru–N and Ru–Ru bonds,still showed the structural inheritance from the Ru(II)monomer,dimer,and tetramer,but using ruthenium chlorides as the Ru source resulted in the nanoscale Ru agglomerations.The ORR testing exhibited that the Ru_(x)N_(y)/C sample derived from the Ru(II)tetramer(Ru_(x)N_(y)/C-T)presents the higher catalytic activity than the other obtained samples in either alkaline or acidic electrolytes.Even in the acidic electrolyte,Ru_(x)N_(y)/C-T shows the comparable ORR activity to that of Pt/C catalysts,and it shows the superior tolerance against methanol and CO.The X-ray absorption spectroscopy and density functional theory calculations demonstrate that these tetra-nuclear Ru-clusters could be the most active site due to their broadened d-orbital bands and lower energy d-band center than those of other subnano species and nanocrystals,and their favorable Yeager-type adsorption of O_(2)-molecules is also contributed to promoting O–O bond cleavage and accelerating the ORR process.

Boosting propane dehydrogenation of defective S-1 stabilized singleatom Pt and ZnO catalysts via coordination environment regulation

Pt single atoms catalysts with precise coordination environment and high stability are expected to achieve high performance of propane dehydrogenation(PDH).In this work,an innovative synthetic strategy is proposed to construct the S-1@0.1Pt9Zn@DPS-1 nanocomposite as a highly efficient PDH catalyst.Defect engineering is applied to induce the formation of defective porous silicalite-1(DPS-1),which is favorable for achieving the uniformly distributed ZnO nanoclusters.The ZnO nanoclusters were further served as anchoring sites to stabilize the isolated Pt atoms.The structural characterization revealed that penta-O coordinated Pt single atom coupled with ZnO nanoclusters decorated on the DPS-1.Moreover,the atomically dispersed Pt atoms with the ideal coordination environment could act as the predominant active sites for PDH process.As expected,the optimal S-1@0.1Pt9Zn@DPS-1 catalyst delivered an excellent PDH performance(propane conversion of 40.7%,propylene selectivity of 97.5%)and good cycling regeneration stability.This work provides a new way for improving the activity and stability of catalysts in the field of industrial catalysts.

Horizontal oscillation processed large MXene with Low Ti–Ti coordination for fast sodium storage

MXene stands out as a rising family of transition metal carbides/nitrides with exceptional size-dependent properties and versatile potential applications. However, the realization of large MXene with a controllable surface at atomic level remains challenging to keep the balance among the conductivity, stability and activity. Herein, the horizontal oscillation-induced delamination(HOD)strategy is proposed to acquire Ti_(3)C_(2) flakes with large size and low Ti–Ti coordination(HO-Ti_(3)C_(2)). The average size of the asobtained flakes can reach 6.48 μm to keep the overall conductive skeleton and merits from large size. Simultaneously, metal atoms at surface can be partially removed due to the enhanced local vibrational turbulence during the reciprocating horizontal oscillation process. Such MXenes with clear and unique surface states exhibit high potentials in ion adsorption together with satisfied electric conductivity and stability. As proof of concept, HO-Ti_(3)C_(2) anode exhibits remarkable rate capability and longterm stability during sodium storage. A capacity of 100.5 m Ah g^(-1)with a long-life cycle(4,500 cycles) at a high rate of 1.0 A g^(-1)originates from the increased s-d interaction between Na and Ti. Therefore, the HOD strategy provides a controllable surface design to promote the clear criteria into size-dependent research on MXene.

Precisely Tailoring the First Coordination Shell of Metal Centers in Porous Nitrogen-Doped Carbon Promoting Electroreduction of CO^(2)Under Neutral Condition

Precise regulation of the coordination environment of a metal active center is very important but remains a challenge.Here,single-atom Ni catalysts with a combined N-and C-coordination structure(Ni-NC_(3))and N-coordination structure(Ni-N4)were prepared by modulating the side groups of organic ligands in the corresponding precursor metal–azolate frameworks.Compared with the Ni-N4 site,the d-band center of 3d orbitals of the Ni atom in Ni-NC_(3)was more significantly shifted to the Fermi energy level;thus,the Ni-NC_(3)catalytic site was superior to activating CO_(2)molecule into the*COOH intermediate.As a result,Ni-NC_(3)exhibited an exceptionally high performance for CO_(2)-to-CO conversion with a Faradaic efficiency of 98.4%,an energy efficiency of>50%,as well as an industrial current density of∼300 mA cm^(−2) in neutral electrolyte.Such high performance could be retained for at least 70 h.This work reveals the importance of modulating the coordination environment in the electrochemical CO_(2)reduction reaction and provides a possible way to rational design of electrocatalysts for highly efficient conversion of CO_(2)to target products.

Study on Tourism Landscape Real Estate in China

Landscape real estate is a high-grade product of tourism development and real estate industry, and a new real estate development mode integrating both investment and consumption. This paper, based on analyzing concepts and characteristics of tourism landscape real estate, elaborated basic principles of landscape real estate development by taking Guosetianxiang in Chengdu City for example, and proposed suggestions for the future development of tourism landscape real estate.

Recent developments in the use of single-atom catalysts for water splitting

Electrochemical water splitting is regarded as the most promising approach to produce hydrogen.However,the sluggish electrochemical reactions occurring at the anode and cathode,namely,the oxygen evolution reaction(OER)and the hydrogen evolution reaction(HER),respectively,consume a tremendous amount of energy,seriously hampering its wide application.Recently,single-atom catalysts(SACs)have been proposed to effectively enhance the kinetics of these two reactions.In this minireview,we focus on the recent progress in SACs for OER and HER applications.Three classes of SACs have been reviewed,i.e.,alloy-based SACs,carbon-based SACs and SACs supported on other compounds.Different factors affecting the activities of SACs are also highlighted,including the inherent element property,the coordination environment,the geometric structure and the loading amount of metal atoms.Finally,we summarize the current problems and directions for future development in SACs.

Atom-level interfacial synergy of single-atom site catalysts for electrocatalysis

Single-atom site catalysts(SACs)have made great achievements due to their nearly 100%atomic utilization and uniform active sites.Regulating the surrounding environment of active sites,including electron structure and coordination environment via atom-level interface regulation,to design and construct an advanced SACs is of great significance for boosting electrocatalytic reactions.In this review,we systemically summarized the fundamental understandings and intrinsic mechanisms of SACs for electrocatalytic applications based on the interface site regulations.We elaborated the several different regulation strategies of SACs to demonstrate their ascendancy in electrocatalytic applications.Firstly,the interfacial electronic interaction was presented to reveal the electron transfer behavior of active sites.Secondly,the different coordination structures of metal active center coordinated with two or three non-metal elements were also summarized.In addition,other atom-level interfaces of SACs,including metal atom–atom interface,metal atom-X-atom interface(X:non-metal element),metal atom-particle interface,were highlighted and the corresponding promoting effect towards electrocatalysis was disclosed.Finally,we outlooked the limitations,perspectives and challenges of SACs based on atomic interface regulation.