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.

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.

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.

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.

Regulating local coordination environment of rhodium single atoms in Rh/CeO_(2) catalysts for N_(2)O decomposition

Rh single atom catalysts(SACs)have been insensitively investigated recently due to the maximum utilization efficiency of Rh,one of the most expensive precious metals.Although great efforts have been made in the development and application of Rh SACs,there are few reports on the precise control of the local coordination environment of Rh single sites on CeO_(2) and their catalytic performance for N_(2)O decomposition.Herein,Rh/CeO_(2) catalysts with different Rh-O coordination numbers(CNs)were successfully prepared using different CeO_(2) supports and a simple incipient wetness impregnation(IWI)method.It is observed that the Rh/CeO_(2) catalyst with slightly higher CN of Rh-O(Rh/CeO_(2)-H)prepared from CeO_(2) shows much higher N_(2)O decomposition activity than the catalyst with lower CN of Rh-O(Rh/CeO_(2)-L)obtained from Ce(OH)_(x).The Rh species within Rh/CeO_(2)-H are found to be more reactive than those within Rh/CeO_(2)-L,which can better facilitate the O_(2)desorption once formed during N_(2)O deco mposition.In additio n,more surface oxygen vacancies are present on Rh/CeO_(2)-H than on Rh/CeO_(2)-L,well explaining the superior N_(2)O adsorption and activation capability on the former catalyst.It is concluded that more abundant oxygen vacancies and reactive Rh single atom sites with slightly higher CN of Rh-O and significantly higher reducibility altogether contribute to the superior N_(2)O decomposition activity on the Rh/CeO_(2)-H catalyst.

Tuning coordination environment of iron ions to ensure ultra-high pseudocapacitive capability in iron oxide

The mechanism governing the pseudocapacitive lithium storage behavior is one of the most critical unsolved issues in conversion-type anodes for lithium-ion batteries.In this work,we,for the first time,demonstrate that the pseudocapacitive capability of iron oxide-based anodes is closely associated with the electronic structures of iron ions.As proof of concept,the introduction of amorphization,nitrogen doping,oxygen vacancies reduces the coordination of iron ions and contributes significantly to the pseudocapacitive lithium storage capability of iron oxide,reaching up to 96%of the specific capacity at 1 mV·s^(−1).Due to the significantly modulated coordination environment,the 3d electrons of Fe(II)are delocalized with increased spin state and the energy band gap is narrowed,accompanied by an upshift of Fermi energy.The redox activity and carrier mobility of iron oxides are substantially increased,which substantially enhance the exchange current density and thereby improve the pseudocapacitive capability of iron oxide.

Identification of the highly active Zn-N_(4) sites with pyrrole/pyridine-N synergistic coordination by dz^(2)+s-band center for electrocatalytic H_(2)O_(2) production

Single metal atoms anchored on nitrogen-doped carbon materials(M-N_(4))have been identified as effective active sites for catalyzing the two-electron oxygen reduction reaction(2e-ORR).However,the relationship between the local atomic/electronic environments of the M-N_(4) sites(metal atoms coordinated with different types of N species)and their catalytic activity for 2e-ORR has rarely been elaborated clearly,which imposes significant ambiguity for the rational design of catalysts.Herein,guided by the comprehensive density-functional theory calculations and predictions,a series of Zn-N_(4) single-atom catalysts(SACs)are designed with pyrrole/pyridine-N(N_(Po)/N_(Pd))synergistic coordination and prepared by controlling the pyrolysis temperature(600,700,and 800℃),Among them,the dominated Zn-N_(4) configurations with rationally combined N_(Po)/N_(Pd)coordination show~*OOH adsorption strength close to the optimal value,much superior to those with mono N species.Thus,the as-prepared catalyst exhibits a high H_(2)O_(2) selectivity of over 90%both in neutral and alkaline environments,with a superb H_(2)O_(2) yield of up to 33.63 mol g^(-1)h^(-1)in an alkaline with flow cell.More importantly,a new descriptor,dz^(2)+s band center,has been proposed,which is especially feasible for predicting the activity for metal types with fully occupied s and d orbitals.This work thus presents clear guidance for the rational design of highly active SACs toward ORR and provides a complement to the d-band theory for more accurately predicting the catalytic activity of the materials.

Modulating the local coordination environment of single-atom catalysts for enhanced catalytic performance

The local coordination environment of catalysts has been investigated ftor an extended period to obtain enhanced catalytic performance.Especially with the advancement of single-atom catalysts(SACs),research on the coordination environment has been advanced to the atomic level.The surrounding coordination atoms of central metal atoms play important roles in their catalytic activity,selectivity and stability.In recent years,remarkable improvements of the catalytic performance of SACs have been achieved by the tailoring of coordination atoms,coordination numbers and second-or higher-coordination shells,which provided new opportunities for the further development of SACs.In this review,the characterization of coordination environment,tailoring of the local coordination environment,and their related adjustable catalytic performance will be discussed.We hope this review will provide new insights on further research of SACs.

Tuning the coordination environment of single-atom catalyst M-N-C towards selective hydrogenation of functionalized nitroarenes

Fine-tuning of the coordination environment of single-atom catalysts(SACs)is effective to optimize their catalytic performances,yet it remains challenging due to the vulnerability of SACs.Herein,we report a new approach to engineering the coordination environment of M-N-C(M=Fe,Co,and Ni)SACs by using glutamic acid as the N/C source and pyrolysis atmosphere as a regulator.Compared with that in N2,NH3 was able to promote the doping of N at 7<700℃yet etch the N-species at higher temperatures,by which the M-N coordination number(CN)and the electronic structure were delicately tuned.It was found that the electron density of Ni single atoms increased with the decrease of Ni-N CN.As a consequence,the capability of Ni-N-C to dissociate H2 was greatly enhanced and a higher catalytic activity in chemoselective hydrogenation of functionalized nitroarenes was achieved.Moreover,this modulation method could be applied to other transition metals including Fe and Co.In particular,the as-synthesized Co-N-C SAC afforded a turnover frequency of 152.3 h~1 with 99%selectivity to 3-vinylaniline in the hydrogenation of 3-nitrostyrene,which was the highest ever reported thus far and was at least one order of magnitude more active than state-of-the-art noble-metal-free M-N-C catalysts,demonstrating the great potential of engineering the coordination environment of SACs.

Engineering local coordination environments and site densities for high-performance Fe-N-C oxygen reduction reaction electrocatalysis

Fe-N-C catalysts represent very promising cathode catalysts for polymer electrolyte fuel cells,owing to their outstanding activity for the oxygen reduction reaction(ORR),especially in alkaline media.In this review,we summarize recent advances in the design and synthesis of Fe-N-C catalysts rich in highly dispersed FeNx active sites.Special emphasis is placed on emerging strategies for tuning the electronic structure of the Fe atoms to enhance the ORR activity,and also maximizing the surface concentration of FeNx sites that are catalytically accessible during ORR.While great progress has been made over the past 5 years in the development of Fe-N-C catalyst for ORR,significant technical obstacles still need to be overcome to enable the large-scale application of Fe-N-C materials as cathode catalysts in real-world fuel cells.

Coordination environments tune the activity of oxygen catalysis on single atom catalysts:A computational study

Designing highly efficient bifunctional electrocatalysts for oxygen reduction and evolution reaction(ORR/OER)is extremely important for developing regenerative fuel cells and metal-air batteries.Single-atom catalysts(SACs)have gained considerable attention in recent years because of their maximum atom utilization efficiency and tunable coordination environments.Herein,through density functional theory(DFT)calculations,we systematically explored the ORR/OER performances of nitrogencoordinated transition metal carbon materials(TM-N_(x)-C(TM=Mn,Fe,Co,Ni,Cu,Pd,and Pt;x=3,4))through tailoring the coordination environment.Our results demonstrate that compared to conventional tetra-coordinated(TM-N_(4)-C)catalysts,the asymmetric tri-coordinated(TM-N_(3)-C)catalysts exhibit stronger adsorption capacity of catalytic intermediates.Among them,Ni-N_(3)-C possesses optimal adsorption energy and the lowest overpotential of 0.29 and 0.28 V for ORR and OER,respectively,making it a highly efficient bifunctional catalyst for oxygen catalysis.Furthermore,we find this enhanced effect stems from the additional orbital interaction between newly uncoordinated d-orbitals and p-orbitals of oxygenated species,which is evidently testified via the change of d-band center and integral crystal orbital Hamilton population(ICOHP).This work not only provides a potential bifunctional oxygen catalyst,but also enriches the knowledge of coordination engineering for tailoring the activity of SACs,which may pave the way to design and discover more promising bifunctional electrocatalysts for oxygen catalysis.

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.

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.

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.

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.