Mesoporous silica stabilized MOF nanoreactor for highly selective semi-hydrogenation of phenylacetylene via synergistic effect of Pd and Ru single site

Selective semi-hydrogenation of phenylacetylene to styrene is a crucial step in the polystyrene industry.Although Pd-based catalysts are widely used in this reaction due to their excellent hydrogenation activity,the selectivity for styrene remains a great challenge.Herein,we designed a mesoporous silica stabilized Pd-Ru@ZIF-8(MS Pd-Ru@ZIF-8)nanoreactor with novel Pd and Ru single site synergistic catalytical system for semi-hydrogenation of phenylacetylene.The nanoreactor exhibited a superior performance,achieving 98%conversion of phenylacetylene and 96%selectivity to styrene.Turnover frequency(TOF)of nanoreactor was up to as high as 2,188 h^(−1),which was 25 times and 5 times more than the single metal species catalysts,mesoporous silica stabilized Pd@ZIF-8 nanoreactor(MS Pd@ZIF-8),and mesoporous silica stabilized Ru@ZIF-8 nanoreactor(MS Ru@ZIF-8).This catalytic activity was attributed to the synergistic effect of Pd and Ru single site anchored strongly into the framework of ZIF-8,which reduced the desorption energy of styrene and increased the hydrogenation energy barrier of styrene.Importantly,since the ordered mesoporous silica was introduced into the nanoreactor shell to stabilize ZIF-8,MS Pd-Ru@ZIF-8 showed excellent reusability and stability.After the five cycles,the catalytical activity and selectivity still remained.This work provides insights for a synergistic catalytic system based on single-site active sites for selective hydrogenation reactions.

Single-atomic Pt sites anchored on defective Ti0_(2) nanosheets as a superior photocatalyst for hydrogen evolution

Single-atomic site catalysts have drawn considerable attention because of their maximum atom-utilization efficiency and excellent catalytic activity.In this work,a highly active single-atomic Pt site photocatalyst was synthesized through employing defective Ti0_(2) nanosheets as solid support for photo-catalytic water splitting.It indicated that the surface oxygen vacancies on defective Ti0_(2) nanosheets could effectively stabilize the single-atomic Pt sites through constructing a three-center Ti-Pt-Ti structure.The Ti-Pt-Ti structure can hold the stability of isolated single-atomic Pt sites and facilitate the separation and transfer of photoinduced charge carriers,thereby greatly improving the photocatalytic H2 evolution.Notably,our synthesized photocatalyst exhibited a remarkably enhanced H2 evolution performance,and the H2 production rate is up to 13460.7μmol h^(-1)·g^(-1),which is up to around 29.0 and 4.7 times higher than those of Ti0_(2) nanosheets and Pt nanoparticles-Ti0_(2).In addition,a plausible enhanced reaction mechanism was also proposed combining with photo-electrochemical characterizations and density functional theoiy(DFT)calculation results.Ultimately,it is believed that this work highlights the benefits of a single-site catalyst and paves the way to rationally design the highly active and stable single-atomic site photocatalysts on metal oxide support.

Asymmetrically ligated single atomic nickel sites for efficient hydrogen peroxide electrosynthesis

Atomic transition-metal-nitrogen-carbon electrocatalysts hold great promise as alternatives to benchmark Pt in the oxygen reduction reaction.The pristine metal centers with quasi square-planar D_(4h) configuration,however,still suffer from unfavorable energetics and thereby strong activity/selectivity trade-off during the catalytic process.Here we present a ligand-field engineering of single-atom Ni-N-C catalysts to boost the sluggish kinetics via rationally constructing prototypical asymmetrically ligated Ni-N_(3)O_(1) sites.The as-obtained Ni-supported multi-walled carbon nanotubes with molten salt-treated(defined as Ni/CNS)catalyst delivered an excellent H_(2)O_(2) selectivity(>90%)within a wide potential window(0.2–0.7 V vs.reversible hydrogen electrode(RHE))and robust stability(for 10 h)in alkaline medium.Combined electron paramagnetic resonance and theoretical analysis rationalize this finding and demonstrate that the broken symmetry facilitates the electron transfer of a σ* to O–O orbital as compared to the Ni-N_(4) counterpart,playing an indispensable role in efficient O_(2) activation.

Monitoring dynamics of defects and single Fe atoms in N-functionalized few-layer graphene by in situ temperature programmed scanning transmission electron microscopy

In this study,we aim to contribute an understanding of the pathway of formation of Fe species during top-down synthesis of dispersed Fe on N-functionalized few layer graphene,widely used in electrocatalysis.We use X-ray absorption spectroscopy to determine the electronic structure and coordination geometry of the Fe species and in situ high angle annular dark field scanning transmission electron microscopy combined with atomic resolved electron energy loss spectroscopy to localize these,identify their chemical configuration and monitor their dynamics during thermal annealing.We show the high mobility of peripheral Fe atoms,first diffusing rapidly at the trims of the graphene layers and at temperatures as high as 573 K,diffusing from the edge planes towards in-plane locations of the graphene layers forming three-,four-coordinated metal sites and more complexes polynuclear Fe species.This process occurs via bond C-C breaking which partially reduces the extension of the graphene domains.However,the vast majority of Fe is segregated as a metal phase.This dynamic interconversion depends on the structural details of the surrounding graphitic environment in which these are formed as well as the Fe loading.N species appear stabilizing isolated and polynuclear Fe species even at temperatures as high as 873 K.The significance of our results lies on the fact that single Fe atoms in graphene are highly mobile and therefore a structural description of the electroactive sites as such is insufficient and more complex species might be more relevant,especially in the case of multielectron transfer reactions.Here we provide the experimental evidence of the formation of these polynuclear Fe-N sites and their structural characteristics.

Three-Dimensional Welded Mn_(1) Site Catalysts with nearly 100% Singlet Oxygen Fabrication for Contaminant Elimination

Reactive oxygen species(ROS)have a significant part in the elimination of recalcitrant organic pollutants and commonly coexist in one advanced oxidation system.It is difficult for us to make clear the effect of the co-instantaneous generation of radicals and nonradicals,which would cover and obscure the transformation pathway.Herein,a coordinate welding process is presented for fabricating accessible Mn1 site catalysts(Mn SSCs)in order to clarify the nonradical(singlet oxygen/^(1)O_(2))generated pathway and transformation in oxidative removal of contaminants.The Mn SSCs achieve nearly 100%^(1)O_(2) fabrication by activating peroxymonosulfate,which displays an excellent sulfamethoxazole elimination performance,super anti-anion interference,and extraordinary stability.As revealed by density functional theory calculations,the Mn SSCs with a special welded three-dimensional nanostructure could significantly boost the activation process by oxidizing the peroxymonosulfate at the interlayer of Mn SSCs and reducing dissolved oxygen on the surface of Mn SSCs.This design of Mn SSCs with a three-dimensional welded nanostructure might offer a potential approach for employing single site catalysts for environmental remediation.

Single-Site Cu-Doped PdSn Wavy Nanowires for Highly Active,Stable,and CO-Tolerant Ethanol Oxidation Electrocatalysis

Developing a catalyst to break the tradeoff relation-ship between the catalytic activity and antipoisoning property toward the ethanol oxidation reaction(EOR)is of critical importance to the development of direct ethanol fuel cells(DEFCs),but remains challenging.Here,we developed a unique class of single-site Cu-doped PdSn wavy nanowires(denoted as SS Cu−PdSn WNWs)with promoted activity and durability toward alkaline EOR.Detailed characterizations reveal the atomic isolation of Cu species dispersed on the surface of the PdSn WNWs with distinct wavy structure and grain boundaries.The created SS Cu−PdSn WNWs exhibit an enhanced EOR performance in terms of mass activity,which is higher than those of PdSn WNWs,commercial Pd black,and commercial Pd/C,respectively.Moreover,the SS Cu−PdSn WNWs can also show improved stability as compared to other catalysts due to the improved antipoisoning property from the unique surface anchoring structure.Further investigations demonstrate that the doped SS Cu can strongly inhibit the adsorption of CO and promote the reaction process of EOR.DFT results reveal that the doped Cu shifts down the d-band center of PdSn,thereby modifying the adsorption of intermediates and reducing the reaction barrier of EOR.This work maps a pathway for optimally boosting EOR performance with surface engineering via atomic doping.

Highly dispersed L1_(2)-Pt_(3)Fe intermetallic particles supported on single atom Fe-N_(x)-C_(y)active sites for enhanced activity and durability towards oxygen reduction

Highly active and durable oxygen reduction reaction(ORR)catalysts with sufficient activity and stability of Pt are beneficial for the commercialization of proton exchange membrane fuel cells.Here we report an effective approach to prepare a composite catalyst comprising of ordered L1_(2)-Pt_(3)Fe intermetallic nanoparticles interact with single atom Fe-N_(x)-C_(y)active sites.The addition of Fe and the confinement effect of hierarchical porous structure limit the growth of intermetallic particle size(around2.5 nm).The ligand effect of the electron transfer from Fe to Pt and the synergistic interaction between L1_(2)-Pt_(3)Fe and Fe-N_(x)-C_(y)work together to reduce oxygen intermediates adsorption and improve kinetics process.Experimentally,the L1_(2)-Pt_(3)Fe/C_(Fe-N-C)catalyst shows high mass activity and specific activity at 1.010 A/mg_(Pt)and 1.166 mA/cm^(2),respectively,which are 5.8 and 5.1 times higher than those of commercial Pt/C(0.174 A/mg_(Pt)and 0.230mA/cm^(2)).Thanks to the more stable L1_(2)structure,L1_(2)-Pt_(3)Fe/C_(Fe-N-C)exhibits better durability(14mV E_(1/2)loss of L1_(2)-Pt_(3)Fe/C_(Fe-N-C)and 33 mV E_(1/2)loss of commercial Pt/C)after 30,000 cycles accelerated stress tests.The strategy to design and prepare small particle Pt-based intermetallic alloys coordinated with M-N-C active sites provides a new direction to obtain low-cost and easily prepared effective ORR catalysts.

Optimizing geometric configuration of single Zn-N_(4) sites for boosting reciprocal transformation between aromatic alcohols and aldehydes

It is significant to optimize geometric configuration of metal catalytic sites and boost their catalytic activity.Herein,we synthesized isolated single Zn-N_(4)sites on N-doped carbon(Zn-CN)by pyrolyzing zeolite imidazole framework-8(ZIF-8)at different temperatures.For the reciprocal transformation between benzyl alcohol and benzaldehyde,the catalytic activities of Zn-CN catalysts exhibited a volcano-like trend as the pyrolysis temperatures increased.The optimal catalyst was Zn-CN-900,with outstanding catalytic activity exceeding commercial 20 wt.%Pd/C and 20 wt.%Pt/C,promising to substitute the noble metalbased catalysts.X-ray absorption near-edge structure(XANES)measurements and density functional theory(DFT)calculation revealed the gradual transformation from tetrahedral ZnN_(4)sites of ZIF-8 into planar ZnN_(4)sites above 700℃,with the maximum planar ZnN_(4)sites in Zn-CN-900.The stronger adsorption between reactants and planar ZnN_(4)sites facilitated the activation of reactants compared with tetrahedral ZnN_(4)sites.This work will provide valuable insight into rational design of efficient catalysts by optimizing geometric configuration of catalytic sites.

Covalent Organic Frameworks Based Single-site Electrocatalysts for Oxygen Reduction Reaction

Single site catalysts(SSCs)are a new type of heterogeneous catalysts formed by isolated metal atoms supported on kinds of substrates.SSCs have shown great potential for energy conversion and storage in recent years,especially for oxygen reduction reactions(ORR).Typically,SSCs are confined on the substrate by strong chemical interactions,such as coordination bonds.Therefore,the surface chemical environment and porous properties of the supports are crucial to the performance of SSCs.In recent years,COFs have become excellent candidates for preparing SSCs as they can precisely assemble monomers into highly ordered crystalline porous materials with a fine structure and definite components.In this review,we not only summarize the characteristics and advantages of COFs based SSCs,but also highlight the applications of COFs constructed from different single active sites for ORR in recent years.Finally,challenges in practical application,feasible strategies and perspectives are proposed for the of COFs based SSCs.

Cobalt single atom site catalysts with ultrahigh metal loading for enhanced aerobic oxidation of ethylbenzene

The oxidation of hydrocarbons to produce high value-added compounds(ketones or alcohols)using oxygen in air as the only oxidant is an efficient synthetic strategy from both environmental and economic views.Herein,we successfully synthesized cobalt single atom site catalysts(Co SACs)with high metal loading of 23.58 wt.%supported on carbon nitride(CN),which showed excellent catalytic properties for oxidation of ethylbenzene in air.Moreover,Co SACs show a much higher turn-over frequency(19.6 h^(−1))than other reported non-noble catalysts under the same condition.Comparatively,the as-obtained nanosized or homogenous Co catalysts are inert to this reaction.Co SACs also exhibit high selectivity(97%)and stability(unchanged after five runs)in this reaction.DFT calculations reveal that Co SACs show a low energy barrier in the first elementary step and a high resistance to water,which result in the robust catalytic performance for this reaction.

Single copper sites dispersed on hierarchically porous carbon for improving oxygen reduction reaction towards zinc-air battery

The demand for high-performance non-precious-metal electrocatalysts to replace the noble metal-based catalysts for oxygen reduction reaction(ORR)is intensively increasing.Herein,single-atomic copper sites supported on N-doped three-dimensional hierarchically porous carbon catalyst(Cu_(1)/NC)was prepared by coordination pyrolysis strategy.Remarkably,the Cu_(1)/NC-900 catalyst not only exhibits excellent ORR performance with a half-wave potential of 0.894 V(vs.RHE)in alkaline media,outperforming those of commercial Pt/C(0.851 V)and Cu nanoparticles anchored on N-doped porous carbon(CuNPs/NC-900),but also demonstrates high stability and methanol tolerance.Moreover,the Cu_(1)/NC-900 based Zn-air battery exhibits higher power density,rechargeability and cyclic stability than the one based on Pt/C.Both experimental and theoretical investigations demonstrated that the excellent performance of the as-obtained Cu_(1)/NC-900 could be attributed to the synergistic effect between copper coordinated by three N atoms active sites and the neighbouring carbon defect,resulting in elevated Cu d-band centers of Cu atoms and facilitating intermediate desorption for ORR process.This study may lead towards the development of highly efficient non-noble metal catalysts for applications in electrochemical energy conversion.

Highly active sites of low spin Fe^(Ⅱ)N_(4)species:The identification and the ORR performance

Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe_(3)C/C and Fe_(2)N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH_(4)/H_(2)and pure NH_(3),respectively.By acid leaching of Fe_(2)N/C sample,only single sites of FeN_(4)species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN_(4)in ORR.A correlation was conducted between the concentration of Fe^(Ⅱ)N_(4)in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin Fe^(Ⅱ)N_(4) species as highly active sites for the ORR.

Single atom and defect engineering of CuO for efficient electrochemical reduction of CO_(2) to C_(2)H_(4)

Electrochemical CO_(2) transformation to high‐value ethylene(C_(2)H_(4))at high currents and efficiencies is desired and yet remains a grand challenge.We show for the first time that coupling single Sb atoms and oxygen vacancies of CuO enable synergistic electrocatalytic reduction of CO_(2) to C_(2)H_(4) at low overpotentials.Highly dispersed Sb atoms occupying metal substitutional sites of CuO are synthesized under mild conditions.The overall CO_(2) reduction faradaic efficiency(FE)reaches 89.3±1.1%with an FE toward C_(2)H_(4) exceeding 58.4%at a high‐current density of 500 mA/cm^(2).Addition of the p‐block metal is found to induce transformation of CuO from flakes to nanoribbons rich in nanoholes and oxygen vacancies,greatly enhancing CO_(2) adsorption and activation while suppressing hydrogen evolution.Further density functional theory calculations with in situ X‐ray diffraction reveal that combining Sb sites and oxygen vacancies prominently lessen the dimerization energy of adsorbed CO intermediate,thus boosting the conversion of CO_(2) to produce C_(2)H_(4).This study provides a new perspective for promoting selective C-C coupling for electrochemical CO_(2) reduction.

超低密度的单原子钴位点高效去除抗生素

单原子位点催化剂(SSCs)由于能够产生丰富的活性物质来清除类芬顿体系中的污染物,而显示出广阔的潜力.然而,在高级氧化工艺中,实现金属原子100%的利用率和减少金属浸出以满足环境安全标准是困难的.在此基础上,利用强极化力获得了Co原子含量极低(~0.17%)的催化剂,提高了金属原子利用率,降低了抗生素消除过程中金属浸出的风险.正如预期,该催化剂具有有限的Co位点,伴随着丰富的缺陷和大量从大孔到中孔再到微孔分布的骨架,实现了快速的四环素降解(0.07133 min^(−1))和优异的归一化速率常数(k per-site,2.4726×10^(5) min^(−1) M^(−1)).实验和理论结果均表明,充分暴露具有丰富C-N缺陷的Co位点,可以提高Co活性位点的电子密度,降低过硫酸盐(PDS)的吸附能,从而优化Co原子对PDS活化的利用.该研究为设计高性能、环境友好的水修复用SSCs提供了有价值的见解.

Porous γ-Fe_(2)O_(3) nanoparticle decorated with atomically dispersed platinum: Study on atomic site structural change and gas sensor activity evolution

Decorating semi-conducting metal oxide with noble metal has been recognized as a viable approach to improve the sensitivity of gas sensor. However, conventional method which relys on noble metal nanoparticles is confronted with drawback of significantly increased cost. To maximize the atom efficiency and reduce the cost for practical industrial application, designing sensor material with noble metal isolated single atom sites (ISAS) doping is a desired option. Here, we report an atomically dispersed platinum on one-dimensional arranged porous γ-Fe2O3 nanoparticle composites as highly efficient ethanol gas sensor. The optimized sample (Pt1-Fe2O3-ox) exhibited a high response (Ra/Rg = 102.4) and good selectivity to ethanol gas. It is demonstrated only the Pt single atom sites with high valance can effectively promote the adsorption capacity to ethanol and consequently enhance the sensitivity of sensing process by changing the electrical structure of Fe2O3 support. This work indicates the single atom sites could play a vital role in improving the performance of conventional metal oxides gas sensors and pave way for the exploration of ISAS-enhanced gas sensor for other volatile organic compounds (VOCs).

Simultaneous diffusion of cation and anion to access N,S cocoordinated Bi-sites for enhanced CO_(2) electroreduction

Developing highly active single-atom sites catalysts for electrochemical reduction of CO_(2) is an effective and environmental-friendly strategy to promote carbon-neutral energy cycle and ameliorate global climate issues.Herein,we develop an atomically dispersed N,S co-coordinated bismuth atom sites catalyst(Bi-SAs-NS/C)via a cation and anion simultaneous diffusion strategy for electrocatalytic CO_(2) reduction.In this strategy,the bonded Bi cation and S anion are simultaneously diffused into the nitrogen-doped carbon layer in the form of Bi2S3.Then Bi is captured by the abundant N-rich vacancies and S is bonded with carbons.support at high temperature,formed the N,S co-coordinated Bi sites.Benefiting from the simultaneous diffusion of Bi and S,different electronegative N and S can be effectively co-coordinated with Bi,forming the uniform Bi-N_(3)S/C sites.The synthesized.Bi-SAs-NS/C exhibits a high selectivity towards CO with over 88%Faradaic efficiency in a wide potential range,and achieves a maximum FE_(CO)of 98.3%at-0.8 V vs.RHE with a current density of 10.24 mA·cm^(-2),which can keep constant with negligible degradation in 24 h continuous electrolysis.Experimental results and theoretical calculations reveal that the significantly improved catalytic performance of Bi-SAs-NS/C than Bi-SAs-N/C is ascribed to the replacement of one coordinated-N with low electronegative S in Bi-N_(4)C center,which can greatly reduce the energy barrier of the intermediate formation in rate-limiting step and increase the reaction kinetics.This work provides an effective strategy for rationally designing highly active single-atom sites;catalysts for efficient electrocatalysis with optimized electronic structure.

Defect engineering on constructing surface active sites in catalysts for environment and energy applications

The precise engineering of surface active sites is deemed as an efficient protocol for regulating surfaces and catalytic properties of catalysts.Defect engineering is the most feasible option to modulate the surface active sites of catalysts.Creating specific active sites on the catalyst allows precise modulation of its electronic structure and physicochemical characteristics.Here,we outlined the engineering of several types of defects,including vacancy defects,void defects,dopant-related defects,and defect-based single atomic sites.An overview of progress in fabricating structural defects on catalysts via de novo synthesis or post-synthetic modification was provided.Then,the applications of the well-designed defective catalysts in energy conversion and environmental remediation were carefully elucidated.Finally,current challenges in the precise construction of active defect sites on the catalyst and future perspectives for the development directions of precisely controlled synthesis of defective catalysts were also proposed.

Rational design of Ru species on N-doped graphene promoting water dissociation for boosting hydrogen evolution reaction

In this study,the morphological distribution of Ru on nitrogen-doped graphene(NG)could be rationally regulated via modulating the combination mode between Ru precursor and the zeolite imidazolate framework-8(ZIF-8).The cation exchange and host-guest strategies respectively resulted in two different combination modes between Ru precursor and ZIF-8 anchored on graphene.Following pyrolysis of the above precursors,Ru single-atom sites(SASs)with and without Ru nanoparticles(NPs)were formed selectively on NG(denoted as Ru SASs+NPs/NG and Ru SASs/NG,respectively).Ru SASs+NPs/NG exhibited excellent hydrogen evolution reaction(HER)performance in alkaline solutions(η_(10)=12 mV,12.57 A mg^(-1)_(Ru) at 100 mV),which is much better than Ru SASs/NG.The experimental and theoretical study revealed that Ru SASs could adsorb hydrogen with optimal adsorption strength,while Ru NPs could lower the barrier of water molecule dissociation,and thus Ru SASs and Ru NPs could synergistically promote the catalytic performance of HER in alkaline solutions.

Radiofrequency field enhanced chemical ionization with vacuum ultraviolet lamp for miniature time-of-flight mass spectrometer

It is difficult to rapidly and on-line detect trace volatile organic compounds for miniature massspectrometry due to its limited sampling volume at slow pumping speed. In this paper, we developed anew radiofrequency field enhanced chemical ionization source （RF-ECI） with vacuum ultraviolet （VUV）lamp by coupling radiofrequency electric field and direct-current field together. The experiment resultsshowed that the sensitivity of benzene, toluene, hydrogen sulfide and other compounds increased by 2-3orders of magnitude under the introduction of RF-ECI comparing to traditional single photon ionization（SPI）. At the same time, the reagent ion of O2＋ realized the charge transfer reaction chemical ionization,and the RF-ECI effectively expanded the detection range of the VUV lamp based SPI. The VUV lamp hasinherent advantages in the on-site analytical instrument for its small size and low power consumption,and the VUV lamp based RF-ECI miniature time-of-flight mass spectrometer （TOFMS） has a limit-of-detection for H2S as low as 0.0571 mg/m3, and it is expected to be used widely in the field of on-site rapidanalvsis.