The activation of CO on iron-based materials is a key elementary reaction for many chemical processes.We investigate CO adsorption and dissociation on a series of Fe,Fe_(3)C,Fe_(5)C_(2),and Fe_(2)C catalysts through d...The activation of CO on iron-based materials is a key elementary reaction for many chemical processes.We investigate CO adsorption and dissociation on a series of Fe,Fe_(3)C,Fe_(5)C_(2),and Fe_(2)C catalysts through density functional theory calculations.We detect dramatically different performances for CO adsorption and activation on diverse surfaces and sites.The activation of CO is dependent on the local coordination of the molecule to the surface and on the bulk phase of the underlying catalyst.The bulk properties and the different local bonding environments lead to varying interactions between the adsorbed CO and the surface and thus yielding different activation levels of the C-O bond.We also examine the prediction of CO adsorption on different types of Fe-based catalysts by machine learning through linear regression models.We combine the features originating from surfaces and bulk phases to enhance the prediction of the activation energies and perform eight different linear regressions utilizing the feature engineering of polynomial representations.Among them,a ridge linear regression model with2nd-degree polynomial feature generation predicted the best CO activation energy with a mean absolute error of 0.269 eV.展开更多
In order to study the influence of three-grid assembly thermal deformation caused by heat accumulation on breakdown times and an ion extraction process,a hot gap test and a breakdown time test are carried out to obtai...In order to study the influence of three-grid assembly thermal deformation caused by heat accumulation on breakdown times and an ion extraction process,a hot gap test and a breakdown time test are carried out to obtain thermal deformation of the grids when the thruster is in 5 k W operation mode.Meanwhile,the fluid simulation method and particle-in-cell-Monte Carlo collision（PICMCC） method are adopted to simulate the ion extraction process according to the previous test results.The numerical calculation results are verified by the ion thruster performance test.The results show that after about 1.2 h operation,the hot gap between the screen grid and the accelerator grid reduce to 0.25–0.3 mm,while the hot gap between the accelerator grid and the decelerator grid increase from 1 mm to about 1.4 mm when the grids reach thermal equilibrium,and the hot gap is almost unchanged.In addition,the breakdown times experiment shows that 0.26 mm is the minimal safe hot gap for the grid assembly as the breakdown times improves significantly when the gap is smaller than this value.Fluid simulation results show that the plasma density of the screen grid is in the range 6？×10^（17）–6？×？10^（18） m^（13） and displays a parabolic characteristic,while the electron temperature gradually increases along the axial direction.The PIC-MCC results show that the current falling of an ion beam through a single aperture is significant.Meanwhile,the intercepted current of the accelerator grid and the decelerator grid both increase with the change in the hot gap.The ion beam current has optimal perveance status without thermal deformation,and the intercepted current of the accelerator grid and the decelerator grid are 3.65 m A and 6.26 m A,respectively.Furthermore,under the effect of thermal deformation,the ion beam current has over-perveance status,and the intercepted current of the accelerator grid and the decelerator grid are 10.46 m A and 18.24 m A,respectively.Performance test results indicate that the breakdown times increase obviously.The intercepted current of the accelerator grid and the decelerator grid increases to 13 m A and 16.5 m A,respectively,due to the change in the hot gap after 1.5 h operation.The numerical calculation results are well consistent with performance test results,and the error comes mainly from the test uncertainty of the hot gap.展开更多
The selective cleavage of C-O and C-C is facing a challenge in the field of catalysis.In the present work,we studied the influence of doped Ni on the structure and electronic properties,as well as the selective C-O/C-...The selective cleavage of C-O and C-C is facing a challenge in the field of catalysis.In the present work,we studied the influence of doped Ni on the structure and electronic properties,as well as the selective C-O/C-C bond cleavages in the hydrodeoxygenation of palmitic acid over Ni-Mo_(2)C catalyst.The catalytic activity on Ni doped Mo_(2)C with TOF of 6.9×10^(3)h^(-1)is much superior to intrinsic Mo_(2)C catalyst,which is also higher than most noble metal catalysts.Structurally,the doped Ni raises the active particle dispersion and the coordination numbers of Mo species(Mo-C and Mo-O),improves the graphitization degree to promote the electron transfer,and increases the amount of Lewis and Br?nsted acid,which are responsible for the excellent hydrodeoxygenation performance.The Ni promotes simultaneously C-O and C-C bonds cleavage to produce pentadecane and hexadecane owing to the increase of electron-rich Mo sites after Ni doping.These findings contribute to the understanding of the nature of Ni-doped Mo_(2)C on the roles as catalytic active sites for C-O and C-C bonds cleavage.展开更多
Individuals tend to move freely when there is enough room but would act collectively for their survival under external stress.In the case of living cells,for instance,when a drop of low-density flagellated bacterial s...Individuals tend to move freely when there is enough room but would act collectively for their survival under external stress.In the case of living cells,for instance,when a drop of low-density flagellated bacterial solution is transferred onto the agar surface,the initially disordered movement of individual bacteria would be replaced with coordinated cell swarming after a lag phase of a few hours.Here,we study how such cooperation is established while overcoming the disorder at the onset of the lag phase with single nanoparticle tracking.Upon the spreading of the droplet,the bacteria in the solution cluster and align near the almost immobilized contact line confining the drop,forming a narrow ring of cells.As individual cells move in and out of the ring continuously,certain flow patterns emerge in the inter-bacterial fluid.We reveal high-speed long-distance unidirectional flows with definite chirality along the outside of the ring,along the inside of the ring and across the ring.We speculate that these flows enable the fast and efficient transport,facilitating the communication and unification of the bacterial community.展开更多
Solid surfaces usually reach thermodynamic equilibrium through particle exchange with their environment under reactive conditions.A prerequisite for understanding their functionalities is detailed knowledge of the sur...Solid surfaces usually reach thermodynamic equilibrium through particle exchange with their environment under reactive conditions.A prerequisite for understanding their functionalities is detailed knowledge of the surface composition and atomistic geometry under working conditions.Owing to the large number of possible Miller indices and terminations involved in multielement solids,extensive sampling of the compositional and conformational space needed for reliable surface energy estimation is beyond the scope of ab initio calculations.Here,we demonstrate,using the case of iron carbides in environments with varied carbon chemical potentials,that the stable surface composition and geometry of multielement solids under reactive conditions,which involve large compositional and conformational spaces,can be predicted at ab initio accuracy using an approach that combines the bond valence model,Gaussian process regression,and ab initio thermodynamics.Determining the atomistic structure of surfaces under working conditions paves the way toward identifying the true active sites of multielement catalysts in heterogeneous catalysis.展开更多
Chemical-disordered materials have a wide range of applications whereas the determination of their structures or configurations isone of the most important and challenging problems. Traditional methods are extremely i...Chemical-disordered materials have a wide range of applications whereas the determination of their structures or configurations isone of the most important and challenging problems. Traditional methods are extremely inefficient or intractable for large systemsdue to the notorious exponential-wall issue that the number of possible structures increase exponentially for N-body systems.Herein, we introduce an efficient approach to predict the thermodynamically stable structures of chemical-disordered materials viaactive-learning accompanied by first-principles calculations. Our method, named LAsou, can efficiently compress the samplingspace and dramatically reduce the computational cost. Three distinct and typical finite-size systems are investigated, including theanion-disordered BaSc(O_(x)F_(1−x))3 (x = 0.667), the cation-disordered Ca_(1−x)Mn_(x)CO_(3) (x = 0.25) with larger size and the defect-disordered ε-FeC_(x) (x = 0.5) with larger space. The commonly used enumeration method requires to explicitly calculate 2664, 1033,and 10496 configurations, respectively, while the LAsou method just needs to explicitly calculate about 15, 20, and 10configurations, respectively. Besides the finite-size system, our LAsou method is ready for quasi-infinite size systems empoweringmaterials design.展开更多
Constructing and understanding the doping effect of secondary metal in transition metal carbide(TMC)catalysts is pivotal for the design of low-cost hydrogen evolution reaction(HER) electrocatalysts. In this work, we d...Constructing and understanding the doping effect of secondary metal in transition metal carbide(TMC)catalysts is pivotal for the design of low-cost hydrogen evolution reaction(HER) electrocatalysts. In this work, we developed a wet-chemistry strategy for synthesizing Co-modified Fe_5C_2 nanoparticles((Fe_(1-x)Cox)_5C_2 NPs) as highly active HER electrocatalysts in basic solution. The structure of(Fe_(1-x)Cox)_5C_2 NPs was characterized by X-ray diffraction(XRD), extended X-ray absorption fine structure spectra(EXAFS) and scanning/transmission electron microscopy(S/TEM), indicating that the isomorphous substitution of cobalt in the lattice of Fe_5C_2.(Fe_(0.75) Co_(0.25))_5C_2 exhibited the best HER activity(174 mV for j = -10 mA/cm^2). Computational calculation results indicate that Co provides the most active site for HER. X-ray adsorption spectra(XAS) studies further suggested that the electron transfer in Fe–C bonds are enhanced by the substitution of Co, which modulates the hydrogen adsorption on the adjacent electronic-enriched carbon, and therefore promotes HER activity. Our results affirm the design of lowcost bimetallic TMCs based HER catalysts.展开更多
Fun dame ntal un derstandi ng of chemistry confined to nano space remains a challe nge since molecules en capsulated in confined microe nviron merits are difficult to be characterized.Here,we show that CO adsorptio n ...Fun dame ntal un derstandi ng of chemistry confined to nano space remains a challe nge since molecules en capsulated in confined microe nviron merits are difficult to be characterized.Here,we show that CO adsorptio n on Pt(111)8nfined un der mono layer hexago nal boron nitride(h-BN)can be dynamically imaged using near ambient pressure seanning tunneling microscope(NAP-STM)and thanks to tunneling transparency of the top h-BN layer.The observed CO superstructures on Pt(111)in different CO atmospheres allow to derive surface coverages of CO adlayers,which are higher in the 8nfined nano space between h-BN and Pt(111)than those on the ope n Pt surface un der the same conditions.Dynamic NAP-STM imaging data together with theoretical calculations confirm confinement-induced molecule enrichment effect within the 2D nano space,which reveals new chemistry aroused by the confined nano reactor.展开更多
基金financially supported from the National Natural Science Foundation of China (No.22002008)Ningxia Key Research and Development Project,China (Nos.2022BEE03002 and 2022BSB03056)funding support from Synfuels China,Co.,Ltd.and Beijing Advanced Innovation Center for Materials Genome Engineering。
文摘The activation of CO on iron-based materials is a key elementary reaction for many chemical processes.We investigate CO adsorption and dissociation on a series of Fe,Fe_(3)C,Fe_(5)C_(2),and Fe_(2)C catalysts through density functional theory calculations.We detect dramatically different performances for CO adsorption and activation on diverse surfaces and sites.The activation of CO is dependent on the local coordination of the molecule to the surface and on the bulk phase of the underlying catalyst.The bulk properties and the different local bonding environments lead to varying interactions between the adsorbed CO and the surface and thus yielding different activation levels of the C-O bond.We also examine the prediction of CO adsorption on different types of Fe-based catalysts by machine learning through linear regression models.We combine the features originating from surfaces and bulk phases to enhance the prediction of the activation energies and perform eight different linear regressions utilizing the feature engineering of polynomial representations.Among them,a ridge linear regression model with2nd-degree polynomial feature generation predicted the best CO activation energy with a mean absolute error of 0.269 eV.
基金supported by the National Key Laboratory Fund of Science and Technology on Vacuum Technology & Physics (Grant No.6142207030103)National Natural Science Foundation of China (Grant No.11702123)
文摘In order to study the influence of three-grid assembly thermal deformation caused by heat accumulation on breakdown times and an ion extraction process,a hot gap test and a breakdown time test are carried out to obtain thermal deformation of the grids when the thruster is in 5 k W operation mode.Meanwhile,the fluid simulation method and particle-in-cell-Monte Carlo collision（PICMCC） method are adopted to simulate the ion extraction process according to the previous test results.The numerical calculation results are verified by the ion thruster performance test.The results show that after about 1.2 h operation,the hot gap between the screen grid and the accelerator grid reduce to 0.25–0.3 mm,while the hot gap between the accelerator grid and the decelerator grid increase from 1 mm to about 1.4 mm when the grids reach thermal equilibrium,and the hot gap is almost unchanged.In addition,the breakdown times experiment shows that 0.26 mm is the minimal safe hot gap for the grid assembly as the breakdown times improves significantly when the gap is smaller than this value.Fluid simulation results show that the plasma density of the screen grid is in the range 6？×10^（17）–6？×？10^（18） m^（13） and displays a parabolic characteristic,while the electron temperature gradually increases along the axial direction.The PIC-MCC results show that the current falling of an ion beam through a single aperture is significant.Meanwhile,the intercepted current of the accelerator grid and the decelerator grid both increase with the change in the hot gap.The ion beam current has optimal perveance status without thermal deformation,and the intercepted current of the accelerator grid and the decelerator grid are 3.65 m A and 6.26 m A,respectively.Furthermore,under the effect of thermal deformation,the ion beam current has over-perveance status,and the intercepted current of the accelerator grid and the decelerator grid are 10.46 m A and 18.24 m A,respectively.Performance test results indicate that the breakdown times increase obviously.The intercepted current of the accelerator grid and the decelerator grid increases to 13 m A and 16.5 m A,respectively,due to the change in the hot gap after 1.5 h operation.The numerical calculation results are well consistent with performance test results,and the error comes mainly from the test uncertainty of the hot gap.
基金financially supported by the National Natural Science Foundation of China(21972099)the Application Foundation Program of Sichuan Province(2021YJ0305)+1 种基金the 111 project(B17030).Shanghai Synchrotron Radiation Facility(SSRF)for XAS experiments and the support by the project from NPL of CAEP(2019BB08)。
文摘The selective cleavage of C-O and C-C is facing a challenge in the field of catalysis.In the present work,we studied the influence of doped Ni on the structure and electronic properties,as well as the selective C-O/C-C bond cleavages in the hydrodeoxygenation of palmitic acid over Ni-Mo_(2)C catalyst.The catalytic activity on Ni doped Mo_(2)C with TOF of 6.9×10^(3)h^(-1)is much superior to intrinsic Mo_(2)C catalyst,which is also higher than most noble metal catalysts.Structurally,the doped Ni raises the active particle dispersion and the coordination numbers of Mo species(Mo-C and Mo-O),improves the graphitization degree to promote the electron transfer,and increases the amount of Lewis and Br?nsted acid,which are responsible for the excellent hydrodeoxygenation performance.The Ni promotes simultaneously C-O and C-C bonds cleavage to produce pentadecane and hexadecane owing to the increase of electron-rich Mo sites after Ni doping.These findings contribute to the understanding of the nature of Ni-doped Mo_(2)C on the roles as catalytic active sites for C-O and C-C bonds cleavage.
基金supported by the National Natural Science Foundation of China(21425519,21621003,91853105 and 22127807).
文摘Individuals tend to move freely when there is enough room but would act collectively for their survival under external stress.In the case of living cells,for instance,when a drop of low-density flagellated bacterial solution is transferred onto the agar surface,the initially disordered movement of individual bacteria would be replaced with coordinated cell swarming after a lag phase of a few hours.Here,we study how such cooperation is established while overcoming the disorder at the onset of the lag phase with single nanoparticle tracking.Upon the spreading of the droplet,the bacteria in the solution cluster and align near the almost immobilized contact line confining the drop,forming a narrow ring of cells.As individual cells move in and out of the ring continuously,certain flow patterns emerge in the inter-bacterial fluid.We reveal high-speed long-distance unidirectional flows with definite chirality along the outside of the ring,along the inside of the ring and across the ring.We speculate that these flows enable the fast and efficient transport,facilitating the communication and unification of the bacterial community.
基金This work was financially supported by the National Science Fund for Distinguished Young Scholars of China(grant no.22225206)the National Key R&D Program of China(no.2022YFA1604103)+6 种基金the National Natural Science Foundation of China(nos.21972157 and 21972160)the CAS Project for Young Scientists in Basic Research(YSBR-005)the Key Research Program of Frontier Sciences CAS(ZDBS-LY-7007)the Major Research Plan of the National Natural Science Foundation of China(92045303)the Informatization Plan of the Chinese Academy of Sciences(grant no.CAS-WX2021SF0110)the Youth Innovation Promotion Association CAS(2020179)Funding support was also received from the Beijing Advanced Innovation Center for Materials Genome Engineering,Synfuels China Co.,Ltd.,and the Institute of Coal Chemistry,Chinese Academy of Sciences.
文摘Solid surfaces usually reach thermodynamic equilibrium through particle exchange with their environment under reactive conditions.A prerequisite for understanding their functionalities is detailed knowledge of the surface composition and atomistic geometry under working conditions.Owing to the large number of possible Miller indices and terminations involved in multielement solids,extensive sampling of the compositional and conformational space needed for reliable surface energy estimation is beyond the scope of ab initio calculations.Here,we demonstrate,using the case of iron carbides in environments with varied carbon chemical potentials,that the stable surface composition and geometry of multielement solids under reactive conditions,which involve large compositional and conformational spaces,can be predicted at ab initio accuracy using an approach that combines the bond valence model,Gaussian process regression,and ab initio thermodynamics.Determining the atomistic structure of surfaces under working conditions paves the way toward identifying the true active sites of multielement catalysts in heterogeneous catalysis.
基金The authors are grateful for the financial support from the National Key R&D Program of China(No.2022YFA1604103)National Science Fund for Distinguished Young Scholars of China(Grant No.22225206)+5 种基金the National Natural Science Foundation of China(Nos.21972157,21972160 and 21703272)CAS Project for Young Scientists in Basic Research(YSBR-005),Key Research Program of Frontier Sciences CAS(ZDBS-LY-7007)Major Research plan of the National Natural Science Foundation of China(92045303)CAS Project for Internet Security and Information Technology(CAS-WX2021SF0110)Science and Technology Plan Project of Inner Mongolia Autono-mous Region of China(2021GG0309)funding support from Beijing Advanced Innovation Center for Materials Genome Engineering,Synfuels China,Co.Ltd,and Institute of Coal Chemistry(CAS).Q.P.would like to acknowledge the support provided by LiYing Program of the Institute of Mechanics,Chinese Academy of Sciences(Grant No.E1Z1011001).
文摘Chemical-disordered materials have a wide range of applications whereas the determination of their structures or configurations isone of the most important and challenging problems. Traditional methods are extremely inefficient or intractable for large systemsdue to the notorious exponential-wall issue that the number of possible structures increase exponentially for N-body systems.Herein, we introduce an efficient approach to predict the thermodynamically stable structures of chemical-disordered materials viaactive-learning accompanied by first-principles calculations. Our method, named LAsou, can efficiently compress the samplingspace and dramatically reduce the computational cost. Three distinct and typical finite-size systems are investigated, including theanion-disordered BaSc(O_(x)F_(1−x))3 (x = 0.667), the cation-disordered Ca_(1−x)Mn_(x)CO_(3) (x = 0.25) with larger size and the defect-disordered ε-FeC_(x) (x = 0.5) with larger space. The commonly used enumeration method requires to explicitly calculate 2664, 1033,and 10496 configurations, respectively, while the LAsou method just needs to explicitly calculate about 15, 20, and 10configurations, respectively. Besides the finite-size system, our LAsou method is ready for quasi-infinite size systems empoweringmaterials design.
基金supported by the National Natural Science Foundation of China(91645115,21473003,21673273,21473229,21821004,and 91545121)the National Basic Research Program of China(2013CB933100)+4 种基金the financial support of China Postdoctoral Science Foundation(2016M590216)the financial support of China Postdoctoral Science Foundation(2015M580011)National Thousand Young Talents Program of ChinaHundred-Talent Program of Chinese Academy of SciencesShanxi Hundred-Talent Program
文摘Constructing and understanding the doping effect of secondary metal in transition metal carbide(TMC)catalysts is pivotal for the design of low-cost hydrogen evolution reaction(HER) electrocatalysts. In this work, we developed a wet-chemistry strategy for synthesizing Co-modified Fe_5C_2 nanoparticles((Fe_(1-x)Cox)_5C_2 NPs) as highly active HER electrocatalysts in basic solution. The structure of(Fe_(1-x)Cox)_5C_2 NPs was characterized by X-ray diffraction(XRD), extended X-ray absorption fine structure spectra(EXAFS) and scanning/transmission electron microscopy(S/TEM), indicating that the isomorphous substitution of cobalt in the lattice of Fe_5C_2.(Fe_(0.75) Co_(0.25))_5C_2 exhibited the best HER activity(174 mV for j = -10 mA/cm^2). Computational calculation results indicate that Co provides the most active site for HER. X-ray adsorption spectra(XAS) studies further suggested that the electron transfer in Fe–C bonds are enhanced by the substitution of Co, which modulates the hydrogen adsorption on the adjacent electronic-enriched carbon, and therefore promotes HER activity. Our results affirm the design of lowcost bimetallic TMCs based HER catalysts.
基金the National Natural Science Foundation of China(Nos.21688102,21621063,91545204,and 21703274)the Ministry of Science and Technology of China(No.2016YFA0200200)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB17020000).
文摘Fun dame ntal un derstandi ng of chemistry confined to nano space remains a challe nge since molecules en capsulated in confined microe nviron merits are difficult to be characterized.Here,we show that CO adsorptio n on Pt(111)8nfined un der mono layer hexago nal boron nitride(h-BN)can be dynamically imaged using near ambient pressure seanning tunneling microscope(NAP-STM)and thanks to tunneling transparency of the top h-BN layer.The observed CO superstructures on Pt(111)in different CO atmospheres allow to derive surface coverages of CO adlayers,which are higher in the 8nfined nano space between h-BN and Pt(111)than those on the ope n Pt surface un der the same conditions.Dynamic NAP-STM imaging data together with theoretical calculations confirm confinement-induced molecule enrichment effect within the 2D nano space,which reveals new chemistry aroused by the confined nano reactor.
