本文研究了2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面解离的可能微观反应机理,使用完全线性同步和二次同步变换(complete LST/QST)方法确定解离反应的过渡态.采用基于第一性原理的密度泛函理论与周期平板模型相结合的方法,优化了2-丙醇和...本文研究了2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面解离的可能微观反应机理,使用完全线性同步和二次同步变换(complete LST/QST)方法确定解离反应的过渡态.采用基于第一性原理的密度泛函理论与周期平板模型相结合的方法,优化了2-丙醇和1,1,1-三氟-2-丙醇裂解反应过程各物种在Ni(100)表面的top,hollow和bridge位的吸附模型,计算了能量,并对布局电荷进行了分析,得到了各物种的有利吸附位.结果表明:2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面都存在β-H和γ-H两个平行竞争的解离过程,其中2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为64.7 k J·mol-1猯,而γ-H解离速控步骤活化能为233.1 k J·mol-1猯,故β-H解离过程占优势,主要产物是CH3COCH3;相反,1,1,1-三氟-2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为257.1 k J·mol-1猯,而γ-H解离速控步骤活化能为148.1 k J·mol-1猯,故γ-H解离过程占优势,主要产物是CF3CH=CH2.由此说明,电负性更大的氟原子取代2-丙醇中的氢原子之后,2-丙醇在Ni表面的解离机理发生了改变.理论预测结果与实验结论一致.展开更多
Density functional theory was used to study the NH3 behavior on Ni monolayer covered Pt（111） and WC（001）. The electronic structure of the surfaces, and the adsorption and decomposition of NH3 were calculated and c...Density functional theory was used to study the NH3 behavior on Ni monolayer covered Pt（111） and WC（001）. The electronic structure of the surfaces, and the adsorption and decomposition of NH3 were calculated and compared. Ni atoms in the monolayer behave different from that in Ni（111）. More dz2 electrons of Ni in monolayer covered systems were shifted to other regions compared to Ni（111）, charge density depletion on this orbital is crucial to NH3 adsorption. NH3 binds more stable on Ni/Pt（lll） and Ni/WC（001） than on Ni（111）, the energy barriers of the first N-H bond scission were evidently lower on Ni/Pt（111） and Ni/WC（001） than on Ni（111）, these are significant to NH3 decomposition. N recombination is the rate-limiting step, high reaction barrier implies that N2 is produced only at high temperatures. Although WC has similar properties to Pt, differences of the electronic structure and catalytic activities are observed for Ni/Pt（111） and Ni/WC （001）, the energy barrier for the rate-determined step increases on Ni/WC（001） instead of decreasing on Ni/Pt（lll） when compared to Ni（111）. the N recombination barrier by modifying To design cheaper and better catalysts, reducing Ni/WC（001） is a critical question to be solved.展开更多
This paper investigated the influences of surface properties of carbon support and nickel precursors(nickel nitrate, nickel chloride and nickel acetate) on Ni nanoparticle sizes and catalytic performances for steam re...This paper investigated the influences of surface properties of carbon support and nickel precursors(nickel nitrate, nickel chloride and nickel acetate) on Ni nanoparticle sizes and catalytic performances for steam reforming of toluene. Treatment with nitric acid helped to increase the amount of functional groups on the surface and hydrophilic nature of carbon support, leading to a homogeneous distribution of Ni nanoparticles. The thermal decomposition products of nickel precursor also played an important role, Ni nanoparticles supported on carbon treated with acid using nickel nitrate as the precursor exhibited the smallest mean diameter of 4.5 nm. With the loading amount increased from 6 wt% to 18 wt%, the mean particle size of Ni nanoparticles varied from4.5 nm to 9.1 nm. The as-prepared catalyst showed a high catalytic activity and a good stability for toluene steam reforming: 98.1% conversion of toluene was obtained with the Ni content of 12 wt% and the S/C ratio of3, and the conversion only decreased to 92.0% after 700 min. Because of the high activity, good stability, and low cost, the as-prepared catalyst opens up new opportunities for tar removing.展开更多
Crystal structures of nonstoichiometric La(Ni, Sn)5+x (x = 0.1～0.4) alloys prepared by different methods were investigated by using powder X-ray diffraction and Rietveld refinement analysis. Space group of this type ...Crystal structures of nonstoichiometric La(Ni, Sn)5+x (x = 0.1～0.4) alloys prepared by different methods were investigated by using powder X-ray diffraction and Rietveld refinement analysis. Space group of this type of alloys belongs to P6/mmm, in which Sn only occupies the 3g sites. It has been demonstrated that some of the 1a sites of the nonstoichiometric alloy are replaced by the NiNi dumb-bells which have a strong correlation with the anisotropic thermal parameter B33. The preparation methods have an effect on the number of dumb-bells that can substitute the 1a sites. It was found that the annealed alloys have more NiNi dumb-bells in the structure than the rapid solidified and as-cast alloys have while still keep good crystallinity.展开更多
The orientation control of graphene overlayers on metal surface is an important issue which remains as a challenge in graphene growth on Ni surface. Here we have demonstrated that epitaxial graphene overlayers can be ...The orientation control of graphene overlayers on metal surface is an important issue which remains as a challenge in graphene growth on Ni surface. Here we have demonstrated that epitaxial graphene overlayers can be obtained by annealing a nickel carbide covered Ni（111） surface using in situ surface imaging techniques. Epitaxial graphene islands nucleate and grow via segregation of dissolved carbon atoms to the top surface at about 400 ℃. This is in contrast to a mixture of epitaxial and non-epi- taxial graphene domains grown directly on Ni（111） at 540 ℃. The different growth behaviors are related to the nucleation dynamics which is controlled by local carbon densities in the near surface region.展开更多
Dissociative chemisorption of methane on a nickel surface is a prototypical system for studying mode-specific chemistry in gassurface reactions.We recently developed a fifteen-dimensional potential energy surface for ...Dissociative chemisorption of methane on a nickel surface is a prototypical system for studying mode-specific chemistry in gassurface reactions.We recently developed a fifteen-dimensional potential energy surface for this system which has proven to be chemically accurate in reproducing the measured absolute dissociative sticking probabilities of CHD_3in thermal conditions and with vibrational excitation on Ni(111)at high incident energies.Here,using this new potential energy surface,we explored mode specificity and bond selectivity for CHD_3and CH_2D_2dissociative chemisorption at low incidence energies down to^50 k J/mol via a quasi-classical trajectory method.Our calculated dissociation probabilities are consistent with previous theoretical and experimental ones with an average shift in translational energy of^8 k J/mol.Our results very well reproduce the C–H/C–D branching ratio upon the C–H local mode excitation,which can be rationalized by the sudden vector projection model.Quantitatively,however,the calculated dissociative sticking probabilities are systematically larger than experimental ones,due presumably to the artificial zero point energy leakage into reaction coordinate.Further high-dimensional quantum dynamics calculations are necessary for acquiring a chemically accurate description of methane dissociative chemisorption at low incident energies.展开更多
Cost-efficient electrocatalysts composed of earth-abundant elements are highly desired for enhanced oxygen evolution reaction (OER).As a promising candidate,metallic Co4N already demonstrated electrocatalytic performa...Cost-efficient electrocatalysts composed of earth-abundant elements are highly desired for enhanced oxygen evolution reaction (OER).As a promising candidate,metallic Co4N already demonstrated electrocatalytic performance relying on specific nanostructures and electronic configurations.Herein,nickel was introduced as the dopant into one-dimensional (1D) hierarchical Co4N structures,achieving effective electronic regulation of Co4N toward high OER performance.The amount of Co3+increased after Ni-doping,and the in-situ formed surface oxyhydroxide during OER enhanced the electrocatalytic kinetics.Meanwhile,the 1D hierarchical structure further promoted the performances of Co4N owing to the high electrical conductivity and abundant activesites on the rough surface.As expected,the optimal Ni-doped Co4N with a Ni/Co molar ratio of 0.25 provides a small overpotential of 233 mV at a current density of 10 mA cm^(-2),with a low Tafel slope of 61 mV dec^(-1),and high long-term stability in 1.0 mol L^(-1)KOH.Following these results,the enhancement by doping the Co4N nanowire bundles with Fe and Cu was further evidenced for the OER.展开更多
Based on the results of slot milling experiments on the DD5 Ni-based single crystal superalloy(001) crystal plane along the [110]crystal direction, in this paper, efforts were devoted to investigate the tool wear proc...Based on the results of slot milling experiments on the DD5 Ni-based single crystal superalloy(001) crystal plane along the [110]crystal direction, in this paper, efforts were devoted to investigate the tool wear process, wear mechanism and failure modes of the physical vapor deposition(PVD)-AlTiN and TiAlN coated tools under dry milling and water-based minimum quantity lubrication(MQL) conditions. The scanning electron microscope(SEM) morphological observation and energy dispersive X-ray spectroscopy(EDX) elements analysis methods were adopted. Moreover, under the water-based MQL condition, the surface integrity such as surface roughness, dimensional and shape accuracy, microhardness and microstructure alteration were researched. The results demonstrated that the tool edge severe adhesion with the work material, induced by the high Al content in the PVD-AlTiN coating caused the catastrophic tool tip fracture. In contrast, the PVD-TiAlN tool displayed a steady and uniform minor flank wear, even though the material peeling and slight chipping also occurred in the final stage. In addition, due to the high effective cooling and lubricating actions of the water-based MQL method, the PVD-TiAlN coated tool demonstrated intact tip geometry; consequently it could be repaired and reused even if the failure criterion was attained. Moreover, as the accumulative milling length and the tool wear increased, all indicators of the surface integrity forehand were deteriorated.展开更多
文摘本文研究了2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面解离的可能微观反应机理,使用完全线性同步和二次同步变换(complete LST/QST)方法确定解离反应的过渡态.采用基于第一性原理的密度泛函理论与周期平板模型相结合的方法,优化了2-丙醇和1,1,1-三氟-2-丙醇裂解反应过程各物种在Ni(100)表面的top,hollow和bridge位的吸附模型,计算了能量,并对布局电荷进行了分析,得到了各物种的有利吸附位.结果表明:2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面都存在β-H和γ-H两个平行竞争的解离过程,其中2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为64.7 k J·mol-1猯,而γ-H解离速控步骤活化能为233.1 k J·mol-1猯,故β-H解离过程占优势,主要产物是CH3COCH3;相反,1,1,1-三氟-2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为257.1 k J·mol-1猯,而γ-H解离速控步骤活化能为148.1 k J·mol-1猯,故γ-H解离过程占优势,主要产物是CF3CH=CH2.由此说明,电负性更大的氟原子取代2-丙醇中的氢原子之后,2-丙醇在Ni表面的解离机理发生了改变.理论预测结果与实验结论一致.
文摘Density functional theory was used to study the NH3 behavior on Ni monolayer covered Pt（111） and WC（001）. The electronic structure of the surfaces, and the adsorption and decomposition of NH3 were calculated and compared. Ni atoms in the monolayer behave different from that in Ni（111）. More dz2 electrons of Ni in monolayer covered systems were shifted to other regions compared to Ni（111）, charge density depletion on this orbital is crucial to NH3 adsorption. NH3 binds more stable on Ni/Pt（lll） and Ni/WC（001） than on Ni（111）, the energy barriers of the first N-H bond scission were evidently lower on Ni/Pt（111） and Ni/WC（001） than on Ni（111）, these are significant to NH3 decomposition. N recombination is the rate-limiting step, high reaction barrier implies that N2 is produced only at high temperatures. Although WC has similar properties to Pt, differences of the electronic structure and catalytic activities are observed for Ni/Pt（111） and Ni/WC （001）, the energy barrier for the rate-determined step increases on Ni/WC（001） instead of decreasing on Ni/Pt（lll） when compared to Ni（111）. the N recombination barrier by modifying To design cheaper and better catalysts, reducing Ni/WC（001） is a critical question to be solved.
基金Supported by the National Natural Science Foundation of China(21606008,21436002)the National Basic Research Foundation of China(2013CB733600)the Fundamental Research Funds for the Central Universities(ZY1630,JD1617,buctrc201616,and buctrc201617)
文摘This paper investigated the influences of surface properties of carbon support and nickel precursors(nickel nitrate, nickel chloride and nickel acetate) on Ni nanoparticle sizes and catalytic performances for steam reforming of toluene. Treatment with nitric acid helped to increase the amount of functional groups on the surface and hydrophilic nature of carbon support, leading to a homogeneous distribution of Ni nanoparticles. The thermal decomposition products of nickel precursor also played an important role, Ni nanoparticles supported on carbon treated with acid using nickel nitrate as the precursor exhibited the smallest mean diameter of 4.5 nm. With the loading amount increased from 6 wt% to 18 wt%, the mean particle size of Ni nanoparticles varied from4.5 nm to 9.1 nm. The as-prepared catalyst showed a high catalytic activity and a good stability for toluene steam reforming: 98.1% conversion of toluene was obtained with the Ni content of 12 wt% and the S/C ratio of3, and the conversion only decreased to 92.0% after 700 min. Because of the high activity, good stability, and low cost, the as-prepared catalyst opens up new opportunities for tar removing.
基金This work was supported by the National Natural Science Foundation of China (50071052) and National Natural Science Key Foundation of China (50131040)
文摘Crystal structures of nonstoichiometric La(Ni, Sn)5+x (x = 0.1～0.4) alloys prepared by different methods were investigated by using powder X-ray diffraction and Rietveld refinement analysis. Space group of this type of alloys belongs to P6/mmm, in which Sn only occupies the 3g sites. It has been demonstrated that some of the 1a sites of the nonstoichiometric alloy are replaced by the NiNi dumb-bells which have a strong correlation with the anisotropic thermal parameter B33. The preparation methods have an effect on the number of dumb-bells that can substitute the 1a sites. It was found that the annealed alloys have more NiNi dumb-bells in the structure than the rapid solidified and as-cast alloys have while still keep good crystallinity.
基金Acknowledgments This work was supported by the National Natural Science Foundation of China （21373208, 91545204, and 21321002）, the National Basic Research Program of China （2016YFA0200200, 2013CB834603, and 2013CB933100）, and the Strategic Priority Research Program of the Chinese Academy of Sciences （XDB 17020200）. The authors are grateful for the support for Nano-X from Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences （SINANO）.
文摘The orientation control of graphene overlayers on metal surface is an important issue which remains as a challenge in graphene growth on Ni surface. Here we have demonstrated that epitaxial graphene overlayers can be obtained by annealing a nickel carbide covered Ni（111） surface using in situ surface imaging techniques. Epitaxial graphene islands nucleate and grow via segregation of dissolved carbon atoms to the top surface at about 400 ℃. This is in contrast to a mixture of epitaxial and non-epi- taxial graphene domains grown directly on Ni（111） at 540 ℃. The different growth behaviors are related to the nucleation dynamics which is controlled by local carbon densities in the near surface region.
基金supported by the National Key R&D Program of China (2017YFA0303500)the National Natural Science Foundation of China (91645202, 21722306, 21573203)+1 种基金Anhui Initiative in Quantum Information Technologiespartially supported by Fundamental Research Funds for the Central Universities (WK2060190082, WK2340000078)
文摘Dissociative chemisorption of methane on a nickel surface is a prototypical system for studying mode-specific chemistry in gassurface reactions.We recently developed a fifteen-dimensional potential energy surface for this system which has proven to be chemically accurate in reproducing the measured absolute dissociative sticking probabilities of CHD_3in thermal conditions and with vibrational excitation on Ni(111)at high incident energies.Here,using this new potential energy surface,we explored mode specificity and bond selectivity for CHD_3and CH_2D_2dissociative chemisorption at low incidence energies down to^50 k J/mol via a quasi-classical trajectory method.Our calculated dissociation probabilities are consistent with previous theoretical and experimental ones with an average shift in translational energy of^8 k J/mol.Our results very well reproduce the C–H/C–D branching ratio upon the C–H local mode excitation,which can be rationalized by the sudden vector projection model.Quantitatively,however,the calculated dissociative sticking probabilities are systematically larger than experimental ones,due presumably to the artificial zero point energy leakage into reaction coordinate.Further high-dimensional quantum dynamics calculations are necessary for acquiring a chemically accurate description of methane dissociative chemisorption at low incident energies.
基金financial support from China Postdoctoral Science Foundation (2020M673056)the National Key Research and Development Program of China (2018YFA0209402)the National Natural Science Foundation of China (21773093)。
文摘Cost-efficient electrocatalysts composed of earth-abundant elements are highly desired for enhanced oxygen evolution reaction (OER).As a promising candidate,metallic Co4N already demonstrated electrocatalytic performance relying on specific nanostructures and electronic configurations.Herein,nickel was introduced as the dopant into one-dimensional (1D) hierarchical Co4N structures,achieving effective electronic regulation of Co4N toward high OER performance.The amount of Co3+increased after Ni-doping,and the in-situ formed surface oxyhydroxide during OER enhanced the electrocatalytic kinetics.Meanwhile,the 1D hierarchical structure further promoted the performances of Co4N owing to the high electrical conductivity and abundant activesites on the rough surface.As expected,the optimal Ni-doped Co4N with a Ni/Co molar ratio of 0.25 provides a small overpotential of 233 mV at a current density of 10 mA cm^(-2),with a low Tafel slope of 61 mV dec^(-1),and high long-term stability in 1.0 mol L^(-1)KOH.Following these results,the enhancement by doping the Co4N nanowire bundles with Fe and Cu was further evidenced for the OER.
基金supported by the National Natural Science Foundation of China(Grant No.51375082)
文摘Based on the results of slot milling experiments on the DD5 Ni-based single crystal superalloy(001) crystal plane along the [110]crystal direction, in this paper, efforts were devoted to investigate the tool wear process, wear mechanism and failure modes of the physical vapor deposition(PVD)-AlTiN and TiAlN coated tools under dry milling and water-based minimum quantity lubrication(MQL) conditions. The scanning electron microscope(SEM) morphological observation and energy dispersive X-ray spectroscopy(EDX) elements analysis methods were adopted. Moreover, under the water-based MQL condition, the surface integrity such as surface roughness, dimensional and shape accuracy, microhardness and microstructure alteration were researched. The results demonstrated that the tool edge severe adhesion with the work material, induced by the high Al content in the PVD-AlTiN coating caused the catastrophic tool tip fracture. In contrast, the PVD-TiAlN tool displayed a steady and uniform minor flank wear, even though the material peeling and slight chipping also occurred in the final stage. In addition, due to the high effective cooling and lubricating actions of the water-based MQL method, the PVD-TiAlN coated tool demonstrated intact tip geometry; consequently it could be repaired and reused even if the failure criterion was attained. Moreover, as the accumulative milling length and the tool wear increased, all indicators of the surface integrity forehand were deteriorated.
