Thermal treatment is a general and efficient way to synthesize intermetallic catalysts and may involve complicated physical processes.So far,the mechanisms leading to the size and composition heterogeneity,as well as ...Thermal treatment is a general and efficient way to synthesize intermetallic catalysts and may involve complicated physical processes.So far,the mechanisms leading to the size and composition heterogeneity,as well as the phase segregation behavior in Pt-Co nanoparticles(NPs)are still not well understood.Via in-situ environmental transmission electron microscopy,the formation dynamics and segregation behaviors of Pt-Co alloyed NPs during the thermal treatment were investigated.It is found that Pt-Co NPs on zeolitic imidazolate frameworks-67-derived nanocarbon(NC)are formed consecutively through both particle migration coalescence and the Ostwald ripening process.The existence of Pt NPs is found to affect the movement of Co NPs during their migration.With the help of theoretical calculations,the correlations between the composition and migration of the Pt and Co during the ripening process were uncovered.These complex alloying processes are revealed as key factors leading to the heterogeneity of the synthesized Pt-Co alloyed NPs.Under oxidation environment,the Pt-Co NPs become surface faceted gradually,which can be attributed to the oxygen facilitated relatively higher segregation rate of Co from the(111)surface.This work advances the fundamental understanding of design,synthesis,and durability of the Pt-based nanocatalysts.展开更多
原子尺度原位研究金属纳米颗粒的氧化过程,对理解金属氧化反应机理和合理设计金属纳米材料有重要意义。长期以来,研究人员通过热重分析、X射线衍射、X射线光电子能谱等手段对金属块体材料和薄膜材料的氧化行为和反应机理开展了广泛研究...原子尺度原位研究金属纳米颗粒的氧化过程,对理解金属氧化反应机理和合理设计金属纳米材料有重要意义。长期以来,研究人员通过热重分析、X射线衍射、X射线光电子能谱等手段对金属块体材料和薄膜材料的氧化行为和反应机理开展了广泛研究。但当金属的尺寸缩小到纳米尺度时,其比表面积、电子结构都与块体材料显著不同,从而导致其氧化行为和反应机理也与块体材料产生差异。由于纳米颗粒体积小,氧化速率快,传统方法很难对其微观的氧化机理进行原位研究。受益于环境控制的电子显微镜技术(atmosphere controlled TEM technologies)的发展,人们有机会在原子尺度对金属纳米颗粒的氧化行为进行系统研究,包括柯肯达尔效应、氧化动力学过程等。然而目前对金属纳米颗粒氧化的研究仍然处于初期阶段,其氧化初期的形核过程仍有待揭示,温度、氧气分压、载体作用对金属纳米颗粒氧化的影响仍有待进一步研究。本文主要以近几年利用原位TEM研究金属纳米颗粒氧化的工作为例,简要介绍这些工作在认识金属氧化理论和推进反应机理的理解方面的最新进展,并探讨了未来研究的机遇和挑战。展开更多
基金the National Natural Science Foundation of China(Nos.52072345,U21A20328,22103047,and 12174348)the China Postdoctoral Science Foundation(No.2021T140621)+3 种基金the Natural Science Foundation of Henan Province(No.222300420077)Henan Center for Outstanding Overseas Scientists(No.GZS201903)support from Strategic Priority Research Program(B)(No.XDB33030200)of Chinese Academy of Sciencesperformed at the Center for Functional Nanomaterials,which is a US DOE Office of Science Facility,at Brookhaven National Laboratory under Contract No.DESC0012704.
文摘Thermal treatment is a general and efficient way to synthesize intermetallic catalysts and may involve complicated physical processes.So far,the mechanisms leading to the size and composition heterogeneity,as well as the phase segregation behavior in Pt-Co nanoparticles(NPs)are still not well understood.Via in-situ environmental transmission electron microscopy,the formation dynamics and segregation behaviors of Pt-Co alloyed NPs during the thermal treatment were investigated.It is found that Pt-Co NPs on zeolitic imidazolate frameworks-67-derived nanocarbon(NC)are formed consecutively through both particle migration coalescence and the Ostwald ripening process.The existence of Pt NPs is found to affect the movement of Co NPs during their migration.With the help of theoretical calculations,the correlations between the composition and migration of the Pt and Co during the ripening process were uncovered.These complex alloying processes are revealed as key factors leading to the heterogeneity of the synthesized Pt-Co alloyed NPs.Under oxidation environment,the Pt-Co NPs become surface faceted gradually,which can be attributed to the oxygen facilitated relatively higher segregation rate of Co from the(111)surface.This work advances the fundamental understanding of design,synthesis,and durability of the Pt-based nanocatalysts.
文摘原子尺度原位研究金属纳米颗粒的氧化过程,对理解金属氧化反应机理和合理设计金属纳米材料有重要意义。长期以来,研究人员通过热重分析、X射线衍射、X射线光电子能谱等手段对金属块体材料和薄膜材料的氧化行为和反应机理开展了广泛研究。但当金属的尺寸缩小到纳米尺度时,其比表面积、电子结构都与块体材料显著不同,从而导致其氧化行为和反应机理也与块体材料产生差异。由于纳米颗粒体积小,氧化速率快,传统方法很难对其微观的氧化机理进行原位研究。受益于环境控制的电子显微镜技术(atmosphere controlled TEM technologies)的发展,人们有机会在原子尺度对金属纳米颗粒的氧化行为进行系统研究,包括柯肯达尔效应、氧化动力学过程等。然而目前对金属纳米颗粒氧化的研究仍然处于初期阶段,其氧化初期的形核过程仍有待揭示,温度、氧气分压、载体作用对金属纳米颗粒氧化的影响仍有待进一步研究。本文主要以近几年利用原位TEM研究金属纳米颗粒氧化的工作为例,简要介绍这些工作在认识金属氧化理论和推进反应机理的理解方面的最新进展,并探讨了未来研究的机遇和挑战。
