单原子合金催化剂热稳定性的反应力场分子动力学研究

Reactive Force Field Model Molecular Dynamics Study on the Thermal Stability of Single Atom Alloy Catalysts

  • 摘要: 通过反应力场(ReaxFF)模型分子动力学模拟,研究了负载模型和掺杂模型单原子催化剂(分别记为M1/Cu(111)和M1@Cu(111),M=Pt,Ni,Ag,Fe)的热稳定性.模拟结果显示:对于M1@Cu(111)掺杂模型,Pt(Ni,Fe)1@Cu(111)的稳定性远高于Ag1@Cu(111),温度大于500 K时依旧可以保持稳定.而负载模型M1/Cu(111)除了Fe1/Cu(111)以外,其余模型在100~500 K的温度范围中均无法保持稳定,单个金属原子会在Cu(111)表面迁移并相互聚集最终形成纳米颗粒.同时发现,随着温度的升高,Fe不同于其他金属单原子的烧结过程,会向亚表层扩散,进入合金体相.此外,还优化了Cu/Pt/H/O的力场参数,并研究了H2气氛对单原子催化剂(SAA)催化剂模型表面稳定性的影响,发现H2气氛的存在导致M1@Cu(111)模型稳定性降低.理论模拟结果发现M1/Cu(111)型SAA催化剂即使在低温下也不是一个很好的候选催化剂,而多数M1@Cu(111)型催化剂在较高温度下依旧可以保持稳定.

     

    Abstract: Reactive force field model (ReaxFF) molecular dynamics simulation was performed to study the stability of supported-atom (or ad-atom) modellabeled as M1/Cu(111), M=Pt, Ni, Ag, Fe and the embedded (or doped) modelsnoted as M1@/Cu(111) systems. For the M1@/Cu(111) catalyst models, it was found that the Pt(Ni, Fe)1@/Cu(111) is more stable compared to Ag1@/Cu(111) model (temperature>500 K). For supported-atom models, except for Fe1/Cu(111) none of them can exist stably at 100~500 K. And these single metal atoms migrate to each other and then aggregate to form large nanoparticles besides Fe atoms diffusing to subsurface as temperature increases. In addition, the effect of H2 and O2 atmosphere on the surface of single atom alloy(SAA) catalyst model and thermal stability was invesgated by the optimized Cu/Pt/C/H/O force field parameter. It was found that the presence of H2 reduces the stability of M1@Cu(111) catalysts. The simulation results show that M1/Cu(111) of SAA are not good candidates for catalysts even at relatively low temperature while most M1@Cu(111) models can exist stable over high reaction temperature.

     

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