尤峻汉,刘当波,高海翔.固体表面填隙H的化学活性起源于泡利排斥效应[J].分子催化编辑部,2019,33(5):399-411
固体表面填隙H的化学活性起源于泡利排斥效应
The Chemical Activity of an Interstitial Hydrogen on the Solid Surface Arises from Pauli Repulsion
投稿时间:2019-08-29  修订日期:2019-09-20
DOI:
中文关键词:  固体表面氢  多相催化  泡利排斥  氢化反应
英文关键词:heterogeneous catalysis mechanism  Pauli repulsion  Pauli hole  subsurface H atom  hydrogenation
基金项目:国家自然科学基金(No.U1631101,11665022,11233006);上海市自然科学基金(16ZR1417200)
作者单位E-mail
尤峻汉 上海交通大学 物理与天文学院天文系, 上海 200240  
刘当波 上海交通大学 物理与天文学院天文系, 上海 200240
上海交通大学 上海粒子物理和宇宙学重点实验室, 上海 200240 
dbliu@sjtu.edu.cn 
高海翔 上海交通大学 致远学院, 上海 200240  
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中文摘要:
      各类固体表面常对外来原子(离子)施加泡利排斥作用.它明显改变了表面填隙或者替位原子(离子)的物理性质.我们首先说明泡利排斥作用广泛存在于各类固体表面.并引进"泡利穴"的概念,用来定量计算固体表面低凹处填隙位置上的外来原子在泡利排斥作用下性质的改变.重点讨论了多相催化中最重要的过渡金属表面的"泡利穴".然后简短介绍我们已经发表的工作,即泡利穴中H原子薛定谔方程的解析.进一步,将填隙H的基态波函数和基态能与自由H原子做比较,显示其性质的改变.由此详细论证,填隙H化学活性增加的两个关键的物理原因是,填隙H电离能的明显降低及诱导电矩的存在.我们把这种激活方式简称为"固体表面填隙H的泡利激活",并讨论它对加氢反应的贡献.同时,对近年来催化研究中一个令人困惑的实验结果给出我们自己的解释.实验明确表明,对加氢反应起关键作用的是过渡金属"表面下的H原子",它们在加氢反应中非常活跃.而"表面H原子"没有参与加氢反应.我们论证,过渡族金属"表面下的H原子"正是被泡利激活的填隙H.
限于讨论多相催化问题(固体表面填隙H原子的催化).但是"泡利激活"原则上可以推广到均相催化中.因为在均相催化中经常使用的催化剂通常也具有类似的泡利穴结构.我们只讨论泡利穴中填隙H的催化,但是原则上不难推广到其他元素,例如用类似方法探讨石墨烯表面填隙锂原子的泡利激活.
近来的天文观测中发现,很多有机分子云团中(例如H2O,CH4,C2H2,C2H4…等云团),同时存在一些尺寸约0.001~10 μm的尘埃物质(如C颗粒,SiO2颗粒等等).两者的并存使我们猜测,或许这些尘埃物质(包括纳米颗粒)本身就是多相催化剂,其表面存在的"泡利穴"可能对分子的形成有重要贡献.
英文摘要:
      The surface of various solids often exerts a Pauli repulsive force on the adsorbed atoms/ions, interstitial and/or substitutional, which markedly changes the physical properties of foreign surface atoms/ions. We first demonstrate that Pauli repulsion widely exists at the surface of various solids. We introduce a concept of ‘Pauli hole’ to describe a depression on solid surface, where a foreign interstitial/substitutional atom sited in, and suffers from the Pauli repulsive force of the surrounding substrate atoms/ions. Then a quantitative estimation of the changes of atom properties under Pauli repulsion is obtained by this way. We pay more attention to the special Pauli hole on the surface of transition metals, the most important materials in heterogeneous catalysis. In order to easy to read this paper, we briefly introduce the work we have published, with regard to the schrodinger equation of an interstitial hydrogen in Pauli hole and its solution. Accordingly, both the obtained wave function and the energy of ground state of the interstitial hydrogen atom are compared to that of a free hydrogen, which indeed shows a change of properties of surface hydrogen. The marked change results a significant increase of chemical activity. By using these results, we further explain that, the increase of chemical activity mainly depends on two factors:the marked reduction of ionization energy (electronic affinity) and the effect of induced electric dipole of the interstitial hydrogen. We refer this kind of excitation as ‘Pauli excitation of interstitial hydrogen’, and emphasize its significant contribution to the hydrogenation. To date, there is a long ongoing question in the catalysis study. Experiments show that, the most active component in the hydrogenation reaction is the ‘subsurface hydrogen atoms’, located under the surface of transition metals, rather than the ‘surface hydrogen’. The latter has little contribution to reaction. In this paper, we argue that, the ‘subsurface hydrogen’ is just the Pauli-excited interstitial hydrogen.
Limited to discuss the heterogeneous catalysis (catalysis of interstitial hydrogen at solid surface). But in principle, the Pauli excitation can be extended to the homogeneous catalysis, where exists analogous Pauli hole too. Besides, we limited ourself to discuss the catalysis of interstitial hydrogen. But, it is easy to apply to other interstitial atoms. For example, it can be used to study the Pauli excitation of interstitial Li atom at surface of graphene.
Astronomical observations in recent years show that, in many molecular clouds (e.g., H2O, CH4, C2H2, C2H4, et al.), there are plenty of dusts with size 0.001~10 μm (e.g., C or SiO2 particles) coexist with molecules. The coexistence of both the molecules and the dust particles could imply that the dusts, including some nano-particles, are just the necessary heterogeneous catalyzers, which have the Pauli hole structures at its surface.
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