物理化学学报 >> 2020, Vol. 36 >> Issue (9): 1911050.doi: 10.3866/PKU.WHXB201911050

所属专题: 精准纳米合成

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二氧化铈表面构建固体“受阻”Lewis酸碱对用于小分子活化

张赛, 张铭凯, 瞿永泉()   

  • 收稿日期:2019-11-12 录用日期:2020-01-13 发布日期:2020-02-05
  • 通讯作者: 瞿永泉 E-mail:yongquan@mail.xjtu.edu.cn
  • 作者简介:Dr Yongquan Qu received his BS in Materials Science and Engineering from Nanjing University in 2001, MS in Chemistry from the Dalian Institute of Chemical Physics in 2004, and PhD in Chemistry from the University of California, Davis, in 2009. He worked as a postdoctoral research fellow in the University of California, Los Angeles, from 2009 to 2011. He became a faculty member of the Center for Applied Chemical Research, Frontier Institute of Science and Technology, Xi'an Jiaotong University, China, in 2012. His research interests focus on heterogeneous catalysis in the areas of organic synthesis, clean energy production and environmental remediation. Details can be found at: http://gr.xjtu.edu.cn/web/yongquan
  • 基金资助:
    国家自然科学基金(21872109);中国博士后科学基金(2018T111034);中央高校基本科研业务费(xjj2018033);陕西省自然科学基础研究计划青年项目(2019JQ-039)

Solid Frustrated Lewis Pairs Constructed on CeO2 for Small-Molecule Activation

Sai Zhang, Mingkai Zhang, Yongquan Qu()   

  • Received:2019-11-12 Accepted:2020-01-13 Published:2020-02-05
  • Contact: Yongquan Qu E-mail:yongquan@mail.xjtu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21872109);the China Postdoctoral Science Foundation(2018T111034);the Cyrus Tang Foundation through the Tang Scholar program. S. Zhang is supported by the Fundamental Research Funds for the Central Universities, China(xjj2018033);the Natural Science Foundation of Shaanxi Province, China(2019JQ-039)

摘要:

近年来,固体“受阻”Lewis酸碱对(FLP)在小分子活化领域受到了广泛的关注和研究。但是,在纳米材料表面构建FLP活性位仍然是一个挑战,并且因此限制了其广泛的应用。作为一种常见的催化剂或者功能性载体,二氧化铈(CeO2)表面同时具有Lewis酸和碱性位点,以及大量容易调控的表面缺陷。当CeO2表面的Lewis酸和碱性位点相互独立时,就有望形成类似于均相FLP活性位点。因此,具有丰富表面性质的纳米CeO2展现极大的可能性去构建固体FLP活性位点。本论文综述了一种通过表面缺陷调控,在CeO2(110)表面成功构建固体FLP的策略。在具有表面氧缺陷团簇的CeO2表面能够成功构建一种由两个相连的Ce3+组成的Lewis酸性位点;该酸性位点与氧缺陷团簇相邻的Lewis碱性的O原子,可以构建成一种新颖的FLP位点。该固体FLP活性位点可以实现H2活化用于不饱和烷烃的加氢反应,也可以用于实现CO2的活化,并且转化为环状碳酸脂。此外,该活性位点理论上可实现CH4分子的活化。最后,该综述还总结了固体FLP发展中的挑战及前景。

关键词: “受阻”Lewis酸碱对, CeO2, 表面氧缺陷, H2活化, CO2活化, CH4活化

Abstract:

Solid materials containing frustrated Lewis pairs (FLPs) as active sites have attracted much attention due to their ability to activate and transform small molecules. However, it is still highly challenging to precisely construct FLP sites on the surfaces of nanomaterials, thereby limiting the applications of these materials. Nanostructured ceria (CeO2) is commonly employed as a catalyst or functional support, and exhibits both Lewis acid and basic properties as well as abundant and easily regulated surface defects, which originate from the reversible Ce3+/Ce4+ redox pair. When the Lewis acid and base sites of CeO2 are independent of each other, the combined Lewis acid-base sites play a similar role to that of homogeneous FLP sites. Thus, the rich surface properties of nanostructured CeO2 provide significant potential for the construction of solid FLPs.

Herein, we demonstrate that solid FLP sites can be successfully constructed on the surface of CeO2(110) via the regulation of surface defect clusters, which can be used to create new Lewis acid sites composed of two adjacent Ce3+ atoms on the surface. Novel interfacial FLP sites can then be formed by combining these Lewis acid sites with neighboring surface lattice oxygens, which act as Lewis base sites. Porous CeO2 nanorods (PN-CeO2) with boundary surface defects were prepared by a special two-step hydrothermal process, and exhibited remarkable catalytic FLP properties. Hydrogen molecules could be effectively activated on the surface of PN-CeO2 with a low activation energy of 0.17 eV via a heterolytic cleavage process. Hydrogenation of alkenes and alkynes to alkanes could then be realized by the activated hydrogen under mild reaction conditions.

PN-CeO2 nanorods with FLP active sites were also able to activate CO2 molecules effectively. Unlike in other solid FLP sites, CO2 molecule activation was realized via a Lewis base site binding with the C atom while two Lewis acid sites bound the two O atoms, owing to the unique configuration of the FLP sites in PN-CeO2. When combined with the epoxidation of olefins by "isolated" Ce3+ sites in PN-CeO2, the FLP-inspired activated CO2 could be used to transform olefins and CO2 to cyclic carbonates through a selective tandem transformation route. In addition, density functional theory studies indicate that the FLP sites on CeO2(110) can activate the C―H bond of CH4 with activation energies as low as 0.63 eV, which can be attributed to the enhanced acidity and basicity of the FLP sites.

With this improved understanding of solid FLP sites constructed on ceria, we have also been able to summarize the challenges and prospects in this field, including their construction, characterization, and mechanism analysis.

Key words: Frustrated Lewis pairs, CeO2, Surface defect, H2 activation, CO2 activation, CH4 activation

MSC2000: 

  • O643