Surface Analogues of Molecular Frustrated Lewis Pairs in : Heterogeneous CO2 Hydrogenation Catalysis
Surface Analogues of Molecular Frustrated Lewis Pairs in : Heterogeneous CO2 Hydrogenation Catalysis
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DOI：
10.1021/acscatal.6b01015
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发表时间：
2016-09-01
期刊：
影响因子：
12.9
通讯作者：
Ozin, Geoffrey A.
中科院分区：
文献类型：
--
作者：
Ghuman, Kulbir Kaur;Hoch, Laura B.;Ozin, Geoffrey A.
同质的、基于溶液的分子受挫刘易斯对（FLPs）的发现，包含可以激活H-2的主族元素，预示着化学和催化领域的范式转变。在FLPs中，未淬灭的Lewis碱和Lewis酸位点（B中心点中心点中心点中心点A中心点）能够极化并异解H-2，形成相邻的质子和氢化物位点（bh中心点中心点中心点AH(+)），从而实现CO2还原等反应。在本文中，我们提请注意这些众所周知的分子FLPs与由近端刘易斯碱和刘易斯酸对组成的表面活性位点之间的关系，这些活性位点在文献中多次报道过，负责驱动各种非均相催化反应。根据我们最近的研究，在负载氧化铟的纳米结构缺陷中描述了一个这样的表面位点，能够激活H-2并使CO2加氢，我们推测这些位点是表面FLPs。值得注意的是，这种氢化反应的转化率在光照下比在黑暗中观察到的要快。动力学测量和密度泛函理论模拟与通过表面FLP进行的反应一致。研究发现，激发态中较高的刘易斯酸度和刘易斯碱度（分别来自于FLP酸和碱位点的光生空穴和电子的捕获）是导致光照下比黑暗下反应活性更高的原因。随着对支持FLP在均相和非均相系统中反应性的化学和物理原理的实验和理论的理解，现在可以合理地构思和合成与均相FLP分子具有组成和结构联系的非均相FLP材料，反之亦然。FLP分子和材料之间的这种协同关系可以在未来的努力中证明是有益的，旨在扩大积累的关于二氧化碳光化学和热化学活化的科学知识，从而在二氧化碳催化转化为增值化学品和燃料中利用这两种系统的已知技术属性。
The discovery of homogeneous, solution-based molecular frustrated Lewis pairs, denoted FLPs, comprising main-group elements that can activate H-2 heralded a paradigm shift in chemistry and catalysis. In FLPs, unquenched Lewis base and Lewis acid sites (B center dot center dot center dot A)are able to polarize and dissociate H-2 heterolytically to form adjacent proton and hydride sites (BH-center dot center dot center dot AH(+)), which can enable reactions such as CO2 reduction. In this paper, we draw attention to a relationship between these well-known molecular FLPs and the surface active sites comprised of proximal Lewis base and Lewis acid pairs, which have been reported multiple times in the literature to be responsible for driving various heterogeneous catalytic reactions. From our recent studies that described one such surface site in a nanostructured defect laden indium oxide, capable of activating H-2 and enabling the hydrogenation of CO2, it was conjectured that these sites are surface FLPs. Significantly, the conversion rate for this hydrogenation reaction is observed to be more rapid in the light than in the dark. Kinetic measurements and density functional theory simulations are consistent with a reaction that proceeds via a surface FLP. It is found that the higher Lewis acidity and Lewis basicity in the excited state, which originates from trapping of the photogenerated hole and electron at the FLP acid and base sites, respectively, is responsible for the higher reactivity in the light in comparison to the dark. With the emerging experimental and theoretical understanding of the chemical and physical principles that underpin the reactivity of FLPs in both homogeneous and heterogeneous systems, it is now possible to rationally conceive and synthetically target heterogeneous FLP materials that bear a compositional and structural connection to homogeneous FLP molecules, and vice versa. This synergistic relationship between FLP molecules and materials could prove beneficial in future efforts aimed at expanding the accrued scientific knowledge on photochemical versus thermochemical activation of CO2 and thereupon to exploit the perceived technological attributes of both systems in the catalytic conversion of carbon dioxide to value-added chemicals and fuels.