Amplification of Elementary Surface Reaction Steps on Transition Metal Surfaces Using Liquid Crystals: Dissociative Adsorption and Dehydrogenation
Amplification of Elementary Surface Reaction Steps on Transition Metal Surfaces Using Liquid Crystals: Dissociative Adsorption and Dehydrogenation
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使用液晶放大过渡金属表面上的元素表面反应步骤：离解吸附和脱氢
DOI：
10.1021/jacs.9b08057
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发表时间：
2019
影响因子：
15
通讯作者：
Abbott, Nicholas L.
中科院分区：
文献类型：
--
作者：
Yu, Huaizhe;Szilvási, Tibor;Wang, Kunlun;Gold, Jake I.;Bao, Nanqi;Twieg, Robert J.;Mavrikakis, Manos;Abbott, Nicholas L.
一系列分子吸附物在过渡金属表面上的基本反应步骤，包括吸附和解离，已在化学催化的背景下得到阐明。在这里，我们利用这些知识来设计支撑在超薄多晶金膜（主要晶面是（111））上的液晶（LC），这些液晶通过分别涉及氯和羧酸的解离吸附和脱氢反应触发进行取向转变，从而将这些原子尺度的表面过程原位放大为宏观光学信号。我们使用电子结构计算来预测，4'-n-戊基-4-联苯甲腈 (5CB)（一种室温向列液晶）不会以在分子氯解离吸附时改变的方向与 Au(111) 结合，这一结果经过实验验证。相比之下，4-氰基-4-联苯甲酸（CBCA）被计算为通过羧酸基团的脱氢在垂直方向上与Au（111）牢固结合，我们使用偏振调制红外反射吸收光谱证实了这一点。金表面上 0.07 单层 CBCA 的最大覆盖足以使 LC 垂直取向。 Cl2 气体在金表面上的解离吸附，导致 Cl 的单层覆盖率为 0.5，取代了 Au(111) 中的 CBCA，从而引发了 LC 方向的惊人可见变化。红外光谱确定了吸附的 CBCA 的方向平行于 Cl 覆盖的表面，COOH 平面垂直于表面，正如第一性原理计算所预测的那样。这些结果证明了使用第一原理计算和过渡金属表面来设计可报告原位目标原子级表面过程的液晶。
Elementary reaction steps, including adsorption and dissociation, of a range of molecular adsorbates on transition metal surfaces have been elucidated in the context of chemical catalysis. Here we leverage this knowledge to design liquid crystals (LCs) supported on ultrathin polycrystalline gold films (predominant crystallographic face is (111)) that are triggered to undergo orientational transitions by dissociative adsorption and dehydrogenation reactions involving chlorine and carboxylic acids, respectively, thus amplifying these atomic-scale surface processes in situ into macroscopic optical signals. We use electronic structure calculations to predict that 4′-n-pentyl-4-biphenylcarbonitrile (5CB), a room temperature nematic LC, does not bind to Au(111) in an orientation that changes upon dissociative adsorption of molecular chlorine, a result validated by experiments. In contrast, 4-cyano-4-biphenylcarboxylic acid (CBCA) is calculated to bind strongly to Au(111) in a perpendicular orientation via dehydrogenation of the carboxylic acid group, which we confirmed using polarization-modulation infrared reflection–absorption spectroscopy. A maximum coverage of 0.07 monolayer of CBCA on the gold surface is sufficient to cause a perpendicular orientation of the LC. Dissociative adsorption of Cl2gas on the gold surface, resulting in 0.5 monolayer coverage of Cl, displaces CBCA from Au(111) and thus triggers a strikingly visible change in orientation of the LC. Infrared spectroscopy established the orientation of adsorbed CBCA to be parallel to the Cl covered surface, with the COOH plane perpendicular to the surface, as predicted by first-principles calculations. These results demonstrate the use of first-principles calculations and transition metal surfaces to design LCs that report in situ targeted atomic-scale surface processes.