Abstract：
In a solid catalyst with ionic liquid layer (SCILL), ionic liquid (IL) coatings are used to improve the selectivity of noble metal catalysts. To understand the origins of this selectivity control, we performed model studies by surface science methods in ultrahigh vacuum (UHV). We investigated the growth and thermal stability of ultrathin IL films by infrared reflection absorption spectroscopy (IRAS). We combined these experiments with scanning tunneling microscopy (STM) to obtain information on the orientation of the ions, the interactions with the surface, the intermolecular interactions, and the structure formation. Additionally, we performed DFT calculations and molecular dynamics (MD) simulations to interpret the experimental data. We studied the IL 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [C2 C1 Im][OTf] on Au(111) surfaces. We observe a weakly bound multilayer of [C2 C1 Im][OTf], which is stable up to 390 K, while the monolayer desorbs at ∼450 K. [C2 C1 Im][OTf] preferentially adsorbs at the step edges and elbows of the herringbone reconstruction of Au(111). The anion adsorbs via the SO3 group with the molecular axis perpendicular to the surface. At low coverage, the [C2 C1 Im][OTf] crystallizes in a glass-like 2D phase with short-range order. At higher coverage, we observe a phase transition to a 6-membered ring structure with long-range order.
摘要：
在具有离子液体层的固体催化剂（SCILL）中，离子液体(IL)涂层用于提高贵金属催化剂的选择性。为了理解这种选择性控制的起源，我们在超高真空（UHV）中通过表面科学方法进行了模型研究。我们通过红外反射吸收光谱（IRAS）研究了超薄IL薄膜的生长和热稳定性。我们将这些实验与扫描隧道显微镜（STM）相结合，以获得有关离子取向的信息，与表面的相互作用，分子间的相互作用，和结构形成。此外,我们进行了密度泛函理论（DFT）计算和分子动力学（MD）模拟来解释实验数据。我们研究了Au（111）表面上的IL1-乙基-3-甲基咪唑盐[C2C1Im][OTf]。我们观察到[C2C1Im][OTf]的弱结合多层，稳定到390K，而单层在〜450K时解吸。[C2C1Im][OTf]优先吸附在Au（111）人字形重建的阶梯边缘和肘部。阴离子通过SO3基团吸附，分子轴垂直于表面。在低覆盖率下，[C2C1Im][OTf]以短程有序的玻璃状2D相结晶。在更高的覆盖率下，我们观察到具有长程有序的6元环结构的相变。
