Abstract：
The concept of a solid catalyst with an ionic liquid layer (SCILL) is a promising approach to improve the selectivity of noble metal catalysts in heterogeneous reactions. In order to understand the origins of this selectivity control, we investigated the growth and thermal stability of ultrathin 1-ethyl-3-methylimidazolium trifluormethanesulfonate [C2C1Im][OTf] films on Pt(111) by infrared reflection absorption spectroscopy (IRAS) and X-ray photoelectron spectroscopy (XPS) in time-resolved and temperature-programmed experiments. We combined these spectroscopy experiments with scanning tunneling microscopy (STM) to obtain detailed insights into the orientation and adsorption geometry of the ions in the first IL layer. Furthermore, we propose a mechanism for the thermal evolution of [C2C1Im][OTf] on Pt(111). We observe an intact IL layer on the surface at temperatures below 200 K. Adsorbed [C2C1Im][OTf] forms islands, which are evenly distributed over the surface. The [OTf]- anion adsorbs via the SO3 group, with the molecular axis perpendicular to the surface. Anions and cations are arranged next to each other, alternating on the Pt(111) surface. Upon heating to 250 K, we observe changes in geometry and structural distribution. Whereas at low temperature, the ions are arranged alternately for electrostatic reasons, this driving force is no longer decisive at 250 K. Here, a phase separation of two different species is discernible in STM. We propose that this effect is due to a surface reaction, which changes the charge of the adsorbates. We assume that the IL starts to decompose at around 250 K, and thus, pristine IL and decomposition products coexist on the surface. Also, IRAS and XPS show indication of IL decomposition. Further heating leads to increased IL decomposition. The reaction products associated with the anions are volatile and leave the surface. In contrast, the cation fragments remain on the surface up to temperatures above 420 K.
摘要：
具有离子液体层的固体催化剂（SCILL）的概念是提高非均相反应中贵金属催化剂选择性的有前途的方法。为了理解这种选择性控制的起源，我们通过红外反射吸收光谱（IRAS）和X射线光电子能谱（XPS）研究了超薄的1-乙基-3-甲基咪唑三氟甲磺酸[C2C1Im][OTf]薄膜在Pt（111）上的生长和热稳定性。时间分辨和温度程序实验。我们将这些光谱学实验与扫描隧道显微镜（STM）相结合，以详细了解第一IL层中离子的取向和吸附几何形状。此外，我们提出了[C2C1Im][OTf]在Pt(111)上的热演化机制。我们在低于200K的温度下观察到表面上完整的IL层。吸附的[C2C1Im][OTf]形成岛，均匀分布在表面上。[OTf]-阴离子通过SO3基团吸附，分子轴垂直于表面。阴离子和阳离子彼此相邻排列，在Pt（111）表面交替。加热到250K时，我们观察到几何形状和结构分布的变化。而在低温下,由于静电原因，离子交替排列，这种驱动力在250K时不再是决定性的，在这里，在STM中两种不同种类的相分离是可辨别的。我们认为这种效应是由于表面反应，改变吸附物的电荷。我们假设IL在250K左右开始分解，因此，原始IL和分解产物共存于表面。此外，IRAS和XPS显示IL分解的指示。进一步加热导致IL分解增加。与阴离子缔合的反应产物是挥发性的并离开表面。相比之下,阳离子片段保留在表面上直至420K以上的温度。
