Catalysis at the atomic-scale: observing single-site promoted polymerization of small hydrocarbons

近年来，单原子催化剂(SACs)以其独特的化学活性和选择性在多相催化领域引起了人们的广泛关注。然而，尽管单位催化剂已经在化工过程中得到应用，但由于对表面反应的原子机理缺乏基本的了解，使得工艺优化仅限于经验数据，影响了催化剂的发展。在这种背景下，表面科学方法已被证明具有指导催化材料工程的潜力，因为它提供了对界面上发生的化学反应的实际原子学理解。然而，这些研究通常局限于超高真空(UHV)条件下，而工业化学过程发生在高压和复杂材料上。在这里，我们的目标是在原子尺度上获得对单位促进反应的力学见解。通过结合高压扫描隧道显微镜(HP-STM)和近环境压力X射线光电子能谱(NAP-XPS)等优化的现场表面科学方法，我们将从模型体系到工业负载型催化剂，研究现实反应条件下单位催化小分子烃聚合的机理。首先，我们将阐明在Ni(111)模型催化剂上的烃类聚合，其中单个Ni吸附原子被认为是囊。在毫秒时间尺度上进行的原位扫描隧道显微镜成像将有助于阐明它们在促进单体附着方面的作用。通过HP-STM和NAP-XPS在mbar压力范围内的表面演化，我们的目标是揭示在超高真空下观察到的烃类聚合过程是如何向工业反应器中常用的条件演化的。然后，我们计划将现场研究扩展到“真实世界”负载的烯烃聚合催化剂，即锚定在超薄氧化铝载体上的茂金属络合物。为此，我们将利用在受控条件下制备的定义良好的体系来制备活性单位催化剂。这一策略将通过先进的原位显微镜和光谱技术进行表征，揭示反应机理并揭示现实反应条件下催化活性物种的性质。通过这种方式，我们旨在澄清长期以来关于单位催化剂在工业化学过程中的作用的问题，并对新催化剂的设计具有潜在的意义。

Over the past few years, single-atom catalysts (SACs) have attracted special attention in the field of heterogeneous catalysis, due to their unique chemical activity and selectivity. However, despite single site catalysts are already used in chemical processes, the lack of a fundamental understanding of atomistic mechanisms driving the surface reactions has so far limited the process optimization to empirical data, affecting the catalyst development. In this context, the surface-science approach has proved to have the potential to steer the engineering of catalytic materials, by providing actual atomistic understanding of chemical reactions occurring at interfaces. Nevertheless, these studies are generally restricted to ultra-high vacuum (UHV) conditions, while industrial chemical processes occur at elevated pressures and on complex materials.Here, we aim to obtain mechanistic insights at the atomic scale into single-site promoted reactions. By combining in-situ surface-science methods optimized to work at elevated pressures, namely high-pressure scanning tunneling microscopy (HP-STM) and near-ambient pressure X-ray Photoelectron Spectroscopy (NAP-XPS), we will study the mechanisms governing single-sites catalyzed polymerization of small hydrocarbons under realistic reaction conditions, from model systems towards industrial supported catalysts.First, we will elucidate the hydrocarbon polymerization on a Ni(111) model catalyst, where individual Ni adatoms have been suggested to act as SACs. In-situ STM imaging performed on the millisecond timescale will allow clarifying their role in facilitating the monomer attachment. Following the surface evolution at pressures in the mbar range, by means of HP-STM and NAP-XPS, we aim to unveil how the hydrocarbon polymerization processes observed under UHV evolves going towards conditions commonly used in industrial reactors.Then, we plan to expand the in-situ studies towards “real-world” supported catalysts for olefin polymerization, namely metallocene complexes anchored to an ultrathin alumina support. For this purpose, we will make use of well-defined systems, prepared under controlled conditions to prepare activated single-sites catalysts. This strategy will enable the characterization by means of advanced in-situ microscopy and spectroscopy techniques, shedding light onto the reaction mechanisms and unveiling the nature of the catalytic active species under realistic reaction conditions.In this way, we aim to clarify long-standing questions about the role of single-site catalysts during industrial chemical processes, with potential implications in the design of new catalysts.