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

近年来，单原子催化剂以其独特的化学活性和选择性在多相催化领域引起了广泛的关注。然而，尽管单位点催化剂已经用于化学过程，但由于缺乏对驱动表面反应的原子机制的基本理解，迄今为止，工艺优化仅限于经验数据，影响了催化剂的开发。在这种情况下，表面科学方法已被证明具有引导催化材料工程的潜力，通过提供在界面上发生的化学反应的实际原子性理解。然而，这些研究通常局限于超高真空（UHV）条件，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单位点促进反应的机制见解。通过结合在高压下优化的原位表面科学方法，即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），我们将研究在现实反应条件下小碳氢化合物单位点催化聚合的机制，从模型系统到工业负载催化剂。首先，我们将阐明在Ni（111）模型催化剂上的碳氢化合物聚合，其中单个Ni附原子被建议作为sac。在毫秒的时间尺度上进行原位STM成像，可以澄清它们在促进单体附着方面的作用。在mbar范围内的压力下，通过HP-STM和napp - xps，我们的目标是揭示在特高压下观察到的碳氢化合物聚合过程如何向工业反应器中常用的条件发展。然后，我们计划将原位研究扩展到“现实世界”的烯烃聚合负载催化剂，即锚定在超薄氧化铝载体上的茂金属配合物。为此，我们将利用在受控条件下制备的良好定义的体系来制备活化的单位点催化剂。该策略将通过先进的原位显微镜和光谱技术进行表征，揭示反应机制，揭示现实反应条件下催化活性物质的性质。通过这种方式，我们的目标是澄清长期存在的关于单位点催化剂在工业化学过程中的作用的问题，对新催化剂的设计具有潜在的影响。

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.