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

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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.