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

• Applicant: Professor Laerte Patera, Ph.D.
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Solid State and Surface Chemistry, Material Synthesis
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 432043087

• Final Report Year: 2022

Final Report Abstract

In this project we investigated the single-site promoted polymerization of small hydrocarbons, from model system towards more complex material platforms. Atomic scale details have been provided exploiting advanced surface science methods, namely scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). On Ni(111) we demonstrated the formation of polyacetylene oligomers occurring already at low pressures. Not only the chemical nature of the products has been clarified by means of highresolution XPS, but complementary in-situ STM provided novel insights into the active sites for the reactions. In particular, at variance with what is commonly assumed, hydrocarbon polymerization does not proceed by chain formation at the substrate step sites, but occurs almost exclusively on the flat terraces. The direct observation of self-poisoning of the step sites points out the potential relevance of individual Ni adatoms in promoting the C-C coupling. Further studies conducted by near-ambient pressure XPS at pressures up to 1 mbar revealed that the observed growth mechanism of hydrocarbon chains can be extended towards more industrially relevant conditions. In the attempt to establish more complex model systems, mimicking the technical catalysts, we investigated the formation and temperature stability of Ni nanoclusters supported on a crystalline alumina layer. This resulted in the establishment of a robust model system for heterogenous catalysis, enabling future in-situ studies of surface reactivity by advanced surface science techniques. Instead, the study of more realistic catalytic platforms, in particular supported homogeneous catalyst has not been successful. In retrospect, this represented the task with the highest risk. Despite potential alternative solutions can be defined, for example exploiting electrospray source for the deposition of fragile molecules from solution, this approach will require dedicated future studies. Finally, we investigated the role of sodium adatoms as potential promoter of on-surface C-C coupling reactions. For the case of hexaazatriphenylene (HAT) molecules, we reveled the peculiar cooperative catalytic role of Na and native metal adatoms in steering both the polymerization and the regioselectivity of the polymerization process.

Publications

• Exploiting Cooperative Catalysis for the On‐Surface Synthesis of Linear Heteroaromatic Polymers via Selective C–H Activation. Angewandte Chemie International Edition, 61(5).
  Liu, Xunshan; Matej, Adam; Kratky, Tim; Mendieta‐Moreno, Jesús I.; Günther, Sebastian; Mutombo, Pingo; Decurtins, Silvio; Aschauer, Ulrich; Repp, Jascha; Jelinek, Pavel; Liu, Shi‐Xia & Patera, Laerte L.
  
• In Situ Observation of C−C Coupling and Step Poisoning During the Growth of Hydrocarbon Chains on Ni(111). Angewandte Chemie International Edition, 62(1).
  Zou, Zhiyu; Sala, Alessandro; Panighel, Mirco; Tosi, Ezequiel; Lacovig, Paolo; Lizzit, Silvano; Scardamaglia, Mattia; Kokkonen, Esko; Cepek, Cinzia; Africh, Cristina; Comelli, Giovanni; Günther, Sebastian & Patera, Laerte L.
  
• On-Surface Synthesis of Polypyridine: Strain Enforces Extended Linear Chains. Chemistry, 4(1), 112-117.
  Patera, Laerte L.; Amler, Josef & Repp, Jascha