Our research aims at obtaining mechanistic insight at the atomic scale into molecular processes occurring at surfaces. 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 study the mechanisms governing single-sites catalyzed polymerization of small hydrocarbons under realistic reaction conditions, from model systems towards industrial supported catalysts. Furthermore, we have recently extended our research interests to the synthesis of atomically thin covalent organic frameworks (COFs). Novel approaches for the synthesis of extended crystallites with domain sizes up to several micrometers are currently under development.