EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The Suzuki coupling reaction is an important method to construct C-C bonds and has been broadly applied in fine-chemical synthesis.[1] Homogeneous Palladium catalysts were confirmed to possess a relatively high efficiency for the Suzuki reaction, but challenges with the recovery of the costly and toxic palladium catalyst were found. The alternative strategy of supported Pd nanoparticles has also faced limitations because of insufficient activity and poor chemoselectivity. Single-atom catalysts that integrate the merits of homogeneous and heterogeneous catalysts may provide an option to overcome the obstacles.[2] Herein, we have developed abundant surface sites for anchoring Pd atomic species on a few-layer polymeric carbon nitride through a wet impregnation method, producing an efficient and stable Pd/CN catalyst for the Suzuki-coupling reaction. IR spectroscopy was used to characterize the supported metal and to investigate the reaction mechanism. We chose CO as probe molecule for in-situ DRIFTS measurements to study the electronic and coordination structure of the surface metal sites, in order to distinguish the Pd single atom from clusters. In-situ ATR-IR measurement and DFT calculation were conducted to study the reactants and intermediate species on the surface metal sites to get an in-depth mechanistic understanding. Besides, for comparison, a Pd cluster catalyst was synthesized using a calcination method with H2 treatment. We evaluate the metal dispersion of both Pd single atom and clusters catalyst via H2 and CO pulse chemisorption technology to explore the relationship among the surface metal size, metal loading, and metal density. This work provides insights into the electronic and coordination structures of single-atom catalysts at the molecular level and contributes to the understanding of the structure-reactivity relationships.

References
1. R. Martin and S. L. Buchwald, Accounts of chemical research 2008, 41, 1461-1473.
2. X. Cui, W. Li, P. Ryabchuk, K. Junge, M. Beller, Nature Catalysis 2018, 1, 385-397.