Search

Site modification and isolation through selective poisoning comprise an effective strategy to enhance the selectivity of palladium catalysts in the partial hydrogenation of triple bonds in acetylenic compounds. The recent emergence of supported hybrid materials matching the stereo- and chemoselectivity of the classical Lindlar catalyst holds promise to revolutionize palladium-catalyzed hydrogenations, and will benefit from an in-depth understanding of these new materials. In this work, we compare the performance of bare, lead-poisoned, and ligand-modified palladium catalysts in the hydrogenation of diverse alkynes. Catalytic tests, conducted in a continuous-flow three-phase reactor, coupled with theoretical calculations and characterization methods, enable elucidation of the structural origins of the observed selectivity patterns. Distinctions in the catalytic performance are correlated with the relative accessibility of the active site to the organic substrate, and with the adsorption configuration and strength, depending on the ensemble size and surface potentials. This explains the role of the ligand in the colloidally prepared catalysts in promoting superior performance in the hydrogenation of terminal and internal alkynes, and short-chain alkynols. In contrast, the greater accessibility of the active surface of the Pd-Pb alloy and the absence of polar groups are shown to be favorable in the conversion of alkynes containing long aliphatic chains and/or ketone groups. These findings provide detailed insights for the advanced design of supported nanostructured catalysts. [ABSTRACT FROM AUTHOR]

Invited for the cover of this issue are the groups of Prof. Javier Pérez-Ramírez at ETH Zurich, Switzerland, and Prof. Núria López at the Institute of Chemical Research of Catalonia (ICIQ), Spain. The cover illustrates major evolutionary changes in the design of palladium catalysts for alkyne semi-hydrogenation. Read the full text of the article at . [ABSTRACT FROM AUTHOR]

The evolutionary tale of palladium‐based catalysts for selective alkyne hydrogenation, from bare to lead‐alloyed, and, most recently, ligand‐modified nanoparticles, is unlocked using flow chemistry. Distinctions in the performance of each catalyst system as well as accessibility constraints arising from the use of ligands are identified and rationalized. For more details, see the Full Paper by J. Pérez‐Ramírez, N. López et al. on page 5926 ff. [ABSTRACT FROM AUTHOR]