Search

• Palladium nanoparticles favour over-hydrogenation in butyne hydrogenation. • In contrast, palladium sulfide catalyst is highly selectivity for butyne hydrogenation. • Pd 4 S offers greater than 90% alkene selectivity for both but-1-yne & but-2-yne as reactants. • DFT calculations show desorption of alkene is more favourable than hydrogenation. The partial hydrogenation of but-1-yne and but-2-yne was studied with a view to probing the difference between external and internal alkynes. Catalysts with Pd and Pd 4 S active phases were prepared on a carbon nanofiber support. Over the simple Pd catalyst over-hydrogenation was common which restricted alkene selectivity greatly – 25–35% depending on temperature. In contrast, the Pd 4 S active phase offered exceptional alkene selectivity (maximum of 92–93% alkene selectivity for both the external and internal alkyne). DFT calculations were subsequently used to rationalise this difference in product selectivity – sulfur appears to change the geometry of the active site in Pd 4 S and create a surface which favours alkene desorption relative to over-hydrogenation. This work further emphases the potential of palladium sulfide phases as an alternative to purely metallic palladium catalysts for partial alkyne hydrogenation. [ABSTRACT FROM AUTHOR]