Palladium sulphide – A highly selective catalyst for the gas phase hydrogenation of alkynes to alkenes

A particular palladium sulphide phase (Pd₄S) supported on carbon nanofibers is shown to be one of the most selective alkyne hydrogenation catalysts reported to date. Propyne and ethyne (in the absence of the corresponding alkene) can be converted in the gas phase to the corresponding alkene with 96% and 83% selectivity at 100% alkyne conversion. A bulk phase PdS powder (pre-reduced at 523 K) also demonstrated excellent performance (79% ethene selectivity). Other bulk phase metal sulphides (Ni₂S₃ and CuS) were tested and whilst the nickel analogue was found to be active/selective the performance was poorer than observed with either supported or unsupported Pd sulphide. Exceptional alkene selectivity extends to mixed alkyne/alkene feeds using the Pd₄S/CNF catalyst – 86% and 95% alkene selectivity for C3 and C2 mixes, respectively. This report opens up exciting possibilities for using metal sulphides as highly selective hydrogenation catalysts.