Selective hydrogenation of mixed alkyne/alkene streams at elevated pressure over a palladium sulfide catalyst

The Pd₄S phase of palladium sulfide is known to be a highly selective alkyne hydrogenation catalyst at atmospheric pressure. Results presented here demonstrate that high selectivity can be retained at the elevated pressures required in industrial application. For example, in a mixed acetylene/ethylene feed, 100% conversion of acetylene was attained with a selectivity to ethylene in excess of 80% at 18 bar pressure. Similarly, almost 85% selectivity can be obtained with mixed C3 feeds containing methyl acetylene, propadiene, propylene and propane at 18 bar pressure. Using a low loaded sample (0.1 wt% Pd) it was possible to estimate the TOF to be 27 s⁻¹. High selectivity was related to the crystal structure of Pd₄S with the unique spatial arrangement thought to favour Pd atoms acting in isolation from one another. Based on these results, it is proposed that this catalyst could be a potential replacement for PdAg alloys currently used by industry.