A MOF-supported Pd-Au dimer catalyses the semihydrogenation of acetylene in ethylene with nearly barrierless activation energy. The dimer, anchored to a metal-organic framework (MOF), achieves >99.99% acetylene conversion and >90% selectivity under industrial conditions (1% acetylene, 89% ethylene, 10% H₂). The reaction proceeds with an apparent activation energy of ~1 kcal mol⁻¹, operating at 35°C with high operational windows and weight hourly space velocities (66,000 ml g⁻¹h⁻¹). Experimental and computational studies reveal cooperativity between Pd and Au atoms, and between atoms and the MOF support, enabling barrierless semihydrogenation. The MOF, derived from S-methyl-L-cysteine, has narrow pores (0.6 nm) and stabilizes the dimer through thioether linkages. The dimer, with >20 wt% loading, catalyses the reaction under simulated front-end industrial conditions (35–150°C), producing ethane as the only by-product. The reaction is nearly barrierless, with Pd as the main adsorption site and Au and MOF sulfur atoms acting as electronic modifiers for Pd, assisting in H₂ dissociation. The dimer shows high stability and recyclability, with no significant changes in XPS and powder X-ray diffraction after catalytic experiments. The catalytic activity of the dimer is much higher than that of zeolites, attributed to its small pore size and high-density Pd-Au catalytic species. Theoretical calculations support the experimental findings, showing that the H₂ dissociation step is the limiting factor in the reaction, with a low activation energy of ~5 kJ mol⁻¹. The dimer's unique structure and properties make it an efficient catalyst for the semihydrogenation of acetylene in ethylene streams.A MOF-supported Pd-Au dimer catalyses the semihydrogenation of acetylene in ethylene with nearly barrierless activation energy. The dimer, anchored to a metal-organic framework (MOF), achieves >99.99% acetylene conversion and >90% selectivity under industrial conditions (1% acetylene, 89% ethylene, 10% H₂). The reaction proceeds with an apparent activation energy of ~1 kcal mol⁻¹, operating at 35°C with high operational windows and weight hourly space velocities (66,000 ml g⁻¹h⁻¹). Experimental and computational studies reveal cooperativity between Pd and Au atoms, and between atoms and the MOF support, enabling barrierless semihydrogenation. The MOF, derived from S-methyl-L-cysteine, has narrow pores (0.6 nm) and stabilizes the dimer through thioether linkages. The dimer, with >20 wt% loading, catalyses the reaction under simulated front-end industrial conditions (35–150°C), producing ethane as the only by-product. The reaction is nearly barrierless, with Pd as the main adsorption site and Au and MOF sulfur atoms acting as electronic modifiers for Pd, assisting in H₂ dissociation. The dimer shows high stability and recyclability, with no significant changes in XPS and powder X-ray diffraction after catalytic experiments. The catalytic activity of the dimer is much higher than that of zeolites, attributed to its small pore size and high-density Pd-Au catalytic species. Theoretical calculations support the experimental findings, showing that the H₂ dissociation step is the limiting factor in the reaction, with a low activation energy of ~5 kJ mol⁻¹. The dimer's unique structure and properties make it an efficient catalyst for the semihydrogenation of acetylene in ethylene streams.