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Improving the selectivity for catalytic hydrogenation of alkynes is a key step in upgrading feedstocks for olefin polymerization. Herein, dilute Pd_xAu_1–x alloy nanoparticles embedded in raspberry colloid-templated silica (x = 0.02, 0.04, and 0.09) are demonstrated to be highly active and selective for the gas-phase hydrogenation of 1-hexyne, exhibiting higher selectivity than pure Pd at high conversion. The conversion of 1-hexyne remains high even for the very low amounts of Pd in Pd_0.02Au_0.98. These catalysts are highly resistant to sintering—addressing a long-standing challenge in the use of Au-based catalysts. Clear evidence is presented that the addition of the second hydrogen to the half-hydrogenated intermediate is the rate-limiting step and that the stability of the half-hydrogenated intermediate of the alkyne is higher than the half-hydrogenated alkene, which explains the high selectivity even at high …