Spillover hydrogenation is facet specific and occurs on atomically dispersed Pd catalyst on Cu(100). Knowing this, cost-effective catalysts with extremely low Pd loading are fabricated that successfully catalyse the semi-hydrogenation of a broad range of alkynes with high activity and selectivity. Hydrogen spillover is a well-known phenomenon in heterogeneous catalysis; it involves H(2)cleavage on an active metal followed by the migration of dissociated H species over an 'inert' support(1-5). Although catalytic hydrogenation using the spilled H species, namely, spillover hydrogenation, has long been proposed, very limited knowledge has been obtained about what kind of support structure is required to achieve spillover hydrogenation(1,5). By dispersing Pd atoms onto Cu nanomaterials with different exposed facets, Cu(111) and Cu(100), we demonstrate in this work that while the hydrogen spillover from Pd to Cu is facet independent, the spillover hydrogenation only occurs on Pd-1/Cu(100), where the hydrogen atoms spilled from Pd are readily utilized for the semi-hydrogenation of alkynes. This work thus helps to create an effective method for fabricating cost-effective nanocatalysts with an extremely low Pd loading, at the level of 50 ppm, toward the semi-hydrogenation of a broad range of alkynes with extremely high activity and selectivity.