“…To improve atom utilization efficiency of the “site-isolated” methods, our group and Li et al independently reported that atomically dispersed Pd catalysts are able to provide excellent ethylene selectivity while exhibiting the maximized atom utilization efficiency in the partial hydrogenation of alkynes. − The Pd atom of these Pd single-atom catalysts (SACs) normally anchors over oxide or carbon supports through Pd–O, Pd–N, or Pd–C bonds, resulting in the partially positive charge on Pd species. − It weakens the adsorption of products, that is, ethylene here, on the Pd atoms, leading to excellent selectivity. However, the weak adsorption of reactants, the sluggish H 2 dissociation dynamics, and the change of the reaction path due to the lack of ensemble metal sites of SACs − will reduce its hydrogenation reactivity, which is evidenced by the higher reaction temperature required to achieve the around 100% conversion for the Pd 1 catalyst than that for its nanoparticle counterparts (180 vs 20 °C) . Constructing a fully exposed cluster catalyst could have the benefit of a rich surface ensemble site, thus enabling different adsorption modes and reaction paths. ,, Particularly, decorating the core metal atom with a second metal atom can change the coordination environment and the electronic structure of the latter. − Meanwhile, we have reported recently that the supported Cu 1 atom could catalyze the semi-hydrogenation of acetylene, but the reaction temperature needed to reach the desired reactivity is even higher .…”