Copper nanoparticles supported on silica are an earth-abundant catalyst efficient for alkyne hydrogenation, yielding high selectivity towards (Z)-olefin when organic ligands are added. Here, we investigate the origin of this selectivity by studying kinetics of the hydrogenation of the prototypical 1-phenyl-1-propyne substrate. Hydrogenation occurs stepwise on the unmodified catalyst, with first the formation of the (Z)-alkene followed by overhydrogenation to the alkane. Adsorption isotherms and kinetic modelling evidence that these consecutive processes result from the high adsorption constant of the alkyne onto Cu compared to that of the alkene, as confirmed by DFT calculations. Ligands (tricyclohexylphosphine and an NHC) display adsorption constants similar to that of the alkyne, which allows for its hydrogenation but leads to the displacement of the generated alkene from the catalyst, thereby preventing the overhydrogenation. Our findings thus rationalize the observed selectivity and guide the choice of ligands for selective semihydrogenation to (Z)-olefins with Cu-based catalysts.

负载在二氧化硅上的铜纳米粒子是一种有效的炔烃加氢催化剂，在添加有机配体时对（Z）烯烃具有高选择性。在这里，我们通过研究典型的1-苯基-1-丙炔底物的氢化动力学来研究这种选择性的起源。加氢在未改性的催化剂上逐步进行，首先形成（Z）-烯烃，然后加氢成烷烃。吸附等温线和动力学模型证明，这些连续的过程是由于炔烃对铜的高吸附常数（与烯烃的吸附常数相比）所致，正如DFT计算所证实的那样。配体（三环己基膦和NHC）显示出与炔烃相似的吸附常数，从而允许其氢化，但会导致生成的烯烃从催化剂中置换出来，从而防止了过度氢化。因此，我们的发现合理化了观察到的选择性，并指导了使用铜基催化剂选择性半氢化为（Z）烯烃的配体的选择。