The selective hydrogenation of acetylene to ethylene is a critical step in the synthesis of polyethylenes. Achieving high conversion to ethylene without over-hydrogenation to ethane is a challenge that requires control of the transition metal site, which we achieve through a ligand-coordinated supported catalyst (LCSC) strategy. Using Pd catalysts coordinated to 1,10-phenanthroline-5,6-dione (PDO) ligands on CeO₂ supports, we have discovered that the reaction selectivity depends strongly on the ligand:metal ratio with higher selectivity when more ligand is present in the catalyst. Catalyst structure was examined by extended X-ray absorption fine structure spectroscopy, transmission electron microscopy, and CO adsorption, which indicate single-atom character of the Pd. The ligand:metal ratio is determined by X-ray photoelectron spectroscopy measurements and correlated with hydrogenation reactions under steady-state flow conditions to examine trends in hydrogenation activity and selectivity. Those trends can be better understood by density functional theory calculations that indicate hydrogen binding on the ligand to guide reaction selectivity toward the desired ethylene hydrogenation product. These results demonstrate the importance of considering the dynamic character of LCSCs and inform the design of future single-site heterogeneous catalysts.

乙炔选择性加氢制乙烯是聚乙烯合成的关键步骤。在不过度氢化成乙烷的情况下实现乙烯的高转化率是一项挑战，需要控制过渡金属位点，我们通过配体配位负载催化剂 (LCSC) 策略来实现这一点。_{使用与 CeO 2}上的 1,10-phenanthroline-5,6-dione (PDO) 配体配位的 Pd 催化剂我们发现，当催化剂中存在更多的配体时，反应选择性强烈依赖于配体：金属的比例，具有更高的选择性。通过扩展 X 射线吸收精细结构光谱、透射电子显微镜和 CO 吸附检查催化剂结构，这表明 Pd 的单原子特征。配体：金属比由 X 射线光电子能谱测量确定，并与稳态流动条件下的氢化反应相关，以检查氢化活性和选择性的趋势。这些趋势可以通过密度泛函理论计算更好地理解，该计算表明氢结合在配体上以引导反应选择性朝向所需的乙烯加氢产物。