Tuning of catalysts for the selective hydrogenation of acetylene with high stability and selectivity: Ligand coordination effects

Selectivity of acetylene over CeO2 supported single Pd catalyst (Pd1/CeO2(1 1 1)) and 1,10-phenanthroline-5,6dione (PDO)-liganded Pd single catalyst (Pd1-PDO/CeO2(1 1 1)) was studied by density functional theory calculations combined with microkinetic modeling as well as ab initio molecular dynamics (AIMD) in this work. The present results show that the PDO-ligand can stabilize the single Pd catalyst through strong Pd-O/Pd-N interaction, which is further conformed by AIMD simulation. In the presence of PDO ligand, which contains Pd-O/PdN bonds, the single atom Pd is oxidized and becomes more stable. It was also found that the adsorption strength of C2H2 is weaker than C2H4 on single Pd, whereas opposite trend holds for PDO-liganded Pd single catalyst, indicating potential higher C2H4 formation electivity for Pd1-PDO/CeO2(1 1 1). Reaction mechanism analysis and microkinetic modeling demonstrate that the catalytic activity of C2H2 hydrogenation decreases but the C2H4 formation selectivity increases when PDO ligand was introduced, which agrees with the experimental observation. Moreover, the free energy change of C2H4 desorption as well as its further hydrogenation was quantitative studied by AIMD simulation, verifies that the PDO ligand indeed helps ethene desorption at high reaction temperature. It is hoped the present work may extend to other ligands which contain -O or -N groups that can bind with single metal atom strongly like -OH groups.