Breaking the activity limitation of iridium single-atom catalyst in hydrogenation of quinoline with synergistic nanoparticles catalysis

Single-atom catalysts (SACs) with the advantages of homogeneous and heterogeneous catalysts have become a hot-spot in catalysis field. However, for lack of metal–metal bond in SACs, H₂ has to go through heterolytic dissociation pathway, which has higher barrier than homolytic dissociation pathway, and thus limits the hydrogenation activity of SACs. Herein, we propose and demonstrate through constructing synergistic iridium single atoms and nanoparticles co-existed catalyst (denoted as Ir_1+NPs/CMK) to boost the catalytic activity of quinoline hydrogenation. Both experimental and density functional theory calculation results confirm that Ir₁ single sites activate quinoline, while Ir nanoparticles boost hydrogen dissociation. H atoms generated at Ir nanoparticles migrate to the quinoline bounded Ir₁ single sites to complete hydrogenation. The Ir_1+NPs/CMK catalyst exhibits much higher reactivity with turnover frequency of 7,800 h⁻¹ than those counterpart Ir₁/CMK and Ir_NPs/CMK catalysts, and is 20,000 times higher activity of commercial Ir/C benchmark catalyst for hydrogenation of quinoline under the same reaction conditions. This synergistic catalysis strategy between single atoms and nanoparticles provides a solution to further improve the performance of SACs for hydrogenation.