Stabilizing undercoordinated single-atom Pd^δ+ sites on CeO_2-x nano-island for efficient hydrogenation of nitrile butadiene rubber

Palladium single-atom catalysts show exceptional catalytic performance in nitrile butadiene rubber (NBR) hydrogenation due to their unique unsaturated coordination environments. However, the hydrogenation activity and atomic efficiency are seriously limited by inherent instability of undercoordinated Pd^δ+ sites and poor support structure, leading to decreased hydrogenation degree and cycling stability. In this work, a novel single-atom palladium catalysts was developed, where undercoordinated single-atom Pd^δ+ sites are steadily anchored onto CeO_2-x nano-islands supported by SiO₂ (Pd₁/CeO_2-x/SiO₂). The strong metal-interaction of CeO_2-x nano-islands immobilize the undercoordinated Pd^δ+ sites to enhance adsorption of olefin bonds in NBR, while SiO₂ promotes mass transfer diffusion of NBR and atomic efficiency of palladium. The Pd₁/CeO_2-x/SiO₂ thus achieves an unprecedented hydrogenation degree of up to 99.8% without decrease over a 10-runs stability test in selective hydrogenation of NBR, outperforming previously state-of-the-art catalysts. Consequently, this work will offer a new strategy for single-atom catalysts to achieve high steady-state activity in selective hydrogenation.