A Novel Magnetically Recoverable Ni-CeO2-x/Pd Nanocatalyst with Superior Catalytic Performance for Hydrogenation of Styrene and 4-Nitrophenol.

Metal/support nanocatalysts consisting of various metals and metal oxides not only retain the basic properties of each component but also exhibit higher catalytic activity due to their synergistic effects. Herein, we report the creation of a highly efficient, long-lasting, and magnetic recyclable catalyst, composed of magnetic nickel (Ni) nanoparticles (NPs), active Pd NPs, and oxygen-deficient CeO2-x support. These hybrid nanostructures composed of oxygen deficient CeO2-x and active metal nanoparticles could effectively facilitate diffusion of reactant molecules and active site exposure that can dramatically accelerate the reaction rate. Impressively, the rate constant k and k/m of 4-nitrophenol reduction over 61 wt % Ni-CeO2-x/0.1 wt % Pd catalyst are 0.0479 s-1 and 2.1 × 104 min-1 g-1, respectively, and the reaction conversion shows negligible decline even after 20 cycles. Meanwhile, the optimal 61 wt % Ni-CeO2-x/3 wt % Pd catalyst manifests remarkable catalytic activity toward styrene hydrogenation with a high TOF of 6827 molstyrene molPd-1 h-1 and a selective conversion of 100% to ethylbenzene even after eight cycles. The strong metal-support interaction (SMSI) between Ni NPs, Pd NPs, and oxygen-deficient CeO2-x support is beneficial for superior catalytic efficiency and stability toward hydrogenation of styrene and 4-nitrophenol. Moreover, Ni species could boost the catalytic activity of Pd due to their synergistic effect and strengthen the interaction between reactant and catalyst, which seems responsible for the great enhancement of catalytic activity. Our findings provide a new perspective to develop other high-performance and magnetically recoverable nanocatalysts, which would be widely applied to a variety of catalytic reactions.