Continuous synthesis of metal oxide-supported high-entropy alloy nanoparticles with remarkable durability and catalytic activity in the hydrogen reduction reaction

Metal oxide-supported multielement alloy nanoparticles are very promising as highly efficient and cost-effective catalysts with a virtually unlimited compositional space. However, controllable synthesis of ultrasmall multielement alloy nanoparticles (us-MEA-NPs) supported on porous metal oxides with a homogeneous elemental distribution and good catalytic stability during long-term operation is extremely challenging due to their oxidation and strong immiscibility. As a proof of concept that such synthesis can be realized, this work presents a general “bottom-up” l ultrasonic-assisted, simultaneous electro-oxidation–reduction-precipitation strategy for alloying dissimilar elements into single NPs on a porous support. One characteristic of this technique is uniform mixing, which results from simultaneous rapid thermal decomposition and reduction and leads to multielement liquid droplet solidification without aggregation. This process was achieved through a synergistic combination of enhanced electrochemical and plasma-chemical phenomena at the metal–electrolyte interface (electron energy of 0.3–1.38 eV at a peak temperature of 3000 K reached within seconds at a rate of ~105 K per second) in an aqueous solution under an ultrasonic field (40 kHz). Illustrating the effectiveness of this approach, the CuAgNiFeCoRuMn@MgO-P3000 catalyst exhibited exceptional catalytic efficiency in selective hydrogenation of nitro compounds, with over 99% chemoselectivity and nearly 100% conversion within 60 s and no decrease in catalytic activity even after 40 cycles (>98% conversion in 120 s). Our results provide an effective, transferable method for rationally designing supported MEA-NP catalysts at the atomic level and pave the way for a wide variety of catalytic reactions.