Room-Temperature Flow Synthesis of Pd–Ru Solid-Solution Alloy Nanoparticles Using Microreactor and Catalytic Performance of Carbon Monoxide Oxidation

The electronic states of solid-solution alloys can be regulated by tuning their composition, thereby affecting their physical and chemical properties. Through nanosizing, solid solution formation can be achieved even for immiscible elements, but conventional synthesis of such alloy nanoparticles (ANPs) often requires harsh conditions, such as high temperature, pressure, and organic solvents. Therefore, developing simpler, low-temperature, liquid-phase synthesis methods is highly desirable. However, reactant diffusion during insufficient mixing of precursor solutions hinders uniform nucleation and composition control. In this study, we synthesized Pd–Ru ANPs in an aqueous solution at room temperature using a microreactor with excellent mixing performance, which created a uniform reaction field. This technique allowed the simultaneous reduction of different ions before nucleation, enabling precise composition control. The resulting Pd–Ru ANPs exhibited uniform size and composition, and their catalytic properties showed enhanced activity compared to monometallic nanoparticles, as evaluated via carbon monoxide (CO) oxidation rate measurements. Notably, under room-temperature conditions, increasing Ru content resulted in a reduced crystallinity and induced localized structural disorder. This unique structural feature enabled optimal CO oxidation activity at a lower Pd composition than that reported previously. This method provides a simple and effective approach for the synthesis of ANPs with controlled compositions under mild conditions.