Microwave-Assisted Polyol Synthesis of Pt/Pd and Pt/Rh Bimetallic Nanoparticles in Polymer Solutions Prepared by Batch and Continuous-Flow Processing

Colloidal dispersions of Pt/Pd and Pt/Rh bimetallic nanoparticles have been synthesized by a microwave-assisted polyol method using ethylene glycol and glycerol as a solvent in the presence of poly(N-vinyl-2-pyrrolidone) (PVP). The structure of bimetallic nanoparticles has been investigated by means of high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS) elemental mapping, and extended X-ray absorption fine structure (EXAFS). The effectiveness of the batch and continuous-flow processing was demonstrated for the preparation of various bimetallic nanoparticles under multimode or single-mode microwave irradiation. In the single-mode microwave-assisted continuous-flow processing in contrast to the batch processing, the well-dispersed colloidal bimetallic nanoparticles were successfully produced at the boiling temperature of solvent. EXAFS analysis indicated that, in the case of Pt/Pd (1/1) and Pt/Rh (1/1) bimetallic nanoparticles prepared using both batch and continuous-flow processing, the distribution of different metallic species in a particle tended to be a "cluster-in-cluster". structure.