Synthesis of Pd−Rh Bimetallic Nanoparticles with Different Morphologies in Reverse Micelles and Characterization of Their Catalytic Properties

Abstract

Synthesis of bimetallic nanoparticles (NPs) of the transition metals Rh and Pd in H2O/AOT/isooctane (where AOT is dioctyl sodium sulfosuccinate) reverse-micelle solutions (RMSs) in the presence of molecular oxygen and quercetin, a flavonoid, is described. The methods for NP synthesis used here enable us to prepare alloyed-type Rh−Pd NPs and core/shell Pd/Rh and Rh/Pd NPs with the metal molar ratio of 1 : 1. With both Rh3+ and Pd2+ ions present in an RMS simultaneously, palladium ions are reduced first, and the formed Pd NPs have an inhibitive effect on reduction of rhodium ions. The stability of a mixture of Rh and Pd NPs in RMSs is investigated, and the mixture of NPs with a mean diameter of ~2.7 nm is found to be stable for at least 25 days. Pd and Rh NP-based catalysts are prepared by absorption of the synthesized NPs on γ-Al2O3, and their catalytic activity is tested in the monomolecular hydrogen isotope exchange reaction. A synergetic effect, manifested as an enhanced catalytic activity, is observed for the catalyst prepared by adsorption of the mixture of Rh and Pd NPs on γ-Al2O3.