Synthesis of Pd-Au bimetallic nanoparticles for application in catalysis

Abstract

The synthesis of Pd-Au bimetallic nanoparticles by sequential and simultaneous reduction of H2PdCl4 and HAuCl4 with hydrazine in the reverse micelles of water/AOT/isooctane at 25 °C was investigated. TEM photographs showed that the Pd-Au NP obtained at a feeding compositions of [HAuCl4]/[H2PdCl4]=2/1 by sequential reduction of Pd and Au, essentially had uniform sizes and mean diameters of about 5.7 nm. In case of simultaneous reduction of Pd and Au at a feeding compositions of [HAuCl4]/[H2PdCl4]=1/1, the NP had uniform sizes and smaller mean diameters of about 3.57 nm. The UV-Vis absorption spectra for NP of palladium suggest that these NP reached their final sizes in less than 24 hours and the formation of Pd-Au bimetallic NPs in less than an hour because the palladium acts as a catalyst of gold during the reaction. The UV-Vis absorption spectra and X-ray diffraction patterns for the bimetallic systems of individual Pd NP suggest the formation of alloyed bimetallic NP, by both sequential and simultaneous reduction synthesis methods. HRTEM photographs suggest the formation of alloyed bimetallic Pd-Au NP by both methods of synthesis. EDX elemental analysis performed to Pd-Au NPs prepared by sequential reduction and the result showed a nanoparticle composition of 76.37 % of Au and 7.77 % of Pd. STEM-HAADF and EDX analysis of Pd-Au Nps prepared by the simultaneous reduction method suggest the formation of Pd-Au alloyed bimetallic NP, where gold and palladium are well dispersed in the NP and sometimes more gold or palladium can be found in the core of the NP.