Adapting the concepts of nonaqueous sol–gel chemistry to metals: synthesis and formation mechanism of palladium and palladium–copper nanoparticles in benzyl alcohol

Abstract

Benzyl alcohol is a versatile reaction medium for the synthesis of different types of nanoparticles. Its ability to act as an oxygen source gave access to metal oxide nanoparticles, while its reducing properties can be harnessed for the preparation of metals. Here we report the synthesis of Pd and PdCu nanoparticles in benzyl alcohol supplemented by a detailed mechanistic study for both systems. To elucidate the chemical formation mechanism of the Pd nanoparticles, we performed in situ attenuated total reflection ultraviolet–visible (ATR-UV–vis) and Fourier transform infrared spectroscopy (ATR-FTIR), providing information on the organic as well as on the inorganic side of the reaction. Potential gaseous products were analyzed by in situ gas chromatography (GC) and mass spectrometry (MS). We observed the formation of benzaldehyde, toluene, and dibenzyl ether as the three main organic products. The formation of the PdCu alloy nanoparticles was studied by ex situ powder X-ray diffraction (PXRD). A time-resolved study of the synthesis at 100 °C indicated that initially three types of particles formed, composed of an alloy with high Pd content, an alloy with high content of copper, and palladium particles, and only later in the reaction course they transformed into an alloy with a Pd-to-Cu ratio close to 1.