Room temperature benzaldehyde oxidation using air over gold–silver nanoalloy catalysts

Abstract

In this study gold–silver alloy nanoparticles were prepared by chemical reduction method using silver nitrate and chloroauric acid as metal precursor, cetyl trimethyl ammonium bromide as protecting agent and sodium borohydride (NaBH4) as a reducing agent. Formation of alloy nanoparticles was monitored using UV–vis absorption spectroscopy and dynamic light scattering (DLS). Stability of alloy nanoparticles was detected by turbiscan. Gold–silver alloy nanoparticles were supported on silica by dispersing silica powder in the suspension of destabilized nanoparticles. Ag–Au/SiO2 samples were characterized by UV–vis absorption spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption–desorption and inductively coupled plasma-optical emission spectroscopy (ICP-OES). The catalysts were tested for the liquid phase oxidation of benzaldehyde (BZ) affording high selectivity to methyl benzoate (MB) as compared to the catalyst prepared by the conventional reported methods. The oxidation of benzaldehyde was subjected to detailed investigations to study the effect of parameters such as time, temperature, amount and different concentration of catalysts, amount of benzaldehyde and concentration of the base. Catalyst containing 1.5 wt% Au–1.5 wt% Ag exhibited the best catalytic performance in benzaldehyde oxidation in the presence of methanol as solvent. The used catalyst was recycled to four cycles without significant loss in its activity.