Sinter-Resistant and Highly Active Sub-5 nm Bimetallic Au-Cu Nanoparticle Catalysts Encapsulated in Silica for...

A novel gold-copper-based silica-encapsulated mixed metal oxide (MMO) core-shell catalyst-with sub-5 nm MMO particles-was successfully synthesized via a reverse micelle process. The SiO₂-encapsulated MMO catalyst was reduced under hydrogen flow to produce an Au-Cu@SiO₂ catalyst. X-ray diffraction and X-ray photoelectron spectroscopy characterization confirmed the presence of Au-Cu nanocomposites in the catalyst, while transmission electron microscopy characterization revealed the core-shell structure of the catalyst with the presence of sub-5 nm Au-Cu nanoparticle cores inside SiO₂ shells. Brunauer-Emmett-Teller surface characterization identified that the catalyst is porous and bimodal in nature. The effects of promoter metal ion, catalyst pretreatment (calcination), and the presence of CO₂ in the feed stream on carbon monoxide (CO) oxidation over the Au-Cu@SiO₂ catalyst were examined in the temperature range of 50-400 °C. A catalyst stability test was performed at 300 °C by conducting a CO oxidation reaction for 116 h on stream. The catalyst exhibited excellent efficacy for CO oxidation, with ∼100% conversion to CO₂ achieved at 400 °C. While the presence of Cu enhanced the CO conversion at low to intermediate temperatures (50-300 °C), silica encapsulation of the Au-Cu nanocomposites facilitated remarkable stability of the catalyst. The activity of the Au-Cu@SiO₂ catalyst is suitable for its application in automotive after-treatment devices, especially in low-temperature combustion engine exhausts.