Sinter-Resistant and Highly Active Sub-5 nm Bimetallic Au–Cu Nanoparticle Catalysts Encapsulated in Silica for High-Temperature Carbon Monoxide Oxidation

Abstract

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 SiO 2 -encapsulated MMO catalyst was reduced under hydrogen flow to produce an Au–Cu@SiO 2 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 SiO 2 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 CO 2 in the feed stream on carbon monoxide (CO) oxidation over the Au–Cu@SiO 2 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 CO 2 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@SiO 2 catalyst is suitable for its application in automotive after-treatment devices, especially in low-temperature combustion engine exhausts.