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.
Keywords: CO oxidation; bimetallic catalysts; core−shell catalysts; gold catalysis; sub-5 nm particles.