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Novel sandwich structure SiO2@AuAg@CeO2 nanospheres (SACs), as low-temperature CO oxidation catalysts, were designed and prepared in this work. The SACs include SiO2 nanosphere support, embedded bimetallic AuAg nanoparticles, and CeO2 shell. The transmission electron microscope (TEM), elemental mapping images, and ultraviolet-visible (UV-vis) spectroscopy indicated the successful fabrication of the SACs sandwich structure. The catalytic performance of SACs varies with the AuAg composition and achieves the best catalytic activity when Au/Ag atomic ratio is 2:1. The strong synergistic effect of AuAg alloy remarkably promotes the CO oxidation through facilitating the adsorption of CO and O2 on the AuAg nanoparticles. The CeO2 non-compact shell not only provides effective protection for AuAg nanoparticles from aggregation but also gives CO full access to the catalysts. With unique sandwich structure and specific chemical composition, the SiO2@Au2Ag1@CeO2 nanospheres with CeO2 shell thickness of 5 nm present excellent low-temperature catalytic activity and high-temperature thermal stability. [ABSTRACT FROM AUTHOR]