Core-shell heterostructures have been utilized as a catalyst that is thermally stable and exhibits a synergistic effect between core and shell, resulting in increased catalytic activity. Here we report on the synthetic procedure involving a Au-144 core with an iron oxide shell which can be varied in thickness. The Au-144@Fe2O3 particles with Au:Fe mass ratios of 1:2, 1:4, and 1:6 were synthesized and then deposited onto silica via colloidal deposition. Using CO oxidation, each Au-144@Fe2O3/SiO2 catalyst gave varying degrees of full CO conversion depending on the thickness of the iron oxide layer. The 1:4 Au-144@Fe2O3/SiO2 catalyst produced the best catalytic activity and was further investigated via thermal treatments, where calcination at 300 A degrees C presented the best results, and the 1:4 ratio was still active at 100 A degrees C after thermal treatments. [GRAPHICS] .