<p>The impacts of PbCl₂ and PbO on Mn–Co catalysts were investigated and compared in the context of low-temperature CO oxidation. The poisoned catalysts were synthesized by impregnating fresh catalysts with aqueous solutions of PbCl₂ and Pb(NO₃)₂, respectively. The activity of the Mn–Co catalyst would be reduced by both Pb species, and PbO was more effective in poisoning it compared to PbCl₂. The Pb species led to a reduction in specific surface area and pore volume. Furthermore, the presence of Pb species decreased the concentrations of Mn³⁺, Co³⁺, and surface lattice oxygen species. In addition, the presence of Pb species led to a decrease in the reducibility, thereby impeding the adsorption activation process of CO as well as the redox cycle. Moreover, the oxidation of CO on the MC catalyst followed the Mars-van Krevelen (MvK) mechanism. CO reacted with Co³⁺ to form the CO–Co³⁺ species. Subsequently, CO–Co³⁺ species reacted with lattice oxygen to generate carbonate species and create oxygen vacancies. The carbonate is further decomposed into CO₂. The presence of Pb inhibited the adsorption of CO and reduced the generation of active intermediates. Besides, the introduction of Pb inhibited the decomposition of carbonate, leading to its accumulation on the catalyst surface, which blocked the active sites and oxygen vacancies.</p>