Pt-based catalysts are promising for the selective catalytic reduction of NO x by CO (CO-SCR), but some technical issues hinder their practical application, including the high Pt loading needed, high reduction temperature, and the low tolerance toward SO 2 . Here, we report a novel Pt catalyst for CO-SCR, which has negatively charged single-atom Pt embedded on CuO squares, and the latter is supported on CoAlO nanosheets. This Pt−CuO/CoAlO catalyst with an ultra-low Pt loading (0.02 wt %) exhibited 91% NO conversion and 80% N 2 selectivity in 3% O 2 at 200 °C. More importantly, it showed almost no activity loss in 200 ppm SO 2 over a 15 h test. The theoretical calculations reveal that the negatively charged Pt has a stronger NO adsorption ability than the positively charged Pt, and Cu serves as the CO adsorption site. The much-weakened SO 2 adsorption on Pt−CuO/ CoAlO relative to the NO and CO adsorption effectively avoids the catalyst poisoning by SO 2 . KEYWORDS: Pt-based catalysts, hydrotalcite-like oxide, negatively charged Pt atoms, NO x reduction by CO, SO 2 tolerance ■ HIGHLIGHTS • A negatively charged Pt single-atom catalyst is synthesized. • This catalyst with an ultra-low Pt loading (0.02 wt%) exhibits an excellent low-temperature (200 °C) activity in the presence of 3% O 2 . • This catalyst displays excellent resistance to SO 2 poisoning (200 ppm for 15 h). • The negatively charged Pt promotes NO adsorption, and Cu acts as a CO adsorption site. • A lower SO 2 adsorption energy on this catalyst than NO and CO adsorption avoids its poisoning.

Developing efficient catalysts for the selective catalytic reduction of NO x by CO (CO-SCR) is the key challenge for commercializing this technology. Ag-based catalysts with relatively low costs are promising but widely believed to be not efficient enough for this reaction. Here, we demonstrate that atomically dispersed Ag supported on ordered mesoporous WO 3 (m-WO 3 ) can serve as a highly active catalyst for CO-SCR under O 2 -containing conditions. By altering the amount of the Ag precursor, the local environment of the Ag atom coordinated with the O atom can be tailored. Furthermore, at 250 °C and an O 2 /CO ratio of 2.5:1, 0.3Ag/m-WO 3 (0.3 wt % Ag) with six-coordinated Ag−O exhibited much better catalytic performance than 5 Ag/m-WO 3 (5 wt % Ag) with twocoordinated Ag−O (e.g., 0.43 vs 0.02 mol NO g Ag −1 h −1 in the reaction rate) and previously reported Ag-based catalysts in the literature. The theoretical calculations confirm that the six-coordinated Ag atoms in 0.3Ag/m-WO 3 possess a more positive oxidation state and a higher d-band center than the two-coordinated Ag atoms in 5Ag/m-WO 3 , promoting its bonding strength with coadsorption of the critical intermediates of N 2 O* and CO*. This work provides a feasible route for regulating the local environment of a Ag single atomic catalyst to enhance its catalytic property for CO-SCR.