Searching excellent catalysts to remove both SO2 and CO of industrial exhaust simultaneously is of great significance to environment. The catalytic activities of clusters PtAu(CO)(n)(n = 0-3) and their anion counterparts, to the reduction of SO2 by CO, are compared based on density-functional theory calculations. The d electrons of the anion catalysts are identified to be closed shell once CO pre-adsorbed, while the d electrons of the neutral clusters' are open-shell configuration. The result is that the negatively charged [PtAu(CO)(n)](-) clusters show less excellent catalytic properties than their corresponding neutral catalysts. The d-band center of the neutral PtAu(CO)(n) with uncoupled d electrons shift down relative to the Fermi level after sulfur dioxide adsorption, which therefore enhances the catalytic properties. Finding from this research will provide guard line to tune the catalytic properties of Pt/Au catalysts. (C) 2015 Elsevier B.V. All rights reserved.