Catalytic role of pre-adsorbed CO in platinum-based catalysts: The reduction of SO₂ by CO on Pt_lAu_m(CO) _n

Using density functional theory, we have investigated the catalytic properties of bimetallic complex catalysts Pt_lAu_m(CO) _n (l + m = 2, n = 1-3) in the reduction of SO₂ by CO. Due to the strong coupling between the C-2p and metal 5d orbitals, pre-adsorption of CO molecules on the Pt_lAu_m is found to be very effective in not only reducing the activation energy, but also preventing poisoning by sulfur. As result of the coupling, the metal 5d band is broadened and down-shifted, and charge is transferred from the CO molecules to the Pt _lAu_m. As SO₂ is adsorbed on the catalyst, partial charge moves to the anti-σ bonding orbitals between S and O in SO₂, weakening the S-O bond strength. This effect is enhanced by pre-adsorbing up to three CO molecules, therefore the S-O bonds become vulnerable. Our results revealed the mechanism of the excellent catalytic properties of the bimetallic complex catalysts.