Excellent sulfur and water resistance for CO oxidation on Pt single-atom-catalyst supported by defective graphene: The effect of vacancy type

Abstract

The competitive adsorption of sulfur dioxide and water molecules will degrade the performance for CO oxidation catalyst in some processes such as automobile exhaust cleaning or Claus tail gas treatment. In order to study the effect of carbon vacancy on the sulfur and humidity resistance, the adsorption of CO, O2, SO2 and H2O molecules on Pt single-atom-catalyst supported by graphene with single carbon vacancy (Pt-SG) and double carbon vacancy (Pt-DG) have been comparatively investigated by using density functional theory calculations. It shows that the active site of Pt-SG can be blocked by the SO2 and H2O molecules due to their strong affinity towards Pt-SG. However, the carbon divacancy makes Pt atom less attractive towards SO2 and H2O molecules on Pt-DG compared with that on Pt-SG, where the pre-adsorbed SO2 and H2O molecules will be substituted by the CO molecule with larger adsorption energy on Pt-DG, which finally achieves the sulfur and water resistance for Pt-DG. In addition, an efficient Termolecular Eley-Rideal reaction path with a low energy barrier of 0.49 eV for CO oxidation is found on Pt-DG. The significant downshift of CO-5σ orbital levels plays an important role in the formation of new O-C bonds in OCOOCO intermediate on Pt-DG, where the O2-1π orbital is weakened due to its interaction with CO-5σ and CO-1π orbital, which finally facilitates the break of O-O bond and the production of CO2 molecules along the TER mechanism. Overall, the double carbon vacancy can enhance the selective adsorption for CO molecule other than the SO2 and H2O molecules on Pt atom, making the Pt-DG to be an efficient CO oxidation catalyst even in sulfur and humid environment.