Alkali metal modified Pt/EG-TiO2 catalysts for CO oxidation with efficient resistance to SO2 and H2O

Abstract

Pt-0.15Na/EG-TiO₂ catalysts obtained by the impregnation method showed better CO oxidation activity as well as resistance to SO₂ and H₂O than the unmodified Pt/EG-TiO₂ catalysts. The physicochemical properties of the catalysts were characterized by means of ICP-AES, TEM, AC-TEM, CO-TPR, ESR, O₂-TPD, in situ DRIFTS, XAFS, XRD, BET, SEM and XPS techniques. Meanwhile, the influence of Na doping on improving the CO oxidation activity as well as SO₂ and H₂O resistance of the Pt/EG-TiO₂ catalysts was investigated in depth. The addition of Na promoted the dispersion of Pt nanoparticles (NPs) in the Pt/EG-TiO₂ catalysts, which led to the uniform dispersion of Pt on the TiO₂ support mainly in the form of nanoclusters and single atoms, thus improving the utilization of Pt. Moreover, it also increased the number of active hydroxyl species on the surface of the Pt/EG-TiO₂ catalysts, which accelerated the formation of COO*, an intermediate product of the CO oxidation reaction process, thereby improving the CO oxidation activity of the Pt/EG-TiO₂ catalysts. The addition of Na did not change the crystal phase structure and surface morphology of the Pt/EG-TiO₂ catalysts; it caused the TiO₂ support to have more active hydroxyl species, which reacted with SO₂ to form sulfite species. At the same time, the presence of active hydroxyl species inhibited the oxidation of SO₂ and reduced the production of sulfate species. Pt–O_x and Na in the Pt-0.15Na/EG-TiO₂ catalysts directly interacted with each other and uniformly dispersed on the EG-TiO₂ support in the form of Pt–O(OH)_x–Na. SO₂ was preferentially adsorbed on Na, and then SO₂ combined with Na to generate Na₂SO₄, which led to the localized sulfation of Na in Pt–O(OH)_x–Na, reducing the adsorption of SO₂ on Pt–O(OH)_x–Na. Thus, reduced SO₂ adsorption on the Pt and TiO₂ support significantly improved the resistance to SO₂ and H₂O of Pt/EG-TiO₂ catalysts.