Enhancing sulfur tolerance in Pt/TiO2 catalysts: Effect of H2O in CO oxidation

Abstract

Herein, we report the high sulfur tolerance of Pt/TiO2 catalysts toward CO oxidation under practical conditions. Pt/TiO2 more effectively retains its CO oxidation activity for significantly longer than Pt/Al2O3 and Pt/SiO2 in the presence of 40 ppm SO2 without H2O, and it increases sulfur tolerance with the TiO2 surface area. Even under harsh conditions of 250 ppm SO2 and 5 % H2O, a sulfur concentration 6 times higher than that under dry conditions, the Pt/TiO2 catalyst showed no activity deactivation for 48 h. Temperature-programmed desorption experiments confirmed that this excellent sulfur tolerance under wet conditions arises from the relatively weak interactions between sulfur and Pt. Further, diffuse reflectance infrared Fourier-transform spectroscopy showed that H2O promotes the migration of sulfur species from the Pt surface to the TiO2 support, thereby removing sulfur from the Pt surface and maintaining the CO oxidation activity of the catalyst. Specifically, under the wet conditions, sulfur initially adsorbed as SO3 on Pt and migrates as SO42-to the TiO2 support. Our findings provide insights into the behavior of sulfur on Pt/TiO2 catalysts and will facilitate the development of active and stable CO oxidation catalysts for practical sulfur-containing environments.