Study of CO2 Adsorption Properties on the SrTiO3(001) Surface with Ambient Pressure XPS.

Abstract

The adsorption properties of CO₂ on the SrTiO₃(001) surface were investigated using ambient pressure X-ray photoelectron spectroscopy under elevated pressure and temperature conditions. On the Nb-doped TiO₂-enriched (1 × 1) SrTiO₃ surface, CO₂ adsorption, i.e., the formation of CO₃ surface species, occurs first at the oxygen lattice site under 10^-6 mbar CO₂ at room temperature. The interaction of CO₂ molecules with oxygen vacancies begins when the CO₂ pressure increases to 0.25 mbar. The adsorbed CO₃ species on the Nb-doped SrTiO₃ surface increases continuously as the pressure increases but starts to leave the surface as the surface temperature increases, which occurs at approximately 373 K on the defect-free surface. On the undoped TiO₂-enriched (1 × 1) SrTiO₃ surface, CO₂ adsorption also occurs first at the lattice oxygen sites. Both the doped and undoped SrTiO₃ surfaces exhibit an enhancement of the CO₃ species with the presence of oxygen vacancies, thus indicating the important role of oxygen vacancies in CO₂ dissociation. When OH species are removed from the undoped SrTiO₃ surface, the CO₃ species begin to form under 10^-6 mbar at 573 K, thus indicating the critical role of OH in preventing CO₂ adsorption. The observed CO₂ adsorption properties of the various SrTiO₃ surfaces provide valuable information for designing SrTiO₃-based CO₂ catalysts.