New Photon-Mediated Mechanism for SO2 and NO2 Adsorption of Reducible Transition Metal Oxides: Operando Studies on TiO2 Surfaces
- David Langhammer (Uppsala University, Sweden)
- Tuesday 31 March 2020
- Hotel NH Noordwijk Conference Centre Leeuwenhorst
David Langhammer1, Jolla Lundgren1 and Lars Österlund1
1Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, PO Box 534, SE-75121 Uppsala, Sweden
Photo-stimulated adsorption of SO2 and NO2 on anatase and rutile TiO2 nanoparticles were studied by means of operando Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations. On the perfect anatase TiO2 (101) and rutile TiO2 (110) surfaces SO2 and NO2 do not adsorb above 150 K. An increased adsorption is however found on reduced TiO2 which is attributed to formation of sub-surface oxygen vacancies and reactive Ti3+ species at the surface . In contrast, during bandgap illumination with ultraviolet light, SO2 and NO2 are efficiently photo-adsorbed on TiO2 without the presence of surface defects and are thus readily adsorbed on the perfect stoichiometric surface. Corroborated by DFT calculations a new mechanism for SO2 and NO2 adsorption is found that leads to formation of SO3 and NO3-like surface species by reactions with oxidized surface oxygen atoms and nearby reduced subsurface Ti atoms that are formed upon interband absorption. A delicate interplay between adsorbate orbital filling and electrostatic interaction with the reduced subsurface Ti atom is found to govern the adsorbate structure. The adsorption mechanism proposed here should be applicable for other similar adsorbates and reducible transition metal oxides exhibiting sufficiently strong exciton binding energy, and possibly be a widely occurring solar-light activated geochemical reaction mechanism.
This work was funded by the Swedish Research Agency (VR) contract numbers 2015-04757 and 2019-05614.
- David Langhammer, Jakob Thyr, and Lars Österlund, J. Phys. Chem. C 2019, 123, 24549−24557