Formation of sulfite-like species on Cr_2O_3 after SO_2 chemisorption

摘要

The adsorption of sulfur dioxide (SO_2) on polycrystalline Cr_2O_3 was experimentally investigated using temperature-programmed desorption (TPD). The chemisorption of SO_2 on the (0001) surface was also studied using theoretical methods. Different adsorption geometries were explored for SO_2 adsorption on the α-Cr_2O_3 (0001) surface. Two similar adsorption configurations were found to be the most stable with chemisorption energies of - 3.09 and - 2.79 eV/molecule. In both calculated stable adsorption configurations the appearance of sulfite-like species is predicted on the (0001) surface after adsorption. It is important to emphasize that these results are predicted only within the DFT + U framework. Under these conditions and despite great efforts, no stable sulfate-like geometry was found on this surface. The TPD spectrum exhibit a desorption peak at Tp≈870 ℃ with a heating rate of β≈0.12 ℃/s. The desorption energy calculated by the analysis given by Redhead and Adams, assuming the rate of desorption is given by a Polanyi-Wigner equation, is≈ -3.12 eV. This value is in good agreement with the predicted one using DFT + U calculations. To our knowledge, this is the first theoretical study of SO_2 adsorption on the Cr_2O_3 (0001) surface.