Formation of sulfite-like species on Cr 2O 3 after SO 2 chemisorption

Abstract

The adsorption of sulfur dioxide (SO 2) on polycrystalline Cr 2 O 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 2 O 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 T p ≈ 870 °C with a heating rate of β ≈ 0.12 °C/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 2 O 3 (0001) surface.