Mechanism of the desulfurization route of the reduction of SO₂ on carbons. Dimerization of Disulfur and Tetrasulfur

The desulfurization of carbons modified with SO 2 was studied as a dispersion in boiling cyclohexane (81°C) using activated carbon (mAC) and graphene oxide (mGO), modified by SO 2 . The steady‐state species in the carbon matrix after the catalytic reduction of SO 2 was considered a trisulfane. For mAC, there was a burst of a sulfur species identified as S 2 by UV spectrum with a maximum at 217 nm (ε M at 217 nm = 2.56 × 10 3 ) that showed a second‐order decay of absorbance with = 47.29 M ‐1 ·sec ‐1 ( = 18.1 kcal·mol ‐1 ). The product was postulated to be S 4 . No other consecutive reaction was observed because of the possible adsorption of S 4 in the carbon matrix. The desulfurization of mGO was shown by XPS and the kinetics were a second‐order decay up to 16 min ( 18.41 M ‐1 ·sec ‐1 ; = 18.8 kcal·mol ‐1 ) followed by a second‐order increase of absorbance with = 3.84 M ‐1 ·sec ‐1 ( = 19.9), where the product showed a double maximum at 260‐285 nm typical of S 8 . These results are consistent with a mechanism of consecutive thermodynamically favorable dimerizations of S 2 and S 4 and with the desulfurization mechanism that has been previously postulated.