Reactive intermediates of the reduction of SO₂ on activated carbon

Abstract

The reduction of SO 2 on activated carbon was studied in the range of 600-700 C in a differential reactor under steady-state conditions and under chemically controlled kinetics. Initial rates of carbon conversion and gas reagent were calculated from the mass balance of the gaseous products. The kinetics was first-order with respect to carbon and first-order with respect to the partial pressure of SO 2 . The activation parameters were ÁH 6 ¼ ¼ 21.5 kcal mol À1 and ÁS 6 ¼ ¼ À211 cal mol À1 K À1 . The activated carbon was ca. 10 5 times more reactive than graphite, and determined by the enthalpy of activation. The main reaction products were CO 2 and sulfur. CO and COS were produced from consecutive reactions of the primary products. During the pre-steady state, the sulfur content of the carbon increased to a plateau where the reaction reached the steady state condition. This sulfur was shown to be chemically bound to the carbon matrix and represents the stable reactive intermediates of the reduction of SO 2 . The XPS spectrum of the residual carbon C(S) showed two forms of sulfur bound to carbon: non-oxidized sulfur (sulfide and/or disulfide) and oxidized sulfur (sulfone, sulfoxide, sulfenate, sulfinate). The sulfur intermediates C(S) reacted with SO 2 at the same rate as pure activated carbon and with CO 2 to produce SO 2 by the reverse reaction. The reaction of C(S) with CO produced COS.

Interconversion and selective reactivity of sulfur dioxide reduction intermediates inserted on graphene oxide

“…[2] Considering the amount of non-oxidized intermediate formed and the sulfur released after 12 h of reflux at 46°C (54.2%), the rate constant of reduction of the dioxathiolane to episulfide is k red = 1.42 × 10 À5 s À1 with an energetic barrier of ΔG ‡ = 25.81 kcal mol…”

“…[2] In order to increase the amount of material treated at each batch, it was built a proportional larger non-thermal wileyonlinelibrary.com/journal/poc (…”

“…The study of (C + SO 2 ) reaction on different carbons (graphite, charcoal, activated carbon, cokes, and graphene oxide (MPGO)) showed that the reaction proceeds through the same stoichiometry for all carbons (Eqn 1), while the reactivity increases with decreasing crystallinity and increasing oxygen content. [1][2][3][4] SO 2 þ C→ CO 2 þ 1 = 2 S 2 (1) Experimental data obtained from SO 2 reduction on carbons along with theoretical calculations [5] allowed a detailed description of the primary reaction ( Fig. 1), where the diradical zigzag fragment represents the site of insertion of SO 2 in the carbon matrix.…”

“…[2] Sulfur transport out of the matrix proceeds through consecutive reactions of sulfur insertion generating intermediates that release sulfur as S 2 . [6] Sulfur dioxide can also be selectively incorporated in the matrix of MPGO as oxidized intermediates, at ambient temperature, via excitation by non-thermal plasma.…”

Sulfurized activated carbons and their mercury adsorption/desorption behavior in aqueous phase

“…3c, d, the XPS spectra (S 2p region) of AC-DMDS before and after adsorption of mercury are shown. Considering the binding energies of elemental sulfur (164.05 eV) and organic sulfur (163-164.1 eV) (Humeres et al 2003;Feng et al 2006b), the existence of both forms on the surface of AC-DMDS is possible (Fig. 3c).…”