Reduction of Sulfur Dioxide on Carbons Catalyzed by Salts

Abstract

Abstract. The reduction of SO2 on different carbons in the presence of the nitrates and sulfides of sodium, potassium and calcium and potassium polysulfides was studied. The presence of salts increased the initial rate 2-5 fold for all of them and did not change the product distribution. The catalysis was not determined by the cation and there was no difference in the catalytic reactivity between nitrates and sulfides. The sulfur content of the activated carbon increased during the reaction on account of the stable reactive intermediates in the reduction of SO2. In the presence of NaNO3 or Na2S, the amount of sulfur incorporated was in the molar ratio Na:S = 3 ± 0.3, and the XPS spectra of the residual carbon showed an increase of ca. 9% of the non-oxidized form of sulfur in the intermediates. In the absence of salt, it is proposed that after the adsorption of SO2 on the carbon, a 1,3,2-dioxathiolane or 1,2-oxathietene 2-oxide are formed and that decompose to produce CO2 and atomic sulfur. The non-oxidized sulfur intermediate would be an episulfide 3, formed from the reaction of the atomic sulfur with the nearest double bond and followed by consecutive reactions of insertion of atomic sulfur to form a trisulfide. Extrusion of S2 from the trisulfide would regenerate the episulfide, establishing a sulfidedisulfide-trisulfide equilibrium that worked as a capture-release cycle of sulfur. In the presence of salt, the results are consistent with the assumption that the episulfide 3 reacts with the corresponding sulfide anion to form a disulfide anion, which upon reaction with atomic sulfur forms a trisulfide anion that decomposes releasing diatomic sulfur S2, transporting the sulfur and generating a thiolate that is part of the catalytic cycle

Porous carbon with high capacitance and graphitization through controlled addition and removal of sulfur-containing compounds

“…This suggests that the sulfur promotes the graphitization of the carbon matrix despite the fact that air activation usually induces defects. The mechanism for this phenomenon may be explained by sulfur atoms in gaseous SO/SO 2 preferably adsorbing on the defective sites of carbon and reacting with nearby imperfectly located carbon atoms [47][48][49]. In other words, the greater the amount of sulfur oxides gaseous released (sulfur oxides are derived from sulfur on the surface), the higher the degree of graphitization of the carbon.…”

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

“…[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. [4] The calculated X-ray photoelectron spectrum (XPS) composition, using the atom inventory technique, [7] suggested that the insertion occurred along with partial reduction of MPGO and CO 2 generation.…”

Reactive Site Model of the Reduction of SO2 on Graphite

“…We proposed the mechanism of sulfur transport shown in Figure (adapted to the TBA model) where, after the extrusion of atomic sulfur from the benzothiirene site 3 , the sulfur reacts with another benzothiirene site through a thiosulfoxide intermediate to generate a disulfane which eliminates diatomic sulfur and the original unsaturated bond, or consecutively, accepts a third atom and form a trisulfane able to extrude S 2 regenerating the benzothiirene site. Formation of a trisulfane from the disulfane or from the benzothiirene site allows the extrusion of a more stable form of sulfur, a singlet diatomic sulfur 1 S 2 , that would regenerate the benzothiirene site, establishing an equilibrium sulfane-disulfane-trisulfane that would function as a cycle of capture–release of sulfur.…”

“…Episulfide 3 initiates the transport of sulfur out the carbon matrix. 52 The mechanism of CO 2 formation has not been studied yet and will be discussed in this work. For this reason, the fragment of the residual carbon matrix in Figure 1 is not described.…”

“…Sulfur transfer from the oxidized intermediate 1 produces the reduced sulfur intermediate episulfide 3 , observed at 164 eV, by insertion on an unsaturated center along with a corresponding oxidized moiety defined as C­(CO 2 ), that will produce CO 2 in a later step. Episulfide 3 initiates the transport of sulfur out the carbon matrix . The mechanism of CO 2 formation has not been studied yet and will be discussed in this work.…”