Kinetics and mechanisms in flow systems: reduction of SO₂ on carbons

Abstract

Surface‐science studies of some reactions have allowed postulating the mechanisms using a variety of techniques. The surface chemistry of Group IV elements has been particularly studied recently because Si, Ge, and C are semiconductors, and the surface organic chemistry to functionalize these elements has seen immense progress in recent years. In this review article we describe the methodology used to study the mechanism of a solid–gas reaction, the reduction of SO2 on carbons, and the necessary conditions that allowed the measurement of the solid conversion and product distribution when the kinetics was chemically controlled and the reaction had reached the steady state. The reaction was first‐order with respect to SO2 and with respect to carbon and the stoichiometry was determined from the product distribution. The reaction proceeds through two thermally stable reaction intermediates bound to the surface, a six‐membered ring 1,3,2‐dioxathiolane and a five‐membered ring 1,2‐oxathietene 2‐oxide or γ‐sultine, both species being in equilibrium. The reaction was shown to be reversible. The primary product is an episulfide that, after a series of consecutive reactions of atomic sulfur, is able to free sulfur. The reactivity of the intermediates and the episulfide was studied for several reactions and consistent mechanisms were postulated from the X‐ray photoelectron spectroscopy and solid state nuclear magnetic resonance spectra. Aminolysis and the reaction with alkyl halides resulted on the insertion of the alkyl moiety in the episulfide primary product, while the thiolysis and photolytic alcoholysis resulted in the insertion of the alkyl moiety in the oxidized intermediates. Copyright © 2012 John Wiley & Sons, Ltd.

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

“…Reduction of SO 2 on carbons to elemental sulfur is an environmentally important reaction to avoid atmospheric pollution. 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 ), while the reactivity increases with decreasing crystallinity and increasing oxygen content …”

Experimental Study on the Mercury Removal of a H2S-Modified Fe2O3 Adsorbent

“…Figure c shows the peak fitting results of S 2p spectra. It can be divided into four characteristic peaks, including S 2– corresponding to 161.9 eV, S 2 2– corresponding to 162.9 eV, S 0 corresponding to 163.9 eV, and S 6+ corresponding to 168.3 eV. , Among them, S 2– and S 2 2– have at least one lone pair of electrons to interact with Hg 0 , which make them have a high affinity for mercury . Among all sulfur atoms, the atomic ratio of S 2– /S is 0.14 and S 2 2– /S is 0.34, which indicates that the content of FeS 2 in the product is higher than that of FeS and FeS 2 is the main product in the modification process.…”

Impact of Nonoxidized Sulfur Species on Elemental Mercury Removal by SO2 Activated Petroleum Cokes

“…Apart from developing porous structures, SO 2 also can be used for further sulfur functionalization. Humeres et al ,− have systematically investigated the reaction mechanism of SO 2 reduction on carbons as well as the sulfur transport route. It was revealed that SO 2 molecules were first incorporated into the carbon matrix in the form of oxidized sulfur-containing intermediates by interactions with the active sites, and then the oxidized sulfur-containing intermediates decomposed to nonoxidized episulfide intermediates and CO 2 .…”