Chemistry Of SO2 Research Articles

Identification of Intermediates in the Reaction Pathway of SO2 on the CaO Surface: From Physisorption to Sulfite to Sulfate.

The interaction of CaO and Ca(OH)2 with solvated or gaseous SO2 plays a crucial role in the corrosion of urban infrastructure by acid rain or in the removal of SO2 from flue gas. We carried out a combined spectroscopic and theoretical investigation on the interaction of SO2 with a CaO(001) single crystal. First, the surface chemistry of SO2 was investigated at different temperatures using polarization-resolved IR reflection absorption spectroscopy. Three species were identified, and an in-depth density functional theory study was carried out, which allowed deriving a consistent picture. Unexpectedly, low temperature exposure to SO2 solely yields a physisorbed species. Only above 100 K, the transformation of this weakly bound adsorbate first to a chemisorbed sulfite and then to a sulfate occurs, effectively passivatating the surface. Our results provide the basis for more efficient strategies in corrosion protection of urban infrastructure and in lime-based desulfurization of flue gas.

Probing the Electronic Structure and Bond Dissociation of SO3 and SO3- Using High-Resolution Cryogenic Photoelectron Imaging.

The SO3 molecule and its radical anion SO3- are important chemical species atmospherically. However, their thermodynamic properties and electronic structures are not well known experimentally. Using cryogenically cooled anions, we have obtained high-resolution photoelectron images of SO3- and determined accurately the electron affinity (EA) of SO3 and the bond dissociation energy of SO3- → SO2 + O- for the first time. Because of the large geometry changes from the C3v SO3- to the D3h SO3, there is a negligible Franck-Condon factor (FCF) for the 0-0 detachment transition, that defines the EA of SO3. By fitting the high-resolution photoelectron spectra with computed FCFs using structures from high-level ab initio calculations, we have determined the EA of SO3 to be 2.126(6) eV. By monitoring the appearance of the O- signal in the photoelectron images at different photon energies, we are able to measure directly the bond dissociation energy of SO3-(X2A1) → SO2(X1A1) + O-(2P) to be 4.259 ± 0.006 eV, which also allow us to derive the dissociation energy for the spin-forbidden SO3(X1A1') → SO2(X1A1) + O(3P) to be 3.594(6) eV. The excited states of SO3- are calculated using high-level ab initio calculations, which are valuable in aiding the interpretation of autodetachment processes observed at various photon energies. The current study provides valuable information about the fundamental molecular properties of SO3, as well as the radical anion SO3-, which is known in redox reactions involving SO32- and may also play a role in the chemistry of SO2 in the atmosphere.

Spectroscopic Characterization of HSO2• and HOSO• Intermediates Involved in SO2 Geoengineering.

Sulfur-containing radicals HSO2• and HOSO• are key intermediates involved in stratospheric sulfur geoengineering by SO2 injection. The spectroscopic characterization and photochemistry of both radicals are crucial to understanding the chemical impact of SO2 chemistry in the stratosphere. On the basis of the efficient generation of HOSO• by flash pyrolysis of gaseous sulfinic acid, CHF2S(O)OH, a strong absorption is observed at 270 nm along with a shoulder up to 350 nm for HOSO• isolated in low-temperature noble gas matrixes (Ar and Ne). These mainly arise from the excitations from the ground state (X2A) to the C2A/D2A and A2A/B2A states, respectively. Upon a 266 nm laser irradiation, the broad absorption band in the range 320-500 nm for HSO2• appears, and it corresponds to the combination of three excitations from the X2A state to the first (A2A), second (B2A), and third (C2A) excited states. Assignment of the UV-vis spectra is consistent with the photochemistry of HOSO• and HSO2• as observed by matrix-isolation IR spectroscopy and also by the agreement with high-level ab initio calculations.

Oxidation of sulfur dioxide by nitrogen dioxide accelerated at the interface of deliquesced aerosol particles.

Although the multiphase chemistry of SO2 in aerosol particles is of great importance to air quality under polluted haze conditions, a fundamental understanding of the pertinent mechanisms and kinetics is lacking. In particular, there is considerable debate on the importance of NO2 in the oxidation of SO2 in aerosol particles. Here experiments with atmospherically relevant deliquesced particles at buffered pH values of 4-5 show that the effective rate constant for the reaction of NO2 with SO32- ((1.4 ± 0.5) × 1010 M-1 s-1) is more than three orders of magnitude larger than the value in dilute solutions. An interfacial reaction at the surface of aerosol particles probably drives the very fast kinetics. Our results indicate that oxidation of SO2 by NO2 at aerosol surfaces may be an important source of sulfate aerosols under polluted haze conditions.

Simulating the Impact of Long-Range-Transported Asian Mineral Dust on the Formation of Sulfate and Nitrate during the KORUS-AQ Campaign

The atmospheric mineral aerosol reaction (AMAR) model, which was developed to simulate dust-driven heterogeneous chemistry of SO2 and NOx, was combined with the comprehensive air quality model with...

Capture of the Sulfur Monoxide-Hydroxyl Radical Complex.

The elusive hydrogen-bonded sulfur monoxide-hydroxyl radical complex (•OH···OS), a missing intermediate in the atmospheric chemistry of SO2, was generated in the 266 nm laser photolysis of the sulfinyl radical HOSO• in cryogenic Ar-matrixes. In addition to the IR spectroscopic characterization with deuteration, its thermal conversion to HOSO• with an activation barrier of 0.33 ± 0.11 kcal mol-1 (calcd 0.32 kcal mol-1, CCSD(T)-F12a/AVTZ) in the temperature range of 15.0-21.0 K and a H/D kinetic isotope effect of 2.4 at 16.0 K have been observed.

Uptake and surface chemistry of SO2 on natural volcanic dusts

V-dust (v-dust) is a highly variable source of natural particles in the atmosphere, and during the period of high volcanic activity it can provide a large surface for heterogeneous interactions with other atmospheric compounds. Icelandic v-dust was chosen as a case study due to frequency of volcanic eruptions and high aeolian activity in the area. In this study, we focus on the kinetics and mechanism of the reaction of sulfur dioxide (SO2) with natural v-dust samples under atmospheric conditions using coated wall flow tube reactor and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Steady state uptake coefficients determined are in the range of 10−9 to 10−8 depending on the considered v-dust. Concomitantly with SO2 uptake, both sulfites and sulfates are monitored on the surface of v-dust, with sulfates being the final oxidation product, attesting of SO2 surface reaction. Surface hydroxyl groups play a crucial role in the conversion of SO2 to sulfites as evidenced from both flow tube and DRIFTS experiments. Based on these experimental results, a mechanism for SO2 interaction with different surface sites of v-dust is proposed and discussed. This study provides original insights in the kinetics of SO2 uptake under simulated atmospheric conditions and its mechanism and transformation on volcanic material. To that regards, it brings an accurate perspective on SO2 heterogeneous sinks in the atmosphere.

Surface Chemistry of Sulfur Dioxide on Zr(OH)4 Powder: The Role of Water

Operando conditions, such as the presence of H2O, can dramatically alter the reaction pathways of molecular interactions on a surface. Here, we determine how water affects the decomposition chemistry of SO2(g) on dry and wet Zr(OH)4 powder, a material being transitioned for battlefield chemical sequestration and decomposition. Diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy reveal that SO2 decomposition products on dry and wet Zr(OH)4 differ significantly. Sulfites (sulfates) dominate on dry (wet) Zr(OH)4 surfaces. Kinetic analysis of the wet surface shows that H2O interacts with SO2 initially and then with surface OH sites, indicating that the mechanism to form sulfates requires water molecules. The combined IR spectra and density functional theory calculations confirm that sulfites and sulfates bind to both surface terminal and bridging OH sites.

Toward Phase and Catalysis Control: Tracking the Formation of Intermetallic Nanoparticles at Atomic Scale

Summary Intermetallic nanoparticles (iNPs) have yielded enormous successes in catalytic applications by the formation of ordered phases. However, atomic-level understanding of the alloying mechanism, which plays a pivotal role in controlling intermetallic phases and tailoring their catalytic properties, is still elusive. In this study, we discovered a consecutive formation of ordered Pt3Sn and PtSn phases during the growth of Pt-Sn iNP inside a well-defined nano-reactor at elevated temperature by using in situ scanning transmission electron microscopy. We found that the surface-mediated diffusion of Sn controls overall dynamics of the reaction, while the unique coherent interfacial structure is determinative for the PtSn transformation. We then further controlled the phase selection of Pt-Sn iNPs and demonstrated their distinguishable catalytic behaviors. Our findings not only provide detailed experimental evidence on the alloying mechanism in intermetallic nanoscale systems but also pave the way for mechanistic control of synthesis and catalytic properties of iNPs.

Interaction of SO2 with the Surface of a Water Nanodroplet

We present a comprehensive computational study of interaction of a SO2 with water molecules in the gas phase and with the surface of various sized water nanodroplets to investigate the solvation behavior of SO2 in different atmospheric environments. Born-Oppenheimer molecular dynamics (BOMD) simulation shows that, in the gas phase and at a temperature of 300 K, the dominant interaction between SO2 and H2O is (SO2)S···O(H2O), consistent with previous density-functional theory (DFT) computation at 0 K. However, at the surface of a water nanodroplet, BOMD simulation shows that the hydrogen-bonding interaction of (SO2)O···H(H2O) becomes increasingly important with the increase of droplet size, reflecting a marked effect of the water surface on the SO2 solvation. This conclusion is in good accordance with spectroscopy evidence obtained previously (J. Am. Chem. Soc. 2005, 127, 16806; J. Am. Chem. Soc. 2006, 128, 3256). The prevailing interaction (SO2)O···H(H2O) on a large droplet is mainly due to favorable exposure of H atoms of H2O at the air-water interface. Indeed, the conversion of the dominant interaction in the gas phase (SO2)S···O(H2O) to the dominant interaction on the water nanodroplet (SO2)O···H(H2O) may incur effects on the SO2 chemistry in atmospheric aerosols because the solvation of SO2 at the water surface can affect the reactive sites and electrophilicity of SO2. Hence, the solvation of SO2 on the aerosol surface may have new implications when studying SO2 chemistry in the aerosol-containing troposphere.

Surviving in the presence of sulphur dioxide: strategies developed by wine yeasts

Sulphur dioxide has been used as a common preservative in wine since at least the nineteenth century. Its use has even become essential to the making of quality wines because of its antioxidant, antioxidasic and antiseptic properties. The chemistry of SO₂ in wine is fairly complex due to its dissociation into different species and its binding to other compounds produced by yeasts and bacteria during fermentation. The only antiseptic species is the minute part remaining as molecular SO₂. The latter concentration is both dependent on pH and concentration of free bisulphite. However, certain yeast species have developed cellular and molecular mechanisms as a response to SO₂ exposure. Some of these mechanisms are fairly complex and have only been investigated recently, at least for the molecular mechanisms. They include sulphite reduction, sulphite oxidation, acetaldehyde production, sulphite efflux and the entry into viable but not culturable state, as the ultimate response. In this review, the chemistry of SO₂ in wine is explained together with the impact of SO₂ on yeast cells. The different defence mechanisms are described and discussed, mostly based on current knowledge available for Saccharomyces cerevisiae.

A multispecies chemistry model of Io's local interaction with the Plasma Torus

We model the local interaction between the plasma in the torus and Io's neutral corona (inside ∼6 RIo), focusing on the multispecies chemistry outside the collision‐dominated ionosphere. We include a detailed chemistry of S, O, SO2, SO under ionization, charge exchange, and recombination processes in a parcel of plasma that follows a prescribed flow field around Io's ionosphere and interacts with the neutral density profiles in the corona, as constrained by available observations. We compare the model results to the Galileo plasma observations in Io's wake (GLL/J0). We conclude the following: (1) The plasma characteristics along GLL/J0 require a dense SO2 corona confined close to Io (<2 RIo). (2) Molecular SO2 chemistry dominates the interaction, with atomic chemistry playing a negligible role. (3) SO2+ is the main output ion of the local interaction, but it recombines and dissociates rapidly so that the contribution of the local interaction to the global mass and energy supply of the torus is very small. (4) The high density of plasma observed in the wake requires a supplemental ionization source beyond the thermal electrons of the torus, and we estimate the ionization due to the (∼350 eV) field‐aligned electron beams observed around Io. (5) Assuming a SO2 atmosphere/corona with a vertical column of 6 × 1016 cm−2 and a prescribed deceleration of the flow around Io, we estimate a local ion mass production rate of ∼200 kg/s. We also compute a neutral loss rate of ∼2400 kg/s and a pick‐up current of ∼5.2 MAmp, both dominated by the SO2 resonant charge exchange reaction.

Gold nanoparticles on ceria: importance of O vacancies in the activation of gold

Synchrotron-based techniques (high-resolution photoemission, in-situ X-ray absorption spectroscopy, and time-resolved X-ray diffraction) have been used to study the destruction of SO2 and the water-gas shift (WGS, CO + H2O → H2 + CO2) reaction on a series of gold/ceria systems. The adsorption and chemistry of SO2 was investigated on Au/CeO2(111) and AuO x /CeO2 surfaces. The heat of adsorption of the molecule on Au nanoparticles supported on stoichiometric CeO2(111) was 4–7 kcal/mol larger than on Au(111). However, there was negligible dissociation of SO2 on the Au/CeO2(111) surfaces. The full decomposition of SO2 was observed only after introducing O vacancies in the ceria support. AuO x /CeO2 surfaces were found to be much less chemically active than Au/CeO2(111) or Au/CeO2−x (111) surfaces. In a separate set of experiments, in-situ time-resolved X-ray diffraction and X-ray absorption spectroscopy were used to monitor the behavior of nanostructured {Au + AuO x }–CeO2 catalysts under the WGS reaction. At temperatures above 250 °C, a complete AuO x → Au transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au nanoparticles supported on rough ceria films or a CeO2(111) single crystal corroborate that cationic Auδ+ species cannot be the key sites responsible for the WGS activity at high temperatures. The active sites in {Au + AuO x }/ceria catalysts should involve pure gold nanoparticles in contact with O vacancies of the oxide.

Reaction of SO2 with Au∕CeO2(111): Importance of O vacancies in the activation of gold

Synchrotron-based high-resolution photoemission was used to study the adsorption and chemistry of SO(2) on AuCeO(2)(111) and AuO(x)CeO(2) surfaces. The heat of adsorption of the molecule on Au nanoparticles supported on stoichiometric CeO(2)(111) was 4-7 kcalmol larger than on Au(111). However, there was negligible dissociation of SO(2) on the AuCeO(2)(111) surfaces. The full decomposition of SO(2) was observed only after introducing O vacancies in the ceria support. AuO(x)CeO(2) surfaces were found to be much less chemically active than AuCeO(2)(111) or AuCeO(2-x)(111) surfaces. The active sites in {Au + AuO(x)}ceria catalysts should involve pure gold nanoparticles in contact with O vacancies.

Chemistry of SO2, H2S, and CH3SH on Carbide-Modified Mo(110) and Mo2C Powders: Photoemission and XANES Studies

The chemistry of SO2, H2S, and CH3SH on carbide-modified Mo(110) and powders of bulk Mo2C was studied using synchrotron-based high-resolution photoemission and X-ray absorption near-edge spectroscopy (XANES). These studies reveal that molybdenum carbide is very reactive toward sulfur-containing molecules, being able to break S−O, S−H, and S−C bonds at temperatures below 300 K. Upon adsorption of sulfur dioxide on molybdenum carbide at 150 or 300 K, there is dissociation of the adsorbate into S and O, and also formation of SO3 or SO4 by reaction with O adatoms or disproportionation of SO2. The adsorbed SO3 and SO4 species decompose upon heating to 500 K leaving a heavily sulfided and oxidized carbide. In the case of H2S adsorption, the cleavage of the first H−S bond occurs at 80−100 K and the resulting HS intermediate transforms into S at temperatures below 250 K. Finally, for CH3SH on MoCx, the breaking of the C−S bond takes place at temperatures between 250 and 400 K. From 100 to 350 K, CH3S and a second S-containing species (CHyS) coexist on the surface of the carbide. A comparison to results reported in the literature indicates that the chemical reactivity of molybdenum carbide is similar to that of metallic Mo and much larger than that of molybdenum sulfide. The differences in the chemical reactivities of molybdenum carbide and molybdenum sulfide correlate well with changes in the electronic properties of Mo in these systems.

Reaction of SO2 with Cesium and Cesium-Promoted ZnO and MoO2

The chemistry of SO2 on pure metallic Cs and Cs-promoted polycrystalline surfaces of ZnO and MoO2 has been studied using high-resolution synchrotron-based photoemission. Metallic cesium reacts vigorously with SO2 at temperatures between 100 and 300 K. At 100 K, the amount of SO2 that fully dissociates (SO2,gas → Sa + 2Oa) on the alkali metal is relatively small, and SOx (x = 2−4) species predominate on the surface. SO3 and SO4 may be formed as a result of the reaction of SO2 with atomic oxygen (SO2 + nOa → SO2+n,a where n = 1−2), or by disproportionation of chemisorbed SO2. At 300 K the stability of the CsSOx species is lower than at 100 K, and the formation of CsOy and CsSy becomes important. In the Cs/ZnO and Cs/MoO2 systems, the alkali ↔ oxide interactions are very strong. Despite this, the supported Cs atoms retain a large chemical affinity for SO2 and are able to enhance the rate of adsorption of the molecule on the oxide surfaces, even at low coverages (0.1−0.2 ML) of cesium when the alkali atoms are in a highly ionic state (Csδ+). The larger the coverage of Cs on ZnO and MoO2, the faster the rate of adsorption of SO2, and the larger the amount of S and SOx (x = 2−4) species present on the surface. The adsorption of SO2 on ZnO and Cs/ZnO surfaces was examined using ab initio self-consistent-field (SCF) calculations and cluster models. The Cs adatoms provide occupied states that are very efficient for bonding interactions with the LUMO of SO2. Cs atoms supported on Zn-terminated terraces of ZnO respond much more strongly to the presence of SO2 than Cs atoms supported on O-terminated terraces. The bonding interactions between the ZnO(0001)−Zn face and SO2 are weak, and promotion with Cs adatoms considerably improves the energetics for SO2 adsorption.

Reaction of S2 and SO2 with Pd/Rh(111) surfaces: Effects of metal–metal bonding on sulfur poisoning

The surface chemistry of S2 and SO2 on Rh(111), Pd/Rh(111) and polycrystalline Pd has been investigated using synchrotron-based high-resolution photoemission and ab initio self-consistent-field calculations. Pd adatoms lead to an increase in the rate of adsorption of S2 on Rh(111), but they are less reactive than atoms of pure metallic palladium: Rh(111)<Pd/Rh(111)<Pd. The adsorption of sulfur induces a large reduction in the density of states (DOS) near the Fermi level of Pd/Rh(111) surfaces. The decrease in the DOS is smaller than in S/Pd(111) but bigger than in S/Rh(111). The chemistry of SO2 on Rh(111), Pd/Rh(111), and Pd is rich. At 100 K, SO2 adsorbs molecularly on these systems. Above 200 K, the adsorbed SO2 decomposes (SO2,a→Sa+2Oa) or transforms into SO3/SO4 species. The molecular SOx species disappear upon annealing to 450 K and only atomic S and O remain on the surfaces. A Pd monolayer supported on Rh(111) is not very active for the dissociation of SO2. In this respect, the Pd1.0/Rh(111) system is less chemically active than pure Pd or Rh(111). The electronic perturbations associated with the Pd–Rh bonds reduce the electron donor ability of Pd, weakening the interactions between the Pd 4d orbitals and the lowest unoccupied molecular orbitals of S2 and SO2. The behavior of the S2/Pd/Rh(111) and SO2/Pd/Rh(111) systems shows that bimetallic bonding can reduce the reactivity of Pd towards sulfur-containing molecules. A very large drop in reactivity can be expected when Pd is bonded to s,p or early transition metals.

Interaction of SO 2 with CeO 2 and Cu/CeO 2 catalysts: photoemission, XANES and TPD studies

CeO2 and Cu/CeO2 are effective catalysts/sorbents for the removal or destruction of SO2. Synchrotron‐based high‐resolution photoemission, X‐ray absorption near‐edge spectroscopy (XANES), and temperature‐programmed desorption (TPD) have been employed to study the reaction of SO2 with pure and reduced CeO2 powders, ceria films (CeO2, CeO2−x, Ce2O3+x) and model Cu/CeO2 catalysts. The results of XANES and photoemission provide evidence that SO4 was formed upon the adsorption of SO2 on pure powders or films of CeO2 at 300 K. The sulfate decomposed in the 390–670 K temperature range with mainly SO2 and some SO3 evolving into gas phase. At 670 K, there was still a significant amount of SO4 present on the CeO2 substrates. The introduction of O vacancies in the CeO2 powders or films favored the formation of SO3 instead of SO4. Ceria was able to fully dissociate SO2 to atomic S only if Ce atoms with a low oxidation state were available in the system. When Cu atoms were added to CeO2 new active sites for the destruction of SO2 were created improving the catalytic activity of the system. The surface chemistry of SO2 on the Cu‐promoted CeO2 was much richer than on pure CeO2. The behavior of ceria in several catalytic processes (oxidation of SO2 by O2, reduction of SO2 by CO, automobile exhaust converters) is discussed in light of these results.

Surface Chemistry of SO2 on Sn and Sn/Pt(111) Alloys: Effects of Metal−Metal Bonding on Reactivity toward Sulfur

The surface chemistry of SO2 on polycrystalline Sn, Pt(111), and a ( x )R30°-Sn/Pt(111) surface alloy has been investigated using synchrotron-based high-resolution photoemission and ab initio self-...

Surface Chemistry of SO2 on Zn and ZnO: Photoemission and Molecular Orbital Studies

The reaction of SO2 with polycrystalline Zn and ZnO surfaces has been investigated using synchrotron-based high-resolution photoemission spectroscopy and ab initio self-consistent-field calculations. The chemistry of SO2 on Zn surfaces is quite complex and depends on both the temperature of adsorption and the SO2 exposure. At 300 K, SO2 dissociates on a clean Zn surface to form atomic sulfur and atomic oxygen (SO2,gas → Sa + 2Oa; SO2,gas → SOgas + Oa). The Zn ↔ SO2 bonding interactions induce a significant weakening of the S−O bonds. The theoretical calculations suggest the η2-O,O and η2-S,O bonding conformations of SO2 as the two possible precursors for the dissociation of the molecule. The dissociation reactions are much more exothermic than the formation of SO3 or SO4: SO2,gas + nOa → SOx, where x = 3 or 4. At high SO2 exposures (300 K), when most surface sites are blocked and dissociation of SO2 cannot occur, SO3 and SO4 are formed on the Zn surface. Adsorption at 100 K suppresses the SO2 dissociatio...