Conversion Of SO2 Research Articles

Enhanced Sulfate Formation from Gas-Phase SO2 Oxidation in Non–•OH–Radical Environments

Recent research on atmospheric particle formation has shown substantial discrepancies between observed and modeled atmospheric sulfate levels. This is because models mostly consider sulfate originating from SO2 oxidation by •OH radicals in mechanisms catalyzed by solar radiation while ignoring other pathways of non-radical SO2 oxidation that would substantially alter atmospheric sulfate levels. Herein, we use high-level quantum chemical calculations based on density functional theory and coupled cluster theory to show that monoethanolamine (MEA), a typical alkanolamine pollutant released from CO2 capture technology, can facilitate the conversion of atmospheric SO2 to sulfate in a non–•OH–radical oxidation mechanism. The initial process is the MEA-induced SO2 hydrolysis leading to the formation of HOSO2−•MEAH+. The latter entity is thereafter oxidized by ozone (O3) and nitrogen dioxide (NO2) to form HSO4−•MEAH+, which is an identified stabilizing entity in sulfate-based aerosol formation. Results show that the HOSO2−•MEAH+ reaction with O3 is kinetically and thermodynamically more feasible than the reaction with NO2. The presence of an additional water molecule further promotes the HOSO2−•MEAH+ reaction with O3, which occurs in a barrierless process, while it instead favors HONO formation in the reaction with NO2. The investigated pathway highlights the potential role alkanolamines may play in SO2 oxidation to sulfate, especially under conditions that are not favorable for •OH production, thereby providing an alternative sulfate source for aerosol modeling. The studied mechanism is not only relevant to sulfate formation and may effectively compete with reactions with sulfur dioxide and hydroxyl radicals under heavily polluted and highly humid conditions such as haze events, but also an important pathway in MEA removal processes.

Experimental study and modelling of continuous SO2-depolarized electrolysis in hybrid sulfur cycle for hydrogen production

SO2-depolarized electrolysis (SDE) is the key process in the hybrid sulfur cycle for green hydrogen production, but the detailed SDE characteristics including products generation, current efficiency variation, and side reactions are unclear. Herein, a continuous SDE process was experimentally conducted and theoretically modelled. The H2 and H2SO4 production was accelerated and the current efficiency for both electrodes was improved with a proper increase in current density (50−100 mA/cm2) or temperature (293−318 K), but further increasing current density to 150 mA/cm2 or temperature to 333 K led to a negative trend because of the anode corrosion or declined SO2 solubility. The increasing initial H2SO4 concentration (10−40 wt%) facilitated the cathodic H2 production and current efficiency, while negatively influenced the anodic SO2 conversion. The parasitic reactions occurred at cathode consumed H2 and resulted to the cathodic current efficiency well below 100%. A rigorous mathematical regression model correlating the production rates of H2 and H2SO4 with current density, temperature, and initial H2SO4 concentration was developed, and combined with the analysis of variance, current density was suggested the biggest factor affecting products generation in SDE process. These findings demonstrate a practical avenue for efficient SO2 conversion and H2 production in SDE process of hybrid sulfur cycle.

Continuous multiphase Bunsen reactor of iodine-sulfur thermochemical water splitting cycles for hydrogen production: Experimental, Modelling and Design Insights

Thermochemical water splitting cycles (TWSCs) hold promise for sustainable H2 production in future energy systems, with Iodine-Sulfur (IS) and Nickel-Iodine-Sulfur (NIS) processes standing out as efficient options. The core of both these processes lies in the Bunsen reaction, underscoring the need to identify optimal operational conditions and plant solutions for this crucial reaction section. Thus, in this study, a continuous counter-current flow Bunsen reactor fed with 5 NL h−1 of SO2 was constructed and tested. An inventive aspect was the introduction of solid I2 pellets from the top to enhance saturation at the liquid-liquid interface between sulfuric and hydriodic product phases, promoting segregation. This ingenious design achieved nearly complete SO2 conversion and optimal H2SO4 and HI concentrations in the respective product phases, while avoiding undesirable byproduct formation. The study further advanced the modelling of the experimental reactor by employing innovative kinetic and liquid-liquid equilibrium description approaches, and demonstrating exceptional validation accuracy of R2 = 0.9988. Additionally, with the aim of obtaining design charts as a potential tool for Bunsen reactor design, a microscopic model describing the gas phase trend along bubble or packed Bunsen-type reactors was developed. The model’s dimensionless analysis revealed a characteristic times ratio (Bu) comprehensively describing all the phenomena occurring to the gas phase within the Bunsen reaction section, and identified an optimal Bu value of 0.4 for pure SO2 gas inlet. Overall, the study's innovative strategies and models contribute significantly to the advancement of Bunsen reactor engineering.

Reduction of SO2 to Elemental Sulfur in Flue Gas Using Copper-Alumina Catalysts

This study aims to propose an advanced catalyst for the selective catalytic reduction of SO2, as a sustainable process to mitigate the emission of this toxic gas, which is a significant environmental concern. The conversion of SO2 through catalytic reduction with CH4 to elemental sulfur was investigated using Al2O3-Cu catalysts. The reaction was conducted under atmospheric pressure and at a temperature range of 550–800°C. A remarkable 99.9% SO2 conversion rate and 99.5% sulfur selectivity were achieved using the Al2O3-Cu (10%) catalyst at 750°C. The highest conversion rates of SO2 to elemental sulfur, with minimal production of undesirable by-products such as H2S and COS, were obtained when the SO2/CH4 molar feed ratio was set at 2, which is the stoichiometric ratio. Furthermore, the optimal catalyst exhibited excellent long-term stability for SO2 reduction with methane.

Equilibrium and experimental study on carbothermal reduction of sulfur dioxide to elemental sulfur

In order to solve the problem of low utilization value of flue gas desulfurization by-product, reduction of sulfur dioxide to elemental sulfur has emerged as a new process for resource utilization of SO2 with promising application prospects. Herein, the thermodynamic equilibrium calculation was carried out to study the influence of temperatures and C/SO2 molar ratios on the C-SO2 reaction. The effects of reaction temperature, carbon mass, and CO concentration on SO2 reduction by coke and activated carbon were studied on a fixed bed reaction system. The theoretical results demonstrated that the highest equilibrium S yield occurred when the C/SO2 molar ratio is 1, with higher ratios resulting in the formation of COS, CS2, and CO. Experimental data revealed that at temperatures below 700 °C, both SO2 conversion and S yield are notably low. As the temperature increases, both the conversion and yield gradually increase and approach the thermodynamic equilibrium value. The evolution of carbon surface chemical properties under the action of CO was analyzed by FTIR and XPS, which indicated that the presence of CO promotes the decarboxylation reaction, and then increases SO2 conversion and S yield. The conclusion of this study provides guidance for the development of high efficiency SO2 reduction technology.

Integrations of desulfurization, carbon capture, and methanation at an isothermal intermediate temperature

Integrated CO2 capture and conversion (iCCC) technology has been recognized as the most efficient technology for Carbon Capture, Utilization, and Storage (CCUS). However, its industrialization is hindered by some unsolved engineering problems. Typically, sulfur impurities in most industrial flue gas will have significant poisoning effects on the process. Herein, we report integrations of SO2 removal, CO2 capture and conversion (iSCCC) at an isothermal intermediate temperature in a two-fixed-bed column system. By rationally developing the SO2 adsorbent pellets of ZnO-CaO, the CO2 adsorbent pellets of AMS-MgO, and the methanation catalyst pellets of Ni-La/Al2O3, each individual unit is optimized. Specifically, the in-situ dynamic structure evolution observed by the atmospheric aberration-corrected scanning transmission electron microscopy as well as the theoretical dynamics calculation provide an in-depth understanding of the CO2 adsorption and desorption performance changing with the temperature on the AMS-MgO pellets, which builds a bridge for a successful 99.3 % CO2 methanation efficiency. As a result, the matched iSCCC process demonstrates exceptional performance from simulated flue gas containing 1000 ppm SO2 and 20 vol% CO2, with full desulfurization and decarbonation and a CO2 conversion efficiency of 93.6 % after 20 cycles isothermally at 400 °C, superior to all the reported performance so far as we know, providing a promising route to practical large-scale iSCCC towards carbon neutrality.

Cobalt oxide-alumina catalysts for the methane-assisted selective catalytic reduction of SO2 to sulfur

Preventing emission of pollutants in any kind, is a way to protect global environment. The objective of this study is to develop cobalt catalysts supported on alumina for the conversion of the toxic gas SO2 into elemental sulfur using methane. Although several useful catalysts have been proposed, there is still a need to synthesize a catalyst with a high sulfur yield that is also persistent during on-stream stability. To this end, four different catalysts were prepared using the wet impregnation technique, with Co3O4 content ranging from 0 to 15 wt%. Catalytic activity tests were carried out at atmospheric pressure and temperatures ranging from 550 to 800 °C. The Al2O3–Co (15 %) catalyst exhibited superior performance, with a sulfur yield of 98.1 % at 750 °C. The catalytic stability of the best catalyst was examined using a 20 h on-stream stability test under the optimized conditions including an SO2/CH4 molar feed ratio of 2 at 750 °C. The structural changes of the used catalyst after the stability test were investigated using XRD and TPO analyses. It was revealed that sulfidation of Co3O4 after a short while, results in decreasing the sulfur yield from 98.1 % to 89.8 %.

The influence of phenanthrene on the adsorption and conversion of SO2 on the hydroxylated {001} surface of α-quartz: A DFT study

One of the major challenges in environmental and atmospheric science is understanding the effects of mineral dust’s surface physiochemical properties and pre-adsorbed volatile organic compounds on the conversion of atmospheric pollutants. However, the process of adsorption and conversion of polluting gases on typical mineral dust surface is not fully understood. In this study, we systematically investigated the impact of surficial hydroxyl groups on the α-quartz {001} surface, oxidizers, and adsorbed phenanthrene (Phe) on the adsorption and oxidation process of SO2 by using density functional theory. Our findings indicate that the presence of hydroxyl groups on the α-quartz {001} surface increases SO2 adsorption whereas the presence of Phe decreases the SO2 capture capabilities. On pristine α-quartz {001} surfaces, SO2 tends to form dissociative SO42- groups and adsorb SO3. While surficial hydroxylation of α-quartz {001} facilitates the desorption of SO3, resulting in fewer dissociative SO42- groups and HSO3- salt. These results are consistent with our heterogeneous reaction of SO2 and α-quartz. In addition, O3 is more effective than O2 in the oxidation of SO2. Meanwhile, Phe inhibits the adsorption of HSO3- salt on hydroxylated α-quartz {001} surfaces. This study not only highlights the process surficial hydroxyl groups and adsorbed Phe regulate the evolution of adsorbed SO2 on α-quartz {001}, but also revealed the formation mechanism of the sulfur-containing aerosols.

Study on simultaneous removal of SO2 and NOx from sintering flue gas over Fe-Mn/AC catalyst

In this work, activated coke catalysts were modified with Fe or/and Mn oxides using an impregnation method. The catalysts were thoroughly characterized using various techniques, including XRD, SEM, XPS, TG-DSC and H2-TPR. The effects of Fe and Mn oxides modification on the catalytic performance of AC catalysts for simultaneous removal of SO2 and NOx were studied. The results showed that Fe-Mn/AC catalyst presented excellent catalytic activity for both SO2 and NOx. The co-doping of Fe and Mn oxides resulted in the formation of the microporous structures, which served as active reaction sites on the catalyst surface. The carbonyl group (CO) was found to play an active role in the oxidation of SO2 by forming a hydrogen bond, which reduced the energy barrier for the conversion of SO2 to SO3. Moreover, it was observed that the deposition of MnSO4/FeSO4 over Fe-Mn/AC catalyst was lower than that of Fe/AC and Mn/AC catalysts. Finally, a possible mechanism model for the denitrification and desulfurization processes over Fe-Mn/AC catalyst was proposed.

Synergistic Adsorption and In Situ Catalytic Conversion of SO2 by Transformed Bimetal-Phenolic Functionalized Biomass.

SO2 removal is critical to flue gas purification. However, based on performance and cost, materials under development are hardly adequate substitutes for active carbon-based materials. Here, we engineered biomass-derived nanostructured carbon nanofibers integrated with highly dispersed bimetallic Ti/CoOx nanoparticles through the thermal transition of metal-phenolic functionalized industrial leather wastes for synergistic SO2 adsorption and in situ catalytic conversion. The generation of surface-SO32- and peroxide species (O22-) by Ti/CoOx achieved catalytic conversion of adsorbed SO2 into value-added liquid H2SO4, which can be discharged from porous nanofibers. This approach can also avoid the accumulation of the adsorbed SO2, thereby achieving high desulfurization activity and a long operating life over 6000 min, preceding current state-of-the-art active carbon-based desulfurization materials. Combined with the techno-economic and carbon footprint analysis from 36 areas in China, we demonstrated an economically viable and scalable solution for real-world SO2 removal on the industrial scale.

Trends of inorganic sulfur and nitrogen species at an urban site in western Canada (2004–2018)

A 15-year (2004–2018) record of measurement data of gaseous and particulate sulfur and nitrogen pollutants in air collected at an urban site in Burnaby in western Canada was analyzed for generating their decadal trends using three different methods, including linear regression, Mann-Kendall test and Theil-Sen trend estimator (MK-TS), and ensemble empirical mode decomposition (EEMD). Annual mean concentration of SO2 and SO42− decreased by about 59% and 42%, respectively, during the 15-year period. The slower decreases of SO42− than SO2 were mainly caused by the increased O3 concentration and temperature in spring and summer, which promoted conversion of SO2 to SO42− through gas-phase reaction, and by the increased aerosol pH value and availability of H2O2 in winter, which enhanced aqueous-phase SO42− formation. Accordingly, the sulfur oxidation ratio (SOR) increased by 23% or more in spring, summer, and winter during the 15-year period. Annual mean concentrations of NO2 and NO3− declined by 36% and 38%, respectively, during this period. On seasonal basis, NO3− decreased faster than NO2 in autumn and slower in winter. The non-linear responses of NO3− to NO2 concentration decreases were more evident in winter than the other seasons, partly due to the increased particulate NO3− fraction caused by decreased temperature, increased aerosol pH value, and enhanced NO3− formation caused by increased O3 concentrations. Annual mean concentration of NH3 showed small increases due to stable NH3 emission and reduced conversion of NH3 to NH4+. NH4+ concentration decreased by 51% during the 15-year period. These results suggest that reduced oxidants levels are likely responsible for weakened formation of secondary inorganic aerosols, besides emission reductions for SO2 and NO2.

Multi-Satellite Detection of Long-Range Transport and Transformation of Atmospheric Emissions from the Hunga Tonga-Hunga Ha’apai Volcano

Large volumes of atmospheric pollutants injected into the troposphere and stratosphere from volcanic eruptions can exert significant influence on global climate. Through utilizing multi-satellite observations, we present a large-scale insight into the long-range transport and transformation of sulfur dioxide (SO2) emissions from the Hunga Tonga-Hunga Ha’apai eruption on 15 January 2022. We found that the transport of volcanic emissions, along with the transformation from SO2 to sulfate aerosols, lasted for two months after the Tongan eruption. The emitted volume of SO2 from the volcano eruption was approximately 183 kilotons (kt). Both satellite observation and numerical simulation results show that the SO2 and volcanic ash plumes moved westward at a rate of one thousand kilometers per day across the Pacific and Atlantic Ocean regions and that SO2 transformation in the atmosphere lasted for half a month. The transport and enhancement of aerosols is related to the conversion of SO2 to sulfate. CALIPSO lidar observations show that SO2 reached an altitude of 25–30 km and transformed into sulfate in the stratosphere after 29 January. Sulfate aerosols in the stratosphere deceased gradually with transport and fell back to the background level after two months. Our study shows that satellite observations give a good characterization of volcanic emissions, transport, and SO2-sulfate conversion, which can provide an essential constraint for climate modeling.

Efficient SO2 capture and conversion to cyclic sulfites by protic ionic liquid-based deep eutectic solvents under mild conditions

SO2 capture has been a research hotspot targeting mitigation of SO2 emission, and the subsequent conversion of SO2 is an ingenious protocol, which can avoid regeneration of absorbents and realize utilization of SO2 simultaneously. To this end, a series of protic ionic liquids (PILs)-based deep eutectic solvents (DESs) composed of N-alkylimidazole hydrochloride-based PILs and azoles were designed for the capture and conversion of sulfur dioxide. Among them, [MImH]Cl/2-MIm (1:1) exhibited SO2 loading capacity as high as 1.45 g/g at 1.0 bar and 20 °C, and remarkable SO2 solubility up to 0.56 g/g were achieved at low concentrations (0.6 vol%, 20 °C). In particular, the absorbed SO2 can be directly converted to cyclic sulfites through cycloaddition reaction catalyzed by these DESs under very mild condition (30 °C and 1.0 bar of SO2) without any solvent of additive. By using gas chromatograph-mass spectrometer (GC-MS), yields of cyclic sulfites were determined to be excellent for styrene oxide (98 %) and 1,2-epoxybutane (97 %), and moderate for the sterically hindered epoxides (56 %–76 %). Recycling experiments proved that these DESs maintained good absorption and catalytic performance after five cycles. Furthermore, the absorption and catalytic mechanism were studied by Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR) spectroscopies, and theoretical calculations, revealing the multi-site absorption mechanism and synergic catalysis in PIL-based DES.

Effect of the sulfur compounds structure on the SO2 conversion and capture in a bubbling fluidized-bed combustor

SO2 is the main pollutant produced by fluidized bed boiler. Most studies only consider the effect of operating parameters on SO2, while the influence of sulfur structure in coal is ignored. Combustion experiments using pure char loaded with various sulfur structures in a bench-scale bubbling fluidized bed combustor was carried out in this paper to determine the influence of different sulfur structures on SO2 conversion. Effects of excess air, bed temperature and desulfurization efficiency were also investigated. The experimental results show that the order of SO2 conversion is ferrous sulfate > 1-Dodecanethiol > pyrite > diphenyl sulfide > diphenyl sulfoxide > dibenzothiophene. Most sulfur models showed an increase in SO2 conversion with increasing temperature. When the excess air increases, the oxygen content in the furnace is increased, which is beneficial to the conversion of sulfur model to SO2. The desulfurization efficiency of ferrous sulfate and pyrite is higher than that of organic sulfur.

Synergistic effects between acidity and the crystalline phases of thermally activated layered Zn hydroxide nitrate on the methanolysis of acidic soybean oils

Layered hydroxyl salts (LHS) is a promising catalyst in the field of methanolysis (transesterification and esterification reactions) of oil feedstocks. The catalytic activity of the catalyst can be enhanced with heat treatment. The present study investigated the relationship between thermal stability of the layered Zn hydroxide nitrate (ZHN), their acid-base properties, and the catalytic conversion of oil feedstocks to methyl ester. The solid, predominantly acidic catalyst was prepared at various temperatures (70–170 °C) and tested for the acidic/basic properties using the Hammett indicators and titration method followed by functional group analysis using FTIR, crystallization using X-ray diffraction, and surface morphology using SEM. The combination of various characterization techniques gave an insight into the changes in the phases of the layered Zn hydroxide nitrate catalysts upon thermal treatment. Major phase changes occurred at temperatures somewhat above 80, and 140 °C. The catalysts were extensively studied to understand the underlying effects on the FAME yields obtained from catalytic conversion of oleic acid spiked soy bean oil (a model of an acidic oil feedstock) into methyl esters. The results of the optimization reactions reaffirmed the effect of the phase changes when the highest FAME yield was observed from two activated samples namely, Zn5_80 and Zn5_140. The optimized reactions condition of catalytic conversion of SO containing 10% OA at 5 °C/min heating rate, 3 wt % catalyst concentration, 30:1 methanol to oil molar ratio, reaction time of 100 °C for 2 h gave 92% FAME yield when Zn5_140 was used as the catalyst. The detected of the single phase of Zn5(OH)8(NO3)2 in Zn5_80, Zn5(OH)8(NO3)2 and ZnO in Zn5_140 (2-phase system), including Zn5(OH)8(NO3)2, Zn3(OH)4(NO3)2, and ZnO in Zn5_170 (3-phase system), suggested all three phases contributes to the high catalytic activity in methanolysis of the acidic oils. Both Zn5_140 and Zn5_170 gave a comparably high FAME yields based on statistical analyses. This study ascertained the synergistic effects of the high acidity (>0.4 mmol/g) and the dominant active phases of the thermally treated layered Zn hydroxide nitrate on the high catalytic activity that favours esterification of acidic oil feedstocks.

Self-Assembly Preparation of Al2O3/MoS2 Bifunctional Catalyst for Highly Efficient Reduction of SO2 to Elemental Sulfur

MoS2 has been widely applied in SO2 desulfurization and hydrodesulfurization due to its special two-dimensional sheet structure and high-performance of reduction properties. MoS2 nanospheres assembled by the sheet structure of MoS2 were synthesized through a facile hydrothermal synthesis method with the assistance of a surfactant [polyvinylpyrrolidone (PVP)]. The structure of MoS2 was related to the amount of PVP addition during preparation, where the nanosheets were formed into nanospheres, and the nanospheres were generated into hollow spheres further increasing the amount of PVP addition. Meanwhile, the nanosphere size tended to decline, which was beneficial to the improvement of SO2 conversion. Research indicated that porous Al2O3 grown on the nanospheres exposed a larger amount of Lewis acid on the surfaces than that grown on the nanoflower-like structures. The SO2 conversion and sulfur selectivity were 97.05% and 98.21% under the optimized conditions. The modulation of the MoS2 morphology has been proved to be an available method to enhance the reduction of SO2 to elemental sulfur.

A novel strategy using sulfite for bromate control during UV/persulfate oxidation of bromide-containing waters

The ultraviolet/persulfate (UV/PS) process has attracted more and more attention for water treatment. However, it runs the risk of producing bromate in the presence of bromide ions. In this work, we propose a new strategy using sulfite to inhibit bromate formation. The results show that the addition of sulfite significantly reduced the formed bromate in the UV/PS system by 61.2% and 24.5% in 30 min and 120 min, respectively. Increasing sulfite dosage or pH could enhance bromate control. From the standpoint of reaction kinetics, sulfite is likely to inhibit bromate formation by reducing bromine radicals (Br) back to bromide ions, the energy profile of which was quantified by density functional theory (DFT) calculations. In the UV/PS/sulfite system, the conversion of SO3− to HO was observed, indicating that sulfite also served as a source of reactive radicals. Moreover, sulfite apparently promoted the degradation of benzoic acid and phenol in a UV/PS system, showing advantages over other inorganic reductants. As a result, we discovered that sulfite could not only help control bromate formation in UV/PS but also improve the system’s oxidation capacity.

Experimentation, modeling and optimisation studies of an integrated-packed bed reactor (PBR) for the decomposition of sulphuric acid

Decomposition of sulphur trioxide (SO3) is highly endothermic, catalytic and overall rate-controlling step, in three-step decomposition of sulphuric acid. SO3 decomposition in Packed Bed Reactor (PBR) involves transport resistances in two (multi) scales; macro-voids and micro-pores together with surface reaction. Objective of the present study is to develop a double porosity (multi-scale) model, DPM for the catalytic decomposition of SO3 in a heat recuperated (integrated)-PBR and also to maximize SO3 conversion. DPM and simulation studies are carried out using COMSOL® and the model is validated with experimental studies. Experiments are performed at different flow rates, wall temperature, feed concentration and with two catalyst loadings, where chromium doped iron oxide ‘foam’ type (porous particle) catalyst is used. Simulation study shows, increase in conversion with decrease in particle size, annular gap and with increase in porosity, thermal conductivity of catalyst. Catalyst size is found to be an insignificant parameter, for porosity >0.2 and thermal conductivity is found to be a significant parameter. A conversion close to isothermal conversion has been obtained with the tuned parameters.

Research on the Selective Electrocatalytic Reduction of SO2 to Recover S0 by Pb Electrode

Resource utilization of SO2 from flue gas is a key challenge for the green development of the smelting industry. Recovery of sulfur resources in the form of elemental sulfur (S0), which has a high market demand and is a current focus in the field of SO2 treatment, can reduce the solid waste from desulfurization. In this study, it was found that Pb as a cathode material had good catalytic activity for the electrochemical reduction of SO2 and good selectivity towards elemental sulfur. However, the cathode suffers from sulfur poisoning. The problem was resolved by introducing surfactant, specifically sodium dodecyl benzene sulfonate (SDBS), which significantly lowered the sulfur content ratio on the surface of the electrode from 31.82% to 2.17%. Through the optimization of electrocatalytic parameters, this method enables efficient conversion of SO2 to S0, achieving a selectivity of 83% at pH = 0.25 and E = −0.8 V (vs. SCE).

A novel SO3•- mediated photoelectrocatalytic system based on MoS2/Fe2O3 and CuNW@CF for the efficient treatment of sulfurous and nitrogenous oxides

Sulfurous and nitrogenous oxides, including NOx and SO2, and the generated substances NOx- and SO32- widely exist in air and water as pollutants and thus are difficult to control in the environment. In this study, we designed a novel photoelectrocatalytic (PEC) system for the efficient conversion of SO2 and NOx in mixed gases and NOx- and SO32- in wastewater to N2 and SO42-, respectively, by activating SO32- to form SO3•-. The key ideas include the conversion of SO32- from SO2 and efficient activation of SO32- into SO3•- and further conversion into SO4•- by the MoS2/Fe2O3 photoanode. Simultaneously, NO3-/NO2- originating from NOx was rapidly reduced to NH4+ on the CuNW@CF cathode. Ultimately, the generated NH4+ was selectively oxidized to N2 by SO4•- and SO4•- was reduced to SO42-. The results indicated that 99.9 % of TN was removed and 100 % of SO32- was converted to harmless SO42-. This study provides new insights into the treatment of sulfurous and nitrogenous oxides in air and water.