Oxidation Reaction Of SO2 Research Articles

Microcosmic insights into Hg0-SO2 interaction on CuFe2O4 catalyst

CuFe2O4 is considered as a very promising kind of catalysts for Hg0 oxidation in the industrial flue gas. The flue gas produced by solid-fuel combustion usually contains acid gas component SO2, which can exhibit the versatile effects on Hg0 oxidation. However, the effects of SO2 on Hg0 oxidation catalyzed by CuFe2O4 catalyst and its reaction mechanism remain elusive. Herein, the reaction mechanism governing the effects of SO2 on Hg0 oxidation was investigated via the Hg0 oxidation experiments and density functional theory (DFT) calculations. The experimental results show that the temperature change and SO2 presence can affect the Hg0 removal efficiency of CuFe2O4 catalyst. SO2 has a certain degree of inhibition effect on the Hg0 oxidation of CuFe2O4 catalyst. The inhibition effect of SO2 is relatively weak in the low temperature range of 50–150 °C, which is closely associated with the competitive adsorption between SO2 and Hg0. SO2 exhibits a relatively strong inhibition effect on Hg0 oxidation in the high temperature range of 200–350 °C, which is related to the high-temperature sulfation of CuFe2O4 catalyst surface. Mercury species on the CuFe2O4 catalyst surface mainly exists in the forms of HgSO4 and HgO in the presence of SO2. The DFT-calculation results indicate that the conversion process of SO2 to SO3 includes two steps: SO2 adsorption and SO2 oxidation. The activation energy barrier of SO2 oxidation reaction is 216.42 kJ/mol. The oxidation of Hg0 on the surface of CuFe2O4 catalyst includes four steps: Hg0 adsorption, Hg* oxidation into HgO*, HgO*-to-HgSO4* conversion and HgSO4 desorption. HgSO4 is formed by the bimolecular reaction of HgO* and SO3* on CuFe2O4 catalyst. Hg* oxidation into HgO* is found to be the rate-determining step of HgSO4 formation.

Insights into atmospheric trace gases, aerosols, and transport processes at a high-altitude station (2623 m a.s.l.) in Northeast Asia

As part of the efforts to understand long-range air pollution transport in Northeast Asia, a comprehensive field measurement campaign was conducted at the top of Changbai Mountain (2623 m a.s.l.) from 25th July to 21st August in 2021. The ambient concentrations of trace gases and chemical characteristics of fine particulate matter (PM2.5) were comparable to those at background or free tropospheric locations in China, but exceeded levels at corresponding sites in Europe and the United States. Well-defined diurnal variations were evident in most air pollutants, including carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen oxide (NOx), reflecting the influence of boundary layer development and local anthropogenic activities. Ozone (O3) exhibited a unique diurnal distribution, with lower concentrations during the daytime and higher levels at nighttime, indicating a pronounced impact of downward transport of O3-rich air from the upper troposphere during the nighttime. During the campaign, organic carbon (OC) constituted the predominant component of PM2.5, comprising 43% of the total, while sulfate (SO42−) was the most abundant secondary inorganic component in PM2.5, accounting for 26%. Combining the analysis of air mass backward trajectories, we found that Changbai Mountain is primarily influenced by air masses originating from North Korea and the Sea of Japan, constituting 62% of the total, and local vegetation biological emissions and anthropogenic emissions in North Korea notably affect the observation site. Conversely, the secondary aerosol components were most abundant in marine air mass originating from the marginal seas of China and the strait between the Korean peninsula and southern Japan. Utilizing the Lagrangian photochemical trajectory model (LPTM), a significant increase in particulate SO42− concentrations was observed when air mass passed through the marginal seas of China, primarily due to SO2 oxidation reaction. This study contributes to an improved understanding of the atmospheric chemistry in the high-altitude regions of Northeast Asia and underscores the substantial role of secondary inorganic aerosol formation during the transport of marine air masses.

Probing the dynamics and bottleneck of the key atmospheric SO2 oxidation reaction by the hydroxyl radical

SO2 (Sulfur dioxide) is the major precursor to the production of sulfuric acid (H2SO4), contributing to acid rain and atmospheric aerosols. Sulfuric acid formed from SO2 generates light-reflecting sulfate aerosol particles in the atmosphere. This property has prompted recent geoengineering proposals to inject sulfuric acid or its precursors into the Earth's atmosphere to increase the planetary albedo to counteract global warming. SO2 oxidation in the atmosphere by the hydroxyl radical HO to form HOSO2 is a key rate-limiting step in the mechanism for forming acid rain. However, the dynamics of the HO + SO2 → HOSO2 reaction and its slow rate in the atmosphere are poorly understood to date. Herein, we use photoelectron spectroscopy of cryogenically cooled HOSO2- anion to access the neutral HOSO2 radical near the transition state of the HO + SO2 reaction. Spectroscopic and dynamic calculations are conducted on the first ab initio-based full-dimensional potential energy surface to interpret the photoelectron spectra of HOSO2- and to probe the dynamics of the HO + SO2 reaction. In addition to the finding of a unique pre-reaction complex (HO⋯SO2) directly connected to the transition state, dynamic calculations reveal that the accessible phase space for the HO + SO2 → HOSO2 reaction is extremely narrow, forming a key reaction bottleneck and slowing the reaction rate in the atmosphere, despite the low reaction barrier. This study underlines the importance of understanding the full multidimensional potential energy surface to elucidate the dynamics of complex bimolecular reactions involving polyatomic reactants.

Quantum cascade laser absorption sensor for in-situ, real-time and sensitive measurement of high-temperature SO2 and SO3

We report a mid-infrared quantum cascade laser absorption sensor capable of measuring SO2 and SO3 simultaneously and sensitively at elevated temperatures. In the sensor development, the intense transitions of SO2 and SO3 in the mid-infrared region of 1129 cm−1 and 1398 cm−1 were exploited by two quantum cascade lasers. A high-temperature multipass cell was adopted to increase the absorption path length to 10 m. The quantitative concentrations of SOx were directly obtained from the calibration-free wavelength modulation spectroscopic method, which was validated at varied temperature and pressure conditions. From Allan deviation analysis, we achieved a minimum detection limit of 8 parts per billion (ppb) for SO2 and 3 ppb for SO3, with an average time of 100 s. Lastly, we successfully demonstrated the real-time and sensitive measurement of SO2 and SO3 during the oxidation reaction of SO2 by O3 at 460 K. Our laser sensor shows great potential for in-situ and real-time monitoring of SOx from combustion emissions.

Simulation of Two Series Packed-Bed Reactors for SO2 Oxidation Reaction

Simulation of Two Series Packed-Bed Reactors for SO2 Oxidation Reaction

Electrochemical impedance spectroscopy for studying the SO2 electrocatalytic oxidation on Pt electrodes

The generation of green hydrogen for a more environmentally friendly and energetic environment is in the spotlight of electrocatalysis for a while. One emerging strategy is assisted water electrolysis, in which the oxidative reaction, the limiting one, can be substituted and the SO2 oxidation reaction (SO2OR) is an interesting candidate since it will consume a lethal atmospheric pollutant, at lower potentials. To better comprehend the electrochemical kinetics of this process, in the present work, we applied electrochemical impedance spectroscopy (EIS) as a tool to understand the electrolyte composition's influence on the activity. In this way, we have shown that, despite the three tested electrolytes, 0.5 mol L−1 H2SO4, HClO4, and 1:1 mixture of these two, presented the same DC response, EIS has shown that the adsorption kinetic is different for them all, presenting the different potential of zero charge values, double layer capacitance vs applied potential profiles and very different charge transfer resistance Tafel plots.

Mass Transport Influence in the SO2 Oxidation Reaction on Au Electrodes

AbstractThe use of fossil fuels as energy source is unsustainable in the long term and net‐zero carbon processes need to be implemented to maintain environmental balance. One could make use of assisted water electrolysis to produce clean hydrogen and avoid high overpotentials observed for the oxygen evolution reaction by switching to the SO2 oxidation reaction (SO2OR). This process exhibits a complex mechanism on Au electrodes, which is strongly affected by convection, exhibiting an anti‐Levich behavior, in which the limiting current linearly decreases with the square root of the rotation rate. Likewise, the bi‐stability region observed in the j/E profiles narrows in a sigmoidal profile with the rotation rate, leading to a non‐linear phenomenon with two controlling parameters, mass transport and potential applied. These events were understood to be related to the changing in the reaction mechanism by controlling the electrode rotation, much related to the decrease in the current aforementioned.

Research on the mechanism of bed agglomeration and superheater fouling in CFB boiler fired pure petroleum coke

AbstractCirculating fluidized bed combustion is an effective method for the clean and efficient utilization of high‐sulphur petroleum coke. In the actual production and operation process, there are serious problems of bed agglomeration and superheater fouling. The chemical and mineral compositions of the deposition were analyzed by X‐ray diffraction (XRD) and X‐ray fluorescence spectroscopy (XRF), and the effects of CaO sulphation and V2O5 on bed agglomeration and superheater deposits were studied through targeted experiments. The research results show that the sulphation process of CaO is the cause of bed agglomeration, and the superheater fouling is the result of the combined action of K2SO4 condensation and CaO sulphation; V2O5 in petroleum coke ash catalyzes the oxidation reaction of SO2 to accelerate the sulphation of CaO, thereby accelerating the development of bed agglomeration and superheater fouling.

Boosting SO2 electrocatalytic oxidation reaction on highly dispersed subnanometric Au/TiO2 catalyst

The increase in the consumption of fossil fuels led not only to the increase of atmospheric CO2 level, but also to the increment in sulfur pollutants production, such as SO2. The electrochemical SO2 oxidation reaction (SO2OR) was already shown to be efficiently catalyzed by Au and, to further develop the technological knowledge in this field, the application of nanostructured Au catalysts is highly desirable. Herein we present a highly dispersed subnanometric Au/TiO2 catalyst as active material for SO2OR. The Tafel analysis revealed a change in the reaction mechanism and a substantial increase of the electrocatalytic reaction activity compared to bulk Au, even at conditions where bulk Au presented low activity, such as H2SO4 electrolyte. Electrochemical impedance spectroscopy (EIS) results led to the conclusion that TiO2 is also involved in the reaction, since not only the oxide time constant changes with the applied potential but also adsorbed intermediates were observed. This EIS response is probably related to the Au/TiO2 interface, which reflects on the oxide time constant.

SO2 electrooxidation reaction on Pt single crystal surfaces in acidic media: Electrochemical and in situ FTIR studies

SO2 is a poisonous and anthropogenic gas generated by fossil fuel burning due to the common presence of S-containing contaminants in oil and coal. As a strategy to handle this pollutant and to increase H2 generation, the electrocatalytic SO2 oxidation reaction (SO2OR) is considered. In this way, SO2 is converted to H2SO4, while hydrogen gas is generated at the cathode. To better understand the mechanism and its dependence on the surface crystallography and electrolyte composition, electrochemical and in situ spectroscopic measurements using Pt single crystal electrodes were performed. The crystallographic orientation of the electrode is shown to be critical not only to the SO2OR activity but also to the resulting mechanism. The Pt(100) face is found to be the most active electrode in both H2SO4 and HClO4 aqueous electrolytes, and S2O62− appears as a key intermediate for the mechanism. Volcano plots, drawn considering the Stark tuning slope as a quantity proportional to the adsorption energy, show the importance of S2O62− in the electrode catalytic activity.

The mechanism of the formation of high sulfate concentrations over the Yellow Sea during the KORUS-AQ period: The effect of transport/atmospheric chemistry and ocean emissions

This study investigates the chemical properties of high-concentration sulfate (SO42−) that appeared on the surface of the Yellow Sea during the KORUS-AQ period (April–June 2016). For quantitative analysis, we carry out numerical simulation using the Community Multi-scale Air Quality (CMAQ) model for the KORUS-AQ period (the BASE case) and another simulation of ocean emissions (the OCEAN case) that determines the effect of including ocean emissions on the results of the analysis. CMAQ-simulated (the BASE case) sulfate (SO42−), nitrate (NO3−), ammonium (NH4+), elemental carbon (EC), and organic carbon (OC) show high concentrations of these constituents centering around eastern China, the Liaodong Peninsula, and the western inland area of the Korean Peninsula. SO42−, unlike the other particulate matter constituents, shows high concentrations (up to 14.44 μg/m3) at the surface of the Yellow Sea. Results of the Integrated Process Rate (IPR) analysis show that the chemical production of SO42− over the Yellow Sea can primarily be attributed to the “aerosol process”, which is mainly dependent on weather conditions (e.g., temperature and wind speed) and concentrations of precursors such as SO2 and OH. The results of the analysis of the mechanism of SO42− formation using the Sulfur Tracking Model (STM) show that most chemical SO42− production (79.12%) on the surface of the Yellow Sea is the result of the aqueous-phase chemical reactions following the SO2 oxidation reaction (OH + SO2 → H2SO4 + HO2). Comparing the results of the OCEAN and BASE cases, we find that the primary mechanism of SO42− formation over the Yellow Sea shows no significant change with regard to ocean emissions. These results also confirm that increases in SO42− concentrations (up to 4.79 μg/m3) on the surface of the sea are not proportional to the distribution and amounts of ocean emissions, and in some areas, concentrations could decrease (up to −2.65 μg/m3) as a result of complex non-linear chemical reactions.

Boosting SO2-depolarized electrolysis with anodic HI for efficient and energy-saving hydrogen production

The SO2-depolarized electrolysis (SDE) is a promising method for SO2 capture and hydrogen production. But the SDE is limited by the high overpotential and slow kinetics of anodic SO2 oxidation reaction (SOR). Herein, to boost SDE process, we add hydroiodic acid (HI) to the anolyte and form HI-assisted SO2-depolarized electrolysis (HASDE). The mechanism of HI assisted SOR is explored, the existence of HI reduces the onset potential and impedance, but increases current density and reaction rate of SOR. HI is supposed to change the single-step SOR into three-step reactions, without changing the overall anodic reaction. A HI concentration of less than or equal to 0.02 mol/L and an operating temperature of 50 °C or less are recommendable. The comparison of SDE and HASDE processes indicates that HASDE delivers a lower cell voltage than SDE during continuous constant-current electrolysis, and has negligible effect on cathodic H2 evolution, while it achieves 27.03–48.65% reduction in electric energy consumption compared with SDE. The present work provides an innovative strategy for improving SDE and energy-saving production of value-added chemicals like H2SO4 and H2.

Effects of Trace Components in Reclaimed Water Sludge on Wet Flue Gas Desulfurization Process

The paper designed and built a simulation reaction system for the Wet Flue Gas Desulfurization(WFGD) process to analyze the effects of factors on the Oxidation reaction of SO2 for the reuse of reclaimed water sludge. Six trace components including magnesium, iron, chloride, aluminum, PAM and PFS in reclaimed water sludge from reclaimed water softening were selected for analysis factors. The effects of six factors on the oxidation reaction were tested by single factor experiments. The multi-factor effects on the oxidation reaction was studied by adding different proportion of reclaimed water sludge to the desulfurizer of the simulated reaction system. In addition, the effect of reclaimed water sludge on the crystallization and dehydration of desulfurization slurry was analyzed. The results show that six factors have little effects on the SO2 oxidation rate in the test range. The addition of reclaimed water sludge has a significant effect on the crystalline form and dehydration of gypsum.

Theoretical insight into the oxidation mechanism of NO2 and SO2 on TiO2 surface: The role of H2O, NH3 and SO42-

In this paper, density-functional theory (DFT) was employed to investigate the reaction mechanism of SO2 and NO2 and the important role of intermediate N2O4 formation. In addition, the effect of pure particulate surface (TiO2) and particulate surface containing other atmospheric components (H2O, NH3 and SO42−) on the conversion of SO2 and NO2 to sulfate also was analyzed. The detailed information that intermediate N2O4 acts as the oxidant was demonstrated in this oxidation reaction of SO2 and NO2 (as a rate-determining step). The pure particulate surface (TiO2) has hardly effect on the oxidation process of SO2 and N2O4. Whereas, different amounts of H2O and NH3 molecules as well as SO42−, contained on the particulate surface, can effectively reduce the activation energy of oxidation step. And, the optimal process is that SO2 is oxidized by cis-ONONO2 with the energy barrier of 4.54 kcal/mol when one NH3 molecule and one H2O molecule are contained on the TiO2(101) surface. When more H2O molecules are contained on particulate surface, SO2 tends to form HSO3− first. However, HSO3− is more difficult to be further oxidized by asy-ONONO2 than SO2. This study gains more insight into the contribution of SO2 and NO2 to haze and the potential impact of atmospheric constituents (including H2O/NH3/TiO2 and SO42−/TiO2) on the formation sulfate.

Influence of Anion Chaotropicity on the SO2 Oxidation Reaction: When Spectator Species Determine the Reaction Pathway

AbstractThe electrochemical SO2 oxidation reaction (SO2OR) is a promising alternative to the O2 evolution reaction for H2 electrochemical generation. The SO2OR exhibits a low thermodynamic potential and small kinetic barrier, and Au has been observed to be a very active catalyst. For this material, nonlinear dynamic behavior is observed, which is related to the electrolyte chaotropicity at the solid‐liquid interface. In this work, the influence of the chaotropicity was investigated by electrochemical and spectroelectrochemical techniques, and the main reasons for the dependence on the chaotropicity were investigated. The electrochemical response as a function of the chaotropicity was determined as a function of the mechanism observed, and the reaction pathway selection was related to the intermediate adsorption, which in turn was controlled by the interfacial water structure. The “neutral” chaotropicity was found to be the optimum condition for SO2OR.

Adsorption and oxidation of SO2 on the surface of TiO2 nanoparticles: the role of terminal hydroxyl and oxygen vacancy-Ti3+ states.

Herein, the absorption and oxidation reactions of SO2 on TiO2 nanoparticles (TiO2 NPs) at 296 K under various environmental conditions (humidity, UV irradiation, and ozone copresence) were investigated by using a flow chamber reaction system, synchrotron X-ray absorption near-edge structure (XANES) and high resolution synchrotron X-ray photoelectron spectroscopy (XPS) measurements. The results showed that oxidation of SO2 to sulfate via TiO2 NP catalysis happened at a very rapid rate. The appropriate relative humidity, UV irradiation and co-presence of ozone all markedly promoted SO2 oxidation on TiO2 NPs. High resolution XPS unraveled that the terminal hydroxyl (OHt) and oxygen vacancy (VO)-Ti3+ states on TiO2 NPs were the active sites for SO2 adsorption and oxidation. The data of XPS measurements suggest that SO2 was adsorbed on a OHt next to a Ti3+ VO and reacted to form HSO3-. HSO3- can then transform into SO32-via transfer of a proton. The resulting adsorbed SO32- could bind to a surface bridging O (Ob) atom and transform into SO42-. A H2O molecule could dissociate on VO-Ti3+ into two bridging hydroxyl (OHb) groups, subsequently forming new Ob, which provides an active O site for the adsorbed HSO3-/SO32- and oxidizes them into HSO4-/SO42- on the surface of the TiO2 NPs. The copresence of O3 could promote H2O dissociation into OHb, promoting the formation of Ob. The copresence of O3 may also promote the dissociation of adsorbed H2O into TiO2-O2- and hydroxyl radicals (˙OH) on VOs, facilitating the oxidation of adsorbed HSO3-/SO32-. Under UV irradiation, new VOs were created via oxidation of lattice O by photo-generated holes, resulting in increased Ob and subsequently enhanced oxidation of adsorbed HSO3-/SO32- on TiO2 NPs.

Synergistic Reaction of SO2 with NO2 in Presence of H2O and NH3: A Potential Source of Sulfate Aerosol.

Effect of H2O and NH3 on the synergistic oxidation reaction of SO2 and NO2 is investigated by theoretical calculation using the molecule system SO2-2NO2-nH2O (n = 0, 1, 2, 3) and SO2-2NO2-nH2O-mNH3 (n = 0, 1, 2; m = 1, 2). Calculated results show that SO2 is oxidized to SO3 by N2O4 intermediate. The additional H2O in the systems can reduce the energy barrier of oxidation step. The increasing number of H2O molecules in the systems enhances the effect and promotes the production of HONO. When the proportion of H2O to NH3 is 1:1, with NH3 included in the system, the energy barrier is lower than two pure H2O molecules in the oxidation step. The present study indicates that the H2O and NH3 have thermodynamic effects on promoting the oxidation reaction of SO2 and NO2, and NH3 has a more significant role in stabilizing product complexes. In these hydrolysis reactions, nethermost barrier energy (0.29 kcal/mol) can be found in the system SO2-2NO2-H2O. It is obvious that the production of HONO is energetically favorable. A new reaction mechanism about SO2 oxidation in the atmosphere is proposed, which can provide guidance for the further study of aerosol surface reactions.

Ce promoted V2O5 catalyst in oxidation of SO2 reaction

Harmful environmental effects of SO2 on the start-up of the sulfuric acid plant process motivated studying ceria as a promoter for V2O5 catalyst that is employed in SO2 oxidation. Effects of SO2(%), ceria percentage, temperature and O2/SO2 were investigated to optimize ceria loading on V2O5 catalyst. To determine the main and interaction effects, a full factorial design of experiments including 315 experiments was used. The results showed that the catalyst with 7wt% ceria (VaCe7) possessed the highest catalytic performance. To study the effect of more parameters on this catalyst, other 135 post-experiments with full factorial designs were performed after the optimization of Ce contents. The results revealed that mean SO2 conversion increased with increasing SO2 (%) and O2/SO2 ratio, and decreasing GHSV. Also, the maximum mean conversion was found at the reaction temperature of 450°C by the trade-off of kinetic and thermodynamic factors of the reversible exothermic reaction. VaCe7 was found to have more catalyst activities than that the without-ceria (VaCe0) case. The synthesized catalysts were characterized by XPS, BET, FTIR, SEM, XRD and ICP. The SEM mapping revealed that the cerium oxide had better distribution on VaCe7 than VaCe9&11. FTIR, XRD and XPS showed the presence of CeVO4 in the Ce-promoted catalyst and confirmed that ceria promotes V2O5 by the formation of CeVO4 network, reduces the activation energy of reduction–oxidation and increases the rate of SO2 oxidation reaction. The stability tests demonstrated good catalytic performance stability of the synthesized catalyst up to 50h in the reaction. Results at the initial times of the stability tests showed that the catalyst with ceria promoter (VaCe7) had higher activity than VaCe0 at the start-up time. Also, VaCe7 had higher activity at the start-up than its normal conditions, which could be related to the good oxygen storage capacity of ceria because the catalyst at the start-up is faced to the oxygen of air. This high startup activity caused to use it in starting up of sulfuric acid plants that decreases SO2 emission to the environment.

Preparation, Physiochemical and Kinetic Investigations of V2O5/SiO2 Catalyst for Sulfuric Acid Production

V2O5/SiO2 catalyst was utilized to oxidize SO2 to SO3 species in the presence of oxygen mainly for producing sulfuric acid. For this catalyst, the active phase was a mixture of vanadium pentoxide and basic sulfate/pyrosulfate material. This active phase at the reaction temperature behaved as a liquid filling up the pores of the silica support. On the other hand, amounts of the SO3 and V5+ species in the catalyst necessarily varied with the concentration of the feed material and temperature rendering complexity to the kinetics of the SO2 oxidation reaction. In the current research, the catalyst preparation with different amounts of such materials was undertaken. Purified diatomaceous earth of a Persian Gulf beach was chosen as the support for this catalyst. The suitability of the prepared catalyst to determine the reaction kinetics was confirmed through the XRD, XRF and BET-BJH analyses as well as color analysis. Moreover, the aforementioned reaction kinetics was studied empirically. In addition, a model for the reaction rate using the response surface methodology (RSM) was presented. In this venue, factors including the reaction temperature as well as conversion were considered. This reaction kinetics determined at the operating conditions of 380-420 °C, 0.108 MPa and feed gas composition of 10 wt.% SO2, 18.9 wt.% O2 and 71.1 wt.% N2. It was revealed that, obtained kinetic rate constants satisfied the Arrhenius relationship from which the activation energies were determined.

Detailed kinetic study of the electrochemical Bunsen reaction in the sulfur–iodine cycle for hydrogen production

The electrochemical Bunsen reaction has been proposed as an innovative and promising method compared with the traditional Bunsen reaction for the sulfur–iodine cycle, and its kinetics were studied in this work. Polarization curves were measured using platinum electrode in the different concentrations of SO2–H2SO4–H2O and I2–HI–H2O solutions at a temperature range of 303–353K. Fundamental kinetic parameters, namely exchange current density, Tafel slope, asymmetry factor, were determined for anodic SO2 oxidation reaction and cathodic I2 reduction reaction according to the Tafel plots. The activation energy and pre-exponential factor for the electrode reactions were also analyzed using Arrhenius relation. Results indicated that an increase in the SO2 concentration in the anolyte and the I2 concentration in the catholyte reduced the activation energy, contributing to the easier anode and cathode reaction. Take high electrode reaction rate and easier electrode reactions into account, the initial SO2 concentration of 1.509mol/L and the I2/HI molar ratio of 0.5 could be optimal.