Enhancing AsH3 Detoxification via Electron-Deficient [NiIII-OH (µ-O)] in a Nickel-Modified NaY Zeolite: A Pathway toward As0 Products.

The transformation of toxic arsine (AsH3) gas into valuable elemental arsenic (As0) from industrial exhaust gases is important for achieving sustainable development goals. Although advanced arsenic removal catalysts can improve the removal efficiency of AsH3, toxic arsenic oxides generated during this process have not received adequate attention. In light of this, a novel approach for obtaining stable As0 products was proposed by performing controlled moderate oxidation. We designed a tailored Ni-based catalyst through an acid etching approach to alter interactions between Ni and NaY. As a result, the 1Ni/NaY-H catalyst yielded an unprecedented proportion of As0 as the major product (65%), which is superior to those of other reported catalysts that only produced arsenic oxides. Density functional theory calculations clarified that Ni species changed the electronic structure of oxygen atoms, and the formed [NiIII-OH (µ-O)] active centers facilitated the adsorption of AsH2*, AsH*, and As* reaction intermediates for As-H bond cleavage, thereby decreasing the direct reactivity of oxygen with the arsenic intermediates. This work presents pioneering insights into inhibiting excessive oxidation during AsH3 removal, demonstrating potential environmental applications for recovery of As0 from toxic AsH3.

Sulfur Dioxide Promoted Mercury Fast Deposition over a Selenite-Chloride-Induced Surface from Wet Flue Gas.

Gaseous elemental mercury (Hg0) extraction from industrial flue gases is undergoing intense research due to its unique properties. Selective adsorption that renders Hg0 to HgO or HgS over metal oxide- or sulfide-based sorbents is a promising method, yet the sorbents are easily poisoned by sulfur dioxide (SO2) and H2O vapor. The Se-Cl intermediate derived from SeO2 and HCl driven by SO2 has been demonstrated to stabilize Hg0. Thus, a surface-induced method was put forward when using γ-Al2O3 supported selenite-chloride (xSeO32--yCl-, named xSe-yCl) for mercury deposition. Results confirmed that under 3000 ppm SO2 and 4% H2O, Se-2Cl exhibited the highest induced adsorption performance at 160 °C and higher humidity can accelerate the induction process. Driven by SO2 under the wet interface, the in situ generated active Se0 has high affinity toward Hg0, and the introduction of Cl- enabled the fast-trapping and stabilization of Hg0 due to its intercalation in the HgSe product. Additionally, the long-time scale-up experiment showed a gradient color change of the Se-2Cl-induced surface, which maintained almost 100% Hg0 removal efficiency over 180 h with a normalized adsorption capacity of 157.26 mg/g. This surface-induced method has the potential for practical application and offers a guideline for reversing the negative effect of SO2 on gaseous pollutant removal.

CO2 sequestration and CaCO3 recovery with steel slag by a novel two-step leaching and carbonation method.

The steel smelting process produces extensive CO2 and Ca-containing steel slag (SS). Meanwhile, the low value utilization of steel slag results in the loss of Ca resources. CO2 sequestration utilizing SS can reduce carbon emissions while achieving Ca circulation. However, conventional SS carbon sequestration methods suffer from slow reaction rates, finite Ca usage efficiency, and difficulty separating the CaCO3 product from SS. Herein, an innovative two-step leaching (TSL) and carbonation method was presented based on the variations in leaching efficiency of activated Ca under different conditions, aiming at efficient leaching, carbon sequestration, and high-value reuse of SS. This method employed two NH4Cl solutions in sequence for two leaching operations on SS, allowing the Ca leaching rate to be effectively increased. According to the findings, TSL could increase the activated Ca leaching rate by 26.9 % and achieve 223.15 kg CO2/t SS sequestration compared to the conventional one-step leaching (CSL) method. If part of the CaCO3 is recovered as a slagging agent, about 34.1 % of the exogenous Ca introduction could be saved. In addition, the CO2 sequestration of TSL did not significantly decrease after 8 cycles. This work proposes a strategy that has the potential for recycling SS and reducing carbon emissions.

SO2-Driven In Situ Formation of Superstable Hg3Se2Cl2 for Effective Flue Gas Mercury Removal.

Flue gas mercury removal is mandatory for decreasing global mercury background concentration and ecosystem protection, but it severely suffers from the instability of traditional demercury products (e.g., HgCl2, HgO, HgS, and HgSe). Herein, we demonstrate a superstable Hg3Se2Cl2 compound, which offers a promising next-generation flue gas mercury removal strategy. Theoretical calculations revealed a superstable Hg bonding structure in Hg3Se2Cl2, with the highest mercury dissociation energy (4.71 eV) among all known mercury compounds. Experiments demonstrate its unprecedentedly high thermal stability (>400 °C) and strong acid resistance (5% H2SO4). The Hg3Se2Cl2 compound could be produced via the reduction of SeO32- to nascent active Se0 by the flue gas component SO2 and the subsequent combination of Se0 with Hg0 and Cl- ions or HgCl2. During a laboratory-simulated experiment, this Hg3Se2Cl2-based strategy achieves >96% removal efficiencies of both Hg0 and HgCl2 enabling nearly zero Hg0 re-emission. As expected, real mercury removal efficiency under Se-rich industrial flue gas conditions is much more efficient than Se-poor counterparts, confirming the feasibility of this Hg3Se2Cl2-based strategy for practical applications. This study sheds light on the importance of stable demercury products in flue gas mercury treatment and also provides a highly efficient and safe flue gas demercury strategy.

Reverse Conversion Treatment of Gaseous Sulfur Trioxide Using Metastable Sulfides from Sulfur-Rich Flue Gas.

Sulfur trioxide (SO3) is an unstable pollutant, and its removal from the gas phase of industrial flue gas remains a significant challenge. Herein, we propose a reverse conversion treatment (RCT) strategy to reduce S(VI) in SO3 to S(IV) by combining bench-scale experiments and theoretical studies. We first demonstrated that metastable sulfides can break the S-O bond in SO3, leading to the re-formation of sulfur dioxide (SO2). The RCT performance varied between mono- and binary-metal sulfides, and metastable CuS had a high SO3 conversion efficiency in the temperature range of 200-300 °C. Accordingly, the introduction of selenium (Se) lowered the electronegativity of the CuS host and enhanced its reducibility to SO3. Among the CuSe1-xSx composites, CuSe0.3S0.7 was the optimal RCT material and reached a SO2 yield of 6.25 mmol/g in 120 min. The low-valence state of selenium (Se2-/Se1-) exhibited a higher reduction activity for SO3 than did S2-/S1-; however, excessive Se doping degraded the SO3 conversion owing to the re-oxidation of SO2 by the generated SeO32-. The density functional theory calculations verified the stronger SO3 adsorption performance (Eads = -2.76 eV) and lower S-O bond breaking energy (Ea = 1.34 eV) over CuSe0.3S0.7 compared to those over CuS and CuSe. Thus, CuSe1-xSx can serve as a model material and the RCT strategy can make use of field temperature conditions in nonferrous smelters for SO3 emission control.

Buffer effect of MgO on Na2SO3 to stabilize S(IV) for the enhancement in simultaneous absorption of NOx and SO2 from non-ferrous smelting gas.

Oxidation-reduction-absorption based on sulfite is a promising process for simultaneous removal of NOx and SO2. However, excessive oxidation of sulfite and competitive absorption between NOx and SO2 limit its application. A matching strategy between antioxidants and alkaline agents has been proposed to solve these problems and enhance the absorption process. The comparison results of inhibitors showed that hydroquinone exhibited long-term high-efficiency inhibition of S(IV) (SO32-/HSO3-) oxidation. The comparison of alkaline agents showed that the Na2SO3 solution with heterogeneous mixture of MgO and hydroquinone exhibited better absorption performance than that with other combinations. The absorption amounts of NOx in 0.15 mol/L Na2SO3 50 mL solution added 0.1% hydroquinone (HQ) with 0.09 mol/L MgO were 2.24 mmol, which improved 5 times than that without additives. In addition, studies on the influence of pH showed that the pH of MgO mixture could be stabilized at 9-10 for a long time, while the pH of Na2CO3 mixture decreased faster. Further studies suggested that the hydration of MgO resulted in the solution with MgO keeping high pH. This is also the main reason why the combination of MgO and hydroquinone is superior to the combination of Na2CO3 and hydroquinone in desulfurization and denitration performance.

Production of H2S with a Novel Short-Process for the Removal of Heavy Metals in Acidic Effluents from Smelting Flue-Gas Scrubbing Systems.

Direct sulfidation using a high concentration of H2S (HC-H2S) has shown potential for heavy metals removal in various acidic effluents. However, the lack of a smooth method for producing HC-H2S is a critical challenge. Herein, a novel short-process hydrolysis method was developed for the on-site production of HC-H2S. Near-perfect 100% efficiency and selectivity were obtained via CS2 hydrolysis over the ZrO2-based catalyst. Meanwhile, no apparent residual sulfur/sulfate poisoning was detected, which guaranteed long-term operation. The coexistence of CO2 in the products had a negligible effect on the complete hydrolysis of CS2. H2S production followed a sequential hydrolysis pathway, with the reactions for CS2 adsorption and dissociation being the rate-determining steps. The energy balance indicated that HC-H2S production was a mildly exothermic reaction, and the heat energy could be maintained at self-balance with approximately 80% heat recovery. The batch sulfidation efficiencies for As(III), Hg(II), Pb(II), and Cd(II) removal were over 99.9%, following the solubilities (Ksp) of the corresponding metal sulfides. CO2 in the mixed gas produced by CS2 hydrolysis did not affect heavy metals sulfidation due to the presence of abundant H+. Finally, a pilot-scale experiment successfully demonstrated the practical effects. Therefore, this novel on-site HC-H2S production method adequately achieved heavy metals removal requirements in acidic effluents.

Stepwise Ions Incorporation Method for Continuously Activating PbS to Recover Mercury from Hg0-Rich Flue Gas.

Transition metal elements doping is a conventional strategy for the modification of sulfide-based sorbents to obtain preferable Hg0 adsorption capability. One problem was that such a method could only obtain a temporary promotion to sulfides. To achieve continuous promotion of mercury capture performance, we use the difference of solubility product (Ksp) between sulfides to develop a postsynthesis approach for stepwise doping of PbS by Cu2+ ions. Moreover, it further demonstrated the restoration of PbS surface under a given high temperature, enabled by thermal migration of the foreign Cu2+ ions from outer to interlayer in PbS lattice and rereleased of S sites occupied previously by mercury. The Hg0 adsorption capacity of PbS was enlarged from 0.86 to 2.76 mg·g-1 after the first doping, resulting from the mild oxidization of S2- to S- in the surface layer by foreign Cu2+ ions. Furthermore, regeneration of spent PbS can be implemented by stepwise Cu2+ incorporation due to the renewability of the surface, enabling even better Hg0 adsorption capacity after six cycle tests. This stepwise incorporation method promises the precise utilization of doped elements, as well as offers a tutorial example for the activation and regeneration of sulfide sorbents to recover Hg0 from Hg0-rich flue gas.

Removal of Hg2+ with Polypyrrole-Functionalized Fe3O4/Kaolin: Synthesis, Performance and Optimization with Response Surface Methodology.

PPy-Fe3O4/Kaolin was prepared with polypyrrole functionalized magnetic Kaolin by a simple, green, and low cost method to improve the agglomeration and low adsorption capacity of Kaolin. PPy-Fe3O4/Kaolin was employed to remove Hg2+ and the results were characterized by various methods. Relevant factors, including solution pH, dosage of adsorbent, concentration (C0), and temperature (T), were optimized by Response Surface Methodology (RSM) and Central Composite Designs (CCD). The optimal results show that the importance for adsorption factors is pH > T > C0 > dosage, and the optimal adsorption conditions of PPy-Fe3O4/Kaolin are pH = 7.2, T = 315 K, C0 = 50 mg/L, dosage of 0.05 g/L, and the capacity is 317.1 mg/g. The adsorption process conforms to the pseudo-second-order and Langmuir models. Dubinin-Radushkevich model shows that adsorption process is spontaneous and endothermic. Moreover, the adsorption of mercury by PPy-Fe3O4/Kaolin was achieved mainly through electrostatic attraction, pore diffusion, and chelation between amino functional groups and Hg2+. PPy-Fe3O4/Kaolin has excellent reproducibility, dispersity, and chemical stability, and it is easy to be separated from solution through an external magnetic field. The experiments show that PPy-Fe3O4/Kaolin is an efficient and economical adsorbent towards mercury.

Insight into the interfacial stability and reaction mechanism between gaseous mercury and chalcogen-based sorbents in SO2-containing flue gas.

Chalcogen-based materials have been confirmed to possess large adsorption capacities for gaseous elemental mercury (Hg0) from SO2-containing flue gas. However, the interface reaction mechanisms and the interfacial stability are still ambiguous. Here, we selected some commonly used chalcogen-based sorbents (e.g., X, ZnX, CuX. X = S, Se) to investigate the in-depth reaction mechanisms. The adsorption capacities, structure effect on thermal and surface mercury stability, and interfacial reaction mechanism in the absence/presence of SO2 were evaluated. The experimental results indicated that Cu-chalcogenide had higher Hg0 adsorption capacity and surface Hg-X bonding stability compared with zinc one, while they exhibited an opposite degree of thermal stability. Moreover, all the chalcogenides showed well SO2 tolerance but with a slight difference. Chalcogenides with the same crystal structures, like ZnX or CuX, exhibited similar properties in stability and interfacial Hg0 and SO2 reaction mechanism. X- in chalcogenides have a better affinity to mercury, while in the Hg0 capture process, the existence of multivalent metal elements (like Cu2+ and Cu+) can faster the Hg0 oxidation for the further chemical-adsorption. This work provides a basic understanding of the application for efficiently enriching and recycling gaseous Hg0 from industrial SO2-containing flue gas.

Co-doped ZnS with large adsorption capacity for recovering Hg0 from non-ferrous metal smelting gas as a co-benefit of electrostatic demisters.

The installation of electrostatic demisters (ESDs) makes possible the use of sorbent injection technology for recovering Hg0 from non-ferrous smelting gas. ZnS, as a typical smelting raw material, could be a promising candidate due to the sulfur boding site for mercury. However, the low reaction rate and poor adsorption capacity limited its application. In this study, Co was incorporated into ZnS to enhance adsorption activity for recovering Hg0. Co0.2Zn0.8S exhibited the best Hg0 capture performance among the modified sorbents. The Hg0 adsorption capacity was up to 46.01 mg/g at 50 °C (with 50% breakthrough threshold), and the adsorption rate was as high as 0.017 mg/(g min). Meanwhile, SO2 and H2O had no poison effects on Hg0 adsorption. The chemical adsorption mechanism was proposed, which was Co3+, and sulfur active sites could immobilize Hg0 in the form of stable HgS, following a Mars-Maessen reaction pathway. The spent sorbent will release ultrahigh concentration mercury-containing vapor through the heating treatment, which facilitated centralized recovery of Hg0. Meanwhile, inactivated sorbent can be used as smelting raw material to recover sulfur resources. Therefore, the control of Hg0 emission from non-ferrous smelting gas by Co-adopted ZnS was cost-effective and did not form secondary pollution. Graphical abstract.

Enhancing the catalytic oxidation of elemental mercury and suppressing sulfur-toxic adsorption sites from SO2-containing gas in Mn-SnS2.

It is difficult to stabilize gaseous elemental mercury (Hg°) on a sorbent from SO2-containing industrial flue gas. Enhancing Hg° oxidation and activating surface-active sulfur (S*) can benefit the chemical mercury adsorption process. A Mn-SnS2 composite was prepared using the Mn modification of SnS2 nanosheets to expose more Mn oxidation and sulfur adsorption sites. The results indicate that Mn-Sn2 exhibits better Hg° removal performances at a wide temperature range of 100-250 °C. A sufficient amount of surface Mn with a valance state of Mn4+ is favorable for Hg° oxidation, while the electron transfer properties of Sn can accelerate this oxidation process. Oxidized mercury primary exists as HgS with surface S*. A larger surface area, stable crystal structure, and active valance state of each element are favorable for Hg° oxidation and adsorption. The Mn-SnS2 exhibits an excellent SO2 resistance when the SO2 concentration is lower than 1500 ppm. The effects of H2O and O2 were also evaluated. The results show that O2 has no influence, while H2O and SO2 coexisting in the flue gas have a toxic effect on the Hg° removal performance. The Mn-SnS2 has a great potential for the Hg° removal from SO2-containing flue gas such as non-ferrous smelting gas.

A sulfur-resistant CuS-modified active coke for mercury removal from municipal solid waste incineration flue gas.

Adsorption is a typical method for air pollutant removal from flue gas. A CuS-modified active coke (CuS/AC) sorbent was developed to improve the elemental mercury removal efficiency from municipal solid waste incineration (MSWI) flue gas. The influences of the loading amount of CuS, reaction temperature, and flue gas components including O2, SO2, H2O, and HCl on Hg0 removal efficiency were investigated, respectively. The results showed that the mercury adsorption capacity of CuS/AC(20%) sorbent was about 7.17 mg/g with 50% breakthrough threshold, which is much higher than that of virgin active coke. The analysis of XPS indicated that HgS was the main species of mercury on spent CuS/AC, which implied that adsorption and oxidation were both included in Hg0 removal. S22- played a vital role in the oxidation of physically adsorbed Hg0. Meanwhile, the common components of MSWI flue gas exhibited no significant inhibition effect on Hg0 removal by CuS/AC sorbent. CuS/AC sorbent is a promising sorbent for the mercury removal from MSWI flue gas.

One Step Interface Activation of ZnS Using Cupric Ions for Mercury Recovery from Nonferrous Smelting Flue Gas.

The flue gases with high concentration of mercury are often encountered in the nonferrous smelting industries and the treatment of mercury-containing wastes. To recover mercury from such flue gases, sorbents with enough large adsorption capacity are required to capture and enrich mercury. ZnS is a cheap and readily prepared material, and even can be obtained from its natural ores. In this work, a simple controllable oxidation method-soaking in cupric solution-was developed to improve the interfacial activity of ZnS and its natural ores for Hg0 adsorption. The gaseous Hg0 adsorption capacity of ZnS was enhanced from 0.3 to 3.6 mg·g-1 after such treatment. Further analysis indicated that a new interface rich in S1- ions was formed and provided sufficient active sites for the chemical adsorption of Hg0. In addition, the cyclic Hg0 adsorption and recovery experiments demonstrated that the adsorption performance of spent activated-ZnS was recovered after reactivating sorbents with Cu2+, indicating the recovery of activated interface. Meanwhile, the high concentration of adsorbed mercury at the surface can be collected using a thermal treatment method. Utilization of raw materials from a zinc production process provides a promising and cost-effective method for removing and recovering mercury from nonferrous smelting flue gas.

Facile Synthesis of Polypyrrole-Functionalized CoFe2O4@SiO2 for Removal for Hg(II).

In order to avoid using toxic or harmful operational conditions, shorten synthesis time, enhance adsorption capacity, and reduce operational cost, a novel magnetic nano-adsorbent of CoFe2O4@SiO2 with core⁻shell structure was successfully functionalized with polypyrrole (Ppy). The physical and chemical properties of CoFe2O4@SiO2-Ppy are examined by various means. The as-prepared CoFe2O4@SiO2-Ppy nanomaterial was used to adsorb Hg2+ from water. During the process, some key effect factors were studied. The adsorption process of Hg2+ onto CoFe2O4@SiO2-Ppy was consistent with the pseudo-second-order kinetic and Langmuir models. The Langmuir capacity reached 680.2 mg/g, exceeding those of many adsorbents. The as-prepared material had excellent regeneration ability, dispersibility, and stability. The fitting of kinetics, isotherms, and thermodynamics indicated the removal was endothermic and spontaneous, and involved some chemical reactions. The application evaluation of electroplating wastewater also shows that CoFe2O4@SiO2-Ppy is an excellent adsorbent for Hg2+ ions from water.

Hierarchical Ag-SiO2@Fe3O4 magnetic composites for elemental mercury removal from non-ferrous metal smelting flue gas.

Hierarchical Ag-SiO2@Fe3O4 magnetic composites were selected for elemental mercury (Hg0) removal from non-ferrous metal smelting flue gas in this study. Results showed that the hierarchical Ag-SiO2@Fe3O4 magnetic composites had favorable Hg0 removal ability at low temperature. Moreover, the adsorption capacity of hierarchical magnetic composite is much larger than that of pure Fe3O4 and SiO2@Fe3O4. The Hg0 removal efficiency reached the highest value as approximately 92% under the reaction temperature of 150°C, while the removal efficiency sharply reduced in the absence of O2. The characterization results indicated that Ag nanoparticles grew on the surface of SiO2@Fe3O4 support. The large surface area of SiO2 supplied efficient reaction room for Hg and Ag atoms. Ag-Hg amalgam is generated on the surface of the composites. In addition, this magnetic material could be easily separated from fly ashes when adopted for treating real flue gas, and the spent materials could be regenerated using a simple thermal-desorption method.

Research of mercury removal from sintering flue gas of iron and steel by the open metal site of Mil-101(Cr).

Metal-organic frameworks (MOFs) adsorbent Mil-101(Cr) was introduced for the removal of elemental mercury from sintering flue gas. Physical and chemical characterization of the adsorbents showed that MIL-101(Cr) had the largest BET surface area, high thermal stability and oxidation capacity. Hg0 removal performance analysis indicated that the Hg0 removal efficiency of MIL-101(Cr) increased with the increasing temperature and oxygen content. Besides, MIL-101(Cr) had the highest Hg0 removal performance compared with Cu-BTC, UiO-66 and activated carbon, which can reach about 88% at 250 °C. The XPS and Hg-TPD methods were used to analyze the Hg0 removal mechanism; the results show that Hg0 was first adsorbed on the surface of Mil-101(Cr), and then oxidized by the open metal site Cr3+. The generated Hg2+ was then combined surface adsorbed oxygen of adsorbent to form HgO, and the open metal site Cr2+ was oxidized to Cr3+ by surface active oxygen again. Furthermore, MIL-101(Cr) had good chemical and thermal stability.

Combined effects of Ag and UiO-66 for removal of elemental mercury from flue gas.

The zirconium metal-organic framework material UiO-66 was doped with Ag nanoparticles and investigated for the removal of elemental mercury (Hg0) in flue gas. Physical and chemical characterization of the adsorbents showed that adding Ag did not change the crystal structure and morphology of the UiO-66. Ag doping can improve the redox activity of UiO-66, and the adsorbent exhibited high thermal stability and surface area. Hg0 removal experiments indicated that UiO-66 exhibited the higher performance compared with P25 and activated carbon, and the addition of Ag exhibited a significant synergistic effect with the UiO-66, which had highest Hg0 adsorption capacity (3.7 mg/g) at 50 °C. Furthermore, the Hg0 removal mechanism was investigated, revealing that Hg0 is removed by the formation of an Ag amalgam and channel adsorption at low temperature, and through Ag-activated oxygen oxidation and channel capture at high temperature.

[MoS4]2- Cluster Bridges in Co-Fe Layered Double Hydroxides for Mercury Uptake from S-Hg Mixed Flue Gas.

[MoS4]2- clusters were bridged between CoFe layered double hydroxide (LDH) layers using the ion-exchange method. [MoS4]2-/CoFe-LDH showed excellent Hg0 removal performance under low and high concentrations of SO2, highlighting the potential for such material in S-Hg mixed flue gas purification. The maximum mercury capacity was as high as 16.39 mg/g. The structure and physical-chemical properties of [MoS4]2-/CoFe-LDH composites were characterized with FT-IR, XRD, TEM&SEM, XPS, and H2-TPR. [MoS4]2- clusters intercalated into the CoFe-LDH layered sheets; then, we enlarged the layer-to-layer spacing (from 0.622 to 0.880 nm) and enlarged the surface area (from 41.4 m2/g to 112.1 m2/g) of the composite. During the adsorption process, the interlayer [MoS4]2- cluster was the primary active site for mercury uptake. The adsorbed mercury existed as HgS on the material surface. The absence of active oxygen results in a composite with high sulfur resistance. Due to its high efficiency and SO2 resistance, [MoS4]2-/CoFe-LDH is a promising adsorbent for mercury uptake from S-Hg mixed flue gas.

Novel Effective Catalyst for Elemental Mercury Removal from Coal-Fired Flue Gas and the Mechanism Investigation.

Mercury pollution from coal-fired power plants has drawn attention worldwide. To achieve efficient catalytic oxidation of Hg(0) at both high and low temperatures, we prepared and tested novel IrO2 modified Ce-Zr solid solution catalysts under various conditions. It was found that the IrO2/Ce0.6Zr0.4O2 catalyst, which was prepared using the polyvinylpyrrolidone-assisted sol-gel method, displayed significantly higher catalytic activity for Hg(0) oxidation. The mechanism of Hg(0) removal over IrO2/Ce0.6Zr0.4O2 was studied using various methods, and the Hg(0) oxidation reaction was found to follow two possible pathways. For the new chemisorption-regeneration mechanism proposed in this study, the adsorbed Hg(0) was first oxidized with surface chemisorbed oxygen species to form HgO; the HgO could desorb from the surface of catalysts by itself or react with adsorbed HCl to be release in the form of gaseous HgCl2. O2 is indispensable for the chemisorption process, and the doping of IrO2 could facilitate the chemisorption process. In addition, the Deacon reaction mechanism was also feasible for Hg(0) oxidation: this reaction would involve first oxidizing the adsorbed HCl to active Cl species, after which the Hg(0) could react with Cl to form HgCl2. Additionally, doping IrO2 could significantly improve the Cl yield process. In summary, the novel IrO2 modified catalyst displayed excellent catalytic activity for elemental mercury oxidation, and the proposed reaction mechanisms were determined reasonably.