Asymmetric Coordination of Single-Atom Ru Sites Achieves Efficient N(sp3)-H Dehydrogenation Catalysis for Ammonia Oxidation.

Ruthenium single-atom catalysts have great potential in ammonia-selective catalytic oxidation (NH3-SCO); however, the stable sp3 hybrid orbital of NH3 molecules makes N(sp3)-H dissociation a challenge for conventional symmetrical metallic oxide catalysts. Herein, we propose a heterogeneous interface reverse atom capture strategy to construct Ru with unique asymmetric Ru1N2O1 coordination. Ru1N2O1/CeO2 exhibits intrinsic low-temperature conversion (T100 at 160 °C) compared to symmetric coordinated Ru-based (280 °C), Ir-based (220 °C), and Pt-based (200 °C) catalysts, and the TOF is 65.4 times that of Ag-based catalysts. The experimental and theoretical studies show that there is a strong d-p orbital interaction between Ru and N atoms, which not only enhances the adsorption of ammonia at the Ru1N2O1 position but also optimizes the electronic configuration of Ru. Furthermore, the affinity of Ru1N2O1/CeO2 to water is significantly weaker than that of conventional catalysts (the binding energy of the Pd3Au1 catalyst is -1.19 eV, but it is -0.39 eV for our material), so it has excellent water resistance. Finally, the N(sp3)-H activation of NH3 requires the assistance of surface reactive oxygen species, but we found that asymmetric Ru1N2O1 can directly activate the N(sp3)-H bond without the involvement of surface reactive oxygen species. This study provides a novel principle for the rational design of the proximal coordination of active sites to achieve its optimal catalytic activity in single-atom catalysis.

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.

Roles of the Comproportionation Reaction in SO2 Reduction Using Methane for the Flexible Recovery of Elemental Sulfur or Sulfides.

SO2 reduction with CH4 to produce elemental sulfur (S8) or other sulfides is typically challenging due to high energy barriers and catalyst poisoning by SO2. Herein, we report that a comproportionation reaction (CR) induced by H2S recirculating significantly accelerates the reactions, altering reaction pathways and enabling flexible adjustment of the products from S8 to sulfides. Results show that SO2 can be fully reduced to H2S at a lower temperature of 650 °C, compared to the 800 °C required for the direct reduction (DR), effectively eliminating catalyst poisoning. The kinetic rate constant is significantly improved, with CR at 650 °C exhibiting about 3-fold higher value than DR at 750 °C. Additionally, the apparent activation energy decreases from 128 to 37 kJ/mol with H2S, altering the reaction route. This CR resolves the challenges related to robust sulfur-oxygen bond activation and enhances CH4 dissociation. During the process, the well-dispersed lamellar MoS2 crystallites with Co promoters (CoMoS) act as active species. H2S facilitates the comproportionation reaction, reducing SO2 to a nascent sulfur (Sx*). Subsequently, CH4 efficiently activates CoMoS in the absence of SO2, forming H2S. This shifts the mechanism from Mars-van Krevelen (MvK) in DR to sequential Langmuir-Hinshelwood (L-H) and MvK in CR. Additionally, it mitigates sulfation poisoning through this rapid activation reaction pathway. This unique comproportionation reaction provides a novel strategy for efficient sulfur resource utilization.

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.

Cation Concavities Induced d-Band Electronic Modulation on Co/FeOx Nanostructure to Activate Molecular and Interfacial Oxygen for CO Oxidation.

Cobalt-based catalysts have been identified for effective CO oxidation, but their activity is limited by molecular O2 and interfacial oxygen passivation at low temperatures. Optimization of the d-band structure of the cobalt center is an effective method to enhance the dissociation of oxygen species. Here, we developed a novel Co/FeOx catalyst based on selective cationic deposition to anchor Co cations at the defect site of FeOx, which exhibited superior intrinsic low-temperature activity (100%, 115 °C) compared to that of Pt/Co3O4 (100%, 140 °C) and La/Co2O3 (100%, 150 °C). In contrast to catalysts with oxygen defects, the cationic Fe defect in Co/FeOx showed an exceptional ability to accept electrons from the Co 3d orbital, resulting in significant electron delocalization at the Co sites. The Co/FeOx catalyst exhibited a remarkable turnover frequency of 178.6 per Co site per second, which is 2.3 times higher than that of most previously reported Co-based catalysts. The d-band center is shifted upward by electron redistribution effects, which promotes the breaking of the antibonding orbital *π of the O═O bond. In addition, the controllable regulation of the Fe-Ov-Co oxygen defect sites enlarges the Fe-O bond from 1.97 to 2.02 Å to activate the lattice oxygen. Moreover, compared to CoxFe3-xO4, Co/FeOx has a lower energy barrier for CO oxidation, which significantly accelerates the rate-determining step, *COO formation. This study demonstrates the feasibility of modulating the d-band structure to enhance O2 molecular and interfacial lattice oxygen activation.

Electron Donation from Boron Suboxides via Strong p-d Orbital Hybridization Boosts Molecular O2 Activation on Ru/TiO2 for Low-Temperature Dibromomethane Oxidation.

Low-temperature catalytic oxidation is of significance to the degradation of halogenated volatile organic compounds (HVOCs) to avoid hazardous byproducts with low energy consumption. Efficient molecular oxygen (O2) activation is pivotal to it but usually limited by the insufficient electron cloud density at the metal center. Herein, Ru-B catalysts with enhanced electron density around Ru were designed to achieve efficient O2 activation, realizing dibromomethane (DBM) degradation T90 at 182 °C on RuB1/TiO2 (about 30 °C lower than pristine Ru/TiO2) with a TOFRu value of 0.055 s-1 (over 8 times that of Ru/TiO2). Compared to the limited electron transfer (0.02 e) on pristine Ru/TiO2, the Ru center gained sufficient negative charges (0.31 e) from BOx via strong p-d orbital hybridization. The Ru-B site then acted as the electron donor complexing with the 2π* antibonding orbital of O2 to realize the O2 dissociative activation. The reactive oxygen species formed thereby could initiate a fast conversion and oxidation of formate intermediates, thus eventually boosting the low-temperature catalytic activity. Furthermore, we found that the Ru-B sites for O2 activation have adaptation for pollutant removal and multiple metal availability. Our study shed light on robust O2 activation catalyst design based on electron density adjustment by boron.

Unveiling the Halogenation-Induced Formation of Hg3Se2X2 (X = Cl, Br, and I) Compounds for Multiphase Mercury Cycling.

The interaction between mercury (Hg) and inorganic compounds, including selenium (Se), sulfur (S), and halogens (X = Cl, Br, or I), plays a critical role in the global mercury cycle. However, most previously reported mercury compounds are susceptible to reduction, leading to the release of elemental mercury (Hg0) and causing secondary pollution. In this study, we unveil a groundbreaking discovery that underscores the vital role of halogenation in creating exceptionally stable Hg3Se2X2 compounds. Through the dynamic interplay of Hg, Se, and halogens, an intermediary stage denoted [HgSe]m[HgX2]n emerges, and this transformative process significantly elevates the stabilization of mercury. Remarkably, halogen ions strategically occupy pores at the periphery of HgSe clusters, engendering a more densely packed atomic arrangement of Hg, Se, and halogen components. A marked enhancement in both thermal and acid stability is observed, wherein temperatures ascend from 130 to 300 °C (transitioning from HgSe to Hg3Se2Cl2). This sequence of escalating stability follows the order HgSe < Hg3Se2I2 < Hg3Se2Br2 < Hg3Se2Cl2 for thermal resilience, complemented by virtually absent acid leaching. This innovative compound formation fundamentally alters the transformation pathways of gaseous Hg0 and ionic mercury (Hg2+), resulting in highly efficient in situ removal of both Hg0 and Hg2+ ions. These findings pave the way for groundbreaking advancements in mercury stabilization and environmental remediation strategies, offering a comprehensive solution through the creation of chemically stable precipitates.

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.

Regulation of the Sulfur Environment in Clusters to Construct a Mn-Sn2S6 Framework for Mercury Bonding.

The remarkable chemical activity of metal-sulfur clusters lies in their unique spatial configuration associated with the abundant unsaturated-coordination nature of sulfur sites. Yet, the manipulation of sulfur sites normally requires direct contact with other metal atoms, which inevitably changes the state of the coordinated sulfur. Herein, we facilely construct a Mn-Sn2S6 framework by regulating the sulfur environment of the [Sn2S6]4- cluster with metal ions. Mn-Sn2S6 showed superior removal performance to gaseous elemental mercury (Hg0) at low temperatures (20-60 °C) and exhibited high resistance against SO2. Moreover, Mn-Sn2S6 can completely remove liquid Hg2+ ions with low or high concentrations from acid wastewater. In addition, the adsorption capacities of Mn-Sn2S6 toward Hg0 and Hg2+ reached 21.05 and 413.3 mg/g, respectively. The results of physico-chemical characterizations revealed that compared with Cu2+, Co2+, and Fe2+, the moderate regulation of Mn2+ led to the special porous spherical structure of Mn-Sn2S6 with uniform element distribution, due to the difference of electrode potentials [Eθ(Mn2+/Mn) < Eθ(S/S2-) < Eθ(Sn4+/Sn2+)]. The porous structure was beneficial to Hg0 and Hg2+ adsorption, and the presence of Mn4+/Mn3+ and S1- promoted the oxidation of Hg0, resulting in stable HgS species. The constructed Mn-Sn2S6, thus, is a promising sorbent for both Hg0 ang Hg2+ removal and provides guidelines for cluster-based materials design and tuning.

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.

The Unique CO Activation Effects for Boosting NH3 Selective Catalytic Oxidation over CuOx-CeO2.

Slip NH3 is a priority pollutant of concern to be removed in various flue gases with NOx and CO after denitrification using NH3-SCR or NH3-SNCR, and the simultaneous catalytic removal of NH3 and CO has become one of the new topics in the deep treatment of such flue gases. Synergistic catalytic oxidation of CO and NH3 appears to be a promising method but still has many challenges. Due to the competition for active oxidizing species, CO was supposed to hinder the NH3 selective catalytic oxidation (NH3-SCO). However, it is first found that CO could significantly promote NH3-SCO over the CuOx-CeO2 catalyst. The NH3 conversion rates increased linearly with CO concentrations in the range of 180-300 °C. Specifically, it accelerated by 2.8 times with 10,000 ppm CO inflow at 220 °C. Mechanism studies found that the Cu-O-Ce solid solution was more active for CO oxidation, while the CuOx species facilitated the NH3 dehydrogenation and mitigated the competition of NH3 and CO, further stabilizing the promotion effects. Gaseous CO boosted the generation of active isolated oxygen atoms (Oi) by actuating the Cu+/Cu2+ redox cycle. The enriched Oi facilitated oxidation of NH3 to NO and was conducive to the NH3-SCO via the i-SCR approach. This study tapped the potential of CO for promoting simultaneous catalytic oxidation of coexisting pollutants in the flue gas.

Surface protection method for the magnetic core using covalent organic framework shells and its application in As(III) depth removal from acid wastewater.

Fe3O4-based materials are widely used for magnetic separation from wastewater. However, they often suffer from Fe-leaching behavior under acidic conditions, decreasing their activity and limiting sustainable practical applications. In this study, covalent organic frameworks (COFs) were used as the shell to protect the Fe3O4 core, and the Fe3O4@COF core-shell composites were synthesized for As(III) removal from acid wastewater. The imine-linked COFs can in situ grow on the surface of the Fe3O4 core layer by layer with [COFs/Fe3O4]mol ratio of up to 2:1. The Fe-leaching behavior was weakened over a wide pH range of 1-13. Moreover, such composites keep their magnetic characteristic, making them favorable for nanomaterial separation. As(III) batch adsorption experiments results indicated that, when COFs are used as the shell for the Fe3O4 core, a balance between As(III) removal efficiencies and the thickness of the COF shell exists. Higher As(III) removal efficiencies are obtained when the [COFs/Fe3O4]mol ratios were < 1.5:1, but thicker COF shells were not beneficial for As(III) removal. Such composites also exhibited better As(III) removal performances in the pH range of 1-7. Over a wide pH range, the zeta potential of Fe3O4@COF core-shell composites becomes more positive, which benefits the capture of negative arsenic ions. In addition, thinner surface COFs were favorable for mass transfer and facilitating the reaction of Fe and As elements. Our study highlights the promise of using COFs in nanomaterial surface protection and achieving As(III) depth removal under acidic conditions.

Enhanced simultaneous absorption of NOx and SO2 in oxidation-reduction-absorption process with a compounded system based on Na2SO3.

Oxidation of sulfite and competitive absorption existed in Na2SO3 solution for simultaneous removal of NOx and SO2, inhibited the long-term high-efficiency when used for practical applications. A matching strategy was developed to solve these problems. Antioxidants combination was used to retard the oxidation of antioxidant and enhance inhibition of S(IV) (tetravalent sulfur) oxidation. Hydroquinone (HQ) and sodium thiosulfate (ST) showed a positive synergistic effect on inhibition of S(IV) oxidation. When SO2 concentration was 500 and 2000 ppmV, the addition of 0.1 wt.% HQ and 1 wt.% ST decreased the percentage of S(IV) oxidized by oxygen by over 30% and 40%, respectively. Alkali (Na2CO3) alleviated the competitive absorption between NOx and SO2. Moreover, Na2CO3 exhibited an enhancement effect on the absorption of NOx and SO2 when coupled with anti-oxidants. While the increase of oxygen pressure accelerated the oxidation of S(IV), the anti-oxidants can retard the oxidation. The measurement of pH suggested the removal efficiency of NOx highly depended on SO32⁻ concentration rather than pH. The further investigation of the mechanism suggested the match effect was related to the interaction between ST and the intermediate product of HQ. The match strategy holds a potential for application of SO32⁻ to denitration.

Strengthen the Affinity of Element Mercury on the Carbon-Based Material by Adjusting the Coordination Environment of Single-Site Manganese.

Mercury, as a highly poisonous pollutant, poses a severe threat to the global population. However, the removal of Hg0 can only be carried out at below 100 °C due to the weak binding of the adsorbent. Herein, a series of carbon-based materials with different coordination environments and atomic dispersion of single-site manganese were prepared, and their elemental mercury removal performance was systematically investigated. It was demonstrated that the coordination environment around manganese determines its electronic structure and size, thus affecting its affinity with mercury. The obtained best adsorbents atomically dispersed Mn with atom size near 0.2 nm, achieves high Hg0 removal efficiency and over 13 mg/g Hg0 adsorption capacity at 200 °C. And the SO2 resistance performance of single atoms (∼0.2 nm) is much better than clusters (∼1-2 nm) because of its high selectivity, that the effect of SO2 is only 3%. Density functional theory (DFT) reveals that Mn with four-nitrogen atoms (Mn-N4-C═O) is more active than other number nitrogen coordination materials. Moreover, the presence of carboxyl groups around manganese also promotes affinity for Hg0. This work might shed new light on the enhancement of Hg0 affinity in carbon-based materials and the rational design of the coordination structure of the tunable Hg0 activities.

Metastable Facet-Controlled Cu2WS4 Single Crystals with Enhanced Adsorption Activity for Gaseous Elemental Mercury.

Purposively designing environmental advanced materials and elucidating the underlying reactivity mechanism at the atomic level allows for the further optimization of the removal performance for contaminants. Herein, using well facet-controlled I-Cu2WS4 single crystals as a model transition metal chalcogenide sorbent, we investigated the adsorption performance of the exposed facets toward gaseous elemental mercury (Hg0). We discovered that the decahedron exhibited not only facet-dependent adsorption properties for Hg0 but also recrystallization along the preferential [001] growth direction from a metastable state to the steady state. Besides, the metastable crystals with a predominant exposure of {101} facets dominated the promising adsorption efficiency (about 99% at 75 °C) while the saturated adsorption capacity was evaluated to be 2.35 mg·g-1. Subsequently, comprehensive characterizations and X-ray adsorption fine structure (XAFS), accompanied by density functional theory (DFT) calculations, revealed that it might be owing to the coordinatively unsaturated local environment of W atoms with S defects and the surface relative stability of different facets, which could be affected by the change in surface atom configuration. Hence, the new insight into the facet-dependent adsorption property of transition metal chalcogenide for Hg0 may have important implications, and the atomic-level study directly provides instructions for development and design of highly efficient functional materials.

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.

Atomically Dispersed Manganese on a Carbon-Based Material for the Capture of Gaseous Mercury: Mechanisms and Environmental Applications.

A novel, atomically dispersed carbon-based sorbent was synthesized by anchoring manganese atoms with N atoms for the capture of gaseous elemental Hg (Hg0). Oxygen atoms were also introduced into the synthesis process to adjust the oxidizing ability of the Mn atoms. High-valence Mn (Mn4+) anchored by the O and N atoms (Mn-O/N-C) in the carbon-based materials provided more exposed active sites. The mercury removal efficiency of the composite exceeded 99%. The composite with a Mn loading of 0.9 wt % exhibited high affinity for Hg0, and the capacity for Hg0 adsorption within 275 min at room temperature reached 16.95 mg·g-1. The Mn utilization was ∼56.61%, which is much larger than that of reported Mn-based oxide sorbents. The atomic-level distribution of Mn was well evidenced by aberration-corrected high-angle annular darkfield scanning transmission electron microscopy. Density functional theory calculations were conducted to evaluate the energy for adsorption of Hg0 on Mn-O/N-C. The results indicated that the amount of N and O atoms in the Mn coordination environment determined the Hg0 adsorption energy, and the presence of five optimized Mn adsorption structures in Mn-O/N-C was confirmed by Hg temperature-programmed desorption analysis. These materials may be utilized for mercury removal from disposal sites with high concentrations of mercury, broken mercury-containing lamps, or mercurial thermometers. The strategy of atomic dispersion during synthesis of the materials and adjusting the oxidizing ability in the single-atom strategy may be helpful for the development of environmentally benign functional materials.

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.

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.

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.