Search

The gaseous elemental mercury (Hg 0 ) emitted from coal-fired flue gas is extremely harmful to the atmospheric environment and human health. In this study, a 2D/2D Bi 2 MoO 6 (2 0 0)/g-C 3 N 4 heterojunction photocatalyst was synthesized and exhibited a high visible-light driven Hg 0 removal efficiency up to 99.5% in an atmosphere consisting of N 2 , O 2 (6%), CO 2 (12%), NO (100 ppm), SO 2 (800 ppm), and H 2 O (5%). The introduction of surfactant CTAB led to further exposure of the highly active (2 0 0) crystal facet of Bi 2 MoO 6 , with a higher reactive oxygen species ratio than the original mainly exposed (1 3 1) crystal facet, and inhibited the agglomeration of Bi 2 MoO 6 , thereby greatly reducing the micro-thickness and improving the specific surface area. The smaller thickness effectively promoted the separation of photoinduced carriers and the speed of transfer to the interface. Additionally, through EPR characterization and work function calculation, we observed that the change in the exposed crystal facet regulated the Fermi level of Bi 2 MoO 6 nanosheets, altering the direction of the built-in electric field at the interface with g-C 3 N 4 . This formation of an S-scheme 2D/2D Bi 2 MoO 6 (2 0 0)/g-C 3 N 4 heterostructure further facilitated the recombination of unintentional carriers and strengthened the separation and catalysis of effective photogenerated carriers. To a certain extent, this work provides a guidance for the research of photocatalysis to achieve efficient and sustainable mercury removal from coal-fired flue gas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The elemental mercury was catalytically removed by V 2 O 5 /TiO 2 and Ce doped V 2 O 5 /TiO 2 catalysts under the UV irradiation at 30-160 °C to determine whether the catalysts could simultaneously have both thermo- and photo-catalytic activities. The physicochemical properties of catalysts were characterized by XRD, SEM, EDX, BET, XPS, UV-visible, PER and EIS. The experimental results demonstrated that V 2 O 5 /TiO 2 and Ce-doped catalysts possessed both thermo- and photo-catalytic reactivities. A suitable reaction temperature (120 °C) and UV light had promoting effects on mercury removal efficiency. In addition, owing to the high oxidation capability as well good oxygen storage performance of Ce 4+ , Ce doping could greatly improve the mercury removal properties of the catalyst, reduce the inhibition of SO 2 and make NO the component with enhanced effect. Ce doping also had the capability of enhancing the light absorption intensity in the UV region as well as the separation rate of photoinduced carriers. Finally, DFT calculations of V-Ti and Ce-V-Ti for Hg 0 removal were investigated to further verify the experimental conclusion., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Mercury emitted from human activities has received increasing attention because of its extreme toxicity, persistence and bioaccumulation. The development of highly-efficient sorbent with abundant active sites that exhibit high affinity toward Hg 0 is the key challenge for elemental mercury capture at low temperature. Herein, Cu-In spinel-type sulfides were synthesized through a hydrothermal synthesis. The Hg 0 removal performance of Cu x In 2-x S 2 sorbents was evaluated in the temperature range of 75 °C to 175 °C. The synthesized Cu x In 2-x S 2 sorbents showed excellent performance for Hg 0 removal at low temperatures, which perfectly matches the optimal temperature of flue gas at the downstream of desulfurization system. Hg 0 removal efficiency of Cu x In 2-x S 2 sorbents significantly improved as the Cu proportion increased. CuInS 2 sorbent showed superior mercury removal performance, the mercury removal efficiency reached 99.6% at 125 °C. O 2 and NO showed a slight inhibition on Hg 0 capture. The coexistence of SO 2 and H 2 O showed no obvious negative effects on Hg 0 removal. The CuInS 2 sorbent displayed a superior tolerance to SO 2 and H 2 O. TPD and XPS analyses demonstrated that the adsorbed mercury mainly existed in the form of mercuric sulfides (HgS). Hg 0 adsorption over CuInS 2 sorbent occurred via the Mars-Maessen mechanism. In this mechanism, Hg 0 vapor was physically adsorbed on CuInS 2 sorbent and then converted to HgS. This study provides future potential for applying Cu x In 2-x S 2 sorbents to capture gaseous mercury at low temperature., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Reduction of mercury emission from coal combustion is a serious task for public health and environmental societies. Herein, Ce-doped TiO 2 (Ce/TiO 2 ) catalyst coupling with a novel optical fiber monolith reactor was applied to efficiently remove elemental mercury (Hg 0 ) from coal-fired flue gas. Under the optimal operation condition (i.e., 1.5 mW/cm 2 UV light, 90 °C), above 95% of Hg 0 removal efficiency was attained over the optical fiber monolith reactor coating with 3.40 g/m 2 Ce/TiO 2 catalyst. The effects of flue gas compositions on Hg 0 removal performance were clarified systematically. Gaseous O 2 replenished the surface oxygen, hence maintaining the production of free radicals and promoting the removal of Hg 0 . SO 2 , HCl, and NO inhibited Hg 0 removal in the absence of O 2 due to the competitive adsorption and consumption of free radicals. However, SO 2 and HCl significantly enhanced Hg 0 removal with the participation of O 2 , while NO exhibited obviously inhibitory effect even with the assistance of O 2 . H 2 O also decreased the Hg 0 oxidation capacity owing to the competitive adsorption and reduction of HgO. The optical fiber monolith reactor exhibited much superior Hg 0 removal capacity than the powder reactor. Utilization of Ce/TiO 2 catalyst coupling with an optical fiber monolith reactor provides a cost-effective method for removing Hg 0 from coal-fired flue gas.

Photocatalytic oxidation is an attractive method for Hg-rich flue gas treatment. In the present study, a novel cerium-based TiO 2 nanofibers was prepared and selected as the catalyst to remove mercury in flue gas. Accordingly, physical/chemical properties of those nanofibers were clarified. The effects of some important parameters, such as calcination temperature, cerium dopant content and different illumination conditions on the removal of Hg 0 using the photocatalysis process were investigated. In addition, the removal mechanism of Hg 0 over cerium-based TiO 2 nanofibers focused on UV irradiation was proposed. The results show that catalyst which was calcined at 400 °C exhibited better performance. The addition of 0.3 wt% Ce into TiO 2 led to the highest removal efficiency at 91% under UV irradiation. As-prepared samples showed promising stability for long-term use in the test. However, the photoluminescence intensity of nanofibers incorporating ceria was significantly lower than TiO 2 , which was attributed to better photoelectron-hole separation. Although UV and O 2 are essential factors, the enhancement of Hg 0 removal is more obviously related to the participation of catalyst. The coexistence of Ce 3+ and Ce 4+ , which leads to the efficient oxidation of Hg 0 , was detected on samples. Hg 2+ is the final product in the reaction of Hg 0 removal. As a consequence, the emissions of Hg 0 from flue gas can be significantly suppressed. These indicate that combining photocatalysis technology with cerium-based TiO 2 nanofibers is a promising strategy for reducing Hg 0 efficiently., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A catalyst composed of manganese oxides supported on titania (MnO x /TiO 2 ) synthesized by a sol-gel method was selected to remove nitric oxide and mercury jointly at a relatively low temperature in simulated flue gas from coal-fired power plants. The physico-chemical characteristics of catalysts were investigated by X-ray fluorescence (XRF), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses, etc. The effects of Mn loading, reaction temperature and individual flue gas components on denitration and Hg 0 removal were examined. The results indicated that the optimal Mn/Ti molar ratio was 0.8 and the best working temperature was 240°C for NO conversion. O 2 and a proper ratio of [NH 3 ]/[NO] are essential for the denitration reaction. Both NO conversion and Hg 0 removal efficiency could reach more than 80% when NO and Hg 0 were removed simultaneously using Mn0.8Ti at 240°C. Hg 0 removal efficiency slightly declined as the Mn content increased in the catalysts. The reaction temperature had no significant effect on Hg 0 removal efficiency. O 2 and HCl had a promotional effect on Hg 0 removal. SO 2 and NH 3 were observed to weaken Hg 0 removal because of competitive adsorption. NO first facilitated Hg 0 removal and then had an inhibiting effect as NO concentration increased without O 2 , and it exhibited weak inhibition of Hg 0 removal efficiency in the presence of O 2 . The oxidation of Hg 0 on MnO x /TiO 2 follows the Mars-Maessen and Langmuir-Hinshelwood mechanisms., (Copyright © 2016. Published by Elsevier B.V.)

Novel magnetic biochars (MBC) were prepared by one-step pyrolysis of FeCl 3 -laden biomass and employed for Hg 0 removal in simulated combustion flue gas. The sample characterization indicated that highly dispersed Fe 3 O 4 particles could be deposited on the MBC surface. Both enhanced surface area and excellent magnetization property were obtained. With the activation of FeCl 3 , more oxygen-rich functional groups were formed on the MBC, especially the C═O group. The MBC exhibited far greater Hg 0 removal performance compared to the nonmagnetic biochar (NMBC) under N 2 + 4% O 2 atmosphere in a wide reaction temperature window (120-250 °C). The optimal pyrolysis temperature for the preparation of MBC is 600 °C, and the best FeCl 3 /biomass impregnation mass ratio is 1.5 g/g. At the optimal temperature (120 °C), the Fe 1.5 MBC 600 was superior in both Hg 0 adsorption capacity and adsorption rate to a commercial brominated activated carbon (Br-AC) used for mercury removal in power plants. The mechanism of Hg 0 removal was proposed, and there are two types of active adsorption/oxidation sites for Hg 0 : Fe 3 O 4 and oxygen-rich functional groups. The role of Fe 3 O 4 in Hg 0 removal was attributed to the Fe 3+ (t) coordination and lattice oxygen. The C═O group could act as act as electron acceptors, facilitating the electron transfer for Hg 0 oxidation.

Cobalt oxide loaded magnetospheres catalyst from fly ash (Co-MF catalyst) showed good mercury removal capacity and recyclability under air combustion flue gas in our previous study. In this work, the Hg(0) removal behaviors as well as the involved reactions mechanism were investigated in oxyfuel combustion conditions. Further, the recyclability of Co-MF catalyst in oxyfuel combustion atmosphere was also evaluated. The results showed that the Hg(0) removal efficiency in oxyfuel combustion conditions was relative high compared to that in air combustion conditions. The presence of enriched CO2 (70%) in oxyfuel combustion atmosphere assisted the mercury oxidation due to the oxidation of function group of C-O formed from CO2. Under both atmospheres, the mercury removal efficiency decreased with the addition of SO2, NO, and H2O. However, the enriched CO2 in oxyfuel combustion atmosphere could somewhat weaken the inhibition of SO2, NO, and H2O. The multiple capture-regeneration cycles demonstrated that the Co-MF catalyst also present good regeneration performance in oxyfuel combustion atmosphere.

To remove Hg(0) in coal combustion flue gas and eliminate secondary mercury pollution of the spent catalyst, a new regenerable magnetic catalyst based on cobalt oxide loaded magnetospheres from fly ash (Co-MF) was developed. The catalyst, with an optimal loading of 5.8% cobalt species, attained approximately 95% Hg(0) removal efficiency at 150 °C under simulated flue gas atmosphere. O2 could enhance the Hg(0) removal activity of magnetospheres catalyst via the Mars-Maessen mechanism. SO2 displayed an inhibitive effect on Hg(0) removal capacity. NO with lower concentration could promote the Hg(0) removal efficiency. However, when increasing the NO concentration to 300 ppm, a slightly inhibitive effect of NO was observed. In the presence of 10 ppm of HCl, greater than 95.5% Hg(0) removal efficiency was attained, which was attributed to the formation of active chlorine species on the surface. H2O presented a seriously inhibitive effect on Hg(0) removal efficiency. Repeated oxidation-regeneration cycles demonstrated that the spent Co-MF catalyst could be regenerated effectively via thermally treated at 400 °C for 2 h.

MnO(x)-CeO(2) mixed-oxide supported on TiO(2) (Mn-Ce/Ti) was synthesized by an ultrasound-assisted impregnation method and employed to oxidize elemental mercury (Hg(0)) at 200°C in simulated coal combustion flue gas. Over 90% of Hg(0) oxidation was achieved on the Mn-Ce/Ti catalyst at 200°C under simulated flue gas representing those from burning low-rank coals with a high gas hourly space velocity of 60,000 h(-1). Gas-phase O(2) regenerated the lattice oxygen and replenished the chemisorbed oxygen, which facilitated Hg(0) oxidation. HCl was the most effective flue gas component responsible for Hg(0) oxidation. 10 ppm HCl plus 4% O(2) resulted in 100% Hg(0) oxidation under the experimental conditions. SO(2) competed with Hg(0) for active sites, thus deactivating the catalyst's capability in oxidizing Hg(0). NO covered the active sites and consumed surface oxygen active for Hg(0) oxidation, hence limiting Hg(0) oxidation. Water vapor showed prohibitive effect on Hg(0) oxidation due to its competition with HCl and Hg(0) for active adsorption sites. This study provides information about the promotional or inhibitory effects of individual flue gas components on Hg(0) oxidation over a highly effective Mn-Ce/Ti catalyst. Such knowledge is of fundamental importance for industrial applications of the Mn-Ce/Ti catalyst in coal-fired power plants., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Nanofibers prepared by an electrospinning method were used to remove elemental mercury (Hg(0)) from simulated coal combustion flue gas. The nanofibers composed of different metal oxides (MO(x)) including CuO, In(2)O(3), V(2)O(5), WO(3) and Ag(2)O supported on TiO(2) have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersing X-ray (EDX) and UV-vis spectra. The average diameters of these nanofibers were about 200nm. Compared to pure TiO(2), the UV-vis absorption intensity for MO(x)-TiO(2) increased significantly and the absorption bandwidth also expanded, especially for Ag(2)O-TiO(2) and V(2)O(5)-TiO(2). Hg(0) oxidation efficiencies over the MO(x)-TiO(2) nanofibers were tested under dark, visible light (vis) irradiation and UV irradiation, respectively. The results showed that WO(3) doped TiO(2) exhibited the highest Hg(0) removal efficiency of 100% under UV irradiation. Doping V(2)O(5) into TiO(2) enhanced Hg(0) removal efficiency greatly from 6% to 63% under visible light irradiation. Ag(2)O doped TiO(2) showed a steady Hg(0) removal efficiency of around 95% without any light due to the formation of silver amalgam. An extended experiment with 8 Hg(0) removal cycles showed that the MO(x)-TiO(2) nanofibers were stable for removing Hg(0) from flue gas. Factors responsible for the enhanced photocatalytic activities of the MO(x)-TiO(2) nanofibers were also discussed., (Copyright © 2012 Elsevier B.V. All rights reserved.)

CeO(2)-TiO(2) (CeTi) catalysts synthesized by an ultrasound-assisted impregnation method were employed to oxidize elemental mercury (Hg(0)) in simulated low-rank (sub-bituminous and lignite) coal combustion flue gas. The CeTi catalysts with a CeO(2)/TiO(2) weight ratio of 1-2 exhibited high Hg(0) oxidation activity from 150 to 250 °C. The high concentrations of surface cerium and oxygen were responsible for their superior performance. Hg(0) oxidation over CeTi catalysts was proposed to follow the Langmuir-Hinshelwood mechanism whereby reactive species from adsorbed flue gas components react with adjacently adsorbed Hg(0). In the presence of O(2), a promotional effect of HCl, NO, and SO(2) on Hg(0) oxidation was observed. Without O(2), HCl and NO still promoted Hg(0) oxidation due to the surface oxygen, while SO(2) inhibited Hg(0) adsorption and subsequent oxidation. Water vapor also inhibited Hg(0) oxidation. HCl was the most effective flue gas component responsible for Hg(0) oxidation. However, the combination of SO(2) and NO without HCl also resulted in high Hg(0) oxidation efficiency. This superior oxidation capability is advantageous to Hg(0) oxidation in low-rank coal combustion flue gas with low HCl concentration.

In this study, a simple method combining sol-gel and impregnation techniques was employed to synthesize magnetic Cu/MnFe 2 O 4. The resulting material demonstrated outstanding efficiency in removing mercury, achieving over 90% at reaction temperatures ranging from 150 °C to 200 °C. Through Cu incorporation, the Hg0 removal performance of Cu 0.15 MnFe was significantly enhanced, leading to a high adsorption capacity of 70.1 mg/g. This surpasses the capabilities of many previously reported adsorbents and holds great potential for enhancing the stability of Hg recovery efficiency. Furthermore, the presence of O 2 , HCl, and NO further improved the Hg0 removal. Conversely, H 2 O had an mild inhibitory effect on Hg0 removal. Additionally, the introduction of Cu noticeably mitigated the inhibitory impact of SO 2 on mercury removal characteristics and alleviated the issue of SO 2 poisoning in adsorbents. The primary active sites responsible for the oxidation of elemental mercury are the redox reaction between Cu2+/Cu+ and Mn3+/Mn2+, and adsorbed oxygen species. Through the oxidation process, Hg0 is primarily converted into various compounds, including HgO, Hg(NO 3) 2 , HgCl 2 , and HgSO 4. As a result, the prepared magnetic recyclable adsorbent, with its high mercury adsorption capacity, exhibits promising prospects for industrial application in the low-temperature removal of Hg0 from coal-fired flue gas. [Display omitted] • Magnetic Cu/MnFe 2 O 4 adsorbent was prepared using a simple method. • Cu/MnFe 2 O 4 owned a large Hg adsorption capacity of 70.1 mg/g. • The introduction of Cu greatly alleviated SO 2 poisoning in adsorbents. • Cu2+, Mn3+ and O* play a crucial role as active sites for Hg0 oxidation. [ABSTRACT FROM AUTHOR]

Reduction of mercury emission from coal combustion is a serious task for public health and environmental societies. Herein, Ce-doped TiO2 (Ce/TiO2) catalyst coupling with a novel optical fiber monolith reactor was applied to efficiently remove elemental mercury (Hg0) from coal-fired flue gas. Under the optimal operation condition (i.e., 1.5 mW/cm2 UV light, 90 °C), above 95% of Hg0 removal efficiency was attained over the optical fiber monolith reactor coating with 3.40 g/m2 Ce/TiO2 catalyst. The effects of flue gas compositions on Hg0 removal performance were clarified systematically. Gaseous O2 replenished the surface oxygen, hence maintaining the production of free radicals and promoting the removal of Hg0. SO2, HCl, and NO inhibited Hg0 removal in the absence of O2 due to the competitive adsorption and consumption of free radicals. However, SO2 and HCl significantly enhanced Hg0 removal with the participation of O2, while NO exhibited obviously inhibitory effect even with the assistance of O2. H2O also decreased the Hg0 oxidation capacity owing to the competitive adsorption and reduction of HgO. The optical fiber monolith reactor exhibited much superior Hg0 removal capacity than the powder reactor. Utilization of Ce/TiO2 catalyst coupling with an optical fiber monolith reactor provides a cost-effective method for removing Hg0 from coal-fired flue gas. [ABSTRACT FROM AUTHOR]

Trace elements (TEs) in coal result in substantial pollutant emissions and cause serious damage to the ecological environment and human health in China. The emission and control of TEs, especially mercury, during coal combustion are of significant concern, and extensive studies have been performed in China in recent years. This paper reviews the emission characteristics and control strategies of mercury and other TEs during coal combustion in China. The occurrence of TEs in Chinese coals, including the average content of TEs in Chinese coals, the distribution of TEs in Chinese coals from different coal-forming periods, coal ranks, and coal-bearing regions are summarized. The emission characteristics of five specific TEs (Hg, As, F, Se, and Cr) during coal combustion in China are reviewed in detail. Effects of the coal type, combustion temperature, and combustion mode on the partitioning behaviour and emission characteristics of TEs are discussed. The effects of existing air pollution control devices of coal-fired power plants in China on the speciation and emission of TEs are discussed comprehensively. Various sorbents, such as activated carbon, fly ash, calcium-based sorbents, metal oxides, and mineral sorbents, used for TE removal are also summarized. Moreover, the removal performance of different sorbents for capturing certain TEs is compared comprehensively. Finally, future work for TE emission control in China is proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Compare mercury removal performance of biochar pretreated by hydrothermal technique and wet impregnation. • Mercury removal performance for biochar pretreated by hydrothermal technique reached 90%. • Hydrothermal pretreatment enhanced thermolysis reaction intensity of biomass and extended the specific surface area. • Hydrothermal pretreatment could promote the construction of oxygen-containing active sites. To further widen the specific surface area and enrich functional groups of biochar for improving the mercury removal performance, this paper compared the difference between wet impregnation and hydrothermal pretreatment to preload ferric chloride on active sites construction of biochar surface. Through systematically evaluating the physicochemical properties of biochar modified by various methods, the mechanism of mercury removal was analyzed. The results indicated that the hydrothermal pretreatment at 180 °C could widen the specific surface area of the precursor benefiting for modifiers adsorption and render the apparent activation energy reduced to 34.11 kJ/mol, causing more intense thermolysis reaction during carbonization. In this way, the specific surface of biochar reached to 282.4 m2/g and a more abundant porous structure was constructed. Additionally, after hydrothermal pretreatment, the proportion of chemisorbed oxygen and C O bonds on the surface of biochar was significantly promoted, facilitating the formation of HgO. The improvement of both physical structure and chemical properties of biochar together increases the mercury removal efficiency to over 90 % under the N 2 atmosphere. [ABSTRACT FROM AUTHOR]

Abstract: A novel TiO2-aluminum silicate fiber (TAS) nanocomposite, synthesized by a sol–gel method, is proposed to use as a photocatalyst for the removal of multiple pollutants. The photocatalyst has been characterized by XRD, SEM, EDX, UV–Vis spectra and BET. The TAS calcined at 500°C exhibited the biggest BET surface area and highest photocatalytic activity and was used as the photocatalyst for subsequent experiments. The oxidation and removal efficiencies of SO2, NO and elemental mercury (Hg0) in simulated coal combustion flue gas by the TAS catalyst were tested under UV irradiation. Experiments were conducted in a fixed-bed reactor at temperatures ranging from 30 to 120°C. In simulated flue gas (4% O2, 12% CO2, 2% H2O, 400ppm SO2, 50ppm NO), the removal efficiencies for SO2, NO and Hg0 at 120°C and with UV intensity of 3mWcm−2 can reach 33%, 31% and 80%, respectively. NO inhibited SO2 oxidation due to its competition for active adsorption sites. SO2 also had a prohibitive effect on NO removal. In contrast, SO2 was found to have a promotional effect on Hg0 oxidation due to the formation of HgSO4. NO inhibited the photocatalytic removal of mercury. During the simultaneous removal of SO2, NO and Hg0 on TAS, the photocatalytic oxidation efficiency decreased from 30 to 120°C. O2 exhibited a promotional effect on the photocatalytic oxidation due to the formation of lattice oxygen. However, the addition of water vapor to the simulated flue gas inhibited the oxidation of SO2, NO and Hg0. The UV intensity was the most important factor in the photocatalytic oxidation. Our discussion on the possible reaction mechanism provides some useful information for developing effective photocatalysts to oxidize SO2, NO and Hg0 in simulated coal combustion flue gas. [Copyright &y& Elsevier]

The abatement of mercury from oxyfuel combustion flue gas should be paid special attention due to the metal embrittlement and aluminum corrosion for CO 2 compression device. The effects of enriched CO 2 and H 2 O in oxyfuel combustion atmosphere on mercury removal over biochar (BC) and magnetic biochar (MBC) was studied. Hg0 was firstly captured by physical adsorption and then oxidized to various mercury compounds. A large amount of organic groups, especially C O group, were formed with the assistance of enriched CO 2. As a result, more Hg0 was oxidized over BC and more organic Hg (Hg-OM) was formed on BC and MBC. However, the content of chemisorbed oxygen on MBC was reduced under oxyfuel combustion atmosphere, hence reducing the formation of HgO on MBC compared with air combustion atmosphere. The enriched H 2 O significantly inhibited the removal of mercury over MBC. Chlorine was demonstrated as the most significant active components for mercury removal, since HgCl 2 was the dominant species on MBC. This work clarified the effects of enriched CO 2 and H 2 O on Hg0 adsorption over BC and MBC, which is essential for further improving the adsorption activity. [ABSTRACT FROM AUTHOR]

The regeneration performance of spent catalyst after mercury removal as well as the involved reaction mechanism was investigated. The effects of restoration with or without O 2 and/or HCl, O 2 and HCl concentration, regeneration temperature, and heating rate on regeneration performance were studied, respectively. The results suggested that two steps were essential in the regeneration process: (1) releasing the sulfur and mercury species adsorbed on the catalyst; (2) restoring the surface chemistry of catalyst by O 2 and HCl. Optimal regeneration performance of spent catalyst was attained after thermal desorption at 400 °C and following by the restoration of O 2 and HCl. The changes in surface chemistry of catalyst revealed that the sulfur and mercury species could be fully released by heating at 400 °C, and the deactivated adsorption sites was exposed. With the assistance of O 2 and HCl, the surface chemistry of Cu and Cl was restored close to original CuCl 2 . Four cycles of mercury adsorption−catalyst regeneration showed that the mercury removal capacity did not vary appreciably with respect to fresh catalyst after multiple regeneration. [ABSTRACT FROM AUTHOR]

The Hg 0 adsorption and oxidation sites on the CuCl 2 -MF catalyst as well as the role of atomic Cu and Cl in Hg 0 removal were identified by a temperature programmed desorption (TPD) experiment. The reaction mechanism with the participation of O 2 and HCl was investigated. The changes in surface chemistry of fresh, spent and in situ pretreated catalyst with O 2 and/or HCl were investigated by EPR and XPS to better understand the intermediate reaction products and steps. The results suggested that different mercury adsorption sites are existed on the catalyst: Cl adsorption sites and Cu adsorption sites. The binding energy of mercury on the Cu adsorption sites is higher than that on the Cl adsorption sites. O 2 and HCl significantly affected the state of Cu and Cl on the spent catalyst. The interaction between Hg 0 and CuCl 2 with the participation of O 2 and/or HCl follows three steps mechanism: (1) the reduction of CuCl 2 to CuCl for the interaction with Hg 0 , (2) the reoxidation of CuCl for the interaction with O 2 forming an intermediate copper oxygen chloride species, (3) the rechlorination of oxychloride species resulting in the restoration of CuCl 2 . This demonstrated that the interaction between Hg 0 and CuCl 2 is a cycle when O 2 and HCl are contained in the reaction system. [ABSTRACT FROM AUTHOR]

To remove Hg 0 from coal combustion flue gas and eliminate secondary pollution of spent sorbent, a novel magnetic catalyst based on CuCl 2 modified magnetospheres from fly ash (CuCl 2 -MF) was developed. The solubility tests, electron paramagnetic resonance (EPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and physical property measurement system with vibrating sample magnetometer (PPMS-VSM) were employed to characterize the catalyst. The effects of CuCl 2 loading value and reaction temperature on Hg 0 removal performance were studied using a laboratory-scale fixed-bed reactor. The results suggested that the CuCl 2 loaded on the support is present mostly in an amorphous phase. Different copper coordinations are existed in the catalyst with different Cu loading: at low Cu loading, isolated Cu 2+ ions existed in a chlorine-free coordination; at high Cu loading, associated Cu 2+ ions existed in a chlorine-enriched coordination. The catalyst with optimal loading 6% CuCl 2 attained the highest Hg 0 removal efficiency (90.6%) at 150 °C. The chlorine-enriched coordination acted as the active adsorption sites for Hg 0 , while the chlorine-free coordination is inactive for Hg 0 removal. The CuCl 2 -MF catalyst showed good resistance to SO 2 for Hg 0 removal in the presence of HCl. Further, the management method for spent catalyst containing mercury was proposed, and the economic analysis of the technology was also conducted. [ABSTRACT FROM AUTHOR]

[Display omitted] • An efficient mercury adsorption and recovery agent was designed. • The mercury removal efficiency of different forms of Se were compared. • The morphology and particle size of HgSe generation were explored. • Designed a mercury recovery route to improve the purity of HgSe. Mercury, is a highly toxic chemical that poses serious hazards to both humans and the environment to be controlled. In this paper, Different Se forms have great varying performance of gaseous mercury(Hg0) removal. Nano-amorphous red selenium(ar-Se) has an excellent adsorption effect on Hg0 successfully synthesized by one step oxidation reduction. The factors to ar-Se such as flue gas components, temperature, gas flow rate, and pH affecting mercury removal effect were investigated. The results showed that the ar-Se achieved high utilization (>74.9 %) and mercury affinity (>97 %) at room temperature. Mercury removal rate was almost unaffected by gas components at room temperature, and it kept a stable mercury adsorption in long-time gaseous mercury recovery experiments, which responded to the high electron activity on its surface. Long-range periodic structures with no regular atomic arrangement decide ar-Se in an active state having high specific surface area, surface activity, good dispersion. The HgSe nanoparticles(NPs) was formed by the adsorption of gaseous mercury onto ar-Se. For further recycling of mercury, a recovery route for HgSe has been proposed and oxygen was found having a strong influence on the production of HgSe. [ABSTRACT FROM AUTHOR]

Highlights: [•] Density functional theory is used to study Hg oxidation mechanism. [•] The surface is represented by periodic model, and different sites are considered. [•] The electronic structural changes before and after adsorption are studied. [•] The Hg oxidation reaction occurs through a Langmuir–Hinshelwood mechanism. [•] The energy profile and the transition states and intermediates are examined. [ABSTRACT FROM AUTHOR]

• Two-dimensional layered Bi 2 WO 6 nanosheets were prepared using a hydrothermal method. • C 2 /2D-BWO exhibits a photocatalytic mercury removal efficiency of up to 86.3 %. • The effects of SO 2 and NO in flue gas on Hg oxidation were also studied. • The experiments and DFT calculations showed that CQDs improved the photoactivity of 2D-BWO. Photocatalytic technology has the advantages of environmental friendliness, low energy consumption, and fast reaction speed, which can be applied in the field of visible light mercury removal. High stability and narrow bandgap are fundamental factors for ideal semiconductor photocatalysts. A novel method of hydrothermal synthesis of CQDs/2D-BWO composite catalyst to improve the oxidation efficiency of elemental mercury was proposed. The morphology, physicochemical properties, and optical performance of the materials were fully characterized. The experiment of Hg oxidation efficiency under visible light showed that C 2 /2D-BWO exhibited a Hg removal efficiency of was as high as 86.3 % under visible light and adequate cyclic stability. The effects of SO 2 and NO on Hg oxidation were also studied, and the reasons for the improved of photocatalytic activity of CQDs on 2D-BWO were analyzed based on DFT calculations. The reaction mechanism of the catalytic oxidation of Hg by C 2 /2D-BWO was proposed, and C 2 /2D-BWO was found to be an efficient and stable visible light catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • Swirl diffusion strategy boosts Hg removal effectiveness of magnetospheres injector. • A mathematical model was established to predict the Hg removal efficiency from CC-MF. • Particle coverage increased by 51%, with a Hg removal efficiency of up to 88.7%. • The optimal operating parameters of the CC-MF swirl injector device were determined. The emissions of mercury from coal-fired flue gas poses a major threat to public health and ecosystems. Modified magnetospheres (CC-MF) mercury removal technology provides an economical, reusable, and eco-friendly solution, overcoming the drawbacks of conventional activated carbon injection (ACI) techniques. To address the issues of inadequate particle diffusion and uneven injection in traditional mercury removal injectors, this study developed a single-hole swirl injector. Furthermore, a mathematical model for mercury removal was developed and imported in the form of a UDF into Fluent for the evaluation of section coverage rate and mercury removal efficiency. The simulation results demonstrated that the section coverage rate of the swirl injector improved by 51.0%, reaching 81.0% compared to the direct injector. Additionally, the mercury removal efficiency increased by 41.3%, reaching 88.7%. This work identified the optimal operational parameters for the CC-MF mercury removal system, providing valuable insights for its practical application. [ABSTRACT FROM AUTHOR]

Fe-modified MnO x /TiO 2 (Fe-MnO x /TiO 2 ) was synthesized by a sol-gel method and employed as the catalyst of selective catalytic reduction (SCR) for removing NO and mercury simultaneously from coal combustion flue gas. The experimental results demonstrated that Fe doping modified both NO and Hg 0 removal performance of the catalyst. The optimal temperature for NO conversion was 200–250 °C, exhibiting good low-temperature activity, and lower temperature was also beneficial for Hg 0 removal. The promotion of HCl on Hg 0 removal efficiency was enhanced and the inhibitions of SO 2 and NH 3 were impaired after Fe doping on the catalyst. Effects of O 2 , NO and H 2 O on Hg 0 removal efficiencies over MnO x /TiO 2 and Fe-MnO x /TiO 2 were all similar with each other. NO conversion and Hg 0 removal efficiency could reach 76.8% and 65.6%, respectively, in simulated coal-fired flue gas at 250 °C and be maintained for a relatively long time. The modification mechanism of the Fe doping was investigated by characterization methods including BET, XRD, H 2 -TPR and XPS. The results showed that the introduction of Fe improved the BET surface area, the dispersity of the metal oxides, the redox behavior and surface concentrations of chemisorbed oxygen and Mn 4+ of the catalysts, which was in favor of the catalytic activity. Meanwhile, Mn 4+ could be protected by the existence of Fe to some extent when exposed to SO 2 so that the sulfur resistance of the catalyst was strengthened as well. [ABSTRACT FROM AUTHOR]

Experimental studies on Hg 0 removal by CuCl 2 modified magnetospheres (Cu 6 –MF) injection were performed in an entrained flow reactor system. The factors affecting the Hg 0 removal efficiency were investigated, including the initial Hg 0 concentration, sorbent concentration in flue gas, sorbent particle size, sorbent residence time in flue gas, and flue gas temperature. The results indicated that, as the raise of initial Hg 0 concentration, the Hg 0 removal efficiency increased. The Hg 0 removal efficiency also increased with the increase of sorbent residence time and sorbent concentration in flue gas. When the residence time was 1.61 s and the sorbent concentration was 1.09 g/m 3 , the Hg 0 removal efficiency could reach to 80.6%. However, with the further increase of residence time and sorbent concentration, the Hg 0 removal efficiency did not increase continuously. The smaller particle size was favorable for the Hg 0 removal. In the industrial application, the particle size could be selected as 45–74 μm when comprehensively considering the Hg 0 removal efficiency, the cost of sorbent preparation, and other factors. The acid flue gases have negligible impacts on Hg 0 removal, while moisture plays a slightly negative role in Hg 0 removal under SFG atmosphere. With the superior Hg 0 removal performance, the Cu 6 –MF sorbent may presents great potentials for Hg 0 removal in coal-fired power plants. [ABSTRACT FROM AUTHOR]

Samples of magnetic iron–manganese binary oxide supported on activated carbon fiber (Fe 3−x Mn x O 4 /CNF) were prepared for Hg 0 removal from flue gas. The results showed that the Hg 0 removal performance of Fe 3−x Mn x O 4 /CNF was significantly promoted with the increase of Mn incorporating content into Fe 3 O 4 spinel structure. The optimal sample of Fe 2 MnO 4 /CNF, at the optimal reaction temperature of 150–200 °C, attained above 90% of Hg 0 removal efficiency (E a ). CNF played an important role in Hg 0 removal by Fe 3−x Mn x O 4 /CNF due to the disperation of Fe 3−x Mn x O 4 particles and the enhancement for electron transfer process. O 2 enhanced the Hg 0 removal via the Mars-Maessen mechanism, and NO improved the Hg 0 removal performance slightly because of the formation of NO 2 . SO 2 and H 2 O played an inhibitive role in Hg 0 removal due to the competition of active sites for Hg 0 adsorption. A mechanism of Hg 0 removal over Fe 3−x Mn x O 4 /CNF is proposed, in which both Mn cations and lattice/chemisorbed oxygen were thought to the active sites for Hg 0 adsorption/oxidation. Further, the spent Fe 3−x Mn x O 4 /CNF could be regenerated with no obvious decrease of Hg 0 removal performance by water washing followed by thermal treatment at 450 °C in N 2 and calcination at 200 °C in air. [ABSTRACT FROM AUTHOR]

The Hg 0 removal capacities of magnetospheres from fly ash collected from different power plants were investigated at a wide temperature range of 100–400 °C. The relationship between Hg 0 removal efficiency ( η T ) and iron content/species of magnetospheres was investigated. The magnetospheres attained the optimal Hg 0 removal capacity at 250 °C. The reaction temperature played an important role in Hg 0 adsorption and oxidation behaviors. At low reaction temperature (100 °C and 150 °C), the adsorption of Hg 0 played a predominant role in Hg 0 removal, while the Hg 0 removal mainly depended on the Hg 0 oxidation capacity at high temperature (200–400 °C). The Hg 0 removal capacity increased with the increase of iron content. The percentage of ferrospinel and hematite in magnetospheres is a key factor for determining the Hg 0 removal capacity as well. Hydrogen fluoride (HF) could remove the glass-phase materials on the magnetospheres and the active iron species embedded in the glass phase could be exposed and accessible. After fluorinated by HF, the Hg 0 removal capacity increased in different degree for different magnetospheres, which depended on the content of active iron species in raw magnetospheres. [ABSTRACT FROM AUTHOR]

In this study, manganese oxides supported on titania was prepared by sol-gel method and employed as SCR catalyst for simultaneous NO and mercury removal from coal combustion flue gas. The simultaneous NO and Hg 0 conversion rate on MnO x /TiO 2 was evaluated in different atmospheres, and the interaction between denitration and demercuration was investigated. The results indicated that MnO x /TiO 2 had good activity in simultaneously removing NO and Hg 0 in SCR atmosphere (NH 3 + NO + O 2 + N 2 ). However, both NO conversion and Hg 0 removal efficiency were inhibited in simulated coal combustion flue gas compared to that in SCR atmosphere because of the presence of SO 2 leading to the generation of sulfite and sulfate on the catalyst. H 2 O in simulated coal combustion flue gas had negative effect on the catalytic performance as well. NO conversion in oxy-fuel combustion flue gas was lower than that in air combustion flue gas, while Hg 0 removal efficiency in oxy-fuel combustion flue gas was higher than that in air combustion flue gas. Hg 0 displayed no obvious influence on NO conversion and N 2 selectivity over SCR process. And SCR atmosphere showed almost no inhibition to Hg 0 removal when the temperature was below 300 °C. At the optimal temperature for NO conversion (250 °C), the inhibition of SCR atmosphere on Hg 0 removal became stronger as the space velocity (GHSV) increased, but the inhibitive effect could be ignored when GHSV slowed down to 50,000 h − 1 or less. [ABSTRACT FROM AUTHOR]

Several modified adsorbents were developed by impregnating palygorskite (Pal) with the active substances CuCl 2 , CuBr 2 , NaBr, sulfur (S), MnO 2 and Co 3 O 4 , which were used to conduct experiments via a bench-scale fixed-bed reactor system in simulated flue gas for evaluating their elemental mercury removal capacity. In addition, a variety of characterization methods were applied to understand the physicochemical properties of these adsorbents. Furthermore, adsorbents, namely, CuCl 2 /CuBr 2 -impregnated Pal (Cu-Pal), were chosen for deep exploration under various gas conditions. The results showed that the mercury removal capability of Pal was greatly improved after impregnation. At 120 °C in pure N 2 , the mercury removal efficiency of the adsorbents modified by CuCl 2 and CuBr 2 could reach 90.9% and 95.2%, respectively, while it could be > 80% for the adsorbents modified by the others. The overall trend showed that O 2 and HCl were beneficial to increasing the mercury removal efficiency of Cu-Pal. To be specific, for CuCl 2 -Pal and CuBr 2 -Pal, when adding in 8% O 2 , their efficiencies could be increased by 6.6% and 1.9% respectively, while 50 ppm HCl increased their efficiencies by 2.8% and 2.1%, respectively. Different from O 2 and HCl, SO 2 and NO had negative effects. The removal efficiencies could be reduced by 6.5% for CuCl 2 -Pal and 4.7% for CuBr 2 -Pal with 1200 ppm SO 2 , while they could be reduced by 4.2% and 2.6% with 300 ppm NO. Compared with CuCl 2 -Pal, CuBr 2 -Pal performed better. Combined with the characterization results, Cu 2 + was reduced to Cu + and halogen migrated into new compounds on the surface of Cu-Pal after reaction. Eventually, the mercury removal mechanism of Cu-Pal was analysed and proposed. [ABSTRACT FROM AUTHOR]

The behaviour of mercury is investigated in a 35 MW th large pilot boiler of oxyfuel combustion with dry and wet flue gas recycle (FGR). The mercury species in fly ash particles as well as the involved reaction mechanism are systematically investigated. The results suggest that higher concentration of gas–phase mercury (Hg g ) is contained in oxyfuel combustion flue gas. The conversion of Hg g to particulate associated mercury (Hg p ) is enhanced in oxyfuel combustion. Different mercury species are presented in fly ash collected from air and oxyfuel combustion: trigonal red HgS is the main mercury species in air combustion; mercury bound to organic matter (Hg–OM) and trigonal red HgS are both dominant in the samples from oxyfuel combustion. The prominent difference is the significantly increase of Hg–OM in oxyfuel combustion atmosphere. The oxyfuel combustion atmosphere would favor the formation of oxygen–rich functional groups, especially the C O group, which is responsible for the adsorption of mercury and formation of Hg–OM in fly ash. [ABSTRACT FROM AUTHOR]

[Display omitted] • Basic reference data for Hg migration and control were obtained. • Removal efficiency of HgT by flue gas purification equipment is 92.40%. • CuBr 2 -modified activated carbon exhibits excellent Hg0 removal performance. • Mechanism of CuBr 2 -modified activated carbon for Hg0 removal were revealed. This study evaluated the emission and control characteristics of mercury during hazardous chemical waste incineration. Meanwhile, for the complex flue gas conditions generated by hazardous chemical waste incineration, the commercial activated carbon used in the incineration system was modified with CuBr 2 , and its Hg0 removal performance was tested. The results showed that the major proportion of Hg was in the fly ash, and the content accounted for 74.53 % of the total Hg. The Hg content in the fly ash increased with decreasing fly ash particle size. In the exhaust flue gas, the Hg content was 11.05 % of the total Hg, in which the mass percentages of Hg2+ and Hg0 were 59.08 % and 40.92 %, respectively. The flue gas purification equipment of the incineration system had a removal efficiency of 92.40 % for HgT. The saturated Hg0 removal capacity of the modified activated carbon was improved by 33.51 times. Under simulated incineration flue gas conditions, the modified activated carbon was able to achieve an Hg0 removal efficiency of 92.85 %. The results can contribute to the understanding of Hg emissions from hazardous chemical incineration systems and provide guidance for efficient Hg removal from activated carbon. [ABSTRACT FROM AUTHOR]

• The millimeter-grade Se/SiO 2 adsorbent can be used as a filler in a fixed bed reactor. • The saturated adsorption capacity of mercury is up to 101.04 mg/g. • HgSe is the main product of mercury removal from adsorbent under flue gas conditions. • The carrier of Se/SiO 2 is soluble SiO 2 , and high purity of HgSe can be recovered. Massive Hg emissions from coal-fired units cause serious environmental pollution and result in a substantial waste of Hg resources. In this study, the prepared millimeter-grade Se/SiO 2 adsorbent was applied as a filler to adsorb mercury in a fixed-bed reactor to obtain the high value-added product HgSe, which solved the problem of short contact time and secondary pollution caused by the traditional injection mercury removal adsorbents. Experimental Hg removal showed that the 25 % Se-loaded adsorbent exhibited excellent Hg removal performance at 150 °C, with a saturation adsorption capacity of mercury was as high as 101.04 mg/g, nearly 300 times that of commercial activated carbons. Additionally, the influence of the flue gas composition on the Hg removal performance of Se/SiO 2 was studied. The results showed that O 2 , NO, and HCl increased the efficiency of Hg removal and SO 2 and SO 3 had trivial impact on the Hg removal performance. The Hg temperature-programmed desorption test results showed that the adsorbed Hg appeared predominantly as HgSe on the sample surface. DFT calculations verified that Se loading improved Hg removal performance and defined the adsorption mechanism. Moreover, the prepared Se/SiO 2 adsorbent carrier was soluble SiO 2 , which provided a good condition for the subsequent high-purity collection of HgSe. Finally, the technological process of Hg removal via Se-loaded adsorbents and the recovery of HgSe were proposed, which could offer a new way to achieve the resource utilization of Hg. [ABSTRACT FROM AUTHOR]

A sol–gel synthesized Cu-promoted CeO 2 –TiO 2 (CuCeTi) catalyst was used in the low temperature selective catalytic reduction (SCR) of nitrogen monoxide (NO) with ammonia (NH 3 ). The combination of copper oxide (CuO) and cerium oxide (CeO 2 ) improved SCR performance at low temperatures by increasing the dispersion of active species and the volume of surface oxygen (O 2 ) with low-temperature activity. NO conversion on the CuCeTi catalyst exceeded 90% at temperatures higher than 200 °C. Although the gas hourly space velocity (GHSV) was much higher than that in a real SCR reactor, reaching 27,000 h −1 , its inhibitory effect on NO conversion became insignificant as the temperature increased. Within its flue gas concentration range, O 2 had a negligible effect on NO conversion. The inhibitory effect of water vapor (H 2 O) was reversible, and almost indiscernible at 300 °C. Sulfur-dioxide (SO 2 ) concentration affected NO conversion. At concentrations lower than 100 ppm, SO 2 promoted NO conversion and at SO 2 concentrations higher than 100 ppm, NO conversion decreased. The ammonium sulfates deposited on the surface of the catalyst as a product of the reaction with SO 2 were primarily responsible for the irreversible deactivation of the catalyst at low temperatures. Thus, high temperatures were found to alleviate the inhibitory effect of SO 2 . NO conversion exceeded 80% at 300 °C, even when the concentration of SO 2 was as high as 800 ppm. Mercury vapor and adsorbed mercury oxide (HgO) had negligible effects on NO reduction over the CuCeTi catalyst. This study provides new information on the promotional and inhibitory effects of individual flue-gas parameters and components on NO conversion over a novel CuCeTi catalyst. This information has fundamental implications for industrial applications of the CuCeTi catalyst in coal-fired power plants. [ABSTRACT FROM AUTHOR]

Elemental mercury (Hg0) is a highly hazardous pollutant of coal combustion. The low-temperature SCR catalyst of MnO x /TiO 2 can efficiently remove Hg0 in coal-burning flue gas. Considering its sulfur sensitivity, the effect of SO 3 on the catalytic efficiency of MnO x /TiO 2 and Fe modified MnO x /TiO 2 for Hg0 removal was investigated comprehensively for the first time. Characterizations of Hg-TPD and XPS were conducted to explore the catalytic mechanisms of Hg0 removal processes under different conditions. Hg0 removal efficiency of MnO x /TiO 2 was inhibited irreversibly from 92% to approximately 60% with the addition of 50 ppm SO 3 at 150 ℃, which resulted from the transformation of Mn4+ and chemisorbed oxygen to MnSO 4. The existence of H 2 O would intensify the inhibitory effect. The inhibition almost disappeared and even converted to promotion as the temperature increased to 250 ℃ and above. Fe modification on MnO x /TiO 2 improved the Hg0 removal performance in the presence of SO 3. The addition of SO 3 caused only a slight inhibition of 1.9% on Hg0 removal efficiency of Fe modified MnO x /TiO 2 in simulated coal-fired flue gas, and the efficiency maintained good stability during a 12 h experimental period. This work would be conducive to the future application of MnO x /TiO 2 for synergistic Hg0 removal. [Display omitted] • SO 3 exerted an irreversible influence on Hg0 removal performance of MnO x /TiO 2. • The effect of SO 3 converted from inhibition to promotion as temperature increased. • Fe modification improved Hg0 oxidation efficiency by 4.9%−12.4% at 100–350 ℃. • SO 3 inhibited Hg0 removal efficiency of Fe-MnO x /TiO 2 by 1.9% in simulated flue gas. [ABSTRACT FROM AUTHOR]

• Magnetospheres was modified through H 2 S as an efficient sorbent for Hg0. • Elemental sulfur derived from H 2 S oxidation was responsible high-efficient Hg0 adsorption. • Gaseous Hg0 was immobilized as stable HgS with extremely low leaching ratio. • The application route for Hg0 removal by using magnetospheres with suface sulfidation modification was proposed. Reduction of elemental mercury (Hg0) emission from coal-fired power plants is an enormous challenge. In this work, magnetospheres separated from fly ash was modified through H 2 S as an efficient sorbent (i.e., S-MS) for Hg0. Elemental sulfur with high affinity towards Hg0 was formed on the S-MS surface through selective catalytic oxidation of H 2 S. The sulfidation temperature played an important role in Hg0 adsorption over S-MS, ascribing to the variation of sulfur species on S-MS. The S-MS exhibited above 80% Hg0 adsorption efficiency with a sulfidation temperature of 150 °C for 30 min. The optimal Hg0 adsorption performance was obtained at 50 and 75 °C, implying that the S-MS could be adopted by injecting into the duct upstream of wet electrostatic precipitator (WESP) system. The gaseous Hg0 was immobilized by S-MS as stable mercury sulfide (HgS) owing to the presence of abundant sulfur species that is active for binding Hg0. The leaching ratio of mercury from spent S-MS in WESP effluent was as low as 1%, hence minimizing the secondary mercury pollution from the industrial waste. The cost analysis demonstrates that the mercury removal technology on the basis of magnetospheres adsorbents exhibited much superiority in operation cost compared with commercial activated carbon injection technology. Thus, the S-MS, with specific features, such as high Hg0 adsorption performance, minimized environmental hazardous and recyclability, displayed great potential in Hg0 sequestration. [ABSTRACT FROM AUTHOR]

CuFe 2 O 4 is regarded as a promising candidate of catalyst for Hg0 oxidation in industrial flue gas. However, the microcosmic reaction mechanism governing mercury oxidation on CuFe 2 O 4 remains elusive. Herein, experiments and quantum chemistry calculations were conducted for understanding the chemical reaction mechanism of oxygen-assisted mercury oxidation on CuFe 2 O 4. CuFe 2 O 4 shows the optimal catalytic activity towards mercury oxidation at 150 ºC. The reactivity difference of different lattice oxygen species is associated with its atomic coordination environment. The lattice oxygen coordinating with two octahedral Cu atoms and a tetrahedral Fe atom shows higher catalytic activity towards mercury oxidation than other lattice oxygen atoms. The inverse spinel structure of CuFe 2 O 4 is favorable for O 2 activation due to the Jahn-Teller effect, thereby promoting mercury oxidation. O 2 molecule preferably adsorbs on iron active site and dissociates into active oxygen species. Hg0 oxidation is a three-step reaction process: Hg0 adsorption, Hg(ads) → HgO(ads), and HgO desorption. The energy barrier of mercury oxidation by chemisorbed oxygen is lower than that of mercury oxidation by lattice oxygen. The chemisorbed oxygen preserves higher reactivity towards mercury oxidation than lattice oxygen. Hg(ads) → HgO(ads) is the rate-determining step of mercury oxidation by chemisorbed oxygen because of the higher energy barrier of 116.94 kJ/mol. This work could provide the theoretical guidance for the diversified structure design of highly-efficient catalysts used for elemental mercury oxidation. [Display omitted] • Hg0 oxidation by oxygen species over CuFe 2 O 4 was studied by quantum chemistry. • The reactivity of lattice oxygen is related to its atomic coordination environment. • Hg0 oxidation by chemisorbed oxygen over CuFe 2 O 4 is a three-step reaction process. • Hg0 oxidation shows similar kinetics in the presence and absence of gaseous oxygen. [ABSTRACT FROM AUTHOR]

• The Hg0 removal by CuCl 2 -MF technology was applied to large coal-fired units. • The mercury removal performance of CuCl 2 -MF with different conditions were studied. • The optimal magnetosphere injection parameters were assured by the results of tests. • CuCl 2 -MF showed superior Hg0 removal ability and mercury recovery performance. CuCl 2 –MF was a cost–efficient and highly efficient sorbent for Hg removal from flue gas in coal-fired units. In this study, the Hg0 adsorption and oxidation performance of CuCl 2 –MF with different conditions were studied at a 1000 MW commercial scaled coal-fired power plant. Under the optimal conditions, the total removal efficiency of Hg and the Hg recovery rate reached 98.72% and 52.76% using CuCl 2 –MF injection combined with the existing pollutant control device. The magnetosphere particle size of 45 μm–75 μm exhibited the highest mercury removal capacity. Additionally, the final mercury emission concentration was 0.334 μg/m3 and the corresponding relative mercury removal efficiency was 89.81%. The results of this study proved that elemental mercury removal by CuCl 2 –MF was also suitable for large-scale coal-fired units with a high Hg removal efficiency even in the low concentrations of mercury, which provided a reference for the practical application of this technology in other units in the future and supplied valuable experience for other mercury removal technologies. [ABSTRACT FROM AUTHOR]

Abstract: Effect of SO2 on elemental mercury (Hg0) oxidation over a highly active CeO2–TiO2 catalyst was systematically investigated. SO2 was found to have different, even contrary, effects on Hg0 oxidation under different flue gas conditions. In pure N2 atmosphere, SO2 inhibited Hg0 oxidation. In N2 plus O2 atmosphere, low concentration of SO2 promoted Hg0 oxidation, while high concentration of SO2 deteriorated Hg0 oxidation. The promotional effect of SO2 on Hg0 oxidation was probably due to SO3 generated from SO2 oxidation, and the inhibitive effect of SO2 on Hg0 oxidation was attributed to the competitive adsorption between SO2 and Hg0. The results suggest a balance point for SO2 concentration, where the promotional effect on Hg0 oxidation by SO3 originated from SO2 is equal to the inhibitive effect of SO2 on Hg0 adsorption and subsequent oxidation via the Langmuir–Hinshelwood mechanism. In the presence of NO, SO2 with the aid of O2 exhibited promotional effect on Hg0 oxidation through NO-catalyzed oxidation to form SO3 and hence a balance point of higher SO2 concentration. However, without O2, SO2 greatly limited Hg0 oxidation in the presence of NO. When HCl was present, most Hg0 oxidation was due to reactions between active chlorine species and adsorbed Hg0. SO2 inhibited Hg0 adsorption and therefore deteriorated Hg0 oxidation by chlorine species. When both NO and HCl were present, NO accelerated the conversion of SO2 to SO3, and hence relieved the prohibitive effect of SO2 on Hg0 oxidation by HCl. [Copyright &y& Elsevier]

Abstract: MnO x -CeO2 mixed-oxide supported on TiO2 (Mn-Ce/Ti) was synthesized by an ultrasound-assisted impregnation method and employed to oxidize elemental mercury (Hg0) at 200°C in simulated coal combustion flue gas. Over 90% of Hg0 oxidation was achieved on the Mn-Ce/Ti catalyst at 200°C under simulated flue gas representing those from burning low-rank coals with a high gas hourly space velocity of 60,000h−1. Gas-phase O2 regenerated the lattice oxygen and replenished the chemisorbed oxygen, which facilitated Hg0 oxidation. HCl was the most effective flue gas component responsible for Hg0 oxidation. 10ppm HCl plus 4% O2 resulted in 100% Hg0 oxidation under the experimental conditions. SO2 competed with Hg0 for active sites, thus deactivating the catalyst''s capability in oxidizing Hg0. NO covered the active sites and consumed surface oxygen active for Hg0 oxidation, hence limiting Hg0 oxidation. Water vapor showed prohibitive effect on Hg0 oxidation due to its competition with HCl and Hg0 for active adsorption sites. This study provides information about the promotional or inhibitory effects of individual flue gas components on Hg0 oxidation over a highly effective Mn-Ce/Ti catalyst. Such knowledge is of fundamental importance for industrial applications of the Mn-Ce/Ti catalyst in coal-fired power plants. [Copyright &y& Elsevier]

Abstract: Nanofibers prepared by an electrospinning method were used to remove elemental mercury (Hg0) from simulated coal combustion flue gas. The nanofibers composed of different metal oxides (MO x ) including CuO, In2O3, V2O5, WO3 and Ag2O supported on TiO2 have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersing X-ray (EDX) and UV–vis spectra. The average diameters of these nanofibers were about 200nm. Compared to pure TiO2, the UV–vis absorption intensity for MO x –TiO2 increased significantly and the absorption bandwidth also expanded, especially for Ag2O–TiO2 and V2O5–TiO2. Hg0 oxidation efficiencies over the MO x –TiO2 nanofibers were tested under dark, visible light (vis) irradiation and UV irradiation, respectively. The results showed that WO3 doped TiO2 exhibited the highest Hg0 removal efficiency of 100% under UV irradiation. Doping V2O5 into TiO2 enhanced Hg0 removal efficiency greatly from 6% to 63% under visible light irradiation. Ag2O doped TiO2 showed a steady Hg0 removal efficiency of around 95% without any light due to the formation of silver amalgam. An extended experiment with 8 Hg0 removal cycles showed that the MO x –TiO2 nanofibers were stable for removing Hg0 from flue gas. Factors responsible for the enhanced photocatalytic activities of the MO x –TiO2 nanofibers were also discussed. [Copyright &y& Elsevier]

Abstract: TiO2 supported Mn-Ce mixed oxides (Mn-Ce/Ti) synthesized by an ultrasound-assisted impregnation method were employed to oxidize elemental mercury (Hg0) at low temperatures in simulated low-rank (sub-bituminous and lignite) coal combustion flue gas and corresponding selective catalytic reduction (SCR) flue gas. The catalysts were characterized by BET surface area analysis, X-ray diffraction (XRD) measurement and X-ray photoelectron spectroscopy (XPS) analysis. The combination of MnO x and CeO2 resulted in significant synergy for Hg0 oxidation. The Mn-Ce/Ti catalyst was highly active for Hg0 oxidation at low temperatures (150–250°C) under both simulated flue gas and SCR flue gas. The dominance of Mn4+ and the presence of Ce3+ on the Mn-Ce/Ti catalyst were responsible for its excellent catalytic performance. Hg0 oxidation on the Mn-Ce/Ti catalyst likely followed the Langmuir–Hinshelwood mechanism, where reactive species on catalyst surface react with adjacently adsorbed Hg0 to form Hg2+. NH3 consumed the surface oxygen and limited the adsorption of Hg0, hence inhibiting Hg0 oxidation over Mn-Ce/Ti catalyst. However, once NH3 was cut off, the inhibited mercury oxidation activity could be completely recovered in the presence of O2. This study revealed the possibility of simultaneously oxidizing Hg0 and reducing NO x at low flue gas temperatures. Such knowledge is of fundamental importance in developing effective and economical mercury and NO x control technologies for coal-fired power plants. [Copyright &y& Elsevier]

Abstract: High surface area SiO2–TiO2–V2O5 (STV) catalysts of various titania loadings were synthesized by a sol–gel method. The STV catalysts were tested for oxidation of elemental mercury (Hg0) and its capture in simulated coal combustion flue gas representing those from combustion of low-rank coals (sub-bituminous and lignite). Experiments were conducted in a fixed-bed reactor at temperatures ranging from 26 to 400°C. In simulated flue gas, Hg0 oxidation efficiency over the STV catalysts was found to decrease dramatically from 135 to 300°C. At typical selective catalytic reduction (SCR) operating temperatures, the catalyst''s oxidation activity increased as titania loading of the STV catalysts increased up to 18wt%. The reaction mechanisms over the STV catalysts at SCR operating temperatures were investigated using individual flue gas components (HCl, NO, SO2 and H2O) with O2 balanced in N2. Hg0 oxidation over STV catalysts follows the Eley–Rideal mechanism where active surface species generated from adsorbed flue gas components react with gas-phase or weakly adsorbed Hg0. Fresh STV catalysts had some capability for adsorbing oxidized mercury (Hg2+) at 350°C, and no obvious effect of the adsorbed Hg2+ on subsequent Hg0 oxidation was observed. The presence of HCl with O2 had excellent oxidation and capture efficiency; however, without O2 it remarkably inhibited Hg0 adsorption on the STV catalysts. NO and SO2 promoted Hg0 oxidation and capture in the presence of O2, but their promotional effects were insignificant in the absence of O2. Water vapor showed prohibitive effects on Hg0 oxidation due to its competition with reactive species such as HCl and NO for active adsorption sites. This study demonstrates the feasibility of using STV catalysts for Hg0 removal at typical SCR operating temperatures. The identification of the reaction mechanism provides critical information for developing effective SCR catalysts for Hg0 oxidation in coal combustion flue gas. [Copyright &y& Elsevier]