Typical Flue Gas Research Articles

Adsorption of Carbon Dioxide and Nitrogen in Co3(ndc)3(dabco) Metal-Organic Framework.

Metal-organic frameworks (MOFs) are promising materials for processes such as carbon dioxide (CO2) capture or its storage. In this work, the adsorption of CO2 and nitrogen (N2) in Co3(ndc)3(dabco) MOF (ndc: 2,6-naphthalenedicarboxylate; dabco: 1,4-diazabicyclo[2.2.2]octane) is reported for the first time over the temperature range of 273-323 K and up to 35 bar. The adsorption isotherms are successfully described using the Langmuir isotherm model. The heats of adsorption for CO2 and N2, determined through the Clausius-Clapeyron equation, are 20-27 kJ/mol and 10-11 kJ/mol, respectively. The impact of using pressure and/or temperature swings on the CO2 working capacity is evaluated. If a flue gas with 15% CO2 is fed at 6 bar and 303 K and regenerated at 1 bar and 373 K, 1.58 moles of CO2 can be captured per kg of MOF. The analysis of the multicomponent adsorption of typical flue gas streams (15% CO2 balanced with N2), using the ideal adsorbed solution theory (IAST), shows that at 1 bar and 303 K, the CO2/N2 selectivity is 11.5. In summary, this work reports essential data for the design of adsorption-based processes for CO2 capture using a Co3(ndc)3(dabco) MOF, such as pressure swing adsorption (PSA).

Synthesis and characterization of polydopamine-coated graphene oxide as a multifunctional filler for high-efficiency CO2 separation from flue gas

ABSTRACT In the separation of CO2 from flue gas by membrane technology, the development of high permeability and selectivity, environmentally friendly and inherent merit materials play a vital role in efficient membrane processes. For this purpose, chemically active polydopamine (PDA) was successfully synthesized by solution-oxidation method and used in the functionalization and modification of graphene oxide (GO) and GO-polyethylene glycol (PEG) nanomaterial as bio-fillers were incorporated into polyethersulfone (PES) membrane as the basis of the fabricated mixed membrane matrix (MMM). The chemical, physical, thermal behavior and crystallographic structure of bio-fillers and membranes were studied by several analyses. The related functional groups are successfully obtained during the three steps of synthesis, including PEG-GO, PDA-PEG-GO and PDA-GO synthesis. The separation performance of the synthesized-MMM for 30% CO2/70% N2 gas mixture was studied, which resulted to the selectivity of 577.8 and permeability of 416.05 Barrer for PES-PDA-PEG-GO membrane under humidified condition. As a case study, the separation performance of MMM was evaluated for CO2 separation from a typical flue gas that resulted in a selectivity of 339.56 and permeability of 237.5 Barrer. According to the results obtained from a typical flue, the synthesized membrane has an acceptable potential for CO2 separation and industrial uses.

Valorization of refinery flue gas through tri‐reforming and direct hydrogenation routes

AbstractThe rising amount of greenhouse gases has been contributing to global warming and, subsequently, climate change. Industries such as refineries and power plants emit a significant amount of CO2 into the atmosphere. It is imperative to curb anthropogenic CO2 emissions, and hence, in this effort, we explore the utilization of a refinery emission stream to produce value‐added chemicals. The chosen emission stream for the said purpose is a typical flue gas stream from refineries. Following the capture step, this CO2 stream has been leveraged for subsequent valorization processes. Two strategies have been proposed in this paper to valorize the captured carbon dioxide. The first strategy employs the tri‐reforming process with a refinery‐specific fuel gas stream as the co‐reactant. The resulting syngas from tri‐reforming has been converted to chemicals such as methanol (MET) and ethanol. Furthermore, to improve the amount of CO2 valorized, another approach with green hydrogen has been considered. The second strategy aims at direct hydrogenation of the captured CO2 stream to produce MET and ethanol. The proposed strategies analyze the feasibility of valorizing captured CO2 from flue gas to MET and ethanol in terms of gross margin per feed and percentage of CO2 valorization. The performance assessment and analysis of the proposed processes have been carried out using simulations in Aspen Plus® that exhibited up to 74% valorization of CO2 into valuable chemicals.

Enhancing CO2 adsorption performance of porous nitrogen-doped carbon materials derived from ZIFs: Insights into pore structure and surface chemistry

In this work, a novel approach for the synthesis of porous nitrogen-doped carbon materials (PNCs) with a highly microporous structure through low-temperature carbonization of ZIF-8 and ZIF-61 assisted by KCl and NaCl is reported. The introduction of KCl and NaCl during the carbonization process can adjust the surface chemical properties and pore structures of the PNCs derived from ZIF-8 and ZIF-61. The effects of pore structures and surface groups of PNCs on CO2 adsorption capacity are explored. Results show that the cumulative pore volume in the pore size range of 5–7 Å (V5-7 Å), pyrrolic-N content, and COOH content exert favorable influences on CO2 adsorption capacity at 1 bar and 25 °C. Notably, V5-7 Å is the key factor in enhancing the CO2 adsorption capacity of PNCs. Moreover, the degree of contribution of V5-7 Å, V7-9 Å, pyrrolic-N content, pyridinic-N content, and COOH content to the CO2 adsorption capacity is evaluated by establishing a multiple linear regression equation, and the results show that on the basis of PNCs possessing optimum pore structures (V5-7 Å > 0.10 cm3/g), pyrrolic-N content in PNCs becoming the dominant contributor to CO2 adsorption capacity. The as-prepared 2CN8-KCl-600 sample demonstrates high CO2 adsorption capacity, which reaches 4.61 mmol/g at 25 °C and 6.70 mmol/g at 0 °C (1 bar), respectively. Besides, 2CN8-KCl-600 exhibits high CO2/N2 selectivity (39.5) under the typical flue gas scenario and high cycling stability. This work offers a novel perspective on preparing highly efficient carbon-based adsorbents for CO2 and provides the fundamental understanding for enhanced CO2 adsorption performance on PNCs.

Density functional theory study of high-temperature CO2 adsorption by Li2ZrO3: Effect of typical flue gas components on adsorption energy and electronic properties

Lithium zirconate (Li2ZrO3) is one of the best-performing high-temperature CO2 adsorbents, but the effect of flue gas on its mutual mechanism of action is not clear. The adsorption mechanism of CO2 and flue gas components on the Li2ZrO3 (111) surface is investigated theoretically through density functional theory (DFT), where the selected flue gas components are O2, H2O, and SO2. Theoretical calculations show that O2 exhibits physical adsorption and CO2, H2O, and SO2 exhibit chemisorption on the Li2ZrO3 surface. The energy potential barrier for CO2 adsorption on the Li2ZrO3(111) surface is 0.3 eV. CO2 is gradually desorbed at temperatures above 870 K. When there are flue gas atmospheres present, the desorption temperature of CO2 decreases, to a certain extent. All selected flue gas components inhibit the adsorption of CO2, O2, and H2O, weakening the interaction forces between the surface and CO2 and making it less stable. SO2 has the same adsorption sites as CO2, while SO2 has much higher adsorption energy than CO2. SO2 is more likely to adsorb onto and occupy the active sites of CO2.

Metal-Doped Mesoporous MnO2-CeO2 Catalysts for Low-Temperature Pre-Oxidation of NO to NO2 in Fast SCR Process

Selective catalytic reduction (SCR) is an effective system for treating nitrogen oxides (NOx; mainly NO), and fast SCR requires the equimolar reactants of NO and NO2. This study focused on catalysts for oxidizing 50% of NO to NO2. A series of catalysts composed of a variety of components, such as mesoporous mMnO2-nCeO2 as carrier catalysts (m:n = 9:1 and 7:3) and transition metals (e.g., Fe, Co, Ni, Cu, and Cr), were synthesized and characterized using N2 adsorption, in situ XRD, TEM, and XPS. All samples had a mesoporous structure with pore size around 8 nm. XPS results demonstrated that addition of cerium ion increased the surface area and provided oxygen vacancy due to the formation of Ce3+ within the structure. NO oxidation activity was tested using a feed (205~300 ppm NO and 6% O2) that simulated typical flue gas conditions. Doped mesoporous mMnO2–nCeO2 has higher NO oxidation activity than pristine mMnO2–nCeO2. The doped mMnO2-nCeO2 catalyzed 50% of NO to NO2 at between 140 and 200 °C resulting in an equivalent amount of NO and NO2. Among the transition metals, Cu, Ni, Co, Fe, and Cr have the highest to lowest oxidation activity, respectively. The precatalytic oxidation of NO can potentially be combined with the current SCR system without changes to existing equipment and can be applied to the exhaust gas treatment for de-NOx.

Effect of flue gas components on the removal of cadmium pollutants by transition metal-modified activated carbon: Density functional theory and thermodynamic study

Removal of cadmium (Cd) pollutants from waste incineration (MSW) flue gas by modified activated carbon (AC) is of great potential, yet the influence of flue gas composition on their interaction mechanism is still unclear. Thus, density functional theory and thermodynamic analyses were combined to explore the effects of typical flue gas compositions (O2, HCl, NO, SO2, CO2, and H2O) on Cd species capture over the Fe/AC and Mn/AC surfaces. All flue gas compositions inhibit the adsorption of Cd species, wherein their inhibitory effects are mainly divided into two categories, i.e., one with moderate inhibition (HCl, CO2, and H2O), and the other with significant inhibition (O2, NO, and SO2). For the first category, HCl forms new active sites after adsorption on the surface, while CO2 and H2O have weak competitiveness with Cd species, resulting in mild inhibitory effects. Nevertheless, O atoms of O2/SO2 and N atoms of NO are highly effortless to bond with Fe/Mn atoms, and strongly exclude the Cd adsorption on the active sites, greatly weakening their binding strength. According to thermodynamic analysis, the fixation of Cd species by Fe/AC and Mn/AC spontaneously proceeds with the interference of flue gas components, while the selectivity to Cd species decreases with the increased temperature. In summary, it is instrumental to adjust the operating parameters and AC injection location to attenuate the negative effects of O2, SO2, NO, and high temperature on Cd capture by Fe/AC and Mn/AC.

Rational Design of Carbon-Based Porous Aerogels with Nitrogen Defects and Dedicated Interfacial Structures toward Highly Efficient CO2 Greenhouse Gas Capture and Separation.

CO2 capture from flowing flue gases through adsorption technology is essential to reduce the emission of CO2 to the atmosphere. The rational design of highly efficient carbon-based absorbents with interfacial structures containing interconnected porous structures and abundant adsorption sites might be one of the promising strategies. Here, we report the synthesis of nitrogen-doped carbon aerogels (NCAs) via prepolymerized phenol-melamine-formaldehyde organic aerogels (PMF) by controlling the addition amount of ZnCl2 and the precursor M/P ratio. It has been revealed that NCAs with a higher specific surface area and interconnected porous structures contain a large amount of pyridinic nitrogen and pyrrolic nitrogen. These would act as the intrinsic adsorption sites for highly effective CO2 capture and further improve the CO2/N2 separation efficiencies. Among the prepared samples, NCA-1-2 with a high micropore surface area and high nitrogen content exhibits a high CO2 adsorption capacity (4.30 mmol g-1 at 0 °C and 1 bar) and CO2/N2 selectivity (36.5 at 25 °C, IAST). Under typical flue gas conditions (25 °C and 1.01 bar), equilibrium gas adsorption analysis and dynamic breakthrough measurement associated with a high adsorption capacity of 2.65 mmol g-1 at 25 °C and 1.01 bar and 0.81 mmol g-1 at 25 °C and 0.15 bar. This rationally designed N-doped carbon aerogel with specific interfacial structures and high CO2 adsorption capacity, high selectivity, and adsorption performance remained pretty stable after multiple uses.

Mid-infrared fiber-coupled laser absorption sensor for simultaneous NH3 and NO monitoring in flue gases

We report the development of a mid-infrared fiber-coupled laser absorption sensor for in situ and simultaneous detection of NH3 and NO, which is suitable for flue gas monitoring at the SCR (selective catalytic reduction) exhaust. Two quantum cascade lasers (QCLs) are used to detect the optimal absorption lines of NH3 and NO centered at 1103.45 cm−1 and 1929.03 cm−1, respectively. The two QCLs are coupled into a single hollow-core fiber and delivered to an open-path, single-ended optical probe for in situ gas detection. The gas concentration is determined by an improved calibration-free wavelength modulation spectroscopy (CF-WMS) technique with a reduced line model. A series of experiments are conducted to evaluate the sensor performance at varied temperatures from 296 to 573 K and the pressure of 1 atm. Such a dual-species sensor realizes a minimum detection limit of 30 ppb at 100 s average time for NO and 14 ppb at 70 s for NH3, respectively. The uncertainty of NH3 and NO detection is determined to be less than 5 %. By evaluating the WMS spectra of other species, the current sensor shows negligible spectral interferences under typical flue gas conditions.

Performance Analysis of an Absorption Heat Pump System for Waste Heat and Moisture Cascade Recovery from Flue Gas.

The typical flue gas exhaust temperature of coal-fired boilers is up to 150 °C. There is a considerable amount of waste heat that cannot be efficiently recovered. This study describes a zero-energy consumption absorption heat pump system that can improve the thermal efficiency and recover moisture. In the proposed system, lithium bromide solution serves as the recyclable heat-transfer medium, which absorbs sensible heat at the outlet of the air preheater by a generator. The latent heat of the flue gas is absorbed by an evaporator, and the condensate water appears. Theoretical investigation and mathematical models are built. Meanwhile, the operating parameters of the system are displayed. The results showed that the acid dew point of flue gas is related to the water content. The sorption heat pump efficiency (coefficient of performance) increased to 1.64. Compared with the two-stage heat exchanger system, 24.4 t/h condensate water and 47.21 MW waste heat were recovered. The flue gas temperature at the chimney entrance was reduced by 4.18 °C.

High-temperature filtration demonstration applying Fe-Al intermetallic membrane for a 410 t/h scale coal-fired power plants

High-temperature filtration in coal units is a promising approach for the clean and efficient utilization of coal power. In this paper, a high-temperature precipitator was applied in a 5000 Nm3/h pilot scale platform and especially a full scale 410 t/h pulverized coal boiler, where the precipitator was installed in front of the denitrification unit. The 410 t/h pulverized coal boiler was tested before and after the installation of high-temperature precipitator. The results showed that the particulate matter concentrations at the outlet of the high-temperature precipitator are both less than 8 mg/m3 at nominal 70% and 90% loads. Meanwhile, the outlet concentration increases with the boiler load. The pressure drop for a high-temperature precipitator applying Fe-Al intermetallic membrane is only 500 ± 50 Pa under 90% loads, which is much less than that of conventional fabric filter. Furthermore, gaseous ammonia injection and ammonia escape in the SCR reactor are both decreased under the same denitrification efficiency compared with the typical flue gas pollution post-treatment technologies. The air preheater blockage is potentially the biggest issue for coal-fired power plant and has attracted extensive attention. As expected, the application of the high-temperature precipitator greatly alleviated the negative effects of high fly ash concentrations and reduced the pressure drop for the air preheater during the test. The pressure drops benefit brought by the high-temperature precipitator for the module including high-temperature precipitator, SCR unit, air preheater approaches 1500 ± 50 Pa. Taking a 1000 MWe coal-fired unit and a typical bituminous coal for example, a 1000 MWe coal-fired unit applying the high-temperature precipitator is expected to achieve 30% relevant energy consumption benefit. Furthermore, a total of 4.48 million tons CO2 emission reduction per year could be achievable if 70% of the Chinese national thermal power market employed them by 2060.

Zeolitic imidazolate frameworks with different organic ligands as carriers for Carbonic anhydrase immobilization to promote the absorption of CO2 into tertiary amine solution

Carbonic anhydrase (CA) enzyme-based absorption processes represent a promising approach to flue gas CO2 capture owing to their rapid absorption rates and low energy penalties. However, CA enzymes exhibit poor stability and activity under typical flue gas conditions, thus constraining their industrial utilization. Enzyme immobilization has been proposed as a potential means of improving associated stability and activity levels, thus overcoming these limitations. Herein, a variety of zeolitic imidazolate frameworks including ZIF-8, ZIF-11, and ZIF-90 with a range of organic ligands were synthesized as adsorption-based carriers for CA enzyme immobilization. In a series of experiments, CA immobilized on ZIF-8 (CA/ZIF-8) was found to retain higher activity levels that were approximately 86% of those of the free enzyme, as compared to 44% and 16% for CA/ZIF-11 and CA/ZIF-90, respectively. Immobilized CA and associated carrier frameworks were characterized via XRD, SEM, and BET. Variations in CA enzyme secondary structural characteristics in the context of immobilization were monitored via FTIR and CD to explore the molecular basis for variable activity levels associated with different carriers, revealing more hydrophilic materials to be conducive to the preservation of enzymatic activity. In addition, carrier precursor selection should take both hydrophilicity and the potential inhibitory effects of functional groups on the CA enzyme into account.

An Anomaly Detection Method for Multiple Time Series Based on Similarity Measurement and Louvain Algorithm

Anomaly detection is an important task for data mining. Detecting anomalies in the data collected from Municipal Solid Waste (MSW) incineration process is critical for their post processing, which helps to decrease emissions of typical flue gas pollutants and reduce costs. In this paper, we propose an unsupervised multiple time series anomaly detection model based on similarity measurement and Louvain algorithm, which consists of two stages. The first stage aims to find a subset of correlated time series data. The second stage is to detect anomalies in the subset, which can identify anomalous time windows and anomalous time subseries in the anomaly windows. The proposed method is applied on the data collected from an MSW incinerator in South China. The results demonstrate the effectiveness of the proposed method. In addition, four similarity measure approaches are conducted and the results show that the model performs the best when using Pearson correlation coefficient, with an F2-score of 0.92.

Efficient micropore sizes for carbon dioxide physisorption of pine cone-based carbonaceous materials at different temperatures

Biomass-based activated carbons (ACs) are widely used as CO2 capturing materials. Most plant-based biomass contains a phytolith component that mainly comprises silica, which is an obstacle for developing the porosity of ACs. The silica elimination process (SE) has rarely been studied for developing the porosity of ACs. Here, we prepared pre-carbonized pine cones (CPC) as a starting material to investigate optimizing the micropores of ACs according to the preparation sequence. One was prepared by chemical activation (CA) and the subsequent SE (CPC-CA-SE/ACs) and the other was carried out the SE before CA (CPC-SE-CA/ACs). It was found significant differences on the pore development between two samples, the former showed a specific surface area of 1787 m2 g−1 and the microporosity of ∼92 % while the latter were 2047 m2 g−1 and ∼74 %, respectively. The highest CO2 adsorption capacities were exhibited in CPC-CA-SE/ACs of 6.57 mmol g−1 at 273 K and 1 bar, resulting from the effective pore size (< 1.1 nm). Furthermore, the highest CO2 capture performance of 0.75 mmol g−1 in the typical flue gas condition (15 % CO2/85 % N2) and superior regeneration properties during 10 adsorption–desorption cycles at 313 K were achieved in CPC-CA-SE/ACs. From the results, we found that the preparation sequence had a strong effect on the textural properties of the resultant of biomass-based ACs and their CO2 capture performance.

Pyrolysis of sulfonic acid substituted benzenes and investigation of CO2 capture capability of resulting carbons

Aromatic organic compounds5-sulfosalicylic acid (SSA) and p-toluenesulfonic acid (TsOH) were used to prepare sulfur doped ultramicropore (pores smaller than 0.7 ​nm) containing carbons by pyrolysis under Argon atmosphere. SSA derived carbon processed at 1000 ​°C showed the best CO2 (carbon dioxide) adsorption performance. CO2 sorption capacity of SSA1000 is 3.91 ​mmol g-1at 1 ​bar at 273 ​K and 2.88 ​mmol g-1at 1 ​bar at 298 ​K. Remarkably, at typical flue gas conditions (0.15 ​bar@298 ​K) SSA1000 takes up 0.95 ​mmol ​g-1 CO2. SSA1000 possessed good gas sorption properties, recyclability for regeneration, and Ideal Adsorbed Solution Theory (IAST)-based selectivity of 14.7 (1 ​bar, CO2/N2:0.15/0.85). This work shows the possibility of production of ultramicropore containing sulfur and oxygen doped carbons exhibiting high CO2 uptake capability via simple pyrolysis method from molecular precursors.

A kinetic study of Hg(0) oxidation over Mo-promoted V-based SCR catalyst

A kinetic study of elemental mercury (Hg(0)) oxidation reaction over molybdenum (Mo)-promoted vanadium (V)-based selective catalytic reduction (SCR) catalyst was carried out. To probe the role of HCl and O2 in Hg(0) oxidation over the catalyst, a real-time Hg(0) oxidation experiment was conducted. It was found that Hg(0) adsorption was negligible and HCl adsorbed onto the catalyst surface could show consistent Hg(0) oxidation performances in the presence of O2 at realistic SCR temperatures. NH3 showed competitive adsorption with HCl, resulting in degrading Hg(0) oxidation performance. X-ray Absorption Near-Edge Structure (XANES) data for mercury species showed that HgCl2 was the major mercury species formed onto the spent catalyst under typical flue gas conditions. Based on the current and previous studies, an Eley-Rideal followed by Langmuir-Hinshelwood mechanism was proposed, comprising multiple elementary reaction steps. A steady-state kinetic study was conducted based on an assumption of HgCl formation as a rate-determining step. The kinetic and thermodynamic parameters determined from this study shed light on fundamental insights and practical catalytic reactor designs.

CO2 utilization for methanol production; Part I: Process design and life cycle GHG assessment of different pathways

The process design and life cycle assessment (LCA) of various methanol production processes, including the conventional natural gas reforming process and alternative CO2 utilization-based pathways, are performed in this work. Three main technologies are considered for the CO2 conversion to methanol: direct CO2 hydrogenation, dry reforming and tri-reforming of methane. For each pathway, a process simulation that includes the CO2 capture from typical flue gas of a cement kiln, the methanol synthesis and purification steps, is performed using the Aspen engineering suite. In addition, for each process, several heat integration measures are considered to maximize thermal efficiency. According to the simulation results, the thermal efficiency of the direct CO2 hydrogenation process (47.8 % LHV) is higher than the dry reforming (40.6 % LHV) while it is lower than the conventional (68.4 % LHV) and tri-reforming (57.9 % LHV) processes. The LCA results showed that the direct CO2 hydrogenation pathway is an environmentally friendly option, only when the electricity GHG intensity is lower than 0.17 kg CO2 equivalent per kWh of electricity. As a result, in the context of Canada, the CO2 hydrogenation options can be recommended only for the provinces where low-carbon electricity is available, such as Quebec, British Columbia, Manitoba and Ontario.

Enhancing membrane performance for CO2 capture from flue gas with ultrahigh MW polyvinylamine

Membranes for post-combustion CO2 capture are required to have a high CO2 permeance due to the limited driving force. For facilitated transport membranes synthesized with polyvinylamine (PVAm), a defect-free selective layer of <200 nm is usually required to render sufficient permeance with high CO2/N2 selectivity. In order to meet such a demand through the knife-coating process, the coating solution needs to have a high viscosity at a relatively low concentration to minimize its penetration into the substrate. The demand was met by synthesizing PVAm with an ultrahigh molecular weight (MW) via inverse emulsion polymerization (IEP) in this study. Compared to solution polymerization, IEP isolates the reaction in inverse micelles suspended in a continuous organic phase, which allows excellent dissipation of the heat generated by the reaction and reduces gel formation drastically. The polymerization parameters, including monomer concentration, initiator concentration, and reaction temperature, were investigated to obtain the optimal MW of PVAm for membrane performance. As compared to solution polymerization, IEP enhanced the MW of PVAm from 1.2 to 12.7 MDa, which minimized the penetration of the coating solution into the substrate and hence the extra mass transfer resistance. The effects of MW and degree of hydrolysis of PVAm on the membrane transport properties were studied. Furthermore, by employing PVAm with a MW of 12.7 MDa to strengthen the polymer matrix, the loading of piperazine glycinate in the membrane was increased up to 85 wt.%. The resultant membrane achieved a CO2 permeance of 839 GPU and a CO2/N2 selectivity of 161 at the typical flue gas temperature of 57 °C.

Recyclable chalcopyrite sorbent for mercury removal from coal combustion flue gas

The development of cost-effective and high-efficient technologies for degrading Hg0 pollution from coal combustion flue gas remains a tremendous challenge. In this work, an earth-abundant mineral, i.e., chalcopyrite (CuFeS2), was adopted as an efficient trap for Hg0 sequestration. The CuFeS2 exhibited approximately excellent Hg0 removal performances in a wide temperature ranging from 40 to 100 °C. Typical flue gas components including oxygen (O2), sulfur dioxide (SO2), nitrogen monoxide (NO), and water vapor (H2O) negligibly interfered the Hg0 adsorption ability, which further solidify the application potential of CuFeS2 in coal-fired power plant. The Hg0 adsorption capacity and uptake rate was 37.24 mg·g−1 and 63.40 μg·g−1·min−1, respectively, significantly suppressing those of commercial activated carbons. The superior performance of CuFeS2 were primarily attributed that the disulfide ligands (S22−) could oxidize Hg0 into Hg2+ and subsequently immobilize Hg2+ into mercury sulfide (HgS). The spent CuFeS2 sorbent could be replenished and regenerated by a thermal decomposition method, which pronouncedly save the operation cost. Therefore, the CuFeS2 is a potential trap for cost-effective and efficient Hg0 remediation from coal combustion flue gas.

Reduction of oxidized mercury over NOx selective catalytic reduction catalysts: A review

• The Hg 2+ reduction process over SCR catalysts were reviewed for the first time. • The effects of typical flue gases on Hg 2+ reduction were presented. • The involved reaction mechanisms for Hg 2+ reduction were discussed in details. • Suggestions to alleviate the reduction of Hg 2+ over SCR catalysts were proposed. The control of mercury emission from flue gas has long been a serious task for the global environment and human health. Utilization of selective catalytic reduction (SCR) catalysts to oxidize Hg 0 to form Hg 2+ and subsequent capture the Hg 2+ through a wet flue gas desulfurization (WFGD) scrubber is an efficient and economical technology for Hg 0 removal in coal-fired power plants. Extensive studies have been conducted with regard to Hg 0 oxidation over SCR catalysts. However, recent studies found that the reduction of Hg 2+ , an inverse process to Hg 0 oxidation, also occurred even predominated under some SCR conditions. This new observation overturns the general knowledge that SCR catalysts always enhance Hg 0 oxidation. To avoid the neglect of Hg 2+ reduction and overcome the shortages of existing studies, a critical review of Hg 2+ reduction over SCR catalysts was undertaken. The Hg 2+ reduction behaviors under various SCR conditions were summarized and the effects of typical flue gas components like hydrogen chloride (HCl), sulfur dioxide (SO 2 ), water vapor (H 2 O), volatile organic compounds (VOCs), and carbon monoxide (CO) on Hg 2+ reduction were also presented. The involved reaction mechanisms for Hg 2+ reduction were discussed in details. Moreover, feasible measures to suppress the reduction of Hg 2+ in the SCR system were proposed. We expect to clearly explore the mechanism of the Hg 0 redox process on SCR catalysts in this review to avoid the neglect of Hg 2+ reduction, hence providing guidance for the design of SCR catalysts to achieve an efficient Hg 0 oxidation.