Simulated Coal Combustion Flue Gas Research Articles

Optimizing removal of elemental mercury from flue gas using halide‐impregnated red mud

AbstractMercury (Hg0) emission from coal‐fired industrial plants poses severe threats to ecosystem sustainability and human health, urging the development of novel and cost‐effective adsorbents to treat industrial flue gas. Herein, the modification of industrial residual red mud (RM) through the impregnation of hydrogen halides (HH) and its adsorption characteristics for removing elemental mercury from combustion flue gas was reported. Experimental investigation of HH‐modified RM reveals that the hydrogen iodide (HI)‐modified RM with a concentration of 1.5 M had a maximum Hg0 removal efficiency of 98%, whereas hydrogen bromide (HBr) 1.5 M modified RM had a maximum Hg0 removal efficiency of 90%. The effect of various parameters, such as reaction temperature and halide concentrations, were also found to be influential for the adsorption efficiency of the modified RM. Moreover, it is important to highlight the chemisorption characteristics of HI‐modified RM, which significantly enhances the efficiency of the removal process. The Hg0 removal efficiency increases with the increase in HI concentration (1.5 M @ 93%) with an optimal reaction temperature of 140°C. Furthermore, the maximum Hg0 removal attained with a change in NO concentration was 98% at 200 ppm. However, increasing the SO2 concentration reduces the efficiency of RM for removing Hg0 in simulated coal combustion flue gas. The pseudo‐second‐order model (R2 = 0.98) accurately describes the adsorption of in kinetic investigations, indicating a chemisorption mechanism. This analysis of the chemisorption mechanism highlights the efficiency of halide‐modified industrial solid waste, which has the potential to be used in the design of economical and innovative adsorbents for reducing environmental pollution. The present study employed specific reaction parameters such as reaction temperature, halide loading contents, and different flue gas compositions, which had not been extensively explored.

Facile fabrication of regenerable spherical La0.8Ce0.2MnO3 pellet via wet-chemistry molding strategy for elemental mercury removal

Perovskite-based sorbents have received extensive attention in the field of mercury abatement. However, the excellent Hg0 adsorption performance on the lab scale hardly transforms into industrial-scale utilization because of the elutriation and microcrystalline nature of powdery perovskite sorbent. Hence, the granulation of perovskite into pellets is a strongly solicited and urgent demand. In this work, a universal granulation strategy is exploited for fabricating perovskite sorbent pellets for Hg0 capture from coal combustion flue gas (CCFG) based on a facile wet-chemistry method. This route takes advantages of the unique thermal sensitivity and thermal decomposition characteristics of agar powder and surface tension of medium to simultaneously trade off the molding, pore creation, and mechanical property of perovskite-based sorbent pellets. Besides, silica sol was also added to further enhance the physical strengths of sorbent pellets. The obtained perovskite sorbent pellet (i.e., LCMO-A-Z-2) with a favorable BET surface area of 113.16 m2 g−1 and pore diameter of 8.81 nm, largely facilitating Hg0 diffusion and capture over sorbent pellets. LCMO-A-Z-2 was further employed to Hg0 adsorption experiment under simulated CCFG, which exhibited satisfactory Hg0 adsorption capacity of 2.07 mg g−1 and nearly identical Hg0 adsorption performance after 5 cycles. The weight loss was approximately 13 % after 1000 rotations in the anti-attrition ability experiment suggesting its outstanding mechanical strength. It is reasonable to deduce this granulation method can be readily extended to other powdery sorbents. This work makes first step towards the application of sorbent pellets under application-relevant conditions and support the ultimate implementation of traditional sorbents in various large-scale industrial scenarios.

Low temperature oxidation of o-xylene by Mn-based catalysts prepared by hydrothermal calcination: Influence mechanism of complicated flue gas components and intermediate product

Catalytic oxidation technology has proven to be an effective method for purifying flue gas of CFPPs. However, conventional catalysts face limitations such as limited activity and vulnerability to contamination from SO2 and H2O. This study aims to assess the efficiency of a newly synthesized Mn-based catalyst, prepared via a hydrothermal-calcination technique, in removing VOCs from simulated coal combustion flue gas. The results demonstrate that the catalyst produced through hydrothermal synthesis, followed by calcination at 400 °C, exhibits a catalytic oxidation efficiency of 96.2% for VOCs at 350 ℃. Furthermore, the catalyst demonstrates anti-poisoning properties. To gain a deeper understanding, we utilized DRIFTS to investigate the mechanism of o-xylene adsorption on the catalyst surface, reaction conversion intermediates, and the influence of complex flue gas components (NH3, NO, and SO2) on the catalytic reaction process. Our investigation provides insight in the improvement of Mn-based catalysts for the removal of VOCs from coal flue gas.

Two-Staged Dielectric Barrier Discharge-Urea Configuration for the Removal of NO of NOx in a Simulated Coal-Combustion Flue Gas

NO is a deadly pollutant that makes up more than 90% NOx in a flue gas. NO is insoluble in water; thus, its removal is extremely difficult using the SCR method. This study investigates the feasibility of NO removal and energy efficiency from a coal-combustion flue gas connected to a DBD reactor merged with urea. The results showed that the combined effect of urea and the DBD reactor gave a significant increase in the removal of NO. Comparing the removal efficiencies of NO at different urea mass percentages (9%, 17%, 23%, 29%, and 33%), it was found that the optimum concentration of urea for efficient NO removal was 23% because there is enough NH3 produced at this concentration and less H2O species generated to consume N• free radicals by OH to produce more NO in the system. The removal efficiencies of the optimum 23% urea concentration with oxygen [(NO/N2/O2/CO(NH2)2:23% w/w system] and without oxygen [(NO/N2/CO(NH2)2:23% w/w system] were also compared. It was also found that the addition of urea solution showed a considerably good energy efficiency which implies that the cost of this technology will be effective. The study complements past studies on the efficient removal of NO from the environment.

Copper slag as a catalyst for mercury oxidation in coal combustion flue gas

Copper slag is a byproduct of the pyrometallurgical smelting of copper concentrate. It was used in this study to catalyze elemental mercury (Hg0) oxidation in simulated coal combustion flue gas. The copper slag exhibited excellent catalytic performance in Hg0 oxidation at temperatures between 200 °C and 300 °C. At the most optimal temperature of 250 °C, a Hg0 oxidation efficiency of 93.8% was achieved under simulated coal combustion flue gas with both a high Hg0 concentration and a high gas hourly space velocity of 128,000 h−1. Hydrogen chloride (HCl) was the flue gas component responsible for Hg0 oxidation over the copper slag. The transition metal oxides, including iron oxides and copper oxide in the copper slag, exhibited significant catalytic activities in the surface-mediated oxidation of Hg0 in the presence of HCl. It is proposed that the Hg0 oxidation over the copper slag followed the Langmuir-Hinshelwood mechanism whereby reactive chlorine species that originated from HCl reacted with the physically adsorbed Hg0 to form oxidized mercury. This study demonstrated the possibility of reusing copper slag as a catalyst for Hg0 oxidation and revealed the mechanisms involved in the process and the key factors in the performance. This knowledge has fundamental importance in simultaneously reducing industrial waste and controlling mercury emissions from coal-fired power plants.

Superior activity of CeO2 modified V2O5/AC catalyst for mercury removal at low temperature

CeO2 modified V2O5/AC catalysts (V-Ce/AC) were synthesized by an ultrasound-assisted impregnation method, and were employed to remove elemental mercury (Hg0) from simulated coal combustion flue gas at low temperature (100–200 °C). The effects of several operation conditions, including the loading of CeO2, reaction temperature, the role of O2 and stability of the catalysts were all investigated, respectively. The results showed that 1 V-8Ce/AC catalysts had the highest catalytic activity with 98.3% Hg0 removal efficiency at 150 °C. There was synergistic effect on Hg0 oxidation when V2O5 and CeO2 combined. Characterization by XPS, we found that both lattice oxygen (Oα) and chemisorption oxygen (Oβ) contribute to Hg0 oxidation. Besides, the possible mechanism of Hg0 removal over the catalysts was proposed, in which the critical steps were the adsorption of Hg0 and the oxidation of Hg0 to Hg2+ by the active oxygen on catalysts surface.

Simultaneous NO and mercury removal over MnOx/TiO2 catalyst in different atmospheres

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 Hg0 conversion rate on MnOx/TiO2 was evaluated in different atmospheres, and the interaction between denitration and demercuration was investigated. The results indicated that MnOx/TiO2 had good activity in simultaneously removing NO and Hg0 in SCR atmosphere (NH3+NO+O2+N2). However, both NO conversion and Hg0 removal efficiency were inhibited in simulated coal combustion flue gas compared to that in SCR atmosphere because of the presence of SO2 leading to the generation of sulfite and sulfate on the catalyst. H2O 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 Hg0 removal efficiency in oxy-fuel combustion flue gas was higher than that in air combustion flue gas. Hg0 displayed no obvious influence on NO conversion and N2 selectivity over SCR process. And SCR atmosphere showed almost no inhibition to Hg0 removal when the temperature was below 300°C. At the optimal temperature for NO conversion (250°C), the inhibition of SCR atmosphere on Hg0 removal became stronger as the space velocity (GHSV) increased, but the inhibitive effect could be ignored when GHSV slowed down to 50,000h−1 or less.

Efficient removal of HCHO from simulated coal combustion flue gas using CuO-CeO2 supported on cylindrical activated coke

To achieve novel sorbent-catalysts with low cost and high activity for removing HCHO in flue gas, we prepared and investigated CuO-CeO2 supported on activated coke granules (CuCe/AC) for decomposition of gaseous formaldehyde (HCHO) from simulated coal combustion flue gas. The results indicated that Cu3Ce8/AC exhibited remarkable conversion performance and good stability for HCHO removal. The presence of NO and SO2 exhibited a slight inhibitive effect on HCHO removal in the presence of 6% O2. The physicochemical properties of CuCe/AC were also studied by combination of N2 adsorption/desorption, SEM, XRD, H2-TPR, XPS and FT-IR. The excellent conversion property of Cu3Ce8/AC was related to the high surface area, large pore volume, high dispersion of copper species, good adsorption capacity and great redox ability of metal oxides. Besides, the synergy between Cu and Ce species improved the mobility of activated oxygen species and the content of chemisorption oxygen, which facilitated the conversion of HCHO greatly. FT-IR results suggested that adsorbed HCHO on the samples surface was oxidized into intermediates, which could be further decomposed into H2O and CO2 by the surface active oxygen of Cu3Ce8/AC. Along with the advantages of Cu3Ce8/AC, it would be a promising material for the removal of HCHO in real industrial application.

Influences of Copper(II) Chloride Impregnation on Activated Carbon for Low-Concentration Elemental Mercury Adsorption from Simulated Coal Combustion Flue Gas

In this study, the Hg0 adsorption equilibrium and kinetics of a coconut-shell-based activated carbon impregnated with CuCl2 were examined with respect to their resulting physical and chemical properties. Integrating the results from N2 adsorption isotherm at 77 K, scanning electron microscopy, elemental analysis, X-ray photoelectron spectroscopy, and Hg0 adsorption experiments under N2 and simulated coal-combustion flue gases conditions, it was found that HCl pretreatment could enhance Hg0 adsorption of crude activated carbon; the Hg0 adsorption capacities of crude and HCl-pretreated activated carbon under N2 condition were 95.8 and 225.4 µg g–1, respectively. Additionally, CuCl2 impregnation further increased the adsorption capacity of crude. The Hg0 adsorption capacity of crude activated carbon with 8% CuCl2 impregnation was 631.1 µg g–1. However, the equilibrium Hg0 adsorption capacity decreased when Cu loading exceeded 8 wt%, suggesting that adequate forms of surface Cu, O and Cl interacting with flue gas components and Hg0, as well as the presence of pores with specific size ranges allowing rapid transport of the Hg molecules into the interior of the activated carbon and as energy sinker govern the overall chemisorption process. Pseudo-second-order kinetic model could best describe the adsorption behaviors of tested samples under both test conditions, indicating that Hg0 adsorbed on the activated carbon surface could be explained by bimolecular reaction mechanisms.

Multipollutant removal of Hg0/SO2/NO from simulated coal-combustion flue gases using metal oxide/mesoporous SiO2 composites

This study investigated the multipollutant control effectiveness for Hg0/SO2/NO using V, Mn, and Cu oxides/mesoporous SiO2 particulate composites. The presence of metal oxides decreased the specific surface area and pore volume and altered the surface morphology and sizes of the raw SiO2 particles. V4+/V5+, Mn4+, and Cu+/Cu2+ were the major valence states in the VOx, MnOx, and CuOx/SiO2 composites, respectively. Amorphous and highly dispersed metal oxides presenting in the SiO2 composites was confirmed by the X-ray diffraction characteristic peaks. Multipollutant control of Hg0 and NO using the metal oxide/SiO2 composites was achieved at both 150 and 350°C under the simulated coal-combustion flue gas condition. CuOx/SiO2 with >40% Hg0 removal at 350°C further implies that strong chemical bonds could form between Hg species and the surface groups of CuOx/SiO2. The metal oxide/SiO2 composites had up to 62% NO removal enhancement with injection of NH3 at 350°C, indicating the effectiveness of catalytic reduction of NO. The CuOx/SiO2 composite showed the greatest Hg0 and NO removal performance, which may stem from the presence of active CuOx in high content and its large surface area and mesoporosity.

Catalytic oxidation removal of gaseous elemental mercury in flue gas over niobium‐loaded catalyst

Nb‐Co‐Ce/Al2O3 catalysts prepared by impregnation, sol‐gel method, and co‐precipitation were examined for elemental mercury (Hg0) oxidation in a simulated coal combustion flue gas. The catalysts were characterized by SEM‐EDS, BET, XRD, FTIR, and XPS techniques. The performances of different niobium‐loaded catalysts on Hg0 oxidation efficiency with regard to preparation method, assistant, reaction temperature, and typical individual flue gas were investigated. The results showed that the Hg0 oxidation efficiency performed at the highest value for niobium‐loaded catalysts at 523 K. SO2 was observed to have a negative effect on Hg0 oxidation. The niobium‐loaded catalysts prepared by the sol‐gel method and co‐precipitation exhibited higher Hg0 oxidation efficiency than that prepared by impregnation, due to higher specific surface area and more exposure of active sites. However, it also results in these catalysts being affected by SO2 more easily. An enhancing effect of O2 was observed and an addition of HCl would promote the Hg0 oxidation further. Results also indicated that synergistic effects between NbOx, CoOx, and CeOx could promote the sustainable capacity of Hg0 oxidation for Nb‐Co‐Ce/Al2O3 catalysts. Hg0 oxidation over Nb‐Co‐Ce/Al2O3 catalysts is thought to follow a Mars‐Maessen mechanism in which lattice oxygen derived from NbOx would react with absorbed Hg0.

Catalytic Destruction of a Surrogate Organic Hazardous Air Pollutant as a Potential Co-benefit for Coal-Fired Selective Catalytic Reduction Systems

Catalytic destruction of benzene (C6H6), a surrogate for organic hazardous air pollutants (HAPs) produced from coal combustion, was investigated using a commercial selective catalytic reduction (SCR) catalyst for evaluating the potential co-benefit of the SCR technology for reducing organic HAP emissions. Bench-scale experiments were performed using simulated coal combustion flue gases under a broad range of SCR reaction conditions. C6H6 was added at 1 or 17 ppm into the flue gas mixtures with different concentrations of sulfur dioxide (SO2), nitrogen oxide (NO), hydrogen chloride (HCl), and ammonia (NH3) to simulate the combustion of bituminous and sub-bituminous coals. The destruction of the C6H6 across the catalyst was measured by a total hydrocarbon analyzer and a resonance-enhanced multiphoton ionization time-of-flight mass spectrometer (REMPI–TOFMS) for the experiments with high (17 ppm) and low (1 ppm) concentrations of C6H6, respectively. The operating parameters of the SCR process, including the ...

Removal of Gaseous Elemental Mercury by Cylindrical Activated Coke Loaded with CoOx-CeO2 from Simulated Coal Combustion Flue Gas

Co–Ce mixed oxides were loaded on commercial cylindrical activated coke granules (CoCe/AC) by an impregnation method to remove gaseous elemental mercury (Hg0) from simulated coal combustion flue gas at low temperature (110–230 °C). Effects of the Co/Ce molar ratio in Co–Ce mixed oxides, mixed oxides loading value, reaction temperature, and flue gas components (O2, NO, SO2, H2O) on Hg0 removal efficiency were investigated, respectively. Brunauer–Emmett–Teller analysis, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) analysis were employed to analyze the characteristics of the samples. Results showed that up to 92.5% of Hg0 removal efficiency could be obtained over Co4.5Ce6/AC at 170 °C. The remarkably high Hg0 removal ability of Co4.5Ce6/AC mainly depended on the synergetic effect between cobalt oxide and ceria. Additionally, different with the pure N2 condition, the existence of O2 and NO...

Performance of CuOx–neutral Al2O3 sorbents on mercury removal from simulated coal combustion flue gas

Copper based sorbents are used to control mercury emissions in coal-fired flue gas. CuOx impregnated on neutral Al2O3 (CuOx–Al2O3) sorbents were found to enhance catalytic oxidation of elemental mercury in the presence of hydrogen chloride (HCl). The Hg0 oxidation rates increased along with the increasing HCl concentration and temperature. The mercury oxidation rates were over 65% in the presence of 50ppm HCl and the mercury adsorption amounts were over 75% in the early stage of the mercury removal process. CuOx–Al2O3 sorbents demonstrated good mercury removal capacity. The effect of HCl is due to the formation of active chlorine. CuOx–Al2O3 sorbents also have excellent sulfur resistance in the presence of HCl. A mixture of CuOx–Al2O3 and activated carbon can remove more than 90% Hg0 with a lower mercury removal cost for industrial applications. The characterizations of the CuOx–Al2O3 sorbents were measured suggesting CuOx species work as catalysts via the redox shift between Cu2+ and Cu+. The mercury oxidation mechanism of the sorbents is proposed to follow the Mars–Maessen mechanism.

Removal of Mercury from Simulated Coal Combustion Flue Gas by Iron Sulfide-AC Adsorbent

Iron sulfide-AC adsorbents were prepared and their mercury removal capabilities were evaluated in the simulated coal combustion flue gases. The FeS2 has much higher mercury removal rate than AC although it has much lower BET surface area than AC. FeS2 also shows higher mercury removal rate than FeS, which is probably due to its higher free sulfur content on the FeS2. The mercury removal capability of AC modified FeS2 decreases with increasing of AC content. Temperature programmed desorption/decomposition process (TPDD) shows FeS and FeS2 have more desorption peak than AC and the main peaks of FeS and FeS2 are at around 240°C. The desorption peaks of AC modified FeS2 are shifted to the higher temperature compared with that of FeS2 and more mercury compositions are desorbed by AC modified FeS2.

Study of elemental mercury oxidation over an SCR catalyst with calcium chloride addition

• Hg 0 could be oxidized over CaCl 2 . • Adding CaCl 2 to the SCR catalyst dramatically enhanced the Hg 0 oxidation activity. • Key factors on mercury oxidation over the catalyst added with CaCl 2 were Optimized. • Mercury oxidation was due to the combined action of HCl and Cl ∗ generated by CaCl 2 . Elemental mercury in the flue gas of coal combustion is challenging to remove. A new method is introduced of adding calcium chloride to a commercial SCR catalyst in a fixed bed to evaluate the effect on elemental mercury oxidation. In simulated coal combustion flue gas at 350 °C, the calcium chloride addition dramatically enhanced the Hg 0 oxidation activity over the catalyst. By adding 1.0 wt.% calcium chloride to the catalyst, the Hg 0 oxidation efficiency rose from 7.7% to 78.8%. With a temperature increase from 100 °C to 400 °C, the catalytic oxidation efficiency of elemental mercury considerably increased, and mercury capture by the catalyst dropped. Both oxygen and sulfur dioxide exhibited promotional effects on Hg 0 oxidation, whereas water vapor inhibited it. No apparent difference was observed by varying the nitric oxide concentration. The positive function of calcium chloride addition on elemental mercury oxidation is due to two reasons: hydrogen chloride formed through the hydrolysis process of calcium chloride and active chlorine species generated by calcium chloride. Experimental study showed that no significant effect of calcium chloride addition on NOx reduction and SO 2 –SO 3 conversion has been observed. Because oxidized mercury can be easily removed by traditional pollutant control equipment and because calcium chloride is enriched in the wastewater of the wet flue gas desulfurization system in power plants, this method shows a reasonable simultaneous mercury reduction method.

Kinetic modeling of mercury oxidation by chlorine over CeO2–TiO2 catalysts

Hg0 oxidation by chlorine over CeO2–TiO2 (CeTi) catalysts with different CeO2/TiO2 ratios was investigated both in the absence and the presence of SO2. Experimental data were analyzed using a kinetic model incorporating mass transfer, adsorption equilibrium and mass balance with key variables of interest being residence time, catalyst type and HCl concentration in simulated coal combustion flue gas. The experimental data fitted the proposed kinetic model very well, indicating the validity of the model for describing the mechanism of Hg0 oxidation by chlorine over CeTi catalysts. Important kinetic parameters, i.e. the overall reaction rate constant and the Langmuir adsorption constant, were obtained by fitting the model with experimental data. Without SO2, pure CeO2 exhibited the best performance in catalyzing Hg0 oxidation by chlorine, which had a high reaction rate constant k of 130±16.3s−1. An addition of SO2 did not inhibit the adsorption of HCl on pure CeO2; however, it inhibited reactions between Hg0 and chlorine species over pure CeO2, hence resulting in a decrease of Hg0 oxidation efficiency. Combining CeO2 with TiO2 enhanced its resistance to SO2. Ce1.5Ti exhibited excellent resistance to SO2. Both the overall reaction rate constant and the Langmuir adsorption constant maintained at the same level when 400ppm SO2 was introduced to the flue gas containing N2 and HCl. The identification of the kinetics of heterogeneous oxidation of Hg0 by chlorine in this study is of fundamental importance for scaling up mercury removal by selective catalytic reduction (SCR) plus wet flue gas desulfurization system (WFGD) from a laboratory system to a pilot or full scale.

Regenerable sorbents for mercury capture in simulated coal combustion flue gas

This work demonstrates that regenerable sorbents containing nano-particles of gold dispersed on an activated carbon are efficient and long-life materials for capturing mercury species from coal combustion flue gases. These sorbents can be used in such a way that the high investment entailed in their preparation will be compensated for by the recovery of all valuable materials. The characteristics of the support and dispersion of gold in the carbon surface influence the efficiency and lifetime of the sorbents. The main factor that determines the retention of mercury and the regeneration of the sorbent is the presence of reactive gases that enhance mercury retention capacity. The capture of mercury is a consequence of two mechanisms: (i) the retention of elemental mercury by amalgamation with gold and (ii) the retention of oxidized mercury on the activated carbon support. These sorbents were specifically designed for retaining the mercury remaining in gas phase after the desulfurization units in coal power plants.

Catalytic oxidation of Hg0 by CuO–MnO2–Fe2O3/γ-Al2O3 catalyst

CuO–MnO2–Fe2O3/γ-Al2O3 (CMFA) SCR (selective catalytic reduction) catalyst prepared by improved impregnation method was studied for gas-phase mercury oxidation in a simulated coal combustion flue gas at typical SCR temperatures. Brunauer–Emmet–Teller (BET), X-ray Diffractogram (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the catalyst. The CMFA catalyst yielded more than 70% oxidation efficiency using a simulated flue gas (O2, CO2, HCl, NO, SO2, H2O and balanced with N2). A 3-day experiment indicated that CMFA had a long service life and would be promising in industrial applications. In the presence of O2, an enhancing effect of HCl, NO and SO2 was observed. Without O2, NO still promoted Hg0 oxidation due to the formation of multi-activity NOx species. Meanwhile, SO2 had little effect on Hg0 oxidation and HCl inhibited Hg0 adsorption and subsequent oxidation. Hg0 oxidation over the CMFA catalyst might follow the Eley–Rideal mechanism, where gaseous or weakly bonded Hg0 reacted with adsorbed active species on the catalyst surface to generate Hg2+. Although NH3 would inhibit Hg0 oxidation, once NH3 was cut off, the efficiency fully recovered. This study provided a promising method for simultaneous removal of NO and Hg0 from coal-fired power plants.

Role of flue gas components in mercury oxidation over TiO2 supported MnOx-CeO2 mixed-oxide at low temperature

MnOx-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.