dioxin) with V2O5

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Catalytic conversion of multipollutants (Hg0/ NO/dioxin) with V2O5-WO3/TiO2 catalysts Wei Ting Hsu, Pao-Chen Hung, Shu Hao Chang, Chyi Woei Young, Chi Lang Chen, Hsing Wang Li, Kuan Lun Pan, and Moo Been Chang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b02804 • Publication Date (Web): 18 Oct 2018 Downloaded from http://pubs.acs.org on October 23, 2018

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Industrial & Engineering Chemistry Research

Catalytic conversion of multipollutants (Hg0/NO/dioxin) with V2O5-WO3/TiO2 catalysts Wei Ting Hsu a, Pao Chen Hung a, Shu Hao Chang a, Chyi Woei Young b, Chi Lang Chen b, Hsing Wang Li b, Kuan Lun Pan a, Moo Been Chang a,* a Graduate

Institute of Environmental Engineering, National Central University, 300

Jhong-da Road, Jhongli, Taoyuan 32001 Taiwan, Republic of China b New

Materials R & D Department, China Steel Corporation (CSC), Kaohsiung 812, Taiwan, Republic of China *Telephone/Fax: +886-3-4226774 E-mail: [email protected]

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Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract A multipollutant (Hg0/NO/dioxin)-containing gas stream generating system is developed to investigate the effectiveness of V2O5-WO3/TiO2 catalyst for multi-pollutant control. The results indicate that plate-type 1.52 wt% V2O5 performs much better than two other catalysts for oxidizing Hg0. With a higher vanadium loading of 1.52 wt% V2O5, higher Hg0 conversions (53% → 75%) are observed compared to 0.66 wt% V2O5 (45% → 68%) and 0.26 wt% V2O5 (32% → 63%) for simulated flue gas streams. In addition, the mercury oxidation activity significantly increases with increasing concentration of hydrogen chloride. For the removal of PCDD/Fs, the results show that the removal efficiencies of PCDD/F congeners achieved with V2O5-WO3/TiO2 range from 50% to 65%. It is observed that the removal efficiency of highly chlorinated PCDD/Fs is slightly higher than that of low chlorinated PCDD/Fs. Overall, plate-type catalyst of 1.52 wt% V2O5 shows the highest Hg0/NO/dioxin conversion and reduction efficiency among three catalysts evaluated.

Keywords Mercury oxidation, V2O5-WO3/TiO2 catalyst, Multipollutants control, PCDD/Fs removal, NO conversion


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1. Introduction Mercury in flue gas of thermal processes can be divided into particulate mercury (Hg(p)), gaseous elemental mercury (Hg0) and gaseous oxidized mercury (Hg2+)1. Among them, gaseous elemental mercury is especially of concern due to its low solubility which makes it difficult to remove with end-of-pipe treatment from coal-fired power plants2, leading to bio-concentration and bio-magnification effect in biosphere. Relevant study reported that mercury emitted from coal-fired power plants accounts for 35% of anthropogenic emission globally3. Hence, coal-fired power plants have been regarded as one of the most important anthropogenic sources of mercury. Stringent environmental regulations have been established for reducing mercury emission in many countries due to Minamata Convention on Mercury. For example, Taiwan EPA adopted 5 μg/Nm3 as the emission standard for existing power plants starting January 20154. Various methods including wet flue gas desulfurization (FGD) and selective catalytic reduction (SCR) have been applied to reduce the mercury emissions from coal-fired power plants5-6. Previous study indicates that the fraction of elemental mercury at the SCR inlet of coal-fired power plant is approximately 76% to 92%, with the remaining in the oxidized form and relatively low fraction is measured as particulate mercury (Hg(p)) which can be removed by a particulate control device such as an electrostatic precipitator (ESP) or bag filter (BF)7. Hg2+ is water-soluble and can further be effectively captured by wet flue gas desulfurization (WFGD) systems. Therefore, the co-benefit of combining SCR and FGD plays an important role in mercury removal. In order to enhance the total mercury removal efficiency, converting Hg0 to Hg2+ in coal-fired flue gas streams by SCR and further removed by FGD system is 3 ACS Paragon Plus Environment


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presented as the best available control technology. Relevant studies indicate the effectiveness of converting elemental mercury by SCR system7-8. In recent years, a series of pilot- and bench-scale experimental tests were conducted to investigate the effects of flue gas components on mercury oxidation. With HCl present in the flue gas, previous studies9-11 indicate that significant enhancement of mercury oxidation is observed with SCR. The presence of chlorine species is beneficial for elemental mercury oxidation. Usberti et al. (2016) reveal that the conversion of Hg0 was temperature dependent under various HCl concentrations below 300oC12. In contrast, it was significantly dependent on HCl content of flue gas at high temperatures (>300oC)13. In coal-fired power plant, the SCR system is mainly used for NOx emission control. Hence, some studies have investigated simultaneous Hg0/NO conversion efficiency under different operating conditions14-16. Niksa and Fujiwara (2005) evaluate the effect of NH3/NO ratio on Hg0/NO conversion and indicate that Hg0/NO conversion efficiency ranges from 40% to 60% when NH3/NO ratio is controlled at 0.614. NH3/NO ratio is one of the key parameter affecting Hg0 oxidation at a high area velocity (21~30 m/h)15. The presence of NH3 inhibits mercury oxidation with SCR due to the competition for the same active sites, leading to a high loading of the active sites with HCl on the catalyst surface17-18. Furthermore, the area velocity determines the overall impact of ammonia inhibition for Hg0 oxidation. Increasing the area velocity of a bench-scale SCR reactor results in significantly lower Hg0/NO oxidation efficiency15, 19. Moreover, the effects of O2 on regeneration of lattice oxygen and promotion of oxygen chemisorption on the catalyst surface for Hg0/NO conversion have been investigated17,

20.

In addition, the

presence of Hg0 also promoted NO conversion in flue gas at low temperatures (200-300oC). In contrast, the presence of Hg0 inhibited NO conversion significantly at 4 ACS Paragon Plus Environment

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high temperature (>350oC)21. The NO conversion is slightly enhanced by adding SO2 due to higher acid loading on the catalyst surface, which also simultaneously promoted Hg0 oxidation activity by producing more active sites available for Hg0 oxidation22-23. Previous studies also indicate that water vapor has an inhibitory effect on Hg0/NO conversion due to competition effect of adsorption 24-25. Furthermore, catalytic destruction of gaseous polychlorinated dibenzodioxins and polychlorinated dibenzofuran (PCDD/Fs) via SCR system has been demonstrated26. Commercial SCR catalysts (TiO2-based V2O5-WO3) are effective in the destruction of PCDD/Fs27 and gas-phase PCDD/Fs are mainly converted into CO2, H2O, and HCl28. The vanadium-based catalyst which was originally designed for removing NOx also exhibits good performance in destruction of PCDD/Fs (over 95%) and conversion of NO, respectively29. In industrial applications, it has been applied for the simultaneous removal of NOx and PCDD/Fs. Therefore, SCR system has a good potential for removing multi-pollutants (Hg0/NO/dioxin) from gas streams from the perspective of total environmental management. Relevant study indicates that the activities of major transition metals for mercury oxidation are in the order of MoO3∼V2O5>Cr2O3>Mn2O3>Fe2O3>CuO>NiO and V2O5-WO3/TiO2 are commonly used in coal-fired power plants30. Moreover, in the case of coal-fired power plants, plate-type SCR catalysts are widely used for NOx removal due to the advantage of lower pressure drop for the flue gas containing high concentration of particulate matter in coal-fired power plants31. Therefore, this study aims to investigate the effectiveness of V2O5-WO3/TiO2 plate-type catalysts for the simultaneous conversion or removal of Hg0/NO/dioxin from simulated flue gas streams of a coal-fired power plant.



2. Materials and methods 2.1 Catalyst characterization X-ray diffraction (XRD) patterns were recorded with an X-ray diffraction meter (D8AXRD, Bruker, Germany) using Cu-Kα radiation. The radiation (λ = 1.5415 Å) was operated at 40 kV and 40 mA. Diffraction patterns were obtained within the range of 2θ = 10o-80o at a scanning rate of 6o min-1. Pore properties of catalysts were measured with Brunauer-Emmett-Teller (BET) ASAP2010 (Micromeritics Inc.), while morphology was characterized by scanning electron microscopy (SEM, JSM-6700F, JEOL, Japan). X-ray photoelectron spectra (XPS) were obtained using a PHI Quantera SXM/AES 650 Auger Electron Spectrometer (ULVAC-PHI INC., Japan) equipped with a hemispherical electron analyzer and a scanning monochromated Al Kα (hυ =1486.6 eV) X-ray source. All the binding energies were corrected for the signal of C 1s at 284.6 eV as an internal standard.

2.2

Catalytic reactor for mercury conversion The mercury-containing gas stream generation system developed consists of the

mercury impinger, cooler, temperature-controller and gas flow rate controllers. This system can stably generate the gas stream with the elemental mercury concentration ranging from 6.1 to 62 μg/Nm3. The experimental system is schematically shown in Figure 1. With different flow rates of gas stream being injected into the mercury generating system, the concentration of elemental mercury in the gas stream can be varied. The plate-type catalyst was placed in a stainless steel holder with a length of 0.1 m and a width of 20 mm. The stainless steel holder with fresh catalyst was then installed in an electric furnace and the temperature was controlled by a regulator. The temperature 6 ACS Paragon Plus Environment

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of the catalyst bed was monitored with a K-type thermocouple located in the middle of the reactor. In addition, the gases of ammonia, NO, HCl, CO2 and SO2 are also added to simulate the flue gas composition of a coal-fired power plant. These gas flows are controlled by a set of mass flow controller (MFCs) and further passed through a mixer. Water vapor was introduced into the system using a syringe pump to investigate its effect on Hg0 oxidation. Based on the real flue gas condition in the coal-fired power plant investigated, the gas flow rates of the carrier gas, comprising 6.5% O2, 12% H2O(g), 10% CO2, 90 ppm SO2, 25 ppm HCl, 80 ppm NO, 45 ppm NH3 and balanced with N2, through the reactor were set as 3.4 or 1.7 standard liters per minute (slpm), corresponding to the area velocity of 48 or 24 m/h, respectively. Table 1 shows the experimental conditions of SCR catalyst test for Hg0/NO conversion. Catalytic activity measurements were carried out with the gas stream containing specific mercury concentration and gas composition with three plate-type catalysts at atmospheric pressure in the temperature range of 280-360oC. Moreover, the effects of operating parameters including water vapor contents, catalyst composition and inflow mercury concentration on the oxidation efficiencies of elemental mercury are investigated.

2.3

Catalytic reactor for PCDD/Fs destruction The experimental tests are carried out with a continuous gas flow system. The

dioxin-containing gas stream generation system developed consists of a PCDD/F stock solution injector, temperature-controller, evaporator, and gas flow rate controllers32. Table 1 also shows the experimental conditions for PCDD/F destruction with SCR catalyst. This system can stably generate the gas stream with PCDD/F concentration ranging from 1.0 to 100 ng-TEQ/Nm3, depending on the flow rates of stock solution 7 ACS Paragon Plus Environment


injected and gas stream. With different types of PCDD/F stock solutions being injected into the system, the distributions of PCDD/F congeners in the gas stream can be varied. The PCDD/F stock solution used in this study was prepared by the extraction of fly ash sampled from an ESP of a sinter plant. The extract of the ESP ash was then subjected to clean-up procedures without the addition of PCDD/F standards (13C12-2,3,7,8-substituted congeners). In this study, the PCDD/F contents of real extract being injected were analyzed before conducting PCDD/F removal test. The reproducibility tests indicate that the PCDD/F recovery efficiencies are between 98% and 105%.

2.4 Mercury and NO sample analysis For the measurement of mercury concentration, gases were sampled from the sampling ports of catalytic bed outlet or inlet with an injection needle (2.5 mL). Further, the samples were injected into the sample tube and flowed through a gold amalgamation column housed in a tubular furnace. The remained Hg0 in the gas was adsorbed with gold amalgamation column. The Hg0 concentrated on the gold was then thermally desorbed and sent as a concentrated Hg0 stream to a cold-vapor atomic fluorescence spectrophotometer (CVAFS; Brooks Rand Lab Model III) for analysis. The NO concentration was continuously monitored with a flue gas component analyzer (Testo 350).

2.5 PCDD/F sample collection and analysis In this study, gaseous PCDD/F samples were collected by XAD-2 (Figure 1). Before sampling, the XAD-2 was spiked with known amounts of U.S. EPA Method 23 surrogate standard solution. The PCDD/F sample was collected by XAD-2 and then 8 ACS Paragon Plus Environment

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extracted by Soxhlet extractor with toluene for 24 hours. The toluene extract was then concentrated to about 1 mL by rotary evaporation and was replaced by 5 mL hexane for pretreatment process. The dioxin-containing sample after Soxhlet extraction was concentrated and subjected to a series of clean-up procedure. Finally, seventeen 2,3,7,8-substituted PCDD/F congeners are analyzed with high resolution gas chromatography (HRGC) / high resolution mass spectrometer (HRMS) (Model: Thermo Trace GC/Thermo DFS) using a fused silica capillary column DB-5 MS (60 m × 0.25 mm × 0.25 μm, J&W). The mass spectrometer was operated with a resolution greater than 10,000 under positive EI conditions, and data were obtained in the selected ion monitoring

(SIM)

13C

mode.

12-2,3,7,8-substituted

The

mean

recoveries

of

standards

for

all

PCDD/Fs range from 55% to 105%. The recoveries are all

within the acceptable 40-130% range, set by the U.S. EPA in Method 23. In this study, all TEQ concentrations of PCDD/Fs are calculated with international toxicity equivalent factors (I-TEF). 3. Results and discussion 3.1 Characterization of SCR catalysts A series of V2O5-WO3/TiO2 are especially prepared for the simultaneous control of multi-pollutants including Hg0, NO and PCDD/Fs. Various vanadium-based catalysts including 1.52 wt% V2O5-5.11 wt% WO3/TiO2, 0.66 wt% V2O5-5.86 wt% W/TiO2, and 0.26 wt% V2O5-3.05 wt% WO3/TiO2 are stood for catalyst A, catalyst B, and catalyst C, respectively. XRD result indicates the crystallinity of the TiO2 phase is of anatase form as shown in Figure 2. At first sight the XRD pattern shows a large similarity in all of the samples of peak locations and strengths. Only the diffraction peaks of anatase TiO2 and 9 ACS Paragon Plus Environment


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WO3 are clearly detected in the XRD pattern. The XRD results also imply that apparent crystallinity of V2O5 is not observed on the catalyst surface, indicating that the impregnated vanadium is uniformly dispersed on the SCR catalyst. Figure 3 shows the SEM analysis of these catalysts, indicating that three SCR catalysts present slight aggregation and their particle sizes are not significantly changed due to the same calcination temperature. As shown in Table 2, the specific surface areas of catalyst A, catalyst B, catalyst C are 62.03 m2/g, 76.14 m2/g and 79.77 m2/g, respectively. It is observed that the BET surface area of catalysts decreases with increasing contents of active component, implying that part of the TiO2 pores may be covered, resulting in a lower specific surface area. In addition, it is observed that 1.52 wt% V2O5-5.11 wt% WO3/TiO2 has the biggest average pore diameter compared with others. On the other hand, the XPS spectra of various catalysts are shown in Figure 4. Figure 4a displays the Ti 2p XPS spectra which consist of double peaks (Ti 2p1/2 and 2p3/2). For TiO2, the binding energies of these peaks are 464.5 and 458.6 eV, respectively, indicating that Ti of 3 catalysts prepared exists in the state of Ti4+ 33. It is observed that valences of titanium are not changed with various contents of vanadium (V) and tungsten (W). Relevant studies indicate that valence of TiO2 is generally present in the form of Ti4 if used as supported for V-W-based catalyst

34-36.

V-W-based catalyst may have a good

stability if TiO2 exists in the form of Ti4. In addition, Figure 4b presents O 1s XPS spectra of catalysts prepared, indicating that all SCR catalysts are mainly of 2 broad peaks, which are positioned at 530.0 eV and 532.5 eV, respectively, with could be assigned to lattice oxygen (Olat) and chemisorbed oxygen (Oads). Previous studies indicate that Oads may play an important role for SCR system34-35,

37.

However, some studies

believe that Olat is mainly responsible for catalytic performance, indicating that catalyst 10 ACS Paragon Plus Environment

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with a higher Olat/Oads+Olat ratio possesses better oxygen mobility which is beneficial to catalysis. For example, Zhang et al. (2011) indicate that catalysts with higher Olat/Oads+Olat ratio have the capacity to change the oxidation state to participate in a redox cycle, resulting in good catalytic performance38. In addition, relevant study indicates that catalysts with more lattice oxygen have a higher activity 39. The Olat/Oads+Olat ratios of catalysts are presented at Table 3, indicating that the order of Olat/Oads+Olat ratios is catalyst A > catalyst B > catalyst C. To refer activities of 3 catalysts prepared for the removals of NO and PCDD/F and the oxidation of Hg0 (as shown in Figure 5, 8, and 9). Result of this study seems in accordance with the latter theory. On the other hand, XPS spectra of V 2p are shown in Figure 4c, two peaks of V corresponding to 517.1 and 515.9 eV, which can be assigned to oxidation state of V5+ and V4+, respectively40. It is observed that V in catalyst A and catalyst B may exist in the form of V5+ and V4+ simultaneously. Especially, catalyst A possesses abundant V5+ and V4+ on catalyst. Relevant study indicates that unsaturated valence of V (such as V4+) could promote the adsorption of oxygen and form the reactive oxygen, which enhances the activity of catalyst34. Zhang et al. (2012) report that the reduction species V4+ may be the active site for the formation of superoxide ions that enhance activity of catalyst41. The transformation between V4+ and V5+ contributes to the catalytic activity for NH3-SCR reactions. In addition, previous study pointed out that Hg0 can easily react with V5+on the catalyst surface to form HgO42. From the previous study for XPS 33, it could

be determined that the peaks of W 4d5/2 in

all catalysts at about 247.1 eV could be attributed to W6+ species (as shown in Figure 4d). Previous study indicates that W6+ species could improve the formation of V4+ over V2O5/WO3/TiO2 catalyst 43.



Table 4 shows the atomic concentrations of V, W, Ti, O, C and Si on the catalyst surfaces by XPS analysis. The XPS analysis is only conducted for W4d peak due to the overlapping of peak between W4f and Ti3p. Therefore, it may lead to the deviation of atomic concentration in tungsten content. Considering the non-uniform dispersion of vanadium and tungsten contents on catalyst surface, the XPS results are utilized for reference only. In addition, there are no HgCl compounds existing on the catalyst surface due to the limit of detection of XPS.

3.2 Conversion and reduction of Hg0/NO The capability of the catalyst applied to oxidize Hg0 and reduce NO can be described by Hg0 oxidation and NO conversion efficiencies, respectively, as defined as follows: Hg0 oxidation (%) = ɳ = NO conversion (%) =

[Hg0]in ― [Hg0]out [Hg0]in

[NO]in ― [NO]out [NO]in

× 100%

× 100%

Figure 5a shows the Hg0 oxidation efficiencies achieved with three catalysts at different gas stream conditions. The impact of H2O(g) and area velocity on mercury oxidation efficiency is evaluated. It indicates that oxidation efficiencies of Hg0 achieved with three plate-type catalysts are significantly reduced as water vapor is added into the gas stream. Previous study indicates that addition of water vapor competes for the active sites of catalyst and further reduces the quantities of HCl, NOx and other reactive species being adsorbed on the catalyst surface, resulting in significant reduction of mercury conversion efficiency44. Therefore, the inhibition effect of H2O(g) plays an important role in NO conversion and Hg0 oxidation. In addition, decreasing area velocity promotes Hg0 12 ACS Paragon Plus Environment

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oxidation efficiency due to longer retention time. Relevant study indicates that operating the system with a lower area velocity effectively improves Hg0 oxidation efficiency45. It also demonstrates that the high area velocity may inhibit the mercury oxidation due to the reduction of the contact between mercury molecules and active sites of catalyst, limiting the oxidation rate of Hg0. The result also shows that plate-type catalyst A performs much better than two other catalysts for oxidizing Hg0 under the same operating condition. With a higher vanadium loading of catalyst A, higher Hg0 conversions (53% to 75%) are observed if compared to catalyst B (45% to 68%) and catalyst C (32% to 63%) at the same operating conditions. Obviously, the Hg0 oxidation efficiency achieved increases with increasing vanadium load of the catalysts. Previous study indicates that NO conversion efficiency achieved with SCR catalyst is between 40-60% when NH3/NO ratio is controlled at 0.614. Figure 5b shows the NO conversion efficiencies achieved with three plate-type catalysts at a NH3/NO ratio of 0.6. Results indicate that NO conversion efficiencies achieved are higher than 50% under dry gas stream condition except for catalyst C. Because of the higher vanadium loadings of catalyst A, higher NO conversions (47% to 52%) are observed compared to catalyst C at the same conditions. Experimental results also demonstrate that adding water vapor into simulated flue gas affects NO removal efficiency. That is attributed to the fact that water vapor may reduce the contact between NO molecules and active sites of catalyst, hence, inhibits the rate of reaction. The result also indicates that decreasing area velocity promotes the NO conversion efficiencies of three plate-type catalysts, as expected from previous study15. Referring to Figure 5a and 5b, plate-type catalyst C reveals the lowest efficiency for elemental mercury and NO conversions. On the other hand, catalyst A has the highest Hg0/NO conversion efficiency of these catalysts. Similarly, the NO 13 ACS Paragon Plus Environment


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conversion efficiency achieved increases with increasing vanadium load of these catalysts. Also, it is speculated that performance of catalyst for NO conversion/Hg0 oxidation is related with active oxygen of catalyst surface (namely, higher Olat/ Olat+Oads ratio has a good catalysis).

3.3 Mercury oxidation activity This study also investigates the influence of inlet Hg0 concentration and HCl in the gas stream on mercury oxidation activity. The potential of Hg0 oxidation can be expressed as Hg oxidation activity (K𝐻𝑔) according to equation Eq. (1), in a similar manner to the De-NOx activity of the catalyst: KHg = ―AV × ln(1 ― ɳ)

(1)

K𝐻𝑔 = mercury oxidation activity (m/h) AV = area velocity (m/h) η = oxidation efficiency of elemental mercury (%) In a real scale coal-fired power plant, the Hg0 concentration in flue gas is ranged from 3.8 μg/m3 to 6.9 μg/m3 before SCR system8. Therefore, it is essential to compare the mercury oxidation activities achieved with these catalysts for low Hg0 concentrations. Previous study indicates that the oxidation rate of elemental mercury increases with increasing inlet Hg0 concentration46 and the results presented in Figure 5c also reveal the same trend. With the area velocity of 48 m/h and the operating temperature of 320oC, the mercury oxidation activity achieved with catalyst A increases from 18 m/h to 36 m/h as inlet elemental mercury concentration is increased from 6.1 to 62 μg/m3. The mercury oxidation activities achieved with three catalysts increase to higher than 18 m/h for the gas stream containing 62 μg/m3 Hg0. This result indicates that the inlet elemental mercury 14 ACS Paragon Plus Environment

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concentration is an important factor affecting mercury oxidation activities. As the inlet elemental mercury is controlled at 6.1 μg/m3, however, the oxidation activity of mercury achieved with catalyst C is only 2 m/h. It is possibly attributed to the limitation of mass transfer at such low elemental mercury concentration. More importantly, the effect of relatively low elemental mercury concentrations in real flue gas on catalyst activity should be considered before applying it in a real scale coal-fired power plant. Previous study indicates that about 65% of the elemental mercury oxidation can be achieved with SCR catalytic converter when HCl and O2 are added into gas stream10. Compared with the situation in the absence of these gases, the oxidation efficiency is significantly increased. For mercury oxidation via catalysis, HCl could be regarded as an important source of chlorine, which can effectively be adsorbed on catalyst surface to produce active chlorine. Further, active chlorine can react with Hg0 to form HgCl2. Therefore, presence of chlorine species is beneficial for elemental mercury oxidation. As shown in Figure 5d, the mercury oxidation activities of three catalysts are significantly increased when 15 ppm HCl is added into the gas stream. However, only a slight improvement of mercury oxidation activity is observed when the HCl concentration is further increased beyond 25 ppm. The mercury oxidation activities of three catalysts are higher than 20 m/h with the HCl concentration of 35 ppm. It also shows that the mercury oxidation activities increase with increasing vanadium content of catalyst with various HCl concentrations. However, the mercury oxidation activities of three catalysts are still higher than 4 m/h without the presence of HCl. It may be attributed to the fact that the presence of residual oxygen in flue gas has a promoting effect for Hg0 oxidation. At low HCl concentration, the result shows that the advance effect of HCl is close to linear distribution. In contrast, the trend of mercury oxidation activities changes to moderate at 15 ACS Paragon Plus Environment


higher HCl concentration. This result also evidences the fact that catalyst hardly oxidizes Hg0 without the existence of HCl. Figure 6 shows the mercury oxidation activities of three catalysts. It indicates that variations in mercury oxidation activities are due to different amounts of vanadium supported on catalyst and water vapor content of the flue gas. The Hg0 oxidation activity increases with increasing vanadium contents of catalyst for dry gas stream. The linear regression correlation coefficient (R2) is calculated as 0.993. In contrast, the mercury oxidation activities of three catalysts decrease significantly when water vapor is added into the gas stream. Similar trend of oxidation activity can also be observed with increasing vanadium contents (R2 = 0.915). Therefore, it was found that the inhibitory effect of water vapor is linear in mercury oxidation activity with various vanadium content of catalyst.

3.4 Activation energies of Hg0 oxidation Previous study indicates that the oxidation efficiency of Hg0 achieved with a plate-type catalyst reaches 70% as the operating temperature is controlled at 300oC to 400oC47. The impact of the operating temperature is also investigated in this study and three operating temperatures (280, 320, and 360°C) are selected for testing. In general, the operating temperature of catalyst reactor is one of the key parameter affecting Hg0 oxidation efficiency. Figure 7a shows the oxidation efficiencies of Hg0 achieved with three catalysts at an area velocity at 48 m/h under simulated flue gas conditions in optimum temperature range. The Hg0 oxidation efficiencies achieved with three catalysts were over 50% at a temperature of 280oC. This result also shows that Hg0 oxidation efficiency increases with increasing operating temperature. The highest efficiency can be 16 ACS Paragon Plus Environment

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obtained at 360oC. As the operating temperature is increased to 360oC, the mercury oxidation efficiency achieved with A, B and C catalyst are 80%, 74% and 73%, respectively. Furthermore, catalyst A shows the highest oxidation efficiency of mercury at each operating temperature. This study also investigates the activation energy of Hg0 oxidation with a plate-type SCR catalyst. To simplify the calculation, the pore diffusion resistance and membrane resistance are assumed negligible. The reaction rate constant is calculated with Eq. (2) by combining integral plug flow reactor and Eley-Rideal mechanism model46. ki = ―

F0ln (1 ― ɳoxi)

(2)

C0V𝑅

ki = Rate constant for mercury oxidation (s-1) F0= Hg0 feed rate (mole/sec) C0 = Initial Hg0 concentration (mole/cm3) ɳoxi = Mercury oxidation efficiency V𝑅 = Catalyst volume (cm3) The rate constants (ki) at different temperatures were determined from the slope of the plots. Further, the activation energies and frequency factors are calculated with the Arrhenius equation (3): (3)

k𝑖 = A × exp( ― E𝑎/RT) A = pre-exponential factor Ea = activation energy (J/mol) R = gas constant 8.314 (J/K-mol) T = gas temperature (K)

Figure 7b shows the Arrhenius plots of ln(ki) versus inverse temperature (1/T). As 17 ACS Paragon Plus Environment


shown in Table 5, the activation energies and frequency factors of elemental mercury oxidation are calculated as 10.5-15.0 kJ/mole and 17.2-33.8 sec-1, respectively. This result also reveals that activation energy decreases with increasing vanadium content of catalyst. Previous study indicates that the activation energy obtained is within the range of 75.3-87.8 kJ/mol in simulated flue gas condition (Hg0 = 10 μg/m3, HCl = 10 mg/m3, NO = 300 ppm, SO2 = 500 ppm, H2O = 10%, O2 = 5%, CO2 = 9% and N2 balance)9, 15. Compared with previous study, however, the lower activation energy is obtained in this study (Table 5). It may be attributed to the absence of water vapor in flue gas. Niksa et al. (2001) evaluates the elementary reaction mechanisms for homogeneous Hg0 oxidation when HCl is the primary chlorinated species, as shown in Eqs. (4) and (5)48: Hg0 + HCl = HgCl + H

(4)

HgCl + HCl = HgCl2 + H

(5)

The apparent activation energies of Eqs. (4) and (5) are calculated as 333.1 kJ/mole and 80.2 kJ/mole, respectively48. Compared to the homogeneous oxidation reactions of Eqs. (4) and (5), utilizing the catalyst significantly decreases the activation energy. Moreover, previous study also indicates that activation energy of oxidizing elemental mercury with V2O5-WO3/TiO2 based commercial SCR catalyst is 37.7 kJ/mole for the temperature ranging from 250 to 350oC (reaction condition: Hg0 concentration = 61 μg/m3, HCl = 20 ppm, O2 = 8% and N2 balance)46. Obviously, the activation energy of three catalysts prepared in this study is significantly lower than other studies10, 16, 46. The catalyst A with a higher vanadium loading of 1.52 wt% V2O5 catalyst has good performance for mercury oxidation.

3.5 Removal efficiency of PCDD/Fs 18 ACS Paragon Plus Environment

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The capability of the catalyst applied to remove PCDD/Fs is described by PCDD/Fs removal efficiency and defined as follows: PCDD/F removal (%) =

[PCDD/F]in ― [PCDD/F]out [PCDD/F]in

× 100%

Figure 8a displays the inlet and outlet PCDD/F concentrations of three catalysts, respectively. The inlet PCDD/Fs concentrations of three catalysts are 2.11, 1.96 and 2.06 ng-TEQ/Nm3, respectively, which are close to 2 ng-TEQ/Nm3. The outlet PCDD/F concentrations of three catalysts are in the range of 0.73-1.06 ng-TEQ/Nm3. Our previous study confirmed that the PCDD/F destruction over V2O5-WO3/TiO2 follows Mars-Maessen mechanism, and 84% to 91% PCDD/F destruction efficiencies are achieved with V2O5-WO3/TiO2 honeycomb-type catalysts at 280oC with the space velocity of 5000 h-132. In this study, the PCDD/Fs removal efficiency achieved with the catalyst A reaches 65% which is slightly higher than two other catalysts. Relatively lower PCDD/F removal efficiencies achieved with the plate-type catalysts may be attributed to the high area velocity applied in this study. Previous study also indicates that the catalytic removal efficiency of PCDD/Fs decreases with increasing space velocity due to shorter retention time32. Furthermore, the structure of catalyst is one of the important factors affecting PCDD/F removal. Compared to honeycomb-type catalyst, plate-type catalyst has larger channel sections and results in a reduced contact time and lower collision frequency between PCDD/Fs and active sites. Moreover, the PCDD/F removal efficiency achieved with three catalysts increases with increasing vanadium content of the catalysts. The dioxin removal efficiencies achieved with A, B and C catalyst are 65%, 57% and 50%, respectively, as shown in Figure 8b. This result indicates that the activity of catalyst is significantly affected by the vanadium content in catalyst. 19 ACS Paragon Plus Environment


Several key parameters may influence the removal efficiency of PCDD/Fs congeners including: (i) chlorination degree of congener (ii) space velocity in flue gas (iii) operating temperature of SCR catalyst, and (iv) composition of catalyst49-51. Removal efficiencies of PCDD/F congeners achieved with three catalysts at 320oC are presented in Figure 9. It is worth noting that the removal efficiencies of highly chlorinated PCDD/Fs are slightly higher than that of low chlorinated PCDD/Fs. It may be attributed to the incomplete dechlorination of highly chlorinated PCDD/Fs with a relatively high area velocity. Highly chlorinated PCDD/Fs may convert to lower chlorinated PCDD/Fs via partial dechlorination. The dechlorination mechanism of OCDD leads theoretically to the most toxic congener, 2,3,7,8-TCDD, as was investigated by DFT49. Previous study also observed that the removal efficiency of low chlorinated PCDD/Fs congeners are significantly lower than that of highly chlorinated PCDD/Fs congeners achieved with W-modified catalysts at a high space velocity of 37,000 h-150. It is known that the substitutions of chlorine adjacent to the lateral sites (positions 2,3,7,8) are more stable than those at the position remote from the longitudinal sites (1,4,6,9)51-52. Therefore, it also revealed that thermal or catalytic reactions are tending to dechlorination processes of PCDD/Fs congeners with high chlorination degree and unstable chlorine substitutions. Weber et al. (2001) indicates that volatility and oxidative behavior of the compounds are both important parameters affecting PCDD/Fs removal53. In this study, the removal efficiencies of OCDD achieved with three catalysts are close to 90% at a temperature of 320°C. It may be attributed to the easier adsorption of highly chlorinated PCDD/Fs on the catalyst surface than low chlorinated PCDD/Fs. Therefore, highly chlorinated PCDD/Fs are of more reaction time for oxidation than low chlorinated PCDD/Fs.


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4.

Conclusion A multipollutant-containing gas stream generating system which can stably generate

the gas stream with constant Hg0/NO/dioxin concentrations is developed. This new multipollutant-containing gas stream generating device is applied for the investigation of three plate-type V2O5-WO3/TiO2 catalysts for Hg0/NO/dioxin control. Effects of temperature, water vapor content and area velocity on the conversion or reduction efficiency of Hg0/NO with three catalysts are investigated. The results show that the conversion or reduction efficiency of Hg0/NO achieved with three plate-type catalysts significantly decreases as water vapor is added into the gas stream. That is attributed to the fact that water vapor reduces the contact between Hg0 and active sites, inhibiting Hg0 oxidation with catalyst. With a higher vanadium loading, higher Hg0 oxidation (53% to 75%) efficiencies are obtained with 1.52 wt% V2O5 catalyst compared to two other catalysts. When the inlet elemental mercury concentration is reduced to 6.1 μg/m3, the oxidation activity of mercury achieved with 0.26 wt% V2O5 catalyst is only 2 m/h, possibly due to the diffusion limit. Within the operating temperature ranges of 280-360oC, the activation energies of elemental mercury via three catalysts are between 10.5 and 15.0 kJ/mole. Results indicate that PCDD/Fs congener removal efficiencies show a similar trend of these catalysts. The PCDD/Fs removal efficiency achieved with 1.52 wt% V2O5 catalyst reaches 65% which is slightly higher than two other catalysts. Highly chlorinated PCDD/F congeners are converted to low chlorinated PCDD/Fs via dechlorination mechanism with a high area velocity. Overall, this study compares the effectiveness of three catalysts for Hg0/NO/dioxin conversion, and the results indicate that catalyst with higher vanadium loading has the highest efficiency for multi-pollutants control. 21 ACS Paragon Plus Environment


References (1) Galbreath, K. C.; Zygarlicke, C. J. Mercury Transformations in Coal Combustion Flue Gas. Fuel Process. Technol. 2000, 65, 289. (2) Lee, S. J.; Seo, Y. C.; Jang, H. N.; Park, K. S.; Baek, J. I.; An, H. S.; Song K. C. Speciation and Mass Distribution of Mercury in A Bituminous Coal-fired Power Plant. Atmos. Environ. 2006, 40, 2215. (3) Pirrone, N.; Cinnirella, S.; Feng, X.; Finkelman, R. B.; Friedli, H. R.; Leaner, J.; Mason, R.; Mukherjee, A. B.; Stracher, G. B.; Streets, D. G.; Telmer, K. Global Mercury Emissions to the Atmosphere from Anthropogenic and Natural Sources. Atmos. Chem. Phys. 2010, 10, 5951. (4) Taiwan Environmental Protection Administration. http://ivy5.epa.gov.tw/docfile/040152.pdf, 2015 (last access: January). (5) Pavlish, J. H.; Sondreal, E. A.; Mann, M. D.; Olson, E. S.; Galbreath, K. C.; Laudal, D. L.; Benson, S. A. Status Review of Mercury Control Options for Coal-fired Power Plan. Fuel Process. Technol. 2003, 82, 89. (6) Dίaz-Somoano, M.; Unterberger, S.; Hein, K. R. Mercury Emission Control in Coal-fired Plants: The Role of Wet Scrubbers. Fuel Process. Technol. 2007, 88, 259. (7) Benson, S. A.; Laumb, J. D.; Crocker, C. R.; Pavlish, J. H. SCR Catalyst Performance in Flue Gases Derived from Subbituminous and Lignite Coals. Fuel Process. Technol. 2005, 86, 577. (8) Pudasainee, D.; Lee, S. J.; Lee, S. H.; Kim, J. H.; Jang, H. N.; Cho, S. J.; Seo, Y. C. Effect of Selective Catalytic Reactor on Oxidation and Enhanced Removal of Mercury in Coal-fired Power Plants. Fuel 2010, 89, 804. 22 ACS Paragon Plus Environment

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on

DeNOx-activity,

Mercury

Oxidation

and

SO2/SO3-conversion. Chem. Eng. J. 2013, 222, 274. (23) Rallo, M.; Heidel, B.; Brechtel, K.; Maroto-Valer, M. M. Effect of SCR Operation Variables on Mercury Speciation. Chem. Eng. J. 2012, 198, 87. (24) Li, H.; Wu, C.Y.; Li, Y.; Li, L.; Zhao, Y.; Zhang, J. Role of Flue Gas Components in Mercury Oxidation over TiO2 Supported MnOx-CeO2 Mixed-oxide at Low Temperature. J. Hazard. Mater. 2012, 243, 117.


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(25) Zhang, A.; Zheng, W.; Song, J.; Hu, S.; Liu, Z.; Xiang, J. Cobalt Manganese Oxides Modified Titania Catalysts for Oxidation of Elemental Mercury at Low Flue gas Temperature. Chem. Eng. J. 2014, 236, 29. (26) Finocchio, E.; Busca, G.; Notaro, M. A Review of Catalytic Processes for The Destruction of PCDD and PCDF from Waste Gases. Appl. Catal. B Environ. 2006, 62, 12. (27) Chang, S. H.; Chi, K. H.; Young, C. W.; Hong, B. Z.; Chang, M. B. Effect of Fly Ash on Catalytic Removal of Gaseous Dioxins over V2O5-WO3 Catalyst of A Sinter Plant. Environ. Sci. Technol. 2009, 43, 7523. (28) Xu, Z.; Fritsky, K. J.; Graham, J.; Dellinger, B. Catalytic Destruction of PCDD/F, Lab Test and Performance in A Medical Waste Incinerator. Organ. Compd. 2000, 45, 419. (29) Goemans, M.; Clarysse, P.; Joannès, J.; De Clercq, P.; Lenaerts, S.; Matthys, K.; Boels, K. Catalytic NOx Reduction with Simultaneous Dioxin and Furan Oxidation. Chemosphere 2004, 54, 1357. (30) Kamata, H.; Ueno, S. I.; Sato, N.; Naito, T. Mercury Oxidation by Hydrochloric Acid over TiO2 Supported Metal Oxide Catalysts in Coal Combustion Flue Gas. Fuel Process. Technol. 2009, 90, 947. (31) Nakajima, F.; Hamada, I. The State-of-the-art Technology of NOx Control. Catal. Today 1996, 29, 109. (32) Yang, C. C.; Chang, S. H.; Hong, B. Z.; Chi, K. H.; Chang, M. B. Innovative PCDD/F-containing Gas Stream Generating System Applied in Catalytic Decomposition of Gaseous Dioxins over V2O5-WO3/TiO2-based Catalysts. Chemosphere 2008, 73, 890. 25 ACS Paragon Plus Environment


(33) Chen, L.; Li, J.; Ge, M. J. Promotional Effect of Ce-doped V2O5-WO3/TiO2 with Low Vanadium Loadings for Selective Catalytic Reduction of NOx by NH3. Phys. Chem. C, 2009, 113, 21177. (34) Li, F.; Shen, B.; Tian, L.; Li, G.; He, C. Enhancement of SCR activity and mechanical stability on cordierite supported V2O5-WO3/TiO2 catalyst by substrate acid pretreatment and addition of silica. Powder Technol. 2016, 297, 384. (35) Gen, L.; Guo, F.; Yu, J.; Xu, G. Improved low-temperature activity of V2O5-WO3/TiO2 for denitration using different vanadium precursors. Catalysts 2016, 6, 1. (36) Tran, T. S.; Yu, J.; Li, C.; Guo, F.; Zhang, Y.; Xu, G. Structure and performance of a V2O5-WO3/TiO2-SiO2 catalyst derived from blast furnace slag (BFS) for DeNOx. RSC Adv. 2017, 7, 18108. (37) Chen, C.; Jia, W.; Liu, S.; Cao Y. The enhancement of CuO modified V2O5-WO3/TiO2 based SCR catalyst for Hg◦ oxidation in simulated flue gas. Appl.Surf. Sci. 2018, 436, 1022. (38) Zhang, L.; Dong, L.; Yu, W.; Liu, L.; Deng, Y.; Liu, B.; Wan, H.; Gao, F., Sun, K.; Dong, L. Effect of Cobalt Precursors on The Dispersion, Reduction, and CO Oxidation of CoOx/γ-Al2O3 Catalysts Calcined in N2. J. Colloid Interf. Sci. 2011, 355, 464. (39) Zhu, Y.; Sun, Y.; Niu, X.; Yuan, F.; Fu, H. Preparation of La-Mn-O Perovskite Catalyst by Microwave Irradiation Method and Its Application to Methane Combustion. Catal. Lett. 2010, 135, 152. (40) He, S.; Zhou, J.; Zhu, Y.; Luo, Z.; Ni, M.; Cen, K. Mercury Oxidation over a Vanadia-based Selective Catalytic Reduction Catalyst. Energy Fuels 2009, 23, 253. 26 ACS Paragon Plus Environment

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(41) Zhang, S.; Li, H.; Zhong, Q. Promotional effect of F-doped V2O5-WO3/TiO2 catalyst for NH3-SCR of NO at low-temperature. Appl. Catal. A. 2012, 435, 156. (42) Chen, L.; Li, J.; Ge, M. J. Promotional Effect of Ce-doped V2O5-WO3/TiO2 with Low Vanadium Loadings for Selective Catalytic Reduction of NOx by NH3. Phys. Chem. C 2009, 113, 21177. (43) Zhang, S.; Zhong, Q. Promotional effect of WO3 on O2− over V2O5/TiO2 catalyst for selective catalytic reduction of NO with NH3. J Mol Catal A: Chem. 2013, 373, 108 (44) Li, Y.; Murphy, P.; Wu, C.Y. Removal of Elemental Mercury from Simulated Coal-combustion Flue Gas Using a SiO2-TiO2 Nanocomposite. Fuel Process. Technol. 2008, 89, 567. (45) Stolle, R.; Koeser, H.; Gutberlet, H. Oxidation and Reduction of Mercury by SCR DeNOx Catalysts under Flue Gas Conditions in Coal Fired Power Plants. Appl. Catal. B Environ. 2014, 144, 486. (46) Gao, W.; Liu, Q.; Wu, C. Y.; Li, H.; Li, Y.; Yang, J.; Wu, G. Kinetics of Mercury Oxidation in The Presence of Hydrochloric Acid and Oxygen over A Commercial SCR Catalyst. Chem. Eng. J. 2013, 220, 53. (47) Senior, C. L. Oxidation of Mercury across Selective Catalytic Reduction Catalysts in Coal-fired Power Plants. J. Air Waste Manage. Assoc. 2006, 56, 23. (48) Niksa, S.; Helble, J. J.; Fujiwara, N. Kinetic Modeling of Homogeneous Mercury Oxidation: The Importance of NO and H2O in Predicting Oxidation in Coal-derived Systems. Environ. Sci. Technol. 2001, 35, 3701. (49) Fueno, H.; Tanaka, K.; Sugawa, S. Theoretical Study of The Dechlorination Reaction Pathways of Octachlorodibenzo-p-dioxin. Chemosphere 2002, 48, 771.



(50) Debecker, D. P.; Delaigle, R.; Hung, P. C.; Buekens, A.; Gaigneaux, E. M.; Chang, M. B. Evaluation of PCDD/F Oxidation Catalysts: Confronting Studies on Model Molecules with Tests on PCDD/F-containing Gas Stream. Chemosphere 2011, 82, 1337. (51) Altarawneh, M.; Dlugogorski, B. Z.; Kennedy, E. M.; Mackie, J. C. Mechanisms for Formation, Chlorination, Dechlorination and Destruction of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans (PCDD/Fs). Prog. Energy Combust. Sci. 2009, 35, 245. (52) Thompson, D.; Ewan, B. C. R. A Group Additivity Algorithm for Polychlorinated Dibenzofurans Derived from Selected DFT Analyses. J. Phys. Chem. A 2007, 111, 5043-5047. (53) Weber, R.; Plinke, M.; Xu, Z.; Wilken, M. Destruction Efficiency of Catalytic Filters for Polychlorinated Dibenzo-p-dioxin and Dibenzofurans in Laboratory Test and Field Operation-insight into Destruction and Adsorption Behavior of Semivolatile compounds. Appl. Catal. B Environ. 2001, 31, 195.


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Table Captions Table 1. Experimental conditions of SCR catalyst test. Table 2. The BET analysis of the catalyst. Table 3. X-ray photoelectron spectroscopy (XPS) results for the O1s of catalysts. Table 4. The atomic concentration of SCR catalysts from XPS analysis. Table 5. Activation energy and frequency factor of three catalysts



Page 30 of 45

Table 1 Experimental parameters

Reaction condition

Mercury oxidation

PCDD/Fs destruction

[Hg0] = 62 μg/Nm3, [O2] = 6.5%, [H2O(g)] = 12%, [CO2] = 10%, [O2] = 15%, [CO2] = 10%, [SO2] = 90 ppm, [NH3] = 45 [N2] = balance, [PCDD/Fs] ppm, [NO] = 80 ppm, [HCl] = 25 = 2 ng-TEQ/Nm3 ppm, [N2] = balance

Pre-heater temperature

250oC

690oC

Pre-heated area temperature

150oC

150oC

320oC (optional)

320oC

1oC

-

48 m/h, 24 m/h

48 m/h

3.4 Lpm, 1.7 Lpm

3.4 Lpm

Catalyst bed temperature Hg0 cooler temperature Area velocity Flow rate


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Table 2 Catalyst

BET Surface Area (m2/g)

Pore volume (cm3/g)

Average Pore diameter (nm)

A

62.03

0.212

13.7

B

76.14

0.191

10.0

C

79.77

0.217

10.9

*A, B, and C are 1.52 wt% V2O5-5.11 wt% WO3/TiO2, 0.66 wt% V2O5-5.86 wt% W/TiO2, and 0.26 wt% V2O5-3.05 wt% WO3/TiO2, respectively.



Table 3

Catalysts

Olat/ Olat+Oads

A

0.62

B

0.57

C

0.46

Olat: lattice oxygen; Oads: adsorbed oxygen.


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Table 4 Atomic concentration of elements (at. %) Catalyst Ti

O

V

W

C

Si

A

15.36

62.17

1.56

2.08

13.04

5.78

B

18.37

60.94

0.57

2.81

13.94

2.46

C

13.95

63.13

0.06

0.71

11.81

7.54




Table 5 Catalyst

Ea (kJ/mole)

A (frequency factor, s-1)

A

10.5

17.2

B

14.0

28.2

C

15.0

33.8



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Figure Captions Figure 1. The experimental system of multi-pollutant (Hg0/NO/dioxin) removal. Figure 2. XRD patterns of V2O5-WO3/TiO2 catalysts prepared. Figure 3. SEM images of the SCR catalysts. Figure 4. XPS spectra of (a) Ti 2p, (b) O 1s, (c) V 2p, and (d) W 4d. Figure 5. Performance of three catalysts under different conditions (a) Hg0 oxidation, (b) NO conversion, (c) Hg0 oxidation with various inlet Hg0 concentrations and (d) Hg0 oxidation with various inlet HCl concentrations. Reaction condition: [Hg0] = 62 μg/Nm3, [O2] = 6.5%, [H2O(g)] = 12% or 0% (optional), [CO2] = 10%, [SO2] = 90 ppm, [NH3] = 45 ppm, [NO] = 80 ppm, [HCl] = 25 ppm, [N2] = balance. Figure 6. Mercury oxidation activity of SCR catalyst as a function of vanadium content. Figure 7. (a) Effect of temperature on Hg0 oxidation for three catalysts; (b) Arrhenius plots for the rate constants of Hg0 oxidation by three catalyst. Reaction condition: [Hg0] = 62 μg/Nm3, [O2] = 6.5%, [H2O(g)] = 0%, [HCl] = 25 ppm, [N2] = balance, Area velocity = 48 m/h. Figure 8. (a) Inlet and outlet PCDD/F concentrations, and (b) PCDD/F removal efficiency with three catalysts, respectively. Reaction condition: [PCDD/Fs] = 2 ng-TEQ/Nm3, [O2] = 15%, [CO2] = 10%, [N2] = balance, Area velocity = 48 m/h.



Figure 9. Removal of PCDD/F congeners achieved with three plate-type catalysts in the reactor.

Figure 1 The experimental system of multi-pollutant (Hg0/NO/dioxin) removal.


Page 36 of 45

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(a) Catalyst A (b) Catalyst B (c) Catalyst C

Intensity(a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a)

A-TiO2

(b)

WO3

(c)

10

20

30

40

50

60

70

80

Two theta (degree) Figure 2 XRD patterns of V2O5-WO3/TiO2 catalysts prepared.



Figure 3 SEM images of the SCR catalysts.


Page 38 of 45

Page 39 of 45

(b)

(a) Intensity (a.u.)

Ti 2p1/2

O 1s

Ti 2p3/2

Intensity (a.u.)

(a) Catalyst A (b) Catalyst B (a)

(c) Catalyst C

(b)

(a) (b)

(c)

470

(c)

465

460

455

450

(c)

540

535

525

Intensity (a.u.)

(b) (c)

524

519

W 4d5/2

(a)

(a)

529

530

(d) V 2p

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


514

509

(b) (c)

268

261

Figure 4 XPS spectra of (a) Ti 2p, (b) O 1s, (c) V 2p, and (d) W 4d.


254

247

240

233

Page 40 of 45

100

100

(a)

Dry gas stream, av = 48 m/h

40

with 12% H₂O₍g₎, av = 48 m/h

20

with 12% H₂O₍g₎, av = 24 m/h

NO conversion (%)

60

Catalys B

80

Catalys C

60 40 20 0

0

(c)

Catalys B

Area velocity = 48 m/h

40 30 20 Catalys A

10 0

Catalys B Catalys C

0

10

Dry gas stream, av = 48 m/h

Catalys C Mercury oxidation activity KHg (m/hr)

Catalys A

50

Catalys A

(b)

80

Mercury oxidation activity KHg (m/hr)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Mercury oxidation efficiency (%)


20 30 40 50 Hg0 concentration (μg/m3)

60

70

50

with 12% H₂O₍g₎, av = 48 m/h

with 12% H₂O₍g₎, av = 24 m/h

Area velocity = 48 m/h

(c)

40 30 20 10 0

Catalys A Catalys B Catalys C

0

5

10

15

20

25

HCl concentration (ppm)

30

35

40

Figure 5 Performance of three catalysts under different conditions (a) Hg0 oxidation, (b) NO conversion, (c) Hg0 oxidation with various inlet Hg0 concentrations and (d) Hg0 oxidation with various inlet HCl concentrations. Reaction condition: [Hg0] = 62 μg/Nm3, [O2] = 6.5%, [H2O(g)] = 12% or 0% (optional), [CO2] = 10%, [SO2] = 90 ppm, [NH3] = 45 ppm, [NO] = 80 ppm, [HCl] = 25 ppm, [N2] = balance.


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Mercury oxidation activity KHg (m/hr)

Page 41 of 45

90 80 70 60 50 40 30 20 10 0

y = 14.78x + 44.834 R² = 0.993

y = 13.351x + 17.14 R² = 0.915

without H₂O(g) adding 12% H₂O(g) 0

0.5

1

1.5

2

2.5

3

V2O5 content (mass-%)

Figure 6 Mercury oxidation activity of SCR catalyst as a function of vanadium content.


(a)

Page 42 of 45

100 80 60 40

Catalys A Catalys B

20

Catalys C

0

260

280

300

320

340

360

380

Temperature (oC)

(b)

ln k

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Mercury oxidation efficiency (%)


0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

0.00155

y = -1267.3x + 2.8441 R² = 0.9969 y = -1688.6x + 3.3409 R² = 0.9987 Catalys A Catalys B

y = -1805.2x + 3.52 R² = 0.9999

Catalys C

0.0016

0.00165

0.0017 1/T

0.00175

0.0018

0.00185

Figure 7 (a) Effect of temperature on Hg0 oxidation for three catalysts; (b) Arrhenius plots for the rate constants of Hg0 oxidation by three catalyst. Reaction condition: [Hg0] = 62 μg/Nm3, [O2] = 6.5%, [H2O(g)] = 0%, [HCl] = 25 ppm, [N2] = balance, Area velocity = 48 m/h.


Page 43 of 45

(a) Inlet Outlet

3

PCDD/F concentration (ngI-TEQ/Nm )

2.5

2.0

1.5

1.0

0.5

0.0

Catalyst A

Catalyst B

Catalyst C

Catalyst A

Catalyst B

Catalyst C

(b) 100

80

PCDD/F removal (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60

40

20

0

Figure 8 (a) Inlet and outlet PCDD/F concentrations, and (b) PCDD/F removal efficiency with three catalysts, respectively. Reaction condition: [PCDD/Fs] = 2 ng-TEQ/Nm3, [O2] = 15%, [CO2] = 10%, [N2] = balance, Area velocity = 48 m/h.


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

PCDD/F removal efficiency (%)


100 90 80 70 60 50 40 30 20 10 0

Page 44 of 45

Catalys A Catalys B Catalys C

Figure 9 Removal of PCDD/F congeners achieved with three plate-type catalysts in the reactor.


Page 45 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ACS Paragon Plus Environment

dioxin) with V2O5

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