Removal of Elemental Mercury from Simulated Flue Gas over Peanut

Subscriber access provided by Queen Mary, University of London

Article

Removal of Elemental Mercury from Simulated Flue Gas over Peanut Shells Carbon Loaded with Iodine Ions, Manganese Oxides, and Zirconium Dioxide Jiawen Zeng, Caiting Li, Lingkui Zhao, Lei Gao, Xueyu Du, Jie Zhang, Le Tang, and Guangming Zeng Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02500 • Publication Date (Web): 28 Nov 2017 Downloaded from http://pubs.acs.org on November 29, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 49 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

Energy & Fuels

Removal of Elemental Mercury from Simulated Flue Gas over Peanut Shells Carbon Loaded with Iodine Ions, Manganese Oxides, and Zirconium Dioxide Jiawen Zenga,b, Caiting Li*,a,b, Lingkui Zhaoc,a,b, Lei Gaoa,b, Xueyu Dua,b, Jie Zhanga,b, Le Tanga,b, Guangming Zenga,b a

College of Environmental Science and Engineering, Hunan University, Changsha 410082, PR

China b

Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry

of Education, Changsha 410082, PR China c

College of Environmental Science and Resources, Xiangtan University, Xiangtan 411105, PR

China

*

Corresponding author. Tel: +86 731 88649216; Fax: +86 731 88649216 E-mail address: [email protected]; [email protected] 1

ACS Paragon Plus Environment

Energy & Fuels 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 low-cost material with high adsorption and oxidation ability for Hg0 capture is needed, whereas it is hard to prepare by present methods. Here, halide ions (I-) and metal oxides (MnOx and ZrO2) were both loaded on peanut shells carbon to synthesize 6Mn-6Zr/PSC-I3. Various characterizations and experiments were used to investigate the physiochemical properties and Hg0 removal performances. The sample exhibited an abundant pore structure and the active components dispersed well on its surface. The excellent total Hg0 removal efficiency (more than 90%) was obtained in a wide reaction temperature range (150-300 °C) under N2 + 6% O2 atmosphere. Moreover, the Hg0 adsorption capacity in 1440 min was 5587.0 µg·g-1 and the Hg0 oxidation efficiency after reaching adsorption equilibrium was more than 30%. Further, the reaction mechanism at 150 °C was proposed. The main chemical adsorption sites of carboniodine groups dominates Hg0 removal at initial reaction stage. As reaction progressing, chemical adsorption is weakened due to the gradual saturation of adsorption sites whereas catalytic oxidation caused by lattice oxygen and hydroxyl oxygen substitutes chemical adsorption and dominates Hg0 removal at final reaction stage. Thus, the 6Mn-6Zr/PSC-I3 with economic and environmental benefits has a promising prospect in industrial applications.

2


Page 2 of 49

Page 3 of 49 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

Energy & Fuels

1. Introduction Mercury, an element that can lead to persistent and highly toxic harm to wildlife and human beings1, 2, has caused extensive concern in recent years. To preserve human health and environment from mercury contamination, 128 nations have signed the Minamata Convention on Mercury in October 20133. As the main producer and consumer of mercury, China discharges 633 t of mercury to the air in 20104 and its atmospheric mercury emissions account for 27% of the global total5. Among the various emission sources, coal-fired power plants are regarded as the primary anthropogenic sources of mercury emissions6, 7. In this case, it is an urgent need to lower mercury emissions from power plants.

In coal-fired flue gas, mercury exists in three forms: elemental mercury (Hg0), oxidized mercury (Hg2+), and particle-bound mercury (Hgp). Hg2+ and Hgp can be effectively removed by a wet flue gas desulfurization (WFGD) system and dust control units (electrostatic precipitator and bag houses), respectively. However, Hg0 is difficult to be captured with current air pollution control devices (APCD) for its low solubility in water and high volatility8. Many sorbents have been developed for controlling Hg0 emissions, including activated carbon9, 10, metal oxides11, 12, zeolite13, fly ash14, 15, Ca-based sorbent16, 17, etc. Among these, Hg0 removal with activated carbon is considered as one of the most promising techniques due to its high surface area, adequate pore size distribution, and relatively high mechanical strength18. Nevertheless, the major defect of using activated carbon to remove Hg0 is the high cost, which hinders its further development. Hence, various low-cost porous carbonaceous materials are developed with an aim 3


Energy & Fuels 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

to as activated carbon alternatives by the pyrolysis of cheaper source material such as bamboo19, coconut shells20, coffee husks21, corn cobs22, and rice straw23. Peanut shells, one of the agricultural biomass wastes, are quite cheap and available as the high global annual yield (7.44 million tons)24. It's worth noting that the common disposal method of waste biomass is open burning in developing countries and regions25, which will release lots of greenhouse gases and dust, leading to severe pollution26. Significantly, some researchers used peanut shells as the precursors for production of carbon sorbents which could suffice for the removal of pollutants. For example, a carbon material prepared by peanut shells was successfully used for treatment of soil eluent containing explosive contaminants27. Thus, using peanut shells carbon derived from the pyrolysis of peanut shells as activated carbon alternatives for controlling Hg0 emissions possess both the economic and environmental benefits.

However, raw pyrolysis products exist the same problem that their Hg0 removal performances are relatively poor. Thus, various modification methods are utilized to enhance the Hg0 removal performances. The methods can be divided into two kinds. One is introduction of nonmetal element onto the raw products surface such as sulfur28, 29, iodine30, 31, bromine32, 33, and chlorine34, 35

, which can clearly improve the Hg0 adsorption ability. In particular, impregnation of raw

products using halides has shown great potential, especially iodine36. The other is introduction of metal oxides including MnOx, CeOx, and CoOx37-42, to oxidize Hg0 to form HgO. Among these metal oxides, MnOx has been widely studied as modifier for Hg0 removal because of its high redox potential, low cost, and environmental friendliness43, 44. In addition, the insertion of ZrO2 4


Page 4 of 49

Page 5 of 49 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

Energy & Fuels

into other metal oxides can effectively improve the Hg0 removal performances45, 46. According to our previous study47, the addition of ZrO2 could contribute to strong redox ability, great mobility of surface oxygen, and growing total amount of chemisorbed oxygen and lattice oxygen, which was responsible for the enhanced activity of Hg0 removal. Generally, the high Hg0 adsorption ability usually warrants the fast adsorption rate and the excellent Hg0 oxidation ability can keep the Hg0 removal process continuing. The modified sample with these two natures is very important in practical application. However, it is hard to achieve by using one kind of modification methods mentioned above. Consequently, the introduction of both halide ions (I-) and metal oxides (MnOx and ZrO2) on raw products seems to be a possible way to gain a high Hg0 adsorption and oxidation ability, and that has not yet been reported.

In this work, the raw pyrolysis product (peanut shells carbon) was employed as the support and halide ions (I-(NH4I)), metal oxides (MnOx(Mn(CH3COO)2·4H2O) and ZrO2(ZrOCl2·8H2O)) were used as the active components to synthesize the sample 6Mn-6Zr/PSC-I3 for Hg0 removal. The effects of active components, loading value, reaction temperature, and oxygen concentration on Hg0 removal performances were investigated. The effects of simulated flue gas (SFG) atmosphere (N2 + 6% O2 + 12% CO2 + 300 ppm NO + 400 ppm SO2 + 8% H2O) were also researched. A mercury speciation conversion system was applied to distinguish the adsorption and oxidation efficiency. In addition, the various characterization techniques were used to determine physiochemical property such as proximate and ultimate analysis, BET, SEM, ICPAES, XRF, XRD, FTIR, and XPS. Further, the involved mechanism of Hg0 removal over 6Mn5


Energy & Fuels 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

6Zr/PSC-I3 was proposed. 2. Experimental Section 2.1. Sample Preparation In preliminary experiment (Table S1), orthogonal experiment was used to identify the optimal raw material and its treatment methods. The result indicated that peanut shells (0.120-0.109 mm) pyrolyzed at 600 °C possessed the best performance for the mercury removal at low temperature (30 °C). Therefore, peanut shells were chosen to be the raw material for further study.

Peanut shells carbon supports were synthesized via physical steam activation of peanut shells using pure N2 as the carrier gas. Firstly, the raw material (peanut shells) was washed with deionized water and then dried at an oven for 24 h at 90 °C. After that, the dried peanut shells were pulverized and sieved in a 120-140 Chinese mesh (0.120-0.109 mm). The pyrolysis reactor was a quartz tube reactor (60 mm in diameter and 850 mm in length) . The peanut shells (0.1200.109 mm) were placed in the reactor and stably heated from room temperature to 600 °C under pure N2 atmosphere (100 mL·min-1) at a heating rate of 5 °C·min-1, and then maintained for 2 h. The obtained peanut shells carbon supports are denoted as PSC and the yield ratio of PSC was 30.27%.

To load halide ions on PSC, the PSC was impregnated with ammonium halides aqueous solutions, including NH4Cl, NH4Br, and NH4I. The liquid-solid ratios were set as 20 mL·g-1. Various mixtures were stirred for 2 h and kept static settlement for 12 h. Then, the solid residue 6


Page 6 of 49

Page 7 of 49 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

Energy & Fuels

was separated and dried at an oven for 12 h at 90 °C. The liquid was collected for further use. The derived samples were denoted as PSC-Xb, where X represents the species of halides (X: Cl, Br, and I) and b represents the mass concentration of precursor solutions (b: 1, 3, and 5%).

To load metal oxides (MnOx and/or ZrO2) on PSC, the PSC was impregnated with manganese acetate tetrahydrate (Mn(CH3COO)2·4H2O) aqueous solution and/or zirconium oxychloride octahydrate (ZrOCl2·8H2O) aqueous solution. The liquid-solid ratios were also set as 20 mL·g-1. After continuous stirring for 2 h, the mixtures were dried at an oven for 12 h at 90 °C and then pyrolyzed at 500 °C for 5 h under N2 atmosphere (100 mL·min-1). The obtain samples were named as aMn-aZr/PSC, 2aMn/PSC, and 2aZr/PSC respectively ,where a represents the single metal mass percentage and 2a represents the total metal mass percentage of 6, 12, and 18% (M/(M+PSC), M = manganese and/or zirconium). The sample 6Mn-6Zr/PSC-I3 was prepared by firstly loading halide ions (I-) on the surface of PSC and then loading metal oxides (MnOx and ZrO2) on the surface of PSC. The methods were same as above. 2.2. Characterization Techniques The proximate analysis of peanut shells and peanut shells carbon was determined by Chinese National standards (GB/212-2008). The ultimate analysis of peanut shells and peanut shells carbon was measured using the Elementar Analysensysteme GmbH vario (Elementar Ltd Corp, Germany). The content of halogens in samples was obtained by X-ray fluorescence (XRF, LAB CENTER XRF-1800, Japan). Inductively Coupled Plasma–Atomic Emission Spectrometry (ICP–AES, SPECTRO BLUE SOP, Germany) was used to measure the content of metal in 7


Energy & Fuels 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

samples. The Brunauer–Emmett–Teller (BET) specific surface area, pore volume, and average pore diameter of samples were determined from N2 adsorption isotherms, which were performed at 77 K using a Micromeritics 180 Tristar II 3020 analyzer (Micromeritics Instrument Crop, USA). The samples were degassed at 180 °C for 5 h before analysis. The surface morphology of samples was acquired by the scanning electron microscope (SEM, Nova NanoSEM230, USA). Before analysis, all of the samples were coated with Au. The crystal form of manganese species and/or zirconium species on the samples was determined by X-ray diffraction (XRD, Rigaku D/Max 2500, Rigaku Corporation, JPN) in the scanning angles (2θ) rang of 10 to 80° with Cu– Kα radiation. The surface functional group of samples was qualitatively characterized by fourier transform infrared spectroscopy (FTIR, Nicolet 6700, USA). The element valence state was analyzed by X-ray photoelectron spectroscopy (XPS, K-Alpha 1063 system, Thermo Fisher Scientific, UK). The binding energy was calibrated with the C 1s peak at 284.6 eV. 2.3. Mercury Removal Experiment The elemental mercury(Hg0) removal performances over obtained samples were studied by a mercury adsorption fixed-bed system, as shown in Figure 1. In each test, a 40 mg sample was placed in a quartz tube reactor (10 mm in internal diameter) and headed to a needed temperature by a digital temperature controller. The total flow rate of flue gas feed into the reaction system was controlled at 1000 mL·min-1 by various mass flow controllers, corresponding to a gas hourly space velocity (GHSV) of approximately 150000 h-1. An on line mercury analyzer (Lumex RA915 M, Russia) with the measurement accuracy of 0.1 ug·m-3 was used to monitor the Hg0 concentration in the inlet and outlet flue gas. The Hg0 concentration in the inlet flue gas (Hg0in ) 8


Page 8 of 49

Page 9 of 49 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

Energy & Fuels

was about 300 ug·m-3, which was a result of a Hg0 permeation tube (VICI Metronics) at a certain temperature and flow rate of high-purity nitrogen. After the Hg0 concentration in the inlet flue gas keeping steady for 5 h (the variation of Hg0 concentration less than 1%), the test could be started and the mercury analyzer was in turn used to monitor the Hg0 concentration in the outlet flue gas. To better understanding the adsorption and oxidation behaviors of Hg0 over samples, a mercury speciation conversion system was applied. The exhaust gas coming from the quartz tube reactor passed through either 10% KCl solution (side 1) or 0.5 mol·L-1 SnCl2/HCl solution (side 2) in this system. On side 1, the oxidized mercury (Hg2+) was captured by KCl solution and only elemental mercury (Hg0out ) concentration was detected. On side 2, the Hg2+ was reduced to Hg0 by SnCl2 and then the concentration of total mercury (HgTout = Hg0out + Hg2+ ) could be measured out by the mercury analyzer. The difference between HgTout and Hg0out was the Hg2+ concentration. out

The total Hg0 removal efficiency (ET, %), the Hg0 oxidation efficiency (Eoxi, %), and the Hg0 adsorption efficiency (Eads, %) were defined as follows (eqs 1-4): =

= =

× 100%

(1)

× 100%

(2)

× 100%

(3)

= +

(4)

Where Hg0in and Hg0out represent the Hg0 concentration in the inlet and outlet of the reactor, respectively. HgTout represents the total mercury concentration in the outlet of the reactor. The test time is 2 h. 9


Energy & Fuels 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

Page 10 of 49

The mercury adsorption capacity (Q, µg·g-1) was also calculated as follows: *

= * +Hg "! − Hg "$% & ' d)

(5)

,

Where Hg0in and Hg0out represent the Hg0 concentration in the inlet and outlet of the reactor, respectively. m represents the mass of samples (g), f represents the total flow rate of flue gas (m3·h-1), and t1 and t2 represent the initial and terminate time of the test (h), respectively. As the experimental error is inevitable, all of the removal efficiency presented in this paper is the mean of three parallel experiments and the relative error is no more than 5%.

In this work, the pseudo-first-order kinetic model was employed to describe the Hg0 removal process over samples. The kinetic rate equation was expressed as follows: −

-. -/ & *

= 0 12 − 1* &

(6)

Considering the initial condition: qt(t = 0) = 0,and qt(t = t) = qt, the solution of eq 6 could be obtained: 1* = 12 1 − exp−0 )&&

(7)

Where qt and qe represent the mercury adsorption capacity at time t and at equilibrium time (ug·g-1), respectively. k1 represents the rate constant of the pseudo-first-order equation (min-1). The specific values of these two parameters, qe and k1, were available by fitting the adsorption capacity-time (Q-t) curve.

The experimental conditions are summarized in Table 1. In set 1, the Hg0 removal performances over various samples were compared at 150 °C under N2 + 6% O2 atmosphere. In set 2, the 10


Page 11 of 49 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

Energy & Fuels

optimal mass concentration of ammonium halides and mass percentage of metal were determined. In set 3, the Hg0 removal performances over three samples, 6Mn-6Zr/PSC-I3, PSC-I3, and 6Mn6Zr/PSC, were investigated in a wide temperature range of 50–350 °C with the aim to acquire the most suitable reaction temperature. In set 4, the Hg0 removal performances over three samples were studied under different O2 content of 0, 3, 6 and 9%. In set 5, the Hg0 removal performances over three samples were researched under SFG atmosphere (N2 + 6% O2 + 12% CO2 + 300 ppm NO + 400 ppm SO2 + 8% H2O) for 24 h. Meanwhile, the equilibrium mercury adsorption capacity could also obtained by the pseudo-first-order kinetic model. To better know the involved reaction mechanism over 6Mn-6Zr/PSC-I3, a long time test (72 h) of Hg0 removal was performed in set 6. 3. Results and Discussion 3.1. Sample Characterization 3.1.1. Proximate and Ultimate Analysis The proximate and ultimate analysis of peanut shells (PS) and peanut shells carbon (PSC) are listed in Table 2. The content of ash and volatile in PS were 1.30% and 79.55%, respectively. After pyrolyzing at 600 °C, the content of ash increased whereas the content of volatile significantly decreased. Choi G-G et al48 demonstrated that low content of ash and high content of volatile in raw materials was a key factor for the good pore structure. Thus, it can be inferred that during the pyrolysis processing, the ash is accumulated and blocks pore whereas the volatile is released and promotes the formation of pore. From the ultimate analysis, the C and O were the main elements in PC, which was 49.59% and 40.28%, respectively. The high content of O 11


Energy & Fuels 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

possibly conduce to the development of oxygen-containing functional groups, which is in favor of Hg0 removal. 3.1.2. BET Analysis The pore structure of various samples is listed Table 3. The PSC had an excellent BET surface area (249.718 m2·g-1) and total pore volume (0.117 cm3·g-1), suggesting that it is a suitable support for Hg0 capture. After PSC being modified, however, the BET surface area and total pore volume were affected adversely. For PSC impregnated with ammonium halides aqueous solutions (halide ions-type samples), both the BET surface area and total pore volume followed the order: PSC-Cl3 > PSC-Br3 > PSC-I3. The results reveal that the ammonium halides modification leads to the pore blocking, especially NH4I impregnation. For PSC impregnated with manganese acetate tetrahydrate aqueous solution and/or zirconium oxychloride octahydrate aqueous solution (metal oxides-type samples), the 12Zr/PSC had the highest BET surface (206.667 m2·g-1) and total pore volume (0.100 cm3·g-1). In addition, the BET surface area and total pore volume of 6Mn-6Zr/PSC were bigger than that of 12Mn/PSC. This observation shows that the doping of ZrO2 can improve the dispersity of metal oxides and thereby suppress the blockage of pore. For 6Mn-6Zr/PSC-I3, the BET surface area and total pore volume were 153.908 m2·g-1 and 0.080 cm3·g-1, respectively, which was superior to that of PSC-I3. Therefore, the introduction of metal oxides on PSC-I3 has a positive effect on textural properties. The nitrogen adsorption/desorption isotherms of four samples, 6Mn-6Zr/PSC-I3, 6Mn-6Zr/PSC, PSC-I3, and PSC, are shown in Figure S1. It is observed that all samples exhibit a TypeⅠ isotherm according to the IUPAC classification49. 12


Page 12 of 49

Page 13 of 49 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

Energy & Fuels

3.1.3. SEM, XRF, and ICP-AES Analysis The morphology of samples is shown in Figure 2. Compared to modified samples, the PSC had an more abundant pore structure. Thus, the modification on PSC blocks the pore, which is in line with the BET analysis. It should be noted that the pore in modified samples was still clear, indicating that the blockage of pore result from modification is far from severe. The active components (halide ions and metal oxides) did not be observed from micrograph. This is probably because that they disperse well on the surface of PSC. XRF and ICP-AES were employed to precisely identify the content of metal and halogens in samples, respectively. The results are listed in Table 4. The content of metal (Mn and Zr) in 6Mn-6Zr/PSC-I3 and 6Mn6Zr/PSC was very close. Importantly, the metal in samples may exist in the form of metal oxides, which is conducive to Hg0 removal. Nevertheless, the content of iodine in 6Mn-6Zr/PSC-I3 was slightly lower than that in PSC-I3.The mass percentage of iodine in 6Mn-6Zr/PSC-I3 and PSC-I3 was 0.3588% and 0.4783%, respectively. The corresponding molar loading of iodine was 0.0025 mol%·g-1 and 0.0033 mol%·g-1, respectively. There are two possible reasons for this phenomenon: (1) the content of iodine is diluted due to the addition of metal; (2) part of the iodine escapes during the preparation processing. The iodine in samples can react with carbon atom to form new adsorption sites for Hg0 adsorption. 3.1.4. XRD Analysis The XRD patterns of various samples are shown in Figure 3. For PSC, only one weak diffraction peak at 26.5° was observed, which was assigned to carbon (PDF 26-1076). New peaks appeared after loading MnOx and/or ZrO2 on PSC. For 12Zr/PSC, the peaks at 28.3° and 40.5° attributed 13


Energy & Fuels 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

to baddeleyite (PDF 37-1484). The peaks at 30.1° and 50.2° attributed to zirconium oxide (PDF 49-1642). For 12Mn/PSC, MnO (PDF 07-0230) was the main phase in MnOx and only a few peaks were attributed to MnO2 (PDF 44-0141) and Mn3O4 (PDF 24-0734), respectively. However, the quantity and intensity of the peaks ascribed to MnOx in 6Mn-6Zr/PSC declined compared to that in 12Mn/PSC. Similar situation happened in 6Mn-6Zr/PSC-I3. This proves that the ZrO2 advances the dispersity of MnOx, which may result in a better Hg0 removal performance50. 3.1.5. FTIR Analysis The FT-IR spectra of various samples are shown in Figure 4. The primary functional groups on PSC were –OH (3441 cm-1), carbonyl C=O (1623 cm-1), and aromatic C=C (1565 cm-1). After being modified, the intensity of these functional groups had no significant changes, indicating that the preparation processing would not damage the functional groups. Moreover, the presence of oxygen-containing functional groups(-OH and C=O) is beneficial for Hg0 removal51, 52. 3.2. Mercury Removal Performances 3.2.1. Effect of Active Components To comprehend the Hg0 removal performances over samples that modified by different active components, Hg0 removal efficiencies of seven samples were compared. The results are shown in Figure 5. For halide ions-type samples, the total Hg0 removal efficiency at 2 h (ET(2 h)) followed the order: PSC-I3 > PSC-Br3 > PSC-Cl3. The mass percentage of halogens in PSC-I3, PSC-Br, and PSC-Cl3 was 0.4783%, 0.5205%, and 0.4258%, respectively (Table 4). The corresponding molar loading of halogens was 0.0033 mol%·g-1, 0.0053mol%·g-1, and 14


Page 14 of 49

Page 15 of 49 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

Energy & Fuels

0.0080mol%·g-1, respectively. The PSC-I3 with low molar loading of halogens exhibited a better Hg0 removal performance. There may be two reasons for this phenomenon: (1) The reducibility of halide ions is different (I- > Br- > Cl-). The halide ion with higher reducibility is easier to form covalent bonds with carbon atom that serve as main chemical adsorption sites on the surface of PSC30; (2) the London dispersion forces, one of the Vander Waals forces, which contribute to the adsorption process increase as the atomic size. And halide ions have different size (I- > Br- > Cl-). Thus, the type of halogens in samples is a crucial factor for Hg0 capture. The BET surface area and total pore volume (Table 3) also appeared inconsistent with the Hg0 removal performances. The halide ions-type sample with relative poor porous structure had a better ET(2 h), implying that the Hg0 removal over these samples is mainly through chemisorption. This is because, if the Hg0 removal is mainly through physisorption, the rich porous structure will facilitate the physical adsorption process and result in a better Hg0 removal efficiency. De Mahuya et al36 reported same result that the main mechanism for Hg0 removal with activated carbon changed from physisorption to chemisorption after impregnation with halide ions. For metal oxides-type samples, the ET(2 h) was relatively low. The ET(2 h) of 12Zr/PSC, 12Mn/PSC, and 6Mn6Zr/PSC were 12.06%, 34.67%, and 41.86%, respectively. The results confirm that loading both MnOx and ZrO2 on PSC is more favorable to Hg0 removal. The BET results (Table 3) and the XPS spectra for O 1s (Figure S2) showed the positive effects of ZrO2. The surface area and total pore volume of 6Mn-6Zr/PSC was both higher than that of 12Mn/PSC. The O 1s spectra in 12Mn/PSC could be divided into three peaks at 530.2/530.8 eV (lattice oxygen), 532.0/532.5 eV (hydroxyl oxygen), and 534.1 eV (H2O). However, the peak assigned to H2O was disappeared 15


Energy & Fuels 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

for 6Mn-6Zr/PSC. Moreover, compared to the 12Mn/PSC, the ratio for lattice oxygen and hydroxyl oxygen (Table S2) which was conducive to Hg0 removal increased from 23.30% to 29.49% and from 61.06% to 71.51%, respectively. Besides, research had shown that the doping of zirconium could enhance the reducibility and facilitate the formation of high-oxidation-state manganese45. The sample 6Mn-6Zr/PSC-I3 had nearly the same ET(2 h) as PSC-I3. Hence, the Hg0 removal performance over 6Mn-6Zr/PSC-I3 needs to be further investigated to verify its superiority. 3.2.2. Effect of Mass Concentration of NH4I and Mass Percentage of Metal The optimal mass concentration of ammonium halides and mass percentage of metal were determined by two aspects: ET and cost. The ET of PSC impregnated with different mass concentration of NH4I is shown in Figure 6(A). For raw pyrolysis products PSC, a complete breakthrough was reached in only 20 min, indicating that it has a poor ability at 150 °C for Hg0 removal. After PSC being impregnated with NH4I, the ET was improved. And higher mass concentration resulted in better ET. To explain this phenomenon, the content of iodine in PSC-I1, PSC-I3 and PSC-I5 was measured by XRF (Table 4). With the increase of mass concentration of NH4I , the content of iodine in samples increased, which could possibly facilitate the formation of more chemical adsorption sites and enhance the ET. The promotion of ET, however, was quite limited when the mass concentration increased from 3% to 5%. It may be because that 3%NH4I can form nearly the same amount of adsorption sites on the surface of PSC as 5%NH4I. Figure 6(B) shows the effect of mass percentage of metal on ET. Similarly, the addition of MnOx and ZrO2 also had a active effect on ET. However, the ET was sufficiently close among 3Mn-3Zr/PSC, 16


Page 16 of 49

Page 17 of 49 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

Energy & Fuels

6Mn-6Mn/PSC, and 9Mn-9Zr/PSC. Especially when the mass percentage of metal increased from 12% to 18%, the ET basically remained unchanged. In detail, ET(2 h) of 6Mn-6Mn/PSC and 9Mn-9Zr/PSC was 41.86% and 42.00%, respectively. ICP-AES was used to identified the content of metal in these three samples (Table 4). Although the measured value of mass percentage of metal was slightly smaller than the calculated value of that, it scaled up with the rise of the calculated value. Concretely, three calculated values of 6%, 12%, and 18% corresponded to the measured value of 4.17%, 8.23%, and 13.26%, respectively. The proportion between the calculated value and measured value was nearly 3/2, which showed a good parallelism. This results reveal that although more metal is loaded on the surface of PSC, it is not helpful for Hg0 removal. The aggregation of MnOx and ZrO2 is one of the possibly reasons. 3.2.3. Effect of Reaction Temperature Three samples, PSC-I3, 6Mn-6Zr/PSC and 6Mn-6Zr/PSC-I3, were chosen to survey the effect of reaction temperature on the total Hg0 removal efficiency at 2 h (ET(2 h)) including both the Hg0 adsorption efficiency (Eads) and the Hg0 oxidation efficiency (Eoxi) (if exist). The results are shown in Figure 7. For PSC-I3, there was only Hg0 adsorption during Hg0 removal process. The Eads was improved with the increase of temperature at a low temperature range (50-150 °C) and then remained stabilization (Eads>90%) at a wide temperature range (150-300 °C). The further increase of reaction temperature to 350 °C, Eads declined sharply. The excellent efficiency at entire reaction temperature range indicates that the introduction of halide ions (I-) significantly improves the Hg0 adsorption ability. For 6Mn-6Zr/PSC, the contributions to ET(2 h) came from both Eads and Eoxi, indicating that the introduction of metal oxides (MnOx and ZrO2) could 17


Energy & Fuels 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

generate the Hg0 oxidation ability which did not appear in the sample only loaded with iodine ions. The Eoxi was improved with the increase of temperature at the entire temperature range (50350 °C). This is mainly because the reactants can gain more kinetic energy at high reaction temperature, which promotes the reaction of Hg0 oxidation53. The Eads exhibited a complicated changed trend. At a low temperature range(50-150 °C), Eads decreased with raising reaction temperature. At a high temperature range (150-350 °C), Eads increased with raising reaction temperature from 150 to 200 °C and then sharply decreased with further raising reaction temperature. Apparently, the Eads in PSC-I3 and 6Mn-6Zr/PSC had the different changed trend with the increase of temperature. Since physisorption is a exothermal process and chemisorption is a endothermal process54, it can be inferred that with raising reaction temperature, physisorption is inhibited whereas chemisorption is promoted. Excessively high temperature, however, will accelerate the desorption of mercury from the surface of samples resulting in the decrease of chemisorption55. From this conclusion, the type of adsorption in PSC-I3 and 6Mn6Zr/PSC could be identified. The adsorption occurred in PSC-I3 at the whole temperature range (50-350 °C ) is mainly chemisorption, which is consistent with the result in 3.2.1. While the adsorption occurred in 6Mn-6Zr/PSC at a low temperature range and at a high temperature range is mainly physisorption and chemisorption, respectively. For 6Mn-6Zr/PSC-I3, both excellent Hg0 adsorption performance (Eads>85%) and Hg0 oxidation performance (Eoxi>5%) were obtained at wide reaction temperature range (150-300 °C), showing the successful combinations of the advantage of halide ions and metal oxides. Considering the temperature in coal-fired flue gases is 120-160 °C, the optimal reaction temperature is identified as 150 °C. 18


Page 18 of 49

Page 19 of 49 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

Energy & Fuels

3.2.4. Effect of O2 Concentration Since O2 had positive effects on both Hg0 adsorption and oxidation56, 57, the Hg0 removal performances over three samples were studied under different O2 concentration (0, 3%, 6%, and 9%). The results are shown in Figure 8. Obviously, the Eoxi in both 6Mn-6Zr/PSC and 6Mn6Zr/PSC-I3 increased with enhancing O2 concentration in flue gas. This observation reveals that gaseous O2 participates the Hg0 oxidation process. The probably pathway is that the Hg0 is oxidized by the lattice oxygen supplied by metal oxides into HgO and released, then the gaseous O2 will replenish the lattice oxygen. In this case, the introduction of MnOx on the surface of PSC can fully use the O2 in the flue gas for Hg0 capture. For the Eads, the O2 concentration had different influences towards different samples. The Eads in PSC-I3 were almost constant (>90%) when the O2 concentration was changed. However, the Eads in 6Mn-6Zr/PSC was facilitated by O2 in flue gas. In absence of O2, the Eads was only 18.49%. When 3% O2 was added, the Eads increased to 39.11%. The further enhancing the O2 concentration had no apparent effects. The different influences of O2 concentration on Eads in different samples are mainly because the imparity of chemical adsorption sites. The chemical adsorption sites in bio-chars modified by halides(NH4I) were proven to be C-I groups which oxidized Hg0 into HgI230, 58 whereas that in bio-chars modified by metal oxides were adsorbed oxygen which oxidized Hg0 into adsorbed HgO59. And the C-I groups not only had a stronger ability for Hg0 adsorption than adsorbed oxygen but also did not rely on the O2 concentration in Hg0 adsorption process. The Eads in 6Mn6Zr/PSC-I3 kept near 90% at different O2 concentration, which manifested that the Eads did not depend on the O2 concentration. Therefore, the main chemical adsorption sites on 6Mn-6Zr/PSC19


Energy & Fuels 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

I3 should be C-I covalent groups instead of adsorbed oxygen. From above discussion, the introduction of both iodine ions and metal oxides (MnOx and ZrOx) on the surface of PSC has two superiorities: (1) the C-I groups which can advance the Hg0 adsorption ability is generated; (2) the gaseous O2 easily participates in Hg0 oxidation due to the existence of metal oxides. 3.2.5. Comparison of Hg0 Adsorption Capacities The main components in coal-fired flue gas are CO2, NO, SO2, and H2O, which can affect the Hg0 removal performances over samples. Accordingly, three samples were researched under simulated flue gas (SFG) atmosphere to know the practicability. As shown in Figure 9(A), the total Hg0 removal efficiency (ET) over 6Mn-6Zr/PSC-I3 was significantly inhibited under SFG atmosphere compared with that under N2 + 6% O2 atmosphere. Nevertheless, the ET was still kept at approximately 75% after 120 min Hg0 removal experiment, which revealed the excellent Hg0 removal performance. And the ET over 6Mn-6Zr/PSC-I3 was superior to that over both PSC-I3 and 6Mn-6Zr/PSC under SFG except the initial 200 min (the ET of 6Mn-6Zr/PSC-I3 was slightly lower than that of PSC-I3 in initial 200 min). The Hg0 adsorption capacities of three samples in 1440 min were calculated by eq 5. The results are shown in Figure 9(B). It could be observed that the Hg0 adsorption capacities of 6Mn-6Zr/PSC-I3, PSC-I3, and 6Mn-6Zr/PSC in 1440 min were 5587.0, 4340.8, and 3860.3 µg·g-1, respectively, indicating that the sample 6Mn6Zr/PSC-I3 had a higher adsorption ability. Besides, the Hg0 adsorption capacities at equilibrium time were obtained by the pseudo-first-order kinetic model. The parameters of the pseudo-firstorder kinetic model are listed in Table 5. The results manifested that the Hg0 adsorption capacities of 6Mn-6Zr/PSC-I3, PSC-I3, and 6Mn-6Zr/PSC at equilibrium time were 8778.9, 20


Page 20 of 49

Page 21 of 49 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

Energy & Fuels

5055.9, and 5249.8 µg·g-1, respectively. Moreover, the mercury adsorption rate of 6Mn6Zr/PSC-I3 which represented by the slope of the adsorption capacity-time (Q-t) curve was also faster than that of both PSC-I3 and 6Mn-6Zr/PSC except the initial 200 min. Consequently, 6Mn-6Zr/PSC-I3 has a better Hg0 removal performance as well as prospect of industrial application than PSC-I3 and 6Mn-6Zr/PSC. 3.3. Identification of Involved Reaction Mechanism Both adsorption and oxidation participate in the removal process of Hg0 over 6Mn-6Zr/PSC-I3 at the condition of 150 °C and N2 + 6% O2 atmosphere. To clarify the involved reaction mechanism, the Hg0 removal performance over 6Mn-6Zr/PSC-I3 was studied until reaching adsorption equilibrium (Hg0in = HgTout ). As the experimental error is inevitable, the adsorption equilibrium was regarded as reaching when the Hg0 adsorption efficiency was less than 5%. As shown in Figure 10, the Hg0 oxidation efficiency (Eoxi) was less than 10% in the initial 18 h, which was far below the Hg0 adsorption efficiency (Eads). This observation shows that most of the Hg0 is removed by adsorption process in the initial stage. As the reaction progress, the Hg0 adsorption was gradually replaced by Hg0 oxidation. After 66 h test, the Eads was only 3.10%, suggesting that the adsorption sites became nearly saturation and the adsorption equilibrium was reached. However, The Eoxi after reaching adsorption equilibrium (Eoxi(equilibrium)) surpassed 30%, which meant that Hg0 oxidation process was still continuing. Based on the results and analysis, it can be inferred that adsorption and oxidation dominate at different reaction stages. Besides, a similar experiment (Figure S3) was performed in sample 6Mn-6Zr/PSC for comparison. The Eoxi(equilibrium) of 6Mn-6Zr/PSC was 22.30%, which was inferior to that of 6Mn-6Zr/PSC-I3. 21


Energy & Fuels 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

The result reveals that the presence of iodine facilitates the Eoxi. The possible reason is that in the removal process, Hg0 firstly transfers from gas phase to the surface of samples by intermolecular Vander Waals forces and this forces can be enhanced due to the presence of iodine according to the previous results. Then, Hg0 is further adsorbed by chemical adsorption sites or oxidized by lattice oxygen. Chang et al60 also verified that the adsorption of Hg0 was an important step in Hg0 oxidation. Hence, the iodine promotes not only Hg0 adsorption but also Hg0 oxidation.

To deeply understand the Hg0 removal mechanism, the fresh and used 6Mn-6Zr/PSC-I3 sample tested at optimal reaction temperature and O2 concentration were chosen for XPS analysis. The XPS spectra over the spectral regions of Mn 2p, O 1s, and Hg 4f are shown in Figure 11. The distribution of manganese species and oxygen species is listed in Table 6. The XPS spectra for Mn 2p are shown in Figure 11(A). The peaks at 644.2/644.9, 642.6/642.9, and 641.4/641.6 eV assigned to Mn4+, Mn3+, and Mn2+, respectively. After the sample used, the proportion of Mn3+ decreased from 47.06% to 22.77%, while the proportion of Mn4+ and Mn2+ increased. The result reveals that both the oxidation and reduction of Mn3+ present in the process of Hg0 removal. The XPS spectra for O 1s are shown in Figure 11(B). For the fresh sample, the peaks at 530.2 and 532.0 eV corresponded to lattice oxygen and hydroxyl oxygen, respectively. For the used sample, a new peak at 533.9 eV appeared, which attributed to H2O. In addition, the ratio of lattice oxygen decreased from 36.49% to 29.96% and the ratio of hydroxyl oxygen decreased from 63.51% to 44.28%. This observation indicates that both lattice oxygen and hydroxyl oxygen participate in the Hg0 oxidation process and H2O is a reaction product. Figure 11(C) shows the XPS spectrum 22


Page 22 of 49

Page 23 of 49 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

Energy & Fuels

of Hg 4f. The peak at 102.4 eV for the fresh sample assigned to Si 2p. After the sample used, two new peaks appeared in the spectrum. The characteristic peaks at 104.7 and 100.8 eV corresponded to Hg 4f 5/2 and Hg 4f 7/2, respectively, which demonstrates that the mercury exists in the form of Hg2+ on the sample. Besides, the XPS spectra for Zr 3d are shown in Figure S4. The peaks at 184.8 and 182.4 eV assigned to Zr 3d3/2 and Zr 3d5/2, respectively. Obviously, the binding energy of zirconium on the fresh and used sample is same. This indicates that zirconium does not directly participate in the Hg0 removal process.

From above analysis, the Hg0 removal mechanism over 6Mn-6Zr/PSC-I3 was deduced. The chemical adsorption sites of C-I groups are responsible for the Hg0 adsorption. The adsorption mechanism includes three steps: (1) iodine ions react with carbon atom to form C-I groups; (2) Hg0 transfers from gas phase to the surface of the sample; (3) chemical adsorption sites (C-I) adsorbs Hg0 to form HgI2. These could be described as following reactions: I + C → C − I

(8)

Hg " g& → Hg " ad&

(9)

2Hg " ad& + 2C − I → Hg ; I; ad&

(10)

Hg ; I; + 2C − I → 2HgI; ad&

(11)

The lattice oxygen and hydroxyl oxygen are responsible for the Hg0 oxidation. The oxidation mechanism also includes three steps: (1) Hg0 transfers from gas phase to the surface of the sample; (2) lattice oxygen ([O]) and hydroxyl oxygen (OH) oxidize Hg0 to HgO and it will be 23


Energy & Fuels 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

Page 24 of 49

released into gas phase; (3) O2 in the flue gas replenishes the lattice oxygen and hydroxyl oxygen to keep the oxidation process continuing51. These could be explained as following reactions: Hg " g& → Hg " ad&

(9)

2MnO; → Mn; O? + [O]

(12)

Mn; O? → 2MnO + [O]

(13)

Hg " ad& + [O] → HgO

(14)

Hg " ad& + OH → HgO + H

(15)

2MnO + 1⁄2O; → Mn; O?

(16)

Mn; O? + 1⁄2O; → 2MnO;

(17)

H + 1⁄2O; → OH

(18)

It is important to notice that the first step in the adsorption and oxidation mechanism is same. And this step, physical adsorption, can be facilitated by iodine due to its large atomic size. In addition, the primary removal mechanism changes with the reaction progress (Figure 12). At the initial stage, first 18 h, the Hg0 is removed mainly through the adsorption mechanism. At the middle stage, before reaching adsorption equilibrium, both the adsorption mechanism and the oxidation mechanism engage in the Hg0 removal process. At the final stage, after reaching adsorption equilibrium, the chemical adsorption sites have been saturated. Only the oxidation mechanism is involved. 4. Conclusions In this paper, the Hg0 removal performance over 6Mn-6Zr/PSC-I3 was studied by various 24


Page 25 of 49 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

Energy & Fuels

characterizations and experiments. The sample characterization indicates that the 6Mn-6Zr/PSCI3 has a developed pore structure and the active components disperse well on its surface. The experimental results show that an excellent ET(2 h) (more than 90%) is obtained in a wide reaction temperature range (150-300 °C) under N2 + 6% O2 atmosphere. In addition, the Hg0 adsorption capacity of 6Mn-6Zr/PSC-I3 in 1440 min was 5587.0 µg·g-1 and the Eoxi(equilibrium) of it was more than 30%, which suggests that the introduction of both halide ions (I-) and metal oxides (MnOx and ZrO2) on the surface of peanut shells carbon results in a high adsorption and oxidation ability. The involved mechanism includes both adsorption and oxidation. The chemical adsorption sites of C-I groups are responsible for the Hg0 adsorption, which dominates the Hg0 removal at initial reaction stage. The lattice oxygen and hydroxyl oxygen are responsible for the Hg0 oxidation, which dominates the Hg0 removal at finial reaction stage (after reaching adsorption equilibrium). Meanwhile, they can be replenished by gaseous O2 to keep the oxidation process continuing. In a word, the 6Mn-6Zr/PSC combining the advantage of halide ions and metal oxides was demonstrated to be a good material for Hg0 removal and had a promising prospect in industrial applications. Associated Content Supporting Information Information regarding the orthogonal experiment, nitrogen adsorption/desorption isotherms, XPS results, Hg0 removal test, Tables S1-S2, Figures S1-S4. Author Information Corresponding Author 25


Energy & Fuels 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

*

Tel: +86 731 88649216; Fax: +86 731 88649216 E-mail address: [email protected]; [email protected]

Notes The authors declare no competing financial interest. Acknowledgements This work was financially supported by the National Nature Science Foundation of China (51478173), the National Key Research and Development Program of China (2016YFC0204104), and the Scientific and Technological Major Special Project of Hunan Province in China (2015SK1003).

26


Page 26 of 49

Page 27 of 49 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

Energy & Fuels

References (1) Scheuhammer, A. M.; Meyer, M. W.; Sandheinrich, M. B.; Murray, M. W. Ambio 2007, 36, (1), 12-19. (2) Mergler, D.; Anderson, H. A.; Chan, L. H. M.; Mahaffey, K. R.; Murray, M.; Sakamoto, M.; Stern, A. H. Ambio 2007, 36, (1), 3-11. (3) United Nations Environment Programme (UNEP): Minamata Convention on Mercury; UNEP: Minamata, Japan, 2013. (4) Hui, M.; Wu, Q.; Wang, S.; Liang, S.; Zhang, L.; Wang, F.; Lenzen, M.; Wang, Y.; Xu, L.; Lin, Z.; Yang, H.; Lin, Y.; Larssen, T.; Xu, M.; Hao, J. Environ. Sci. Technol. 2017, 51, (1), 222-231. (5) Arctic Monitoring and Assessment Programme and United Nations Environment Programme (AMAP/UNEP): Technical back-ground report for the global mercury assessment; AMAP/UNEP: Geneva, Switzerland, 2013. (6) United Nations Environment Programme (UNEP). Global Mercury Assessment 2013: Sources, Emissions, Releases and Environmental Transport; UNEP Chemicals Branch: Geneva, Switzerland, 2013. (7) Wu, Q.; Wang, S.; Li, G.; Liang, S.; Lin, C. J.; Wang, Y.; Cai, S.; Liu, K.; Hao, J. Environ. Sci. Technol. 2016, 50, (24), 13428-13435. (8) Driscoll, C. T.; Mason, R. P.; Chan, H. M.; Jacob, D. J.; Pirrone, N. Environ. Sci. Technol. 2013, 47, (10), 4967-4983. 27


Energy & Fuels 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

(9) Lee, S.; Rhim, Y.; Cho, S.; Baek, J. Fuel 2006, 85, (2), 219-226. (10) Hsi, H.-C.; Chen, C.-T. Fuel 2012, 98, 229-235. (11) Li, H.; Wu, S.; Wu, C. Y.; Wang, J.; Li, L.; Shih, K. Environ. Sci. Technol. 2015, 49, (12), 7373-7379. (12) Usberti., N.; Clave., S. A.; Nash., M.; Beretta., A. Appl. Catal. B: Environ. 2016, 193, 121132. (13) Du, W.; Yin, L.; Zhuo, Y.; Xu, Q.; Zhang, L.; Chen, C. Ind. Eng. Chem. Res. 2014, 53, (2), 582-591. (14) Duan, Y.; Zhao, C.; Wang, Y.; Wu, C. Energy Fuels 2010, 24, (1), 220-224. (15) Antonia Lopez-Anton, M.; Diaz-Somoano., M.; Rosa Martınez-Tarazona, M. Ind. Eng. Chem. Res. 2007, 46, 927-931. (16) Wang, Y.; Duan, Y. Energy Fuels 2011, 25, (4), 1553-1558. (17) Xin, G.; Zhao, P.; Zheng, C. P. Combust. Inst. 2009, 32, (2), 2693-2699. (18) Yang, H.; Xu, Z.; Fan, M.; Bland, A. E.; Judkins, R. R. J. Hazard. Mater. 2007, 146, (1-2), 1-11. (19) Xu, H.; Shen, B.; Yuan, P.; Lu, F.; Tian, L.; Zhang, X. Fuel Process. Technol. 2016, 154, 139-146. (20) Yang, K.; Peng, J.; Srinivasakannan, C.; Zhang, L.; Xia, H.; Duan, X. Bioresour. Technol. 2010, 101, (15), 6163-6169. (21) Oliveira, L. C.; Pereira, E.; Guimaraes, I. R.; Vallone, A.; Pereira, M.; Mesquita, J. P.; Sapag, K. J. Hazard. Mater. 2009, 165, (1-3), 87-94. 28


Page 28 of 49

Page 29 of 49 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

Energy & Fuels

(22) Sych, N. V.; Trofymenko, S. I.; Poddubnaya, O. I.; Tsyba, M. M.; Sapsay, V. I.; Klymchuk, D. O.; Puziy, A. M. Appl. Surf. Sci. 2012, 261, 75-82. (23) Gao, P.; Liu, Z. H.; Xue, G.; Han, B.; Zhou, M. H. Bioresour. Technol. 2011, 102, (3), 3645-3648. (24) Duan, F.; Zhang, J.-P.; Chyang, C.-S.; Wang, Y.-J.; Tso, J. Fuel Process. Technol. 2014, 128, 28-35. (25) Huang, X.; Li, M.; Li, J.; Song, Y. Atmos. Environ. 2012, 50, 9-15. (26) Jiang, R.; Bell, M. L. Environ. Health Persp. 2008, 116, (7), 907-914. (27) Xu, W.; Zhao, Q.; Wang, R.; Jiang, Z.; Zhang, Z.; Gao, X.; Ye, Z. Vacuum 2017, 141, 307315. (28) Wei, Y.; Yu, D.; Tong, S.; Jia, C. Q. Environ. Sci. Technol. 2015, 49, (3), 1706-1712. (29) Li, H.; Zhu, L.; Wang, J.; Li, L.; Shih, K. Environ. Sci. Technol. 2016, 50, (17), 9551-9557. (30) Li, G.; Wang, S.; Wu, Q.; Wang, F.; Shen, B. Chem. Eng. J. 2016, 302, 305-313. (31) Tong, L.; Yue, T.; Zuo, P.; Zhang, X.; Wang, C.; Gao, J.; Wang, K. Fuel 2017, 197, 1-7. (32) Tang, H.; Duan, Y.; Zhu, C.; Li, C.; She, M.; Zhou, Q.; Cai, L. Int. J. Coal Geol. 2017, 170, 19-27. (33) Zhou, Q.; Duan, Y.-F.; Hong, Y.-G.; Zhu, C.; She, M.; Zhang, J.; Wei, H.-Q. Fuel Process. Technol. 2015, 134, 325-332. (34) Shen, B.; Tian, L.; Li, F.; Zhang, X.; Xu, H.; Singh, S. Fuel 2017, 187, 189-196. (35) Li, G.; Shen, B.; Li, F.; Tian, L.; Singh, S.; Wang, F. Fuel Process. Technol. 2015, 133, 4350. 29


Energy & Fuels 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

(36) De, M.; Azargohar, R.; Dalai, A. K.; Shewchuk, S. R. Fuel 2013, 103, 570-578. (37) Reddy, G. K.; He, J.; Thiel, S. W.; Pinto, N. G.; Smirniotis, P. G. J. Phys. Chem. C 2015, 119, (16), 8634-8644. (38) He, J.; Reddy, G. K.; Thiel, S. W.; Smirniotis, P. G.; Pinto, N. G. J. Phys. Chem. C. 2011, 115, (49), 24300-24309. (39) Wu, H.; Li, C.; Zhao, L.; Zhang, J.; Zeng, G.; Xie, Y. e.; Zhang, X.; Wang, Y. Energy Fuels 2015, 29, (10), 6747-6757. (40) Wu, J.; Zhao, Z.; Huang, T.; Sheng, P.; Zhang, J.; Tian, H.; Zhao, X.; Zhao, L.; He, P.; Ren, J.; Gao, K. Catal. Commun. 2017, 93, 62-66. (41) Yang, W.; Liu, Y.; Wang, Q.; Pan, J. Chem. Eng. J. 2017, 326, 169-181. (42) Wang, Y.; Chang, H.; Shi, C.; Duan, L.; Li, J.; Zhang, G.; Guo, L.; You, Y. Catal. Commun. 2017, 100, 210-213. (43) Qiao, S.; Chen, J.; Li, J.; Qu, Z.; Liu, P.; Yan, N.; Jia, J. Ind. Eng. Chem. Res. 2009, 48, 3317-3322. (44) Gao, Y.; Zhang, Z.; Wu, J.; Duan, L.; Umar, A.; Sun, L.; Guo, Z.; Wang, Q. Environ. Sci. Technol. 2013, 47, (19), 10813-10823. (45) Xie, J.; Qu, Z.; Yan, N.; Yang, S.; Chen, W.; Hu, L.; Huang, W.; Liu, P. J. Hazard. Mater. 2013, 261, 206-213. (46) Zhao, L.; Li, C.; Li, S.; Wang, Y.; Zhang, J.; Wang, T.; Zeng, G. Appl. Catal. B: Environ. 2016, 198, 420-430. (47) Wang, T.; Li, C.; Zhao, L.; Zhang, J.; Li, S.; Zeng, G. Appl. Surf. Sci. 2017, 400, 227-237. 30


Page 30 of 49

Page 31 of 49 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

Energy & Fuels

(48) Choi, G.-G.; Jung, S.-H.; Oh, S.-J.; Kim, J.-S. Fuel Process. Technol. 2014, 123, 57-64. (49) International Union of Pure and Applied Chemistry (IUPAC) Recommendations. Pure Appl. Chem. 1985, 57, 603-619. (50) Li, Z.; Shen, Y.; Li, X.; Zhu, S.; Hu, M. Catal. Commun. 2016, 82, 55-60. (51) He, C.; Shen, B.; Chen, J.; Cai, J. Environ. Sci. Technol. 2014, 48, (14), 7891-7898. (52) Lopez-Anton, M. A.; Rumayor, M.; Díaz-Somoano, M.; Martínez-Tarazona, M. R. Chem. Eng. J. 2015, 262, 1237-1243. (53) Mochida., I.; Korai., Y.; Shirahama., M.; Kawano., S.; Hada., T.; Seo., Y.; Yoshikawa., M.; Yasutake., A. Carbon 2000, 38, 227-239. (54) Yan, R.; Liang, D. T.; Tsen, L.; Wong, Y. P.; Lee, Y. K. Fuel 2004, 83, (17-18), 2401-2409. (55) Yang, J.; Zhao, Y.; Ma, S.; Zhu, B.; Zhang, J.; Zheng, C. Environ. Sci. Technol. 2016, 50, (21), 12040-12047. (56) Tan, Z.; Sun, L.; Xiang, J.; Zeng, H.; Liu, Z.; Hu, S.; Qiu, J. Carbon 2012, 50, (2), 362-371. (57) Xu, H.; Qu, Z.; Zong, C.; Quan, F.; Mei, J.; Yan, N. Appl. Catal. B: Environ. 2016, 186, 3040. (58) Li, G.; Wang, S.; Wu, Q.; Wang, F.; Ding, D.; Shen, B. Chem. Eng. J. 2017, 315, 251-261. (59) Zhao, B.; Yi, H.; Tang, X.; Li, Q.; Liu, D.; Gao, F. Chem. Eng. J. 2016, 286, 585-593. (60) Chang, H.; Wu, Q.; Zhang, T.; Li, M.; Sun, X.; Li, J.; Duan, L.; Hao, J. Environ. Sci. Technol. 2015, 49, (20), 12388-12394.

31


Energy & Fuels 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

Figure 1. Experimental schematic diagram of mercury adsorption fixed-bed system.

32


Page 32 of 49

Page 33 of 49 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

Energy & Fuels

Figure 2. SEM images of various samples: (a) PSC, (b) PSC-I3, (c) 6Mn-6Zr/PSC, (d) 6Mn6Zr/PSC-I3.

33


Energy & Fuels 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

Figure 3. XRD patterns of various samples: (a) 6Mn-6Zr/PSC-I3, (b) 6Mn-6Zr/PSC, (c) 12Mn/PSC, (d) 12Zr/PSC, (e) PSC.

34


Page 34 of 49

Page 35 of 49 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

Energy & Fuels

Figure 4. FTIR spectra of various samples: (a) 6Mn-6Zr/PSC-I3, (b) 6Mn-6Zr/PSC, (c) 12Mn/PSC, (d) 12Zr/PSC, (e) PSC-I3, (f) PSC-Br3, (g) PSC-Cl3, (h) PSC.

35


Energy & Fuels 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

Figure 5. The effect of active components on total Hg0 removal efficiency. Experimental conditions: O2 = 6%, reaction temperature = 150 °C.

36


Page 36 of 49

Page 37 of 49 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

Energy & Fuels

Figure 6. The comparison of Hg0 removal efficiency over peanut shells carbon impregnated with different mass concentration of NH4I (A) and loaded with different mass percentage of metal (B). Experimental conditions: O2 = 6%, reaction temperature = 150 °C.

37


Energy & Fuels 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

Figure 7. The effect of reaction temperature on total Hg0 removal efficiency including Hg0 oxidation efficiency (the column filled with oblique line) and Hg0 adsorption efficiency (the column filled with solid color). Experimental conditions: O2 = 6%.

38


Page 38 of 49

Page 39 of 49 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

Energy & Fuels

Figure 8. The effect of O2 concentration in flue gas on total Hg0 removal efficiency including Hg0 oxidation efficiency (the column filled with oblique line) and Hg0 adsorption efficiency (the column filled with solid color). Experimental conditions: reaction temperature = 150 °C.

39


Energy & Fuels 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

Figure 9. The effect of simulated flue gas (SFG) atmosphere on total Hg0 removal efficiency (A) and Hg0 adsorption capacities (B). Experimental conditions: reaction temperature = 150 °C.

40


Page 40 of 49

Page 41 of 49 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

Energy & Fuels

Figure 10. The Hg0 adsorption efficiency and Hg0 oxidation efficiency over 6Mn-6Zr/PSC-I3 during the reaction processing. Experimental conditions: O2 = 6%, reaction temperature = 150 °C.

41


Energy & Fuels 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

Figure 11. XPS spectra of fresh and used 6Mn-6Zr/PSC-I3 over the spectral regions of (A) Mn 2p, (B) O 1s, (C) Hg 4f. 42


Page 42 of 49

Page 43 of 49 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

Energy & Fuels

Figure 12. The main mechanism of Hg0 removal over 6Mn-6Zr/PSC-I3 at different reaction stages.

43


Energy & Fuels 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

Page 44 of 49

Table 1. Summary of Experimental Conditions. Experiments set 1

set 2

set 3

set 4

set 5

set 6

Samples 6Mn-6Zr/PSC-I3 PSC-I3 PSC-Br3 PSC-Cl3 6Mn-6Zr/PSC 12Mn/PSC 12Zr/PSC PSC PSC-I1 PSC-I3 PSC-I5 3Mn-3Zr/PSC 6Mn-6Zr/PSC 9Mn-9Zr/PSC 6Mn-6Zr/PSC-I3 PSC-I3 6Mn-6Zr/PSC 6Mn-6Zr/PSC-I3 PSC-I3 6Mn-6Zr/PSC 6Mn-6Zr/PSC-I3 PSC-I3 6Mn-6Zr/PSC 6Mn-6Zr/PSC-I3

Flue gas component N2 + 6% O2

Reaction temperature 150 °C

N2 + 6% O2

150 °C

N2 + 6% O2

50, 100, 150, 200, 250, 300, 350 °C

N2 N2 + 3% O2 N2 + 6% O2 N2 + 9% O2 SFGa (test time:24 h)

150 °C

N2 + 6% O2 (test time:72 h)

150 °C

150 °C

The test time is 2 h except set 5 and set 6. A 40 mg sample is used in each test. The balance gas is N2 and the total flow rate is 1000 mL·min-1. a SFG: simulated flue gas, N2 + 6% O2 + 12% CO2 + 300 ppm NO + 400 ppm SO2 + 8% H2O.

44


Page 45 of 49 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

Energy & Fuels

Table 2. Proximate and Ultimate Analysis of Peanut Shells and Peanut Shells Carbon (airdry basis). Samples PS PSC

M 2.13 1.41

Proximate analysis (wt.% ad) A V FCa 1.30 79.55 17.02 6.39 15.87 76.32

C 49.59 81.60

a

Ultimate analysis (wt.% ad ) H Oa N 5.88 40.28 0.75 2.45 6.70 1.36

S 0.07 0.09

by difference. M, A, V, and FC represent moisture, ash, volatile, and fixed carbon, respectively. M % + A % + V% + FCa % = 100%; C % + H % + Oa % + N % + S % + A % + M % = 100%.

45


Energy & Fuels 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

Page 46 of 49

Table 3. BET Analysis of Samples. Samples PSC PSC-Cl3 PSC-Br3 PSC-I3 12Zr/PSC 12Mn/PSC 6Mn-6Zr/PSC 6Mn-6Zr/PSC-I3

BET surface area (m2·g-1) 249.718 189.723 146.635 122.988 206.667 160.380 180.396 153.908

Total pore volume (cm3·g-1) 0.117 0.077 0.061 0.048 0.100 0.085 0.094 0.080

46


Average pore size (nm) 1.867 1.632 1.594 1.553 1.929 2.115 2.083 2.123

Page 47 of 49 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

Energy & Fuels

Table 4. Content of Metal and Halogens in Samples Obtained by ICP-AES and XRF. Samples PSC-Cl3 PSC-Br3 PSC-I1 PSC-I3 PSC-I5 12Zr/PSC 12Mn/PSC 3Mn-3Zr/PSC 6Mn-6Zr/PSC 9Mn-9Zr/PSC 6Mn-6Zr/PSC-I3

Mn 8.27 2.23 4.13 7.01 4.23

Zr 8.04 1.94 4.10 6.25 4.83

Content of element (wt.%) I Br 0.5205 0.0863 0.4783 1.2261 0.3588 -

47


Cl 0.4258 0.0671

Energy & Fuels 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

Page 48 of 49

Table 5. Parameters of the Pseudo-First Order Model. qe (µg·g-1) 15028.4 8778.9 5055.9 5249.8

Samples and experimental conditions 6Mn-6Zr/PSC-I3 (N2+ 6% O2) 6Mn-6Zr/PSC-I3 (SFG) PSC-I3 (SFG) 6Mn-6Zr/PSC (SFG)

48


k1 (min-1) 4.756 × 10-4 6.892 × 10-4 1.300 × 10-3 9.196 × 10-4

R2 0.9998 0.9995 0.9995 0.9999

Page 49 of 49 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

Energy & Fuels

Table 6. Distribution of Manganese Species and Oxygen Species in 6Mn-6Zr/PSC-I3 Calculated by XPS Results.

Mn 2P3/2

O 1S

Mn4+ Mn3+ Mn2+ Lattice oxygen Hydroxyl oxygen H 2O

Binding energy (eV) 644.2-644.9 642.6-642.9 641.4-641.6 530.2-530.3 532.0-532.2 533.9

49


Relative intensity (%) fresh used 34.55 49.28 47.06 22.77 18.38 27.95 36.49 29.96 63.51 44.28 25.77

Removal of Elemental Mercury from Simulated Flue Gas over Peanut

Recommend Documents