Elemental Mercury Oxidation over FeâTiâMn Spinel: Performance

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Elemental mercury oxidation over Fe-Ti-Mn spinel: Performance, mechanism and reaction kinetics Shangchao Xiong, Xin Xiao, Nan Huang, Hao Dang, Yong Liao, Sijie Zou, and Shijian Yang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b05023 • Publication Date (Web): 07 Dec 2016 Downloaded from http://pubs.acs.org on December 7, 2016

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Environmental Science & Technology

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Elemental mercury oxidation over Fe-Ti-Mn spinel:

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Performance, mechanism and reaction kinetics

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Shangchao Xiong, Xin Xiao, Nan Huang, Hao Dang, Yong Liao, Sijie Zou, Shijian Yang *

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Jiangsu Key Laboratory of Chemical Pollution Control and Resources Reuse, School of

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Environmental and Biological Engineering, Nanjing University of Science and Technology,

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Nanjing, 210094 P. R. China

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1

ACS Paragon Plus Environment


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Abstract:

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The design of a high performance catalyst for Hg0 oxidation and the predicting of the extent of

10

Hg0 oxidation are both extremely limited due to the uncertainties of the reaction mechanism and

11

the reaction kinetics. In this work, Fe-Ti-Mn spinel was developed as a high performance catalyst

12

for Hg0 oxidation, and the reaction mechanism and the reaction kinetics of Hg0 oxidation over

13

Fe-Ti-Mn spinel were studied. The reaction orders of Hg0 oxidation over Fe-Ti-Mn spinel with

14

respect to gaseous Hg0 concentration and gaseous HCl concentration were approximately 1 and 0,

15

respectively. Therefore, Hg0 oxidation over Fe-Ti-Mn spinel mainly followed the Eley-Rideal

16

mechanism (i.e. the reaction of gaseous Hg0 with adsorbed HCl), and the rate of Hg0 oxidation

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mainly depended on Cl* concentration on the surface. As H2O, SO2 and NO not only inhibited Cl*

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formation on the surface but also interfered with the interface reaction between gaseous Hg0 and

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Cl* on the surface, Hg0 oxidation over Fe-Ti-Mn spinel was obviously inhibited in the presence of

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H2O, SO2, and NO. Furthermore, the extent of Hg0 oxidation over Fe-Ti-Mn spinel can be

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predicted according to the kinetic parameter of kE-R, and the predicting result was consistent with

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the experiment result.

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Table of Content

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1.

Introduction

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Mercury emission from coal-fired utility boilers is a serious concern in both developing and

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developed countries,1-4 so nations agree to control mercury emission from coal-fired plants in the

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Minamata Convention. Hg species mainly present in the flue gas from coal combustion as

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particulate-bound mercury (Hgp), elemental mercury (Hg0) and oxidized mercury (Hg2+).5 Hgp can

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be collected by the particulate control devices for example fabric filter (FF) and electrostatic

35

precipitator (ESP),6 and Hg2+ can be effectively removed by wet flue gas desulfurization (FGD)

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due to its water-solubility.5 As Hg0 cannot be removed by currently available control devices in

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coal-fired plants, it is the main Hg species emitted from coal-fired plants to atmosphere.7, 8

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Now, the control of Hg0 emission from coal-fired plants mainly falls into two methods. One is

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the conversion of gaseous Hg0 to Hgp through the adsorption by sorbents,9-12 and the other is the

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catalytic oxidation of Hg0 to Hg2+ by the catalysts with HCl in the flue gas as the oxidant.13 The

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injection of brominated activated carbon is a potential commercial technology to control Hg0

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emission from the flue gas.14 However, it is extremely limited due to the high operation cost and

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the quality deterioration of fly ash.15-18 As the selective catalytic reduction (SCR) catalyst can

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oxidize Hg0 to Hg2+ as a co-benefit of NO abatement, it may be a promising technology to control

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Hg0 emission.13, 19 However, the performance of commercial V2O5-WO3/TiO2 for the catalytic

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oxidation of Hg0 is not satisfied due to its moderate activity and the notable inhibition of injected

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NH3 on Hg0 oxidation.20 Therefore, many researches now focus on developing a high performance

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catalyst for Hg0 oxidation, which is placed in the SCR unit downstream the SCR catalyst. Recently,

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many

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Ce-MnOx/Ti-PILCs,24 Mn/α-Al2O3,25 CeO2-TiO2

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oxidation. The catalytic oxidation of Hg0 generally follows the Mars-Maessen mechanism (i.e. the

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chemical adsorption of gaseous Hg0 on the catalysts as HgO, which then reacts with HCl to

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gaseous HgCl2), the Eley-Rideal mechanism (the reaction of gaseous Hg0 with adsorbed HCl to

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gaseous HgCl2) and the Langmuir-Hinshelwood mechanism (the reaction of physically adsorbed

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Hg0 with adsorbed HCl to gaseous HgCl2).5 However, the specific contributions of the three

56

mechanisms to Hg0 oxidation and the reaction kinetics are both highly uncertain.28 Furthermore,

catalysts

for

example

V2O5/ZrO2-CeO2,21 26

CeO2-WO3,22

and MnOx/Graphene

4


27

IrO2/Ce0.6Zr0.4O2,23 are developed for Hg0

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the chemical components of the flue gas for example SO2, H2O and NO often interfere with Hg0

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oxidation.5 However, the interference mechanism is unclear. As a result, the design of a high

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performance catalyst for Hg0 oxidation and the predicting of the extent of Hg0 oxidation are both

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extremely limited.

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Our previous study demonstrated that Fe-Ti-Mn spinel showed an excellent performance for the

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chemical adsorption of Hg0.29 The superior adsorption of Hg0 on the catalyst may promote Hg0

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oxidation through both the Mars-Maessen mechanism and the Langmuir-Hinshelwood mechanism.

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In this work, Fe-Ti-Mn spinel was developed as a high performance catalyst for Hg0 oxidation.

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Meanwhile, the mechanism of Hg oxidation over Fe-Ti-Mn spinel and the mechanism of the

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interference of SO2, H2O and NO with Hg0 oxidation were investigated using the transient

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reaction study and the steady state kinetic study. The results showed that Hg0 oxidation over

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Fe-Ti-Mn spinel mainly followed the Eley-Rideal mechanism and the rate of Hg0 oxidation mainly

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depended on Cl* radical concentration on the surface. As SO2, H2O and NO not only restrained the

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formation of Cl* but also competed with gaseous Hg0 for Cl* on the surface, Hg0 oxidation over

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Fe-Ti-Mn spinel was obviously restrained in the presence of SO2, H2O and NO. Moreover, the

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extent of Hg0 oxidation can be precisely predicted according to the obtained kinetic parameter.

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2.

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2.1 Catalyst preparation

Experimental

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Fe-Ti-Mn spinel was prepared using the co-precipitation method.29-34 A solution with suitable

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amounts of titanium sulfate, ferrous sulfate, ferric trichloride and manganous sulfate (Fe3+:

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Fe2+:Ti4+:Mn2+=2:2:1:1) was added to an ammonia solution with the continuous stirring at 800

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rpm, resulting in an instantaneous precipitation. The particles were separated by centrifugation at

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4500 rpm for 5 min and they were then washed 3 times using distilled water. After the drying at

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105 °C for 12 h, the particles were calcined at 500 oC for 3 h under air atmosphere.

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V2O5-WO3/TiO2 was prepared using the conventional impregnation method.35, 36

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2.2 Characterization

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X-ray diffraction pattern (XRD), BET surface area and surface analysis were performed on an

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X-ray diffractionmeter (Bruker, AXS D8 Advance), a nitrogen adsorption apparatus

5



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(Quantachrome, Autosorb-1) and an X-ray photoelectron spectroscopy (XPS, Thermo, ESCALAB

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250), respectively.

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2.3 Activity test

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The chemical adsorption of Hg0 and the catalytic oxidation of Hg0 were both performed on a

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fixed-bed quartz tube micro-reactor. The reaction temperature was in the range of 250-400 oC. The

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catalyst mass was in the range of 2-50 mg, the flow rate of the simulated gas was 500 mL min-1,

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and the corresponding gas hourly space velocity (GHSV) was in the range of 600000-15000000

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cm3 g-1 h-1 (i.e. approximately 600000-15000000 h-1). The simulated gas generally contained

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approximately 0.16 mg m-3 of gaseous Hg0, 5% of O2, 10 ppm of HCl (when used), 50 ppm of NO

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(when used), 500 ppm of SO2 (when used), 8% of H2O (when used) and balance of N2. Hg0

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concentration in the outlet was determined online by a cold vapor atomic absorption

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spectrophotometer (CVAAS, Lumex R-915+). Meanwhile, the concentration of total Hg species

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(i.e. Hgt, including both Hg0 and Hg2+) in the outlet was determined online after the reduction of

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Hg2+ to Hg0 by a SnCl2 solution. Then, Hg2+ concentration in the outlet was obtained according to

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the difference between the concentrations of Hgt and Hg0 in the outlet. Temperature programmed

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desorption of Hg (Hg-TPD) was performed on the micro-reactor at a heating rate of 10 oC min-1

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under N2 atmosphere (500 mL min-1).

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The steady state kinetic study of Hg0 oxidation on Fe-Ti-Mn spinel was conducted on the

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fixed-bed micro-reactor. Gaseous Hg0 in the inlet was firstly kept at 160 µg m-3, while gaseous

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HCl concentration in the inlet varied from 10 to 30 ppm. Gaseous HCl concentration in the inlet

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was then kept at 10 ppm, while gaseous Hg0 in the inlet varied from 80 to 320 µg m-3.

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3.

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3.1 Performance for Hg0 oxidation

Results

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Hg0 conversion rate over Fe-Ti-Mn spinel was 18.4 µg g-1 min-1 at 250 oC and it gradually

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increased to 25.2 µg g-1 min-1 with the increase of reaction temperature to 400 oC (shown in Figure

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1a). Hg0 conversion rate over Fe-Ti-Mn spinel was at least thrice that over commercial 1%

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V2O5-WO3/TiO2. Although V2O5 content increased from 1% to 5%, Hg0 conversion rate over

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Fe-Ti-Mn spinel was at least twice that over 5% V2O5-WO3/TiO2. They suggest that the

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performance of Fe-Ti-Mn spinel for Hg0 oxidation was much better than that of V2O5-WO3/TiO2. 6


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There are generally high concentrations of SO2 and water vapor, and a low concentration of NO

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in the flue gas downstream of the SCR unit, which often interfere with Hg0 oxidation.37 Therefore,

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the effects of SO2, NO and H2O on Hg0 oxidation over Fe-Ti-Mn spinel were investigated (shown

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in Figure 1b). H2O, NO and SO2 all interfered with Hg0 oxidation over Fe-Ti-Mn spinel, and the

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inhibition increased in the following sequence: NO0.991). However, the intercepts (i.e. kL-H) were all

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very low. It suggests that the contribution of the Langmuir-Hinshelwood mechanism to Hg0

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oxidation over Fe-Ti-Mn spinel can be approximately neglected. As a result, Hg0 oxidation over

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Fe-Ti-Mn spinel mainly followed the Eley-Rideal mechanism and the rate of Hg0 oxidation was

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approximately directly proportional to gaseous Hg0 concentration.

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Although the adsorption of HCl on Fe-Ti-Mn spinel (i.e. Reaction 5) was restrained with the

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increase of reaction temperature, Reactions 6 and 7 were both promoted. As a result, the catalytic

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oxidation of Hg0 over Fe-Ti-Mn spinel was obviously promoted with the increase of reaction

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temperature (shown in Figure 1a), resulting in an increase of kE-R with the increase of reaction

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temperature (shown in Table 1).

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4.2 Mechanism of the interference of SO2, NO and H2O with Hg0 oxidation

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SO2, NO and H2O all interfered with Hg0 oxidation over Fe-Ti-Mn spinel (shown in Figure 1b).

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The inhibition of SO2, NO and H2O on Hg0 oxidation was often attributed to the competition

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adsorption of SO2, NO and H2O with Hg0.5, 13, 24, 26 However, Hg0 oxidation over Fe-Ti-Mn spinel

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mainly followed the Eley-Rideal mechanism and it did not involve the adsorption of Hg0 on

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Fe-Ti-Mn spinel. Equation 9 suggests that the rate of Hg0 oxidation mainly depended on the

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concentration of Cl* on the surface. Therefore, the inhibition on Hg0 oxidation would be mainly

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attributed to the inhibition on Cl* formation or the interference with the reaction between Cl* and

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gaseous Hg0 (i.e. Reaction 7). To investigate the mechanism of the inhibition of SO2, NO and H2O

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on Hg0 oxidation over Fe-Ti-Mn spinel, the transient reaction of passing Hg0+O2 over HCl+O2

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pretreated Fe-Ti-Mn spinel was preformed (shown in Figure 6). If the inhibition happened as the 12


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gaseous components were added in the pretreating process, Cl* formation on Fe-Ti-Mn spinel was

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restrained by the gaseous components. If the inhibition happened as the gaseous components were

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added with Hg0, the reaction between gaseous Hg0 and Cl* (i.e. Reaction 7) was interfered by the

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gaseous components.

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Figure 6a shows that the concentration of Hg2+ formed during passing Hg0+O2 over

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SO2+HCl+O2 pretreated Fe-Ti-Mn spinel was much less than that during passing Hg0+O2 over

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HCl+O2 pretreated Fe-Ti-Mn spinel. It suggests that the formation of Cl* over Fe-Ti-Mn spinel

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was inhibited by SO2. The formation of Cl* involved the adsorption of HCl on Fe-Ti-Mn spinel

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(i.e. Reaction 5) and the activation of Cl- to Cl* (i.e. Reaction 6). SO2 may compete with HCl for

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the adsorption sites, resulting in a decrease of Cl- concentration on Fe-Ti-Mn spinel. Meanwhile,

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SO2 can react with Fe-Ti-Mn spinel to form sulfate, resulting in a decrease of the oxidation ability

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of Fe-Ti-Mn spinel.41-43 Hinted by Equation 12, both the decrease of the oxidation ability (i.e. k3)

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and the decrease of Cl- concentration on the Fe-Ti-Mn spinel caused the inhibition on Cl*

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formation. Meanwhile, the concentration of Hg2+ formed during passing Hg0+O2+SO2 over

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HCl+O2 pretreated Fe-Ti-Mn spinel was much less than that during passing Hg0+O2 over HCl+O2

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pretreated Fe-Ti-Mn spinel (shown in Figure 6a). It suggests that Reaction 7 was interfered by SO2.

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As SO2 can react with Cl* on the surface, the interference was mainly related to the competition of

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SO2 with gaseous Hg0 for Cl* on the surface.

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Figure 6b shows that the concentration of Hg2+ formed during passing Hg0+O2 over

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H2O+HCl+O2 pretreated Fe-Ti-Mn spinel was slightly less than that during passing Hg0+O2 over

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HCl+O2 pretreated Fe-Ti-Mn spinel. It suggests that the adsorption of HCl or the activation of Cl-

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was inhibited by H2O. Meanwhile, the concentration of Hg2+ formed during passing Hg0+O2+H2O

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over HCl+O2 pretreated Fe-Ti-Mn spinel was at first much less than that during passing Hg0+O2

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over HCl+O2 pretreated Fe-Ti-Mn spinel. It suggests that H2O can react with Cl* on the surface

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(i.e. Reaction 13). However, the product (i.e. HClO) can still oxidize gaseous Hg0. The

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concentration of HClO on the surface gradually increased with the further introduction of

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H2O+Hg0, so the concentration of Hg2+ formation gradually increased (shown in Figure 6b).

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2Cl* +H 2 O → HClO+HCl

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(13)

Figure 6c shows that the concentration of Hg2+ formed during passing Hg0+O2 over 13



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NO+HCl+O2 pretreated Fe-Ti-Mn spinel and that during passing Hg0+O2+NO over HCl+O2

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pretreated Fe-Ti-Mn spinel were both less than that during passing Hg0+O2 over HCl+O2

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pretreated Fe-Ti-Mn spinel. It suggests that NO not only inhibited the formation of Cl* on

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Fe-Ti-Mn spinel but also interfered with Reaction 7. The phenomena were similar to those of SO2.

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The inhibition of SO2 on Hg0 oxidation over Fe-Ti-Mn spinel was much more remarkable than

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that of NO probably because the concentration of SO2 was 10 times that of NO.

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The relationships between the rate of Hg0 oxidation over Fe-Ti-Mn spinel and gaseous Hg0

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concentration in the presence of SO2, H2O and NO were shown in Figure S3 in the Supporting

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Information. Table 1 shows that there were excellent linear relationships between the rate of Hg0

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oxidation over Fe-Ti-Mn spinel and gaseous Hg0 concentration in the presence of SO2, H2O and

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NO (R2>0.972) and the intercepts were close to zero. It suggests that Hg0 oxidation over Fe-Ti-Mn

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spinel in the presence of SO2, H2O and NO mainly followed the Eley-Rideal mechanism.

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4.3 Predicting of the extent of Hg0 oxidation

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As the reaction order of Hg0 oxidation over Fe-Ti-Mn spinel with respect to gaseous Hg0

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concentration was approximately 1 (hinted by Equation 9), the extent of Hg0 oxidation over

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Fe-Ti-Mn spinel can be predicted according to the following equation:44, 45

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Hg 0 conversion% = [1 − exp( − k E-RW /F )] × 100%

(14)

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Where, F and W were the flow rate and the mass of catalyst, respectively. According to

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Equation 14 and kE-R in Table 1, the extents of Hg0 oxidation in the presence of 8% of H2O, 500

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ppm of SO2 and 50 ppm of NO with the GHSV of 600000 cm3 g-1 h-1 at 250, 300, 350 and 400 oC

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were predicted as 93%, 94%, 86% and 82%. The experiment result (shown in Figure 1c) shows

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that the extents of Hg0 oxidation at 250, 300, 350 and 400 oC were 97%, 94%, 90% and 88%,

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respectively. It suggests that the extent of Hg0 oxidation can be precisely predicted according to

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the kinetic parameter of kE-R.

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14


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Corresponding Author

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* School of Environmental and Biological Engineering, Nanjing University of Science and

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Technology. Telephone: 86-18-066068302; E-mail: [email protected].

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Acknowledgements:

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This study was financially supported by the National Natural Science Fund of China (Grant No.

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41372044) and the Natural Science Fund of Jiangsu Province (Grant No. BK20150036).

342

Supporting Information Available

343

This information is available free of charge via the Internet at http://pubs.acs.org/.

344

XRD patterns of Fe-Ti-Mn spinel and V2O5-WO3/TiO2, XPS spectra of Fe-Ti-Mn spinel,

345

dependence of Hg0 oxidation rate over Fe-Ti-Mn spinel on gaseous Hg0 concentration in the

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presence of SO2, H2O and NO, the breakthrough curves of elemental mercury adsorption on

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Fe-Ti-Mn spinel at 250-400 oC, the concentrations of Hg0, Hg2+ and Hgt in the outlet during the

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transient reaction in the presence of SO2, H2O, NH3 and NO, effect of NH3 on Hg0 oxidation over

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Fe-Ti-Mn spinel, and effect of SO2 concentration on Hg0 oxidation over Fe-Ti-Mn spinel.

350

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the catalytic oxidation and adsorption of elemental mercury. Environ. Sci. Technol. 2015, 49,

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6823-6830.

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(28) Usberti, N.; Clave, S. A.; Nash, M.; Beretta, A. Kinetics of Hg degrees oxidation over a

425

V2O5/MoO3/TiO2 catalyst: Experimental and modelling study under deNOx inactive conditions.

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Appl. Catal. B-Environ 2016, 193, 121-132.

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(29) Yang, S.; Guo, Y.; Yan, N.; Wu, D.; He, H.; Xie, J.; Qu, Z.; Jia, J. Remarkable effect of the

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incorporation of titanium on the catalytic activity and SO2 poisoning resistance of magnetic

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Mn-Fe spinel for elemental mercury capture. Appl. Catal. B-Environ 2011, 101, 698-708.

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(30) Yang, S.; Guo, Y.; Yan, N.; Wu, D.; He, H.; Qu, Z.; Yang, C.; Zhou, Q.; Jia, J. Nanosized

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cation-deficient Fe-Ti spinel: A novel magnetic sorbent for elemental mercury capture from flue

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gas. ACS Appl. Mater. Interface. 2011, 3, 209-217.

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(31) Yang, S.; Yan, N.; Guo, Y.; Wu, D.; He, H.; Qu, Z.; Li, J.; Zhou, Q.; Jia, J. Gaseous elemental

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mercury capture from flue gas using magnetic nanosized (Fe3-xMnx)1-δO4. Environ. Sci. Technol.

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2011, 45, 1540-1546.

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(32) Yang, S. J.; Wang, C. Z.; Li, J. H.; Yan, N. Q.; Ma, L.; Chang, H. Z. Low temperature

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selective catalytic reduction of NO with NH3 over Mn-Fe spinel: Performance, mechanism and 18


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kinetic study. Appl. Catal. B-Environ 2011, 110, 71-80.

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(33) Dang, H.; Liao, Y.; Ng, T.; Huang, G.; Xiong, S.; Xiao, X.; Yang, S.; Wong, P. K. The

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simultaneous centralized control of elemental mercury emission and deep desulfurization from the

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flue gas using magnetic Mn-Fe spinel as a co-benefit of the wet electrostatic precipitator. Fuel

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Process. Technol. 2016, 142, 345-351.

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(34) Liao, Y.; Xiong, S.; Dang, H.; Xiao, X.; Yang, S.; Wong, P. K. The centralized control of

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elemental mercury emission from the flue gas by a magnetic rengenerable Fe-Ti-Mn spinel. J.

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Hazard. Mater. 2015, 299, 740-746.

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(35) Xiong, S. C.; Xiao, X.; Liao, Y.; Dang, H.; Shan, W. P.; Yang, S. J. Global kinetic study of

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NO reduction by NH3 over V2O5-WO3/TiO2: Relationship between the SCR performance and the

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key factors. Ind. Eng. Chem. Res. 2015, 54, 11011-11023.

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(36) Yang, S. J.; Wang, C. Z.; Ma, L.; Peng, Y.; Qu, Z.; Yan, N. Q.; Chen, J. H.; Chang, H. Z.; Li, J.

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H. Substitution of WO3 in V2O5/WO3-TiO2 by Fe2O3 for selective catalytic reduction of NO with

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NH3. Catal. Sci. Technol. 2013, 3, 161-168.

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mercury over Ce-MnOx/Ti-PILCs. J. Hazard. Mater. 2016, 304, 10-17.

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Chem. Res. 2011, 50, 9650-9656.

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muti-functional magnetic Fe-Ti-V spinel catalyst for elemental mercury capture and callback from

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(45) Yang, S.; Wang, C.; Li, J.; Yan, N.; Ma, L.; Chang, H. Low temperature selective catalytic

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reduction of NO with NH3 over Mn-Fe spinel: Performance, mechanism and kinetic study. Appl.

476

Catal. B-Environ 2011, 110, 71-80.

477 478 479

20


Page 20 of 29

Page 21 of 29


480

Table 1 Reaction kinetic constants of Hg0 oxidation over Fe-Ti-Mn spinel 0

δ = kE-R [Hg (g) ]+kL-H

o

Temperature/ C

kE-R/m3 g-1 min-1

kL-H/µg g-1 min-1

R2

250

0.108

0.4

0.996

300

0.115

0.8

0.997

350

0.150

-0.1

0.997

400

0.184

-1.2

0.991

250

0.073

-1.0

0.986

Fe-Ti-Mn spinel

300

0.067

-1.1

0.972

with SO2

350

0.061

-0.9

0.976

400

0.066

-1.0

0.972

250

0.089

-0.4

0.993

Fe-Ti-Mn spinel

300

0.102

-0.5

0.998

with H2O

350

0.114

-0.7

0.998

400

0.120

-0.8

0.996

250

0.092

0.2

0.995

Fe-Ti-Mn spinel

300

0.106

-0.4

0.996

with NO

350

0.141

-1.4

0.980

400

0.166

-1.6

0.983

Fe-Ti-Mn spinel

481 482

21



483 484

Figure captions

485

Figure 1 (a), The rates of Hg0 oxidation over Fe-Ti-Mn spinel and V2O5-WO3/TiO2. Reaction

486

conditions: [Hg0]=160 µg m-3, [HCl]=10 ppm, [O2]=5%, catalyst mass=2 mg, total flow rate=500

487

mL min-1 and GHSV=15000000 cm3 g-1 h-1; (b), Effect of the chemical components in the flue gas

488

on Hg0 oxidation over Fe-Ti-Mn spinel. Reaction conditions: [Hg0]=160 µg m-3, [HCl]=10 ppm,

489

[SO2]=500 ppm (when used), [H2O]=8% (when used), [NO]=50 ppm (when used), [O2]=5%,

490

catalyst mass=2 mg, total flow rate=500 mL min-1 and GHSV=15000000 cm3 g-1 h-1; (c), Hg0

491

removal efficiency over Fe-Ti-Mn spinel in the presence of H2O, SO2 and NO. Reaction

492

conditions: [Hg0]=160 µg m-3, [HCl]=10 ppm, [SO2]=500 ppm, [H2O]=8%, [NO]=50 ppm,

493

[O2]=5%, catalyst mass=50 mg, total flow rate=500 mL min-1 and GHSV=600000 cm3 g-1 h-1.

494

Figure 2 (a), The concentrations of Hg0, Hgt and Hg2+ in the outlet during Hg0 adsorption over

495

Fe-Ti-Mn spinel at 300 oC. Reaction conditions: [Hg0]=160 µg m-3, [O2]=5%, catalyst mass=20

496

mg, total flow rate=500 mL min-1 and GHSV=1500000 cm3 g-1 h-1; (b), Hg-TPD profile of

497

Fe-Ti-Mn spinel after Hg0 adsorption; (c), The concentrations of Hg0, Hgt and Hg2+ in the outlet

498

during Hg0 oxidation over Fe-Ti-Mn spinel at 300 oC. Reaction conditions: [Hg0]=160 µg m-3,

499

[HCl]=10 ppm, [O2]=5%, catalyst mass=2 mg, total flow rate=500 mL min-1 and

500

GHSV=15000000 cm3 g-1 h-1; (d), Hg-TPD profile of Fe-Ti-Mn spinel after Hg0 oxidation; (e), the

501

rate of Hg0 oxidation over Fe-Ti-Mn spinel (in the presence of HCl) and that of the chemical

502

adsorption of Hg0 over Fe-Ti-Mn spinel (in the absence of HCl) which resulted from Figure S4 in

503

the Supporting Information.

504

Figure 3 XPS spectra over the spectral region of Hg 4f of: (a), Fe-Ti-Mn spinel after Hg0

505

adsorption (in the absence of HCl); (b), Fe-Ti-Mn spinel after Hg0 oxidation (in the presence of

506

HCl).

507

Figure 4 (a), Transient reaction taken at 300 oC upon passing HCl+O2 to Hg0+O2 presorbed

508

Fe-Ti-Mn spinel. Reaction conditions: [Hg0]=160 µg m-3, [HCl]=10 ppm, [O2]=5%, catalyst

509

mass=250 mg, total flow rate=500 mL min-1 and GHSV=120000 cm3 g-1 h-1; (b), Transient

510

reaction taken at 300 oC upon passing Hg0+O2 to HCl+O2 presorbed Fe-Ti-Mn spinel. Reaction

511

conditions: [Hg0]=160 µg m-3, [HCl]=10 ppm, [O2]=5%, catalyst mass=3 mg, total flow rate=500 22


Page 22 of 29

Page 23 of 29


512

mL min-1 and GHSV=10000000 cm3 g-1 h-1.

513

Figure 5 (a), Dependence of the rate of Hg0 oxidation over Fe-Ti-Mn spinel on gaseous HCl

514

concentration. Reaction conditions: [Hg0]=160 µg m-3, [O2]=5%, catalyst mass=2 mg, total flow

515

rate=500 mL min-1 and GHSV=15000000 cm3 g-1 h-1; (b), Dependence of the rate of Hg0 oxidation

516

over Fe-Ti-Mn spinel on gaseous Hg0 concentration. Reaction conditions: [HCl]=10 ppm,

517


518

Figure 6 (a), Effect of SO2 on Hg2+ formation during the transient reaction; (b), Effect of H2O on

519

Hg2+ formation during the transient reaction; (c), Effect of NO on Hg2+ formation during the

520

transient reaction. Reaction conditions: [Hg0]=160 µg m-3, [HCl]=10 ppm, [O2]=5%, [SO2]=500

521

ppm (when used), [H2O]=8% (when used), [NO]=50 ppm (when used), catalyst mass=3 mg, total

522

flow rate=500 mL min-1 and GHSV=10000000 cm3 g-1 h-1.

23



Page 24 of 29

-1

Hg conversion rate/µg g min

36 30

-1

Fe-Ti-Mn spinel 1% V2O5-WO3/TiO2 5% V2O5-WO3/TiO2

24 18 12

36

control

30

with SO2

with NO

with H2O

24 18 12 6

0

6

0

-1


-1

523

0 250

300

350

400

0 250

300

350

400

o

o

Temperature/ C

Temperature/ C

b

a

80 60 40

0

Hg conversion/%

100

20 0 250

300

350

400

o

Temperature/ C

c 524

Figure 1 (a), The rates of Hg0 oxidation over Fe-Ti-Mn spinel and V2O5-WO3/TiO2. Reaction

525


526

mL min-1 and GHSV=15000000 cm3 g-1 h-1; (b), Effect of the chemical components in the flue gas

527

on Hg0 oxidation over Fe-Ti-Mn spinel. Reaction conditions: [Hg0]=160 µg m-3, [HCl]=10 ppm,

528

[SO2]=500 ppm (when used), [H2O]=8% (when used), [NO]=50 ppm (when used), [O2]=5%,

529

catalyst mass=2 mg, total flow rate=500 mL min-1 and GHSV=15000000 cm3 g-1 h-1; (c), Hg0

530

removal efficiency over Fe-Ti-Mn spinel in the presence of H2O, SO2 and NO. Reaction

531

conditions: [Hg0]=160 µg m-3, [HCl]=10 ppm, [SO2]=500 ppm, [H2O]=8%, [NO]=50 ppm,

532


533 534

24



0

t

Hg

800

2+

Hg

Hg

0

Hg

-3

180

Hg concentration/µg m


-3

Page 25 of 29

150 120 90 60 30

600 400 200 0

0 0

20

40

60

80

100

300

120

350 400

500

550 600 650

Temperature/ C

a

b 800

t

Hg


-3

-3

180


450

o

t/min

150 120 90 60 30 0

t

Hg

0 0

20

40

2+

Hg

60

80

Hg 100

600 400 200 0 300

120

350

400

450

500

550

600

650

o

Temperature/ C

t/min

d 36 30

0

Hg oxidation rate 0 maximum Hg adsorption rate

24 18 12 6

0

-1


-1

c

0 250

300

350

400

o

Temperature/ C

e 0

t

535

Figure 2 (a), The concentrations of Hg , Hg and Hg2+ in the outlet during Hg0 adsorption over

536

Fe-Ti-Mn spinel at 300 oC. Reaction conditions: [Hg0]=160 µg m-3, [O2]=5%, catalyst mass=20

537

mg, total flow rate=500 mL min-1 and GHSV=1500000 cm3 g-1 h-1; (b), Hg-TPD profile of

538

Fe-Ti-Mn spinel after Hg0 adsorption; (c), The concentrations of Hg0, Hgt and Hg2+ in the outlet

539

during Hg0 oxidation over Fe-Ti-Mn spinel at 300 oC. Reaction conditions: [Hg0]=160 µg m-3,

540

[HCl]=10 ppm, [O2]=5%, catalyst mass=2 mg, total flow rate=500 mL min-1 and

541

GHSV=15000000 cm3 g-1 h-1; (d), Hg-TPD profile of Fe-Ti-Mn spinel after Hg0 oxidation; (e), the

542

rate of Hg0 oxidation over Fe-Ti-Mn spinel (in the presence of HCl) and that of the chemical

543

adsorption of Hg0 over Fe-Ti-Mn spinel (in the absence of HCl) which resulted from Figure S4 in 25



544

Page 26 of 29

the Supporting Information.

545 Fe-Ti-Mn spinel 0 after Hg adsorption

Fe-Ti-Mn spinel after the 0 catalytic oxidation of Hg

Hg 4f

Hg 4f

100.8 105.0

108

106

104

102

100

108

98

106

104

102

Binding Energy/eV

Binding Energy/eV

a

b

100

98

546 547

Figure 3 XPS spectra over the spectral region of Hg 4f of: (a), Fe-Ti-Mn spinel after Hg0

548

adsorption (in the absence of HCl); (b), Fe-Ti-Mn spinel after Hg0 oxidation (in the presence of

549

HCl).

550 551

26


Page 27 of 29


0

2+

Hg

-3

Hg

400



-3

552

300 0

200

Hg in HCl in

100

0

Hg off

180 150 120 90 60

HCl off, 0 Hg in 30 HCl in 0

Hg

0

0 0

100

200

300

400

0

500

40

80

120

t

2+

Hg 160

Hg 200

240

t/min

t/min

a

b

553

Figure 4 (a), Transient reaction taken at 300 oC upon passing HCl+O2 to Hg0+O2 presorbed

554

Fe-Ti-Mn spinel. Reaction conditions: [Hg0]=160 µg m-3, [HCl]=10 ppm, [O2]=5%, catalyst

555

mass=250 mg, total flow rate=500 mL min-1 and GHSV=120000 cm3 g-1 h-1; (b), Transient

556

reaction taken at 300 oC upon passing Hg0+O2 to HCl+O2 presorbed Fe-Ti-Mn spinel. Reaction

557


558

mL min-1 and GHSV=10000000 cm3 g-1 h-1.

559 560

27



0

-1


-1

561

30 24 18 12 o

o

250 C o 350 C

6

300 C o 400 C

0 10

15

20

25

30

HCl concentration/ppm

60

0

o

300 C o 400 C

150

200

250 C o 350 C

-1


-1

a

o

45 30 15 0 100

0

250

-3

300

Hg concentration/µg m b 562 563

Figure 5 (a), Dependence of the rate of Hg0 oxidation over Fe-Ti-Mn spinel on gaseous HCl

564

concentration. Reaction conditions: [Hg0]=160 µg m-3, [O2]=5%, catalyst mass=2 mg, total flow

565

rate=500 mL min-1 and GHSV=15000000 cm3 g-1 h-1; (b), Dependence of the rate of Hg0 oxidation

566

over Fe-Ti-Mn spinel on gaseous Hg0 concentration. Reaction conditions: [HCl]=10 ppm,

567


568 569

28


Page 28 of 29


0

-3

passing Hg +O2 over SO2+HCl+O2 presorbed catalyst

120


0

passing Hg +O2 over HCl+O2 presorbed catalyst

100

0

passing SO2+Hg +O2 over HCl+O2 presorbed catalyst

80 60 40

2+

2+


-3

Page 29 of 29

20

0

passing Hg +O2 over H2O+HCl+O2 presorbed catalyst

120

0


100

0

passing H2O+Hg +O2 over HCl+O2 presorbed catalyst

80 60 40 20 0

0 40

80

120

160

0

200

40

80

t/min

t/min

a

b

2+


-3

0

120

160

200

0

passing Hg +O2 over NO+HCl+O2 presorbed catalyst

120

0


100

0

passing NO+Hg +O2 over HCl+O2 presorbed catalyst

80 60 40 20 0 0

40

80

120

160

200

t/min

c 570 571

Figure 6 (a), Effect of SO2 on Hg2+ formation during the transient reaction; (b), Effect of H2O on

572

Hg2+ formation during the transient reaction; (c), Effect of NO on Hg2+ formation during the

573

transient reaction. Reaction conditions: [Hg0]=160 µg m-3, [HCl]=10 ppm, [O2]=5%, [SO2]=500

574

ppm (when used), [H2O]=8% (when used), [NO]=50 ppm (when used), catalyst mass=3 mg, total

575

flow rate=500 mL min-1 and GHSV=10000000 cm3 g-1 h-1.

576

29


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