Simultaneous NO Removal and Hg0 Oxidation over CuO Doped V2O5

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Catalysis and Kinetics

Simultaneous NO removal and Hg0 oxidation over CuO doped V2O5-WO3/TiO2 catalyst in simulated coal-fired flue gas Chuanmin Chen, Wenbo Jia, Songtao Liu, and Yue Cao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03905 • Publication Date (Web): 20 May 2018 Downloaded from http://pubs.acs.org on May 20, 2018

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Energy & Fuels

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Simultaneous NO removal and Hg0 oxidation over CuO doped V2O5-WO3/TiO2 catalyst in

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simulated coal-fired flue gas

3

Chuanmin Chen*, Wenbo Jia, Songtao Liu, Yue Cao

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Department of Environmental Science & Engineering, North China Electric Power University,

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Baoding, 071003, Hebei, China

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*Corresponding Author, E-mail: [email protected]

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Abstract: A series of CuO doped V2O5-WO3/TiO2 based commercial SCR catalysts were

8

synthesized via the improved impregnation method for simultaneous NO removal and Hg0

9

oxidation under simulated coal-fired flue gas at temperature range of 150-400 °C. Several

10

characterization techniques, including BET, XRD, XPS and H2-TPR were used to characterize the

11

catalysts. The results indicated that Cu3-SCR catalyst exhibited the superior catalytic activity and

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wide active temperature window for simultaneous NO removal and Hg0 oxidation. The effects of

13

flue gas components on the catalytic activity were also investigated. The results indicated that Cu3-

14

SCR catalyst showed good performances on SO2 tolerance and H2O resistance. The effect of Hg0 on

15

NO removal was almost negligible. However, the copresence of NO and NH3 obviously inhibited

16

the Hg0 oxidation activity. Further study revealed that this inhibiting effect was weakened as the

17

consumption of NH3. The BET and XRD results suggested that the highly dispersed Cu species was

18

beneficial to the superior catalytic activity of Cu3-SCR catalyst. The XPS and H2-TPR analyses

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indicated that the Cu3-SCR catalyst possessed abundant chemisorbed oxygen and good redox ability,

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which was ascribed to the strong synergy between CuO and V2O5 on the catalyst. The redox cycle

21

of V4++Cu2+↔ V5++Cu+ in Cu3-SCR catalyst significantly improve the catalytic activity for

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simultaneous NO removal and Hg0 oxidation. The mechanism of Hg0 oxidation over Cu3-SCR

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catalyst was also investigated.

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Keywords: Simultaneous removal; Hg0 oxidation; SCR catalyst; CuO modification; simulated

25

coal-fired flue gas 1

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1. Introduction Coal-fired power plants have been targeted as one of the major anthropogenic emission source of

2

1-3

3

NOx (NO, NO2, N2O) and mercury, which have drawn considerable attention recently

. It is

4

generally known that NOx can cause various environmental problems, such as acid rain, urban

5

photochemical smog, greenhouse effects and ozone depletion

6

heavy metal contaminant in the environment due to its volatility, persistence, and bioaccumulation

7

6-8

8

the emission of NOx and mercury from coal-fired power plants in the worldwide 3. For example, the

9

Mercury and Air Toxics Standards (MATS) had been issued by the U.S. Environmental Protection

10

Agency (EPA) in 2011 to control the mercury, acid gases and other harmful air pollutants in coal-

11

fired power plants 9. Consequently, it is an urgent task to develop the efficient and economical

12

technologies to control the emissions of NOx and mercury in coal-fired power plants.

4, 5

. Similarly, mercury is a toxic

. Considering the harm of NOx and mercury, various laws and regulations were enacted to reduce

13

Among the various methods and technologies practiced to control NOx emission, Selective

14

Catalytic Reduction (SCR) is regarded as one of the most efficient process for NOx removal. V2O5-

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WO3/TiO2 based catalyst has been widely used for SCR process due to its high catalytic activity and

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selectivity at 300-400 °C. However, elemental mercury (Hg0), which is the main mercury species

17

existed in coal-fired flue gas, is hard to be removed from the coal-fired power plants because of its

18

high volatility and low solubility

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soluble oxidized mercury (Hg2+) for mercury controlling in coal-fired power plants, because the

20

highly water soluble Hg2+ can be trapped by the slurry of the wet flue gas desulfurization (WFGD)

21

system 13. Luckily, the SCR process exhibits the facilitating effect on Hg0 oxidation. It was found

22

that V2O5, which was the main active component for NO removal over V2O5-WO3/TiO2 catalyst,

23

played an important role for Hg0 oxidation

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commercial SCR catalyst is very limited in the absence of HCl and/or low HCl content 16, 17. The U.

25

S. Energy and Environmental Research Center (EERC) found that the commercial V2O5-WO3/TiO2

10-12

. It is the key technology to oxidize the insoluble Hg0 to the

14, 15

. However, the Hg0 oxidation activity of the

2


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catalyst showed obvious Hg0 oxidation activity in the high HCl contained flue gas, and the

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influence of SCR catalyst on Hg0 oxidation was greatly affected by the coal species 18. Lee et al. 19

3

reported that about 20% of Hg0 oxidation efficiency was obtained over commercial SCR catalyst

4

when less than 10 ppm HCl was present. Gao et al.

5

oxygen complexes in the copresence of HCl and O2 was critical for Hg0 oxidation, which enhanced

6

the Hg0 oxidation ability of commercial SCR catalyst. So it was hard to oxidize Hg0 efficiently over

7

the commercial SCR catalyst in coal-fired power plants, since the chlorine contents in fired-coal

8

were various.

14

found that the formation of the chlorine-

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In recent years, various CuO doped catalysts have been prepared to oxidize Hg0 at low HCl

10

concentration. Xu et al. revealed that CuO/TiO2 catalyst could oxidize Hg0 efficiently at 50-300 °C

11

in the flue gas with low HCl concentration

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copper species in CuO/TiO2 catalyst contributing to Hg0 oxidation. However, further study should

13

investigate the NO removal ability of CuO/TiO2 catalyst. Wang et al.

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Fe2O3/γ-Al2O3 catalyst and achieved more than 70% of Hg0 oxidation efficiency over the catalyst in

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the low chlorine flue gas at 300 °C. It was found that the dominance of Cu2+ and Mn4+ as well as the

16

presence of chemisorbed oxygen was responsible for the excellent Hg0 oxidation performance. Li et

17

al.

18

low temperature, and the synergistic effect between Cu and Ce was responsible to the superior

19

activity for simultaneous NO removal and Hg0 oxidation. However, the co-presence of NO and NH3

20

significantly inhibited the Hg0 oxidation activity of CuO-CeO2/TiO2 catalyst. Further study found

21

that the presence of NH3 could induce the reduction of oxidized mercury species, which lowered the

22

Hg0 oxidation activity of the catalyst

23

with the decrease of the gas hourly space velocity (GHSV)

24

catalytic performance of ZrO2 doped CuO-CeO2/TiO2 catalyst at 150-350 °C. The results indicated

25

that Zr benefited great surface area, weakened crystallinity of TiO2 and then improved the

22, 23

20

. It was also confirmed that Cu2+ was the primary

21

prepared the CuO-MnO2-

reported that CuO-CeO2/TiO2 catalyst exhibited the good performance on Hg0 oxidation at

23

. Fortunately, this inhibiting effect of NH3 was weakened 22

3


. Wang et al.

24

investigated the

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dispersion of metal oxide species. Meanwhile, the synergetic effect of Cu and Ce contributed to Hg0

2

oxidation and NO conversion. Moreover, as found by Gao et al.

3

obviously improve the sulfur tolerance of CeO2 based catalyst. Though the above novel catalysts

4

exhibited good performance on Hg0 oxidation at low HCl concentration, they were different from

5

the V2O5-WO3/TiO2 based commercial SCR catalysts in components and operating temperature.

6

The industrial applications of these novel catalysts may result in the additional equipment cost and

7

operating expense. The V2O5-WO3/TiO2 based commercial SCR catalysts have been widely applied

8

in actual coal-fired power plants for NOx removal because of its high catalytic activity, thermal

9

stability and economic viability. So it is a low-cost option for simultaneous NO removal and Hg0

10

oxidation in coal-fired power plants by enhancing the Hg0 oxidation activity of the commercial

11

V2O5-WO3/TiO2 catalyst. Moreover, it seems that CuO exhibited good performance on Hg0

12

oxidation. However, little study has been made to research the catalytic activity of simultaneous NO

13

removal and Hg0 oxidation over the CuO doped V2O5-WO3/TiO2 based SCR catalyst in simulated

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coal-fired flue gas.

25

, the presence of Cu could

15

In this study, CuO doped V2O5-WO3/TiO2 based commercial SCR catalysts, synthesized by an

16

improved impregnation method, were tested to investigate the catalytic performance of

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simultaneous NO removal and Hg0 oxidation in the absence of HCl at temperature range of 150-

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400 °C. The effects of the reaction conditions (including temperature, Hg0, NO/NH3, SO2, H2O and

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GHSV) on the NO removal and Hg0 oxidation were investigated. Moreover, the physicochemical

20

properties of the catalysts were characterized by the essential characterizations including BET,

21

XRD, XPS and H2-TPR, and the catalytic mechanism was also discussed. The present study aimed

22

to improve the Hg0 oxidation activity of the commercial SCR catalyst in the absence of HCl as well

23

as reveal the possibility of simultaneous NO removal and Hg0 oxidation over CuO doped V2O5-

24

WO3/TiO2 based commercial SCR catalyst.

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2. Experimental 4


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2.1. Preparation of catalysts

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An improved impregnation method was used to synthesize the CuO doped V2O5-WO3/TiO2

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catalysts. The commercial SCR catalyst (consisted of 0.6% V2O5, 8% WO3 and anatase TiO2

4

supported) was used as a carrier, and CuO as a second assistant. The detailed preparation process

5

was as follows: First, the Cu(NO3)2•3H2O (precursor of CuO) was dissolved into the deionized

6

water to form solution. Then, the powdered commercial SCR catalyst (milled through 80 mesh) was

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added to the solution. The suspended slurry was stirred continuously in a 60 °C thermostatic water

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bath for 2h. After drying at 105 °C overnight, the obtained solid was calcined at 500 °C in static air

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for 4 h. All the obtained samples were ground and sieved through 60-80 mesh for catalytic activity

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test. Specifically, the CuO doped V2O5-WO3/TiO2 based commercial SCR catalysts were labeled as

11

Cux-SCR, where x represented the weight percentage of CuO.

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2.2. Catalytic activity test

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The catalytic performances of Cux-SCR catalysts for NO conversion and Hg0 oxidation were

14

analyzed at 150-400 °C in a fixed-bed flow reactor. Figure 1 displayed the schematic diagram of

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the experimental system. Unless otherwise indicated, the quartz tube reactor with 10 mm inner

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diameter was loaded with 0.50 g (about 0.6 mL) catalyst sample. The total flow rate of the

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simulated flue gas was 1 L/min with a GHSV of approximately 1×105 h-1. The cylinder gases were

18

accurately controlled by the corresponding mass flow controller (D08-3E, Seven Star, Beijing,

19

China). A stable feed of Hg0 vapor was generated by the Hg0 penetration device (VICI, Metronics

20

Inc., USA) with 72.0 µg/m3. Water vapor was generated and controlled by the water vapor

21

generator. All Teflon lines that Hg0 and water vapor passed through were heated to 120 °C by

22

heating belts, which could prevent the possible adsorption and condensation on the inner surface

23

before analysis. The Hg0 and NO concentrations at the inlet (Hg ଴୧୬ /NO୧୬ ) and outlet (Hg ଴୭୳୲ /NO୭୳୲ )

24

of the reactor were respectively measured by an online RA-915+ mercury analyzer (Lumex, Russia)

25

and a flue gas analyzer (ECOM-J2KN). The Hg0 concentrations in each test were recorded when the 5


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Page 6 of 41

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process reached equilibrium, which was defined that the fluctuation of Hg0 concentration was less

2

than 5% for more than 30 min

3

reaction tube had no obvious capacity of capturing NO and Hg0, and the impact of flue gas

4

components on test instruments was negligible. In order to avoid possible bias caused by Hg0

5

physical adsorption, the catalysts were firstly saturated with Hg0 under N2 atmosphere at room

6

temperature. It was found that less than 20 min was needed for Hg0 saturation, indicating that the

7

Hg0 physical adsorption capacity of the catalysts was negligible. So the loss of Hg0 at the outlet was

8

ascribed to the oxidized mercury species. Therefore, the NO removal efficiency (ENO) and Hg0

9

oxidation efficiency (Eoxi) could be quantified as follows:

26

. The blank experiment was verified that the Teflon lines and

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ENO (%) =

NO in -NO out × 100% NOin

(1)

11

Eoxi (%) =

Hg 0in -Hg 0out ×100% Hg in0

(2)

12

2.3. Catalysts characterization

13

The Brunauer-Emmett-Teller (BET) surface area, pore volume and average pore diameter of the

14

catalysts were obtained from N2 adsorption isotherms using an ASAP 2020 analyzer (Micromeritics,

15

USA). The specific surface area was calculated by the standard BET equation. Before the analysis,

16

all samples were degassed under vacuum at 120 °C for 5 h. In order to determine the crystallinity

17

and dispersivity of each species on the catalysts, powder X-ray diffraction (XRD) patterns of the

18

catalysts were obtained on a Rigaku X-ray diffractometer with Cu-Kα radiation (35 kV and 20 mA)

19

in the range of 10-70°.The X-ray photoelectron spectroscopy (XPS) was detected using the X-ray

20

photoelectron spectrometer (ESCALAB 250Xi, UK) with an Al-Kα X-ray source. The observed

21

spectra were calibrated by the C1s peak at 284.6 eV. To analyze the redox properties of the

22

catalysts, Temperature-programmed reduction of H2 (H2-TPR) was performed on a PCA-1200

23

chemisorption analyzer using approximately 0.10 g of samples. The 5% H2/Ar mixture was

6


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Energy & Fuels

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switched to a flow rate of 30 mL/min, and the temperature was increased linearly from room

2

temperature to 850 °C at a rate of 10 °C/min while the H2 consumption was recorded continuously.

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3. Results and discussion

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3.1. Catalytic activity of Cu-SCR catalysts

5

3.1.1 NO removal activity

6

As the primary function of a SCR catalyst is to remove NO from the flue gas, the NO removal

7

activity of CuO modified SCR catalysts was firstly investigated under the typical SCR condition at

8

the temperature range of 150-400 °C, and the results were shown in Figure 2. NO removal

9

efficiencies (ENO) of the raw SCR catalyst increased from 150 °C to 350 °C, and then decreased as

10

the temperature continued to rise to 400 °C. More than 80% of ENO were observed at the

11

temperature range of 300-400 °C. However, the NO conversions decreased sharply when the

12

temperature was lower than 250 °C, only 15.6% of ENO was obtained at 150 °C. The result indicated

13

that the optimal active temperature window of raw SCR catalyst for NO removal was 300-400 °C,

14

and the lower temperature suppressed the catalytic activity of the catalyst. For the Cux-SCR catalyst,

15

the addition of CuO significantly improved NO conversions at 150-350 °C when compared with the

16

raw SCR catalyst. For instance, ENO of raw SCR catalyst was only 33.5% at 200 °C, while 83.2% of

17

ENO could be obtained by adding 4% CuO (Cu4-SCR). At 200-400 °C, more than 80% of ENO could

18

be obtained over Cu3-SCR catalyst. It was clearly found that CuO exhibited the co-benefit for NO

19

removal and obviously widened the active temperature window. However, the addition of CuO

20

resulted in a decrease of NO removal at 400 °C, indicating that CuO inhibited NO removal at

21

400 °C. It could be speculated that CuO covered the active sites of V2O5 on the catalyst surface,

22

which restrained the NO removal activity at 400 °C. In other words, CuO could enhance the NO

23

removal activity when the temperature was lower than 350 °C, while V2O5 played a dominant role

24

on NO removal at 400 °C. Fortunately, this inhibiting effect was almost negligible when the CuO

25

content was less than 3%. Moreover, the N2 selectivity of Cu3-SCR catalyst was also investigated as 7


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1

shown in Figure S1. The result indicated that Cu3-SCR catalyst exhibited good N2 selectivity, and

2

more than 95% of N2 selectivity could be obtained at 150-350 °C. In addition, Cu3-SCR catalyst

3

could efficiently oxidize Hg0 at high GHSV. Therefore, in the practical application, Cu3-SCR

4

catalyst could be used at the final layer of the SCR device for Hg0 oxidation and NO removal. This

5

significantly reduced the operating cost for Hg0 removal in coal-fired power plants. Considering

6

both the enhancement of CuO and the active temperature window for NO removal, it seems that the

7

Cu3-SCR is the optimal catalyst among the modified catalysts.

8

3.1.2 Hg0 oxidation activity

9

Hg0 oxidation activity over the raw and Cux-SCR catalysts was evaluated from 150 °C to 400 °C,

10

and the results were displayed in Figure 3. For the raw SCR catalyst, Hg0 oxidation efficiency (Eoxi)

11

increased as the temperature increasing from 150 °C to 300 °C, then decreased with the temperature

12

increasing to 400 °C. Particularly, the optimal Eoxi of raw SCR catalyst was only 25.6%. According

13

to the literature 27, Hg0 oxidation activity of the commercial SCR catalyst was very limited in the

14

absence of HCl. However, the presence of CuO obviously improved the Hg0 oxidation activity of

15

the raw SCR catalyst. As shown, Eoxi was increased from 25.6% to 58.3% by adding 1% CuO at

16

300 °C. Moreover, further increasing the CuO content to 3%, 95.4% of Eoxi could be observed. In

17

addition, more than 90% of Eoxi could be obtained over Cu3-SCR catalyst and Cu4-SCR catalyst at

18

the temperature range of 200-350 °C. Noting that Cu3-SCR catalyst possessed the high catalytic

19

activity and widest active temperature window for NO removal, it seems that Cu3-SCR catalyst is

20

the optimal modified catalyst for simultaneous NO removal and Hg0 oxidation. Besides,

21

considering that the operating temperature of the SCR device in actual application is approximately

22

300-400 °C, the Cu3-SCR catalyst is a low-cost option for simultaneous NO removal and Hg0

23

oxidation, which could lower the equipment cost and operating expense. This superiority could

24

satisfy the technical and economical requirements for efficient oxidation of Hg0 by the existing SCR

25

device in coal-fired power plants. 8


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3.2. Effect of flue gas components on catalytic activity

2

3.2.1 Effect of Hg0 on NO removal

3

In actual applications, Hg0 is the typical component in coal-fired flue gas. As the function of

4

simultaneous NO removal and Hg0 oxidation for Cu-SCR catalyst, the present of Hg0 might

5

influence the SCR activity. So it was necessary to evaluate the effect of Hg0 on NO removal over

6

Cu3-SCR catalyst. As shown in Figure 4, when 72.0 µg/m3 Hg0 was introduced into the flue gas,

7

NO removal activity exhibited a similar trend with that observed in the flue gas without Hg0 at

8

temperature range of 150-400 °C. However, ENO showed slightly decreases after Hg0 addition,

9

indicating that Hg0 had a negative effect on NO removal. It should be pointed out that Hg0

10

concentration was much lower than NO and NH3 concentrations in gas flow so that Hg0 was not

11

capable of competing with NO and NH3 for adsorption sites on the catalyst surface 3, 24. According

12

to the literature

13

accumulated on the surface of catalyst which occupied the active sites and influenced the adsorption

14

of NH3, then resulted in less available active sites for NO removal. It might be the probable reason

15

for the decreases of NO removal activity. To better understand the effect of Hg0 on NO removal, a

16

12 h test was conducted over Cu3-SCR catalyst under SCR atmosphere + Hg0 at 350 °C, and the

17

result was shown in Figure 4 (Inset). When 72.0 µg/m3 Hg0 was added, the NO conversion

18

decreased slowly in the first 3 h, and kept at around 90% after 5 h. It could be speculated that the

19

HgO gradually accumulated on the catalyst surface and occupied the active sites, which slowly

20

decreased the NO conversion. However, the accumulated HgO could be released into flue gas when

21

it was saturated, thus the ENO could remain at a stable level during the long period time. Moreover,

22

when the supply of Hg0 was ended, the NO conversion was slowly restored to 93.9%. The slowly

23

recovering of NO conversion might be due to the slowly increase of active sites resulted by the

24

release of accumulated HgO on the catalyst surface. Conclusively, the effect of Hg0 on NO removal

28

, Hg0 was oxidized to form HgO in the SCR atmosphere, and HgO could be

9


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1

was almost negligible, and Cu3-SCR catalyst showed stable and efficient NO removal activity in

2

SCR atmosphere + Hg0.

3

3.2.2 Effect of NO and NH3 on Hg0 oxidation

4

As a SCR catalyst for simultaneous NO removal and Hg0 oxidation, the co-presence of NO and

5

NH3 could influence the Hg0 oxidation activity of the Cu-SCR catalyst. Hence, the catalytic activity

6

for Hg0 oxidation over Cu3-SCR catalyst was investigated under SCR atmosphere at the

7

temperature range of 150-400 °C, and the results were displayed in Figure 5. Moreover, the effect

8

of NO on Hg0 oxidation was also evaluated as shown in Figure S2. The result suggested that NO

9

exhibited the promoting effect on Hg0 oxidation in the presence of O2. It was reported that some of

10

NO could react with chemisorbed oxygen to form NOx species on the catalyst surface, which was

11

beneficial for Hg0 oxidation

12

NH3 on Hg0 oxidation, the SCR atmosphere at the initial stage of the SCR reactor was simulated by

13

introducing 300 ppm NO and 300 ppm NH3. Similarly, 50 ppm NO and 50 ppm NH3 were added to

14

simulate SCR condition at the end stage of SCR reactor. As depicted in Figure 5, in N2+5% O2

15

atmosphere, Eoxi of Cu3-SCR catalyst increased from 150 °C to 300 °C, and then decreased as the

16

temperature continued to rise to 400 °C. When NO and NH3 were introduced into the gas flow, Hg0

17

oxidation activity showed a similar trend. However, the co-presence of NO and NH3 notably

18

inhibited the Hg0 oxidation activity of Cu3-SCR catalyst, especially at high temperature. For

19

instance, about 9.4% and 5.6% of Eoxi were respectively decreased at the initial stage and end stage

20

at 150 °C, while 24.0% and 12.4% of Eoxi were reduced at 400 °C. Noting that NO could enhance

21

the Hg0 oxidation activity in the presence of O2, the decreases of Hg0 oxidation could be ascribed to

22

the presence of NH3. It was found that the presence of NH3 could competed with Hg0 for the

23

adsorption sites, which inhibited the catalytic activity for Hg0 oxidation 29 30. In addition, Madsen et

24

al

25

when the operating temperature was over 325 °C. This suggested that the Hg0 oxidation and Hg2+

31

34

. In order to better understand the effect of co-presence of NO and

reported that the presence of NH3 resulted in a reduction of oxidized mercury species to Hg0

10


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Energy & Fuels

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reduction were occurred simultaneously, lowering the overall Hg0 oxidation activity of Cu3-SCR

2

catalyst. So it could be speculated that the reduction effect of NH3 enhanced the inhibiting effect of

3

NH3 on Hg0 oxidation at high temperature, which resulted in much loss of Eoxi at temperature range

4

of 350-400 °C. Nonetheless, approximately 72.5% and 82.5% of Eoxi could be obtained at the initial

5

stage and the end stage at 350 °C, respectively. Moreover, more than 80% of Eoxi could be observed

6

at the end stage of the SCR reactor at the temperature range of 200-350 °C. This result indicated

7

that the Hg0 oxidation activity was enhanced with the consumption of NH3, which suggested that

8

Hg0 oxidation was easy at the end stage of the SCR device where NH3 content was relatively low.

9

3.2.3 Effect of SO2 on NO removal and Hg0 oxidation

10

In the actual coal-fired flue gas, SO2 is the main component in the flue gas, which may deactivate

11

the SCR catalyst. So it is necessary to investigate the effect of SO2 on NO removal and Hg0

12

oxidation over Cu3-SCR catalyst. Figure 6 depicted the effect of SO2 on NO removal over the Cu3-

13

SCR catalyst at 150-400 °C. When 500 ppm SO2 was added into the gas flow, NO removal activity

14

showed slight decreases. For instance, less than 3% of ENO was reduced when 500 ppm SO2 was

15

added at 350 °C. In the presence of 1000 ppm SO2, as shown in Figure S3 (a), NO removal

16

efficiencies reduced further. It could be explained that SO2 could react with metal oxides and NH3

17

in the presence of O2 to form metal sulphates and ammonium sulfates, which occupied the active

18

sites and lowered the catalytic activity 9. Nevertheless, more than 80% of ENO was observed in the

19

presence of 500 ppm SO2 at the temperature range of 250-400 °C, and ENO could reach up to 91.2%

20

at 350 °C. In addition, the SO2 resistances of Cu3-SCR catalyst and raw SCR catalyst were also

21

evaluated at the typical SCR reaction temperature of 350 °C, and the results were shown in Figure

22

6 (Inset). When 500 ppm SO2 was added into the gas flow, the NO conversion over the raw SCR

23

catalyst decreased from 90.7% to 80.3% in the first 1 h, and then slowly increased to about 85.0%

24

in the next 3 h. This slowly recovering of NO conversion might be due to the slowly increase of

25

acidity on the catalyst surface resulted by the adsorption of SO2 9. However, for the Cu3-SCR 11


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1

catalyst, only a slight decrease of NO conversion could be observed when 500 ppm SO2 was added.

2

This result indicated that Cu3-SCR catalyst exhibited superior SO2 resistance on NO removal,

3

which could be ascribed to the addition of CuO 25. Moreover, the catalytic performances over both

4

catalysts were nearly restored to their original levels when the supply of SO2 was ended.

5

Conclusively, Cu3-SCR catalyst exhibited the stable and efficient activity on NO removal in the

6

presence of SO2. Such superiority is beneficial for possible practical application.

7

The effect of SO2 on Hg0 oxidation over Cu3-SCR catalyst at temperature range of 150- 400 °C

8

was shown in Figure 7. The presence of 500 ppm SO2 slightly decreased Hg0 oxidation activity

9

when the reaction temperature was lower than 250 °C, while the notable decreases were observed

10

when the temperature was higher than 300 °C. For instance, less than 2% of Eoxi was reduced when

11

500 ppm SO2 was added at 150 °C, while more than 10% of Eoxi was reduced at 400 °C. This result

12

indicated that the inhibiting effect of SO2 on Hg0 oxidation was strengthened with the increase of

13

temperature. Further increased SO2 concentration to 1000 ppm, as shown in Figure S3 (b), the

14

inhibiting effect of SO2 on Hg0 oxidation was enhanced. It was reported that SO2 competed with

15

Hg0 for the adsorption sites, which inhibited the Hg0 oxidation activity

16

temperature was unsuitable for Hg0 adsorption

17

enhanced at high temperature, resulting in a notable inhibiting effect on Hg0 oxidation. Nonetheless,

18

Eoxi could reach up to 86.7% at 350 °C in the presence of 500 ppm SO2, indicating that Cu3-SCR

19

catalyst exhibited good SO2 resistance on Hg0 oxidation. Besides, the result of stability test (Figure

20

7 (Inset)) indicated that Cu3-SCR catalyst exhibited stable and efficient activity on Hg0 oxidation at

21

350 °C in the presence of 500 ppm SO2. Such information suggested that Cu3-SCR catalyst

22

possessed the potential value for industrial application.

23

3.2.4 Effect of H2O on NO removal and Hg0 oxidation

32

. Moreover, the high

26, 33

, so the competitive adsorption of SO2 was

24

Figure 8 showed the effect of H2O on NO removal over the Cu3-SCR catalyst at 150-400 °C.

25

When 8% H2O was added into the gas flow, the NO conversions showed slight decreases, 12


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indicating that H2O exhibited inhibiting effect on NO removal. This could be explained by the

2

competition effect between H2O and NH3 for the adsorption of the active sites 34, 35. In addition, the

3

inhibiting effect of H2O on NO removal decreased with the reaction temperature from 150 °C to

4

400 °C. For instance, more than 10% of ENO was reduced at 150 °C, while less than 4% of ENO was

5

reduced at 400 °C. This result suggested that high temperature reduced the inhibiting effect of H2O

6

on NO removal. This mechanism could be explained that high temperature was adverse to the

7

adsorption of H2O on the active sites. Nonetheless, 90.8% of ENO was obtained at 350 °C, which

8

could meet the requirement of possible industrial application. Moreover, the H2O resistances of the

9

raw SCR catalyst and Cu3-SCR catalyst were investigated at 350 °C, and the results were shown in

10

Figure 8 (Inset). When 8% H2O was added into the gas flow, the NO conversion over the raw SCR

11

catalyst decreased from 91.2% to 84.5% in the first 1 h, and then remained at approximately 86.0%.

12

However, after the introduction of H2O, the NO conversion over Cu3-SCR catalyst slightly

13

decreased from 94.1% to 90.1%, and then remained at approximately 91.1%. After the removal of

14

H2O, the NO conversions over both catalysts were restored to their original levels. It indicated that

15

Cu3-SCR catalyst showed a superior activity of H2O resistance than the raw SCR catalyst.

16

The effect of H2O on Hg0 oxidation over Cu3-SCR catalyst at 150-400 °C was demonstrated in

17

Figure 9. The introduction of 8% H2O slightly decreased the Hg0 oxidation activity of Cu3-SCR

18

catalyst. This result indicated that H2O exhibited inhibiting effect on Hg0 oxidation, which was due

19

to the competitive adsorption between H2O and Hg0

20

activity over Cu3-SCR catalyst was minor, and more than 85% of Eoxi could be obtained at the

21

temperature range of 200-350 °C. Moreover, as shown in Figure 9 (Inset), the result of stability test

22

indicated that Cu3-SCR catalyst showed the stable and efficient activity on Hg0 oxidation at 350 °C

23

in the presence of 8% H2O, which was beneficial to the simultaneous NO removal and Hg0

24

oxidation in the actual coal-fired power plants.

9, 36

. However, the reduction of Hg0 oxidation

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

1

3.3. Simultaneous NO removal and Hg0 oxidation over Cu3-SCR catalyst under simulated

2

coal-fired flue gas

3

In general, the flue gas in actual coal-fired power plant contains a variety of flue gas components,

4

so it is necessary to test the catalytic performance of Cu3-SCR catalyst for simultaneous NO

5

removal and Hg0 oxidation under simulated coal-fired flue gas. Figure 10 displayed the NO

6

conversion and Hg0 oxidation activity over Cu3-SCR catalyst under simulated coal-fired flue gas.

7

The simulated coal-fired flue gas was consisted of 12% CO2, 5% O2, 8% H2O, 500 ppm SO2, 300

8

ppm NO, 300 ppm NH3 and 72.0 µg/m3 Hg0, balanced in N2. For this test, 1.0 g catalyst sample was

9

loaded, which corresponded to the GHSV of 0.5×105 h-1. Cu3-SCR catalyst exhibited superior

10

catalytic activity and wide active temperature window for NO removal. More than 90% of ENO was

11

observed at the temperature range of 250-350 °C, and ENO could reach up to 97.2% at 350 °C.

12

Moreover, 96.3% of ENO could be obtained at 350 °C even after 12 h (Figure 10 (Inset)), indicating

13

that Cu3-SCR catalyst showed the stable and efficient activity on NO removal under real coal-fired

14

simulated flue gas at 350 °C. In simulated coal-fired flue gas, more than 80% of Eoxi was observed

15

at 200-350 °C. However, Hg0 oxidation activity decreased remarkably when the temperature

16

exceeded 350 °C. After 12 h test (Figure 10 (Inset)), Eoxi still remained at around 80% under

17

simulated coal-fired flue gas at 350 °C. Conclusively, Cu3-SCR catalyst exhibited superior catalytic

18

activity, wide operating temperature window and high stability for simultaneous NO removal and

19

Hg0 oxidation under simulated coal-fired flue gas. Such information was corresponded to the actual

20

SCR process in current coal-fired power plants, suggesting that Cu3-SCR catalyst possessed

21

potential value for industrial application.

22

3.4. Characterization results

23

3.4.1 BET

24

The BET surface area and pore structure of the raw SCR and Cu3-SCR catalysts were summed up

25

in Table 1. It was clearly found that the loading of CuO resulted in the decreases of BET surface 14


Page 14 of 41

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Energy & Fuels

1

area and pore volume, which could be explained that the addition of CuO blocked the pores of the

2

SCR catalyst. According to the catalytic activity tests, however, Cu3-SCR catalyst showed the

3

efficient activity for simultaneous NO removal and Hg0 oxidation. This suggested that the decrease

4

of surface area and pore volume had no obvious influence on the catalytic activity. Table 1 The physical characteristics of the catalysts

5

Catalysts

SBET (m2/g)

Vpore (cm3/g)

Dpore (nm)

Raw SCR

62.45

0.235

13.75

Cu3-SCR

58.61

0.217

14.02

6 7

3.4.2 XRD

8

The XRD patterns of the raw SCR catalyst and Cu3-SCR catalyst were shown in Figure 11. For

9

both catalysts, diffraction peaks of anatase TiO2 were obtained. However, no obvious peak of V2O5

10

and WO3 was observed in both catalysts. This could be explained that V and W species were highly

11

dispersed on the catalysts surface

12

SCR catalyst. It could be speculated that the CuO was highly dispersed on the catalyst surface.

13

Researchers have reported that well dispersed active elements on the catalyst surface can improve

14

the catalytic activity 21, 37. So it could be concluded that the highly dispersed CuO could enhance the

15

catalytic activity of Cu3-SCR catalyst. This result was consistent with the activity test that Cu3-SCR

16

catalyst exhibited the superior activity for simultaneous NO removal and Hg0 oxidation.

17

3.4.3 XPS

34

. Moreover, no obvious peak of CuO was detected over Cu3-

18

In order to determine the chemical states and the relative proportion of the elements on the

19

surface of the catalysts, XPS measurements were carried out over the raw SCR (the fresh

20

commercial V2O5-WO3/TiO2 catalyst), Cu3-SCR (the fresh Cu3-SCR catalyst prepared by the

21

improved impregnation method) and spent Cu3-SCR catalyst (the Cu3-SCR catalyst pre-treated in

22

N2+72 µg/m3 Hg0 atmosphere at 350 °C for 6 hours). Figure 12 depicted the O 1s XPS spectra for 15


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Page 16 of 41

1

the raw SCR, Cu3-SCR and spent Cu3-SCR catalyst. The O 1s peaks were fitted into two sub-bands

2

over the catalysts. The peaks at low binding energy (around 530.0-530.3 eV) were regarded as the

3

lattice oxygen (denoted as Oβ) 38, 39, while the peaks at around 532.0-532.3 eV could be assigned to

4

the chemisorbed oxygen (denoted as Oα)

5

oxygen, which played significant role during the oxidation reaction 9, 40, 42. The Oα ratio (calculated

6

by Oα/( Oα+ Oβ)) over Cu3-SCR catalyst was 35.25%, which was higher than that of raw SCR

7

catalyst (21.73%). This suggested that the Oα content notably increased with the presence of CuO,

8

thus the Hg0 oxidation activity was improved. The catalytic activity tests also confirmed that the

9

addition of CuO significantly enhanced Hg0 oxidation activity. The Oα ratio of spent Cu3-SCR

10

catalyst was 26.35%, indicating that the Oα content decreased obviously after 6 hours. This result

11

also suggested that Oα was involved in the Hg0 oxidation reaction. In addition, a small shift in the

12

O 1s binding energy was observed, where a shift from the Oα peak over raw SCR catalyst towards

13

lower value over Cu3-SCR catalyst was obtained. This result suggested that there was electron

14

transfer on Cu3-SCR catalyst when CuO was doped, indicating that there existed the synergistic

15

effect between CuO and V2O5 43.

40, 41

. Researchers have found that Oα is the most active

16

Figure 13 showed the XPS spectra in the V 2p region for the raw SCR, Cu3-SCR and spent Cu3-

17

SCR catalyst. For each catalyst, there were two characteristic peaks at the binding energy of

18

516.4eV and 517.3eV, which could be ascribed to the V4+ and V5+ species, respectively

19

V5+/V4+ ratio of raw SCR catalyst was about 0.65, indicating that the V species on raw SCR catalyst

20

was mainly existed in the form of V4+. However, the V5+/V4+ ratio increased to 1.23 when CuO was

21

introduced, suggesting that some of V4+ was oxidized to V5+ by CuO. This result also indicated that

22

there was synergistic effect between CuO and V2O5. For the spent Cu3-SCR catalyst, the V5+/V4+

23

ratio was about 1.05, indicating that V4+ content increased after the Hg0 oxidation reaction. It could

24

be explained that Hg0 reacted with V5+ species to form the HgO and V4+ species on the catalyst

25

surface. Conclusively, the presence of CuO increased the V5+ species, and the Hg0 oxidation 16


44, 45

. The

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1

resulted in the transformation of V5+ to V4+ species. In other words, the interaction between Cu and

2

V species enhanced the Hg0 oxidation activity.

3

The XPS spectra of Cu 2p for the Cu3-SCR and spent Cu3-SCR catalyst were displayed in Figure

4

14. Cu3-SCR catalyst exhibited a peak of Cu 2p3/2 at 935.2 eV, a peak of Cu 2p1/2 at 954.6 eV,

5

and a shake-up peak located in the binding energy range of 940-946 eV, which were the

6

characteristic features of Cu2+ 46. The characteristic peaks at 933.2 eV and 953.1eV were ascribed to

7

the existence of Cu+ species on the Cu3-SCR catalyst

8

indicating that Cu2+ was the primary Cu species on the Cu3-SCR catalyst surface. Considering that

9

the V4+ was oxidized to V5+ with the presence of CuO, it could be speculated that there existed the

10

redox cycle of V4++Cu2+↔V5++Cu+ on the Cu3-SCR catalyst, which resulted in the presence of Cu+

11

species

12

Moreover, according to the literature 9, this redox cycle could produce the unsaturated chemical

13

bonds, charge imbalance and oxygen vacancy, which were beneficial for the generation of the

14

chemisorbed oxygen on Cu3-SCR catalyst surface. The O 1s XPS result also confirmed that the Oα

15

content increased with the addition of CuO. For the spent Cu3-SCR catalyst, the Cu2+/Cu+ ratio was

16

about 1.32, which indicated that the Cu2+ content decreased after Hg0 oxidation. This could be

17

speculated that the Hg0 oxidation consumed the Cu2+ species in the absence of O2.

18

3.4.4 H2-TPR

43

47, 48

. The Cu2+/Cu+ ratio was about 1.51,

. This result also verified the interaction between Cu and V over Cu3-SCR catalyst.

19

To investigate the redox properties and characteristics of the raw SCR catalyst and Cu3-SCR

20

catalyst, the H2-TPR experiments were conducted. The H2-TPR profiles of Cu3/TiO2 catalyst (3%

21

CuO, TiO2 supported), Cu3-W-TiO2 catalyst (3% CuO, 8% WO3, TiO2 supported) and W-TiO2

22

catalyst (8% WO3, TiO2 supported) were also investigated to verify the reduction peaks of Cu

23

species, and the results were shown in Figure 15. It could be clearly found that only a small

24

reduction peak was observed at around 306 °C over Cu3/TiO2 catalyst. According to the literature 49,

25

TiO2 exhibited no obvious reduction peak, and this H2 consumption peak was attributed to the Cu2+ 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

1

species. This result indicated that only Cu2+ species existed in Cu3/TiO2 catalyst. It could be

2

concluded that there was no interaction between Cu and TiO2 since only Cu2+ species was observed

3

over Cu3/TiO2 catalyst. For Cu3-W-TiO2 catalyst, two reduction peaks were observed at around

4

315 °C and 766 °C, respectively. However, only one peak was obtained at around 768 °C over W-

5

TiO2 catalyst. Since TiO2 exhibited no reduction peak, the higher peak at around 766 °C was

6

ascribed to the reduction of WO3

7

reduction of Cu2+ species. This result also suggested that there was no obvious interaction between

8

Cu and W over Cu3-W-TiO2 catalyst. The raw SCR catalyst exhibited two obvious reduction peaks

9

at around 485 °C and 786 °C, which could be attributed to the reduction of V species and W species

43

, while the lower peak at around 315 °C was attributed to the

10

9

11

around 203 °C, 283 °C, 350 °C and 764 °C, respectively. The reduction peak at 203 °C was

12

attributed to the reduction of Cu+ species, while the peak centered at 283 °C was ascribed to the

13

reduction of Cu2+ species 9, 50. This result was highly consistent with the Cu 2p XPS result that there

14

was a coexistence of Cu+ and Cu2+ species on the Cu3-SCR catalyst. The reduction peaks at around

15

350 °C and 764 °C were probably due to the reduction of the highly dispersed V and W species,

16

respectively. An obvious shift of reduction peak of V from 485 °C to 350 °C was observed after

17

CuO was added, indicating that Cu and V showed the strong interaction on the catalyst surface. So

18

it seems that this strong interaction between Cu and V was predominant, which significantly

19

enhanced the catalytic activity of Cu3-SCR catalyst 43. Moreover, the shift of reduction peak of Cu2+

20

species from 306 °C to 283 °C suggested that Cu3-SCR catalyst possessed better reducibility than

21

Cu3/TiO2. This result also confirmed that the interaction between Cu and V improved the

22

reducibility of the SCR catalyst, which was beneficial for the NO removal. This was also consistent

23

with the test results that Cu3-SCR catalyst exhibited superior activity on NO removal.

24

3.5. Hg0 oxidation mechanism

, respectively. For Cu3-SCR catalyst, however, four H2 consumption peaks were observed at

18


Page 18 of 41

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Energy & Fuels

1

Cu3-SCR catalyst exhibited superior catalytic activity for Hg0 oxidation. It was found that the

2

catalytic activity of Cu3-SCR catalyst was obviously enhanced by the addition of CuO, and the

3

interaction of CuO and V2O5 played an important role on Hg0 oxidation. The XPS results and H2-

4

TPR analyses suggested that there existed the redox cycle of V4++Cu2+⟷V5++Cu+ on the CuO

5

doped commercial SCR catalyst, which was beneficial for the generation of the chemisorbed

6

oxygen on Cu3-SCR catalyst surface. Such abundant chemisorbed oxygen promoted the Hg0

7

oxidation performance. Figure 16 depicted the Hg0 oxidation procedure on the CuO doped

8

commercial SCR catalyst. Gas phase Hg0 (Hg ଴୥ ) was firstly adsorbed on the catalyst surface to form

9

Hg଴ୟୢ . The addition of CuO generated the redox cycle of V4++Cu2+↔V5++Cu+, which created the

10

abundant chemisorbed oxygen. Then, the Hg ଴ୟୢ species reacted with chemisorbed oxygen to form

11

HgO, and the consumed oxygen was replenished from the gas phase O2 in flue gas. Conclusively,

12

the redox cycle of V4++Cu2+ ↔ V5++Cu+ was generated by the addition of CuO, and this redox

13

cycle produced abundant chemisorbed oxygen species for Hg0 oxidation, thus significantly

14

enhanced the Hg0 oxidation activity of the raw SCR catalyst.

15

4. Conclusions

16

A series of CuO doped V2O5-WO3/TiO2 based commercial SCR catalysts were prepared via the

17

improved impregnation method for simultaneous NO removal and Hg0 oxidation under simulated

18

coal-fired flue gas at 150-400 °C. The results indicated that Cu3-SCR catalyst showed the superior

19

catalytic activity and wide active temperature windows for simultaneous NO removal and Hg0

20

oxidation. In simulated coal-fired flue gas, more than 90% of ENO was observed at the temperature

21

range of 250-350 °C, and ENO could reach up to 97.2% at 350 °C. Meanwhile, more than 80% of

22

Eoxi was obtained at 200-350 °C. Cu3-SCR catalyst showed superior performances on SO2 tolerance

23

and H2O resistance, which was beneficial for possible practical application. The effect of Hg0 on

24

NO removal was almost negligible, while the copresence of NO and NH3 obviously inhibited the

25

Hg0 oxidation activity. Fortunately, Hg0 oxidation activity was improved with the decrease of NH3, 19


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

1

which suggested that Hg0 oxidation was easy happened at the end stage of the SCR device with the

2

consumption of NH3. The BET and XRD results suggested that the well dispersed CuO was helpful

3

to the superior catalytic activity of Cu3-SCR catalyst. Moreover, the XPS and H2-TPR analyses

4

indicated that the Cu3-SCR catalyst possessed abundant chemisorbed oxygen and good redox ability,

5

which could be attributed to the synergistic effect of CuO and V2O5. The presence of V4++Cu2+ ↔

6

V5++Cu+ on Cu3-SCR catalyst could greatly enhance the catalytic activity for simultaneous NO

7

removal and Hg0 oxidation. The Hg0 oxidation mechanism could be explained that the Hg ଴ୟୢ species

8

reacted with chemisorbed oxygen to form HgO species, and the consumed oxygen was replenished

9

from the gas phase O2 in flue gas. This work revealed the possibility of simultaneous NO removal

10

and Hg0 oxidation over CuO doped commercial SCR catalyst in simulated coal-fired flue gas.

11

Future work should do some further studies to investigate the mechanisms of the inhibiting effects

12

of H2O, SO2 and Hg0 on the catalytic activity of the catalyst, which can provide more detailed

13

parameters for the practical industrial application of CuO doped V2O5-WO3/TiO2 based commercial

14

SCR catalysts.

15

Supporting Information

16

The N2 selectivity of Cu3-SCR catalyst; effect of NO on Hg0 oxidation over Cu3-SCR catalyst;

17

effects of SO2 and HCl on NO removal and Hg0 oxidation over Cu3-SCR catalyst.

18

Notes

19 20

The authors declare no competing financial interest. Acknowledgments

21

This work was financially supported by the Science and Technology Plan Project of Hebei

22

Province of China (16273703D), and the Fundamental Research Funds for the Central Universities

23

(2018MS118, 2017XS128).

24

References:

25

(1) Busca, G.; Larrubia, M. A.; Arrighi, L.; Ramis, G., Catalytic abatement of NOx: Chemical and 20


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on the heterogeneous catalytic oxidation of elemental mercury in flue gases. Environ. Sci. Technol.

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oxidation of elemental mercury at low flue gas temperatures. Appl. Catal. B-Environ. 2012, 111,

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catalyst in CO2-enriched conditions. Chem. Eng. J. 2015, 263, 356-363.

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oxidation. Chem. Eng. J. 2014, 243, 380-385.

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NO reduction and Hg0 oxidation at low temperatures. Catal. Sci. Technol. 2015, 5, (12), 5129-5138.

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oxidized mercury over CuO-CeO2/TiO2 catalyst. Environ. Sci. Technol. 2015, 49, (12), 7373-7379.

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characterization of ZrO2 support modification on CuO-CeO2/TiO2 catalyst for the simultaneous

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removal of Hg0 and NO. Appl. Surf. Sci. 2017, 400, 227-237.

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catalytic reduction of NO with NH3. Catal. Commun. 2010, 12, (4), 255-258.

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over CuCl2/TiO2-based catalysts in SCR process. Appl. Catal. B-Environ. 2010, 99, 272-278.

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elemental mercury from syngas. Environ. Sci. Technol. 2013, 47, (17), 10056-10062.

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(31) Jensen, M.; Frandsen, A. D.; Thorgersen, F. J., A mechanistic study of the inhibition of the

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elemental mercury and NO from flue gas by V2O5-CeO2/TiO2 catalysts. Appl. Surf. Sci. 2015, 347,

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Environ. Sci. Technol. 2009, 43, (5), 1522-1527.

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ZrO2 catalysts for selective catalytic reduction of NO with NH3. Appl. Surf. Sci. 2014, 317, 955-961.

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22

25


Energy & Fuels

Figure 1 Schematic diagram of the experimental system

1--Hg0 Vapor Generator 2--Water Vapor Generator

NH3 N2

Computer O2

2

CO2 SO2 NO

1

Check valve

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 26 of 41


RA-915+ Vent

Page 27 of 41

Figure 2 NO removal efficiencies over the raw and Cux-SCR catalysts under SCR condition (SFG: 5% O2, 300 ppm NO, 300 ppm NH3 and N2 balanced, T=150-400 °C, GHSV=1×105 h-1, Duration =3h)

100

NO removal efficiency (%)

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

80 Raw SCR Cu1-SCR

60

Cu2-SCR

40

Cu3-SCR Cu4-SCR

20 0

150

200

250

300

Reaction temperature (°C)


350

400

Energy & Fuels

Figure 3 Hg0 oxidation activity over the raw and Cux-SCR catalysts in simulated flue gas (SFG: 5% O2, 72.0 μg/m3 Hg0 and N2 balanced, T=150-400 °C, GHSV=1×105 h-1, Duration =4h)

100

80

60

40

Raw SCR

Cu1-SCR

Cu2-SCR

Cu3-SCR

Cu4-SCR

0

Hg oxidation efficiency (%)

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 28 of 41

20 150

200

250

300

Reaction temperature (°C)


350

400

Page 29 of 41

Figure 4 Effect of Hg0 oxidation on NO removal (SFG: 5% O2, 300 ppm NO, 300 ppm NH3, 72.0 μg/m3 Hg0 and N2 balanced, T=150-400 °C, GHSV=1×105 h-1, Duration =4h)

100 0

80

Without Hg

3

0

With 72 μg/m Hg

60

100

0

add Hg

40

ENO (%)

ENO (%)

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

20

90

150

200

Cu3-SCR

80 70

0

0

stop Hg

0

250

2

4

6 8 Time (h)

300

Temperature (°C)


350

10

12

400

Energy & Fuels

Figure 5 Effect of NO and NH3 on Hg0 oxidation (T=150-400 °C, GHSV=1×105 h-1, Duration =4h)

N2+5% O2 100

Hg0 oxidation efficiency (%)

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 30 of 41

N2+5% O2+300 ppm NO+300 ppm NH3

N2+5% O2+50 ppm NO +50 ppm NH3

80 60 40 20 0

150

200

250

300

Temperature (°C)


350

400

Page 31 of 41

Figure 6 Effect of SO2 on NO removal (SFG: 5% O2, 300 ppm NO, 300 ppm NH3, 500 ppm SO2 and N2 balanced, T=150-400 °C, GHSV=1×105 h-1, Duration =3h)

100 Without SO2

80

With 500 ppm SO2 100

(%)

60

NO

40

E

ENO (%)

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

90

Cu3-SCR

80

20

Raw SCR 70

0

stop SO2

add SO2

150

200

0

250

2

4

300

Temperature (°C)


6

Time (h)

8

350

10

12

400

Energy & Fuels

Figure 7 Effect of SO2 on Hg0 oxidation (SFG: 5% O2, 72.0 μg/m3 Hg0, 500 ppm SO2 and N2 balanced, T=150-400 °C, GHSV=1×105 h-1, Duration =4h)

100 Without SO2

80

With 500 ppm SO2

60

100

add SO2

Eoxi (%)

Eoxi (%)

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 32 of 41

40 20

90 80 70

0

150

200

stop SO2

Cu3-SCR 0

250

2

4

6 8 Time (h)

300

Temperature (°C)


350

10

12

400

Page 33 of 41

Figure 8 Effect of H2O on NO removal (SFG: 5% O2, 300 ppm NO, 300 ppm NH3, 8% H2O and N2 balanced, T=150-400 °C, GHSV=1×105 h-1, Duration =3h)

100 80

Without H2O With 8% H2O 100

60

add H2O

ENO (%)

ENO (%)

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

40 20

90

150

200

Cu3-SCR

80

Raw SCR 70

0

stop H2O

0

250

2

4

6

Time (h)

300

Temperature (°C)


8

350

10

12

400

Energy & Fuels

Figure 9 Effect of H2O on Hg0 oxidation (SFG: 5% O2, 72.0 μg/m3 Hg0, 8% H2O and N2 balanced, T=150-400 °C, GHSV=1×105 h-1, Duration =4h)

100 Without H2O

80

With 8% H2O

60

100

40

Eoxi (%)

Eoxi (%)

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 34 of 41

20

90

Cu3-SCR

80 70

0

stop H2O

add H2O

0

2

4

6

8

10

12

Time (h)

150

200

250

300

Temperature (°C)


350

400

Page 35 of 41

Figure 10 Simultaneous NO removal and Hg0 oxidation over Cu3-SCR catalyst in simulated coalfired flue gas (SFG: 12% CO2, 5% O2, 8% H2O, 500 ppm SO2, 300 ppm NO, 300 ppm NH3 and 72.0 μg/m3 Hg0, balanced in N2, T=150-400 °C, GHSV=0.5×105 h-1, Duration =4h)

100 80

ENO Eoxi

100

60

ENO

90

40

E (%)

E (%)

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

stability test at 350 °C

80

Eoxi

20 70

0

150

200

0

250

2

4

6

Time (h)

300

Temperature (°C)


8

350

10

12

400

Energy & Fuels

Figure 11 XRD patterns of the catalysts

 

Intensity (a.u.)

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

Page 36 of 41

Anatase TiO2



Raw SCR









Cu3-SCR 10

20

30

40

50

2 (°)


60

70

Page 37 of 41

Figure 12 O 1s XPS spectra for raw SCR, Cu3-SCR and spent Cu3-SCR catalyst

Oβ Raw SCR Intensity (a.u.)

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

Energy & Fuels

O 1s

Oα Oβ

Cu3-SCR

Oα

Oβ Spent Cu3-SCR 538

536

Oα 534

532

530

Binding energy (eV)


528

526

Energy & Fuels

Figure 13 V 2p XPS spectra for raw SCR, Cu3-SCR and spent Cu3-SCR catalyst

V

5+

V

4+

V 2p

Raw SCR

Intensity (a.u.)

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

Page 38 of 41

Cu3-SCR

Spent Cu3-SCR

522

520

518

516

Binding energy (eV)


514

512

Page 39 of 41

Figure 14 Cu 2p XPS spectra for the Cu3-SCR and spent Cu3-SCR catalyst

Cu 2p

Cu3-SCR

+

+

Cu

Cu 2+

Cu

Spent Cu3-SCR

+

+

Cu

2+

Cu

2+

Cu 2+

Cu

960

2+

Cu

2+

Cu Intensity (a.u.)

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

Energy & Fuels

Cu

955

950

945

940

Binding energy (eV)


935

930

925

Energy & Fuels

Figure 15 H2-TPR profiles of the catalysts

350 Cu3-SCR 203

283

764 485

Intensity (a.u.)

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

Page 40 of 41

786 Raw SCR 315

766

Cu3-W-TiO2 306 Cu3-TiO2

768 W-TiO2 100

200

300

400

500

600

Temperature (°C)


700

800

Page 41 of 41 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 16 Schematic diagram of Hg0 oxidation over Cu3-SCR catalyst


Simultaneous NO Removal and Hg0 Oxidation over CuO Doped V2O5

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