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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
4
Department of Environmental Science & Engineering, North China Electric Power University,
5
Baoding, 071003, Hebei, China
6
*Corresponding Author, E-mail:
[email protected] 7
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
12
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
19
indicated that the Cu3-SCR catalyst possessed abundant chemisorbed oxygen and good redox ability,
20
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
22
simultaneous NO removal and Hg0 oxidation. The mechanism of Hg0 oxidation over Cu3-SCR
23
catalyst was also investigated.
24
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-
15
WO3/TiO2 based catalyst has been widely used for SCR process due to its high catalytic activity and
16
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
19
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
24
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
2
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-
9
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
12
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.
14
Fe2O3/γ-Al2O3 catalyst and achieved more than 70% of Hg0 oxidation efficiency over the catalyst in
15
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
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. 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
14
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
17
simultaneous NO removal and Hg0 oxidation in the absence of HCl at temperature range of 150-
18
400 °C. The effects of the reaction conditions (including temperature, Hg0, NO/NH3, SO2, H2O and
19
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-
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WO3/TiO2 based commercial SCR catalyst.
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2. Experimental 4
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Energy & Fuels
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
7
added to the solution. The suspended slurry was stirred continuously in a 60 °C thermostatic water
8
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
10
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.
12
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
15
the experimental system. Unless otherwise indicated, the quartz tube reactor with 10 mm inner
16
diameter was loaded with 0.50 g (about 0.6 mL) catalyst sample. The total flow rate of the
17
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,
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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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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
10
ENO (%) =
NO in -NO out × 100% NOin
(1)
11
Eoxi (%) =
Hg 0in -Hg 0out ×100% Hg in0
(2)
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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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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.
3
3. Results and discussion
4
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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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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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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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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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
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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
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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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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
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44, 45
. The
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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
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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
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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
Hgୟୢ . 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
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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
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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
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RA-915+ Vent
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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
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80 Raw SCR Cu1-SCR
60
Cu2-SCR
40
Cu3-SCR Cu4-SCR
20 0
150
200
250
300
Reaction temperature (°C)
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350
400
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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
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20 150
200
250
300
Reaction temperature (°C)
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350
400
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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
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20
90
150
200
Cu3-SCR
80 70
0
0
stop Hg
0
250
2
4
6 8 Time (h)
300
Temperature (°C)
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350
10
12
400
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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
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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)
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400
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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 (%)
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90
Cu3-SCR
80
20
Raw SCR 70
0
stop SO2
add SO2
150
200
0
250
2
4
300
Temperature (°C)
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Time (h)
8
350
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12
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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 (%)
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40 20
90 80 70
0
150
200
stop SO2
Cu3-SCR 0
250
2
4
6 8 Time (h)
300
Temperature (°C)
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10
12
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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
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40 20
90
150
200
Cu3-SCR
80
Raw SCR 70
0
stop H2O
0
250
2
4
6
Time (h)
300
Temperature (°C)
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350
10
12
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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
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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)
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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)
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350
10
12
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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
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Anatase TiO2
Raw SCR
Cu3-SCR 10
20
30
40
50
2 (°)
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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)
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528
526
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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
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Cu3-SCR
Spent Cu3-SCR
522
520
518
516
Binding energy (eV)
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512
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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
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Cu
955
950
945
940
Binding energy (eV)
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930
925
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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
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786 Raw SCR 315
766
Cu3-W-TiO2 306 Cu3-TiO2
768 W-TiO2 100
200
300
400
500
600
Temperature (°C)
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700
800
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Figure 16 Schematic diagram of Hg0 oxidation over Cu3-SCR catalyst
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