Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
Aerosol and Air Quality Research, 18: 655–670, 2018 Copyright © Taiwan Association for Aerosol Research ISSN: 1680-8584 print / 2071-1409 online doi: 10.4209/aaqr.2017.04.0148 In Situ FT-IR and DFT Study of the Synergistic Effects of Cerium Presence in the Framework and the Surface in NH3-SCR Yinming Fan1, Wei Ling1, Lifu Dong1, Shihui Li1, Chenglong Yu1, Bichun Huang1,2*, Hongxia Xi3 1 School of Environment and Energy, South China University of Technology, Guangzhou Higher Education Mega Centre, Guangzhou 510006, China 2 Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, South China University of Technology, Guangzhou Higher Education Mega Centre, Guangzhou 510006, China 3 School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou Higher Education Mega Centre, Guangzhou 510006, China ABSTRACT
Mn-Ce/CeAPSO-34 was prepared, in which manganese and cerium were supported on the surface through using the Ethanol dispersion method, while cerium was incorporated in the SAPO-34 framework by a one-step hydrothermal method. Based on our previous study, a strong synergistic effect of cerium presented in the framework and the surface was existing in Mn-Ce/CeAPSO-34 catalyst, which showed outstanding SO2 tolerance and H2O resistance in the low-temperature NH3-SCR. In situ FT-IR and DFT calculations were used to investigate the synergistic effects. Based on the characterization results of in situ FT-IR study, it was found that more amount of nitrate species and NH3 species adsorbed on the surface of Mn-Ce/CeAPSO-34, while less the amount of sulfate species deposited during reaction process, which in the presence of SO2. Meanwhile, DFT calculations revealed that Ce site supported on the surface, which neighbored by Ce site in the framework more were capable of reacting with NO and NH3. Keywords: Mn-Ce/CeAPSO-34; NH3-SCR; Synergistic effect; SO2 tolerance. INTRODUCTION
Selective catalytic reduction of NO with ammonia (NH3-SCR), as an effective and stable technology, is widely used to eliminate the nitrogen oxides from stationary sources (Bosch, 1988; Nova et al., 2006). While catalysts are the key factor for the SCR technology, which directly determinate the denitrification efficiency. However, the most commercial used catalyst, V2O5-WO3(MoO3)/TiO2, with a relatively narrow and high temperature window of 300–400°C, which need the SCR system be placed upstream of the electrostatic precipitant and desulfurizer to avoid reheating the gas. But the problem is that the catalyst have a short lifetime and easy to be deactivated in the presence of SO2 and H2O (Forzatti et al., 1996; Fuet al., 2014). Hence, there is a great motivation to develop new catalysts to apply in relatively low operating temperatures and resistant to SO2 and H2O. Many kind of of metal oxides (such as Fe, Cu, Mn, Ce) supported on that * Corresponding author.
Tel.: +86 20 39380519 E-mail address: [email protected]
different carriers have been found as efficient catalysts at low temperature (Wang et al., 2012; Xue et al., 2013; Qu et al., 2015; Wang et al., 2017). In particular, Mn-based catalysts (such as nano-MnOx, MnOx/TiO2, MnOx/MWCNTs, MnOx/Graphene, MnOx/ZSM-5 and MnOx/USY) exhibited a relatively higher activity at low temperature (Qi et al., 2003; Wu et al., 2007; Jiang et al., 2009; Fang et al., 2013; Lou et al., 2014; Jiao et al., 2015; Andreoli et al., 2015). However, the vulnerability of these catalysts suffering from the deactivation by SO2 and H2O, which inhibited them for industrial application. Generally speaking, SO2 deactivates the catalysts through the formation of metal sulfites/sulfates, or the deposition of ammonium sulfates that can generate pore plugging and blockage of active sites (Wu et al., 2009; Jin et al., 2010a; Zhang et al., 2014). And H2O inhibited the activity of catalysts by the competitive adsorption with NH3 (Busca et al., 1998; Thirupathi et al., 2011).
Concerning the resistance to SO2 and H2O, it is proved to be an effective method that adding the extra elements (Cu, Sn, Ti, Fe, Zr, Ce) as modified material to the SCR catalysts (Shen et al., 2010; Chang et al., 2013; Cao et al., 2014; Guo et al., 2014; Pan et al., 2014; Zhang et al., 2015; Du et al., 2016; Niu et al., 2016; Zhang et al., 2016). Among them, Ce was widely used for it’s better redox ability, high
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 656
oxygen storage capacity and environmental friendliness. Jin et al. (2010b) found that NO conversion was higher over Mn-Ce/TiO2 catalyst than over Mn/TiO2 sample in the presence of SO2. Adding of Ce metal greatly inhibited the deposition of ammonium sulfates at the surface of catalysts and decreased the formation of metal sulfites/sulfates. Shu et al. (2014) indicated that Ce were sulfated preferentially over Ce-Fe/TiO2 in the presence of SO2, and then the quantities of surface active oxygen species and hydroxyls were increased, which supplied more acid sites. It is the actual reason for the strong SO2 resistance of Ce-Fe/TiO2
catalyst. Ce doping were more effective than other metal oxides to promote the catalytic activity under SO2 atmosphere to a certain extent, but what the most serious problem was that the Ce-modified catalysts would suffering severe deactivation by SO2 permanently at low temperature. Wherefore, the resistance to SO2 and H2O over Ce-modified catalysts need be improved more.
In our previous study (Fan et al., 2017), it was found that a strong synergistic effect was existing between cerium oxides in the framework and the surface of Mn/SAPO-34, which were beneficial to improve the resistance to SO2 and H2O in the low-temperature NH3-SCR. Cerium was incorporated in the SAPO-34 framework by a one-step hydrothermal method and supported on the surface by Ethanol dispersion method, respectively. We found that Ce could prefer to react with SO2 then protect the manganese active sites. Meanwhile, the synergistic effects of cerium existed in the framework and the surface not a simple overlap of single factors but a complex phenomenon. In this work, to investigate the mechanism of the synergistic effects of cerium exist in the framework and the surface, the in situ Fourier translation infrared spectrum (FT-IR) was used to study the behavior of the formed active intermediates and surface species over the catalysts in the presence of SO2 at low temperature NH3-SCR. Meanwhile, DFT calculations were used to research the synergistic effect existing between the cerium in the framework and the surface. EXPERIMENTAL Catalyst Preparation
CeAPSO-34 were synthesized by a one-step hydrothermal method. Diisopropylamine (DIPA, 99 wt%, Aladdin) was used as a template, cerium acetate hydrate (99.9 wt%, Aladdin) as the metal source, phosphoric acid (85 wt%, Aldrich), pseudoboehmite (68 wt%, PetroChina, China) and colloidal silica (30 wt%, Aldrich) as the phosphorus source, aluminum source and silicon source, respectively. The molar ratio used was 1.0P2O5:0.8Al2O3:0.2SiO2:3.0DIPA: 0.3Ce:50H2O in the crystallization solution. The synthesis steps were as follows: cerium acetate hydrate was added to a select quantity of distilled water and fully stirred until the cerium acetate hydrate was completely dissolved. Pseudoboehmite was then added to form a homogeneous gel by stirring. Subsequently, colloidal silica was added to the gel with stirring. Finally, the diisopropylamine was slowly added into the gel mixture and stirred. The resulting gel was transferred to a 100 mL autoclave with a Teflonliner
and statically crystallized for 48 h at 200°C. The crystalline products was filtered and washed with distilled water and dried at 110°C overnight. Then, the samples were calcined at 550°C for 6 h to remove the template. For comparison, SAPO-34 was also prepared according to the above-mentioned methods.
Mn/CeAPSO-34 and Mn-Ce/CeAPSO-34 were prepared successfully by the Ethanol dispersion method in which manganese nitrate (50 wt% in H2O, Aladdin) and cerium nitrate (99.5 wt%, Aladdin) used as precursor, respectively. The detailed process was described in previous study (Yang et al., 2016). For comparison, Mn/SAPO-34 and Mn-Ce/SAPO-34 were also prepared according to the above-mentioned methods. In Situ FT-IR Experiments
FT-IR spectra were conducted on a Nicolet 6700 FTIR spectrometers (2 cm–1 resolution with 100 accumulate scan) equipped with a MCT detector cooled by liquid nitrogen and a transmission reflection accessory with high temperature reaction cell. The catalyst were first mixed with KBr in a ratio of 1/100 by weight and were loaded into an IR cell with CaF2 windows. Prior to each experiment, the sample was pretreated at 350°C in the atmosphere for 60 min to remove any adsorbed species, then cooled down to the reaction temperature of 180°C. The background spectrum was recorded in flowing Ar and automatically subtracted from the sample spectrum during the experiment. The FT-IR experiment included transient response and steady-state response experiments. It must be emphasized that all catalyst samples are pretreated under the same condition in the whole experiment process. Computational Models and Details
All the Calculations were based on DFT and performed by Modeling Dmol3 package (Peng et al., 2015; Wei et al., 2016). SAPO-34 (1 × 1 × 1) model was selected in this study and SAPO-34 (111) face was choose to calculation the adsorption energy. Mn3O4 and CeO2@Ce2O3 crystal molecular were build for active component. All the geometry optimization were performed by local density approximation functional LDA-PWC, and the self-consistent field energy was set to 2.0 × 10−5 Ha. The adsorption energy are calculated as follows: Ead = Egas + Esurface – Egas@surface (1)
where Esurface, Egas and Egas@surface correspond to the energy of surface, an isolated gas molecule and the same molecule adsorbed on the surface, respectively. RESULTS AND DISCUSSION In Situ FT-IR Analysis
The effect of adsorbed NO on SO2 adsorption over Mn/SAPO-34, Mn/CeAPSO-34, Mn-Ce/SAPO-34 and Mn-Ce/CeAPSO-34 were investigated. Fig. 1 shows the in situ FT-IR spectra over the four catalysts in flowing NO + O2 at 180°C for 30 min and then purged with Ar for 30 min,
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 657
finally introduced with SO2. After exposing Mn/SAPO-34 to NO and O2, the bands corresponded to the surface O-H stretching (3800–3500 cm–1) (Jiang et al., 2010; Wang et al., 2014), nitrosyl NO- (1904 and 1847 cm–1) (Qi et al., 2004a; Zhang et al., 2013a), the gaseous or weakly adsorbed NO2 (1626 cm–1) (Jiang et al., 2010), bridging nitrate (1595 cm–1) and nitrite compounds (1407 cm–1) (Xu et al., 2013; Qiu et al., 2015) were detected. The new bands at 1725 cm–1 (N2O4) (Zhou et al., 2011), 1670 cm–1 (bidentate nitrate) (Meng et al.,
2015), 1530 and 1483 cm–1 (monodentate nitrate) (Wu et al., 2010) and 1456 cm–1 (nitrite compounds) (Jin et al., 2010c) were appeared over Mn/CeAPSO-34 and Mn-Ce/SAPO-34. And for Mn-Ce/CeAPSO-34, the new bands shifted to 1743 and 1697 cm–1 (N2O4) (Zhou et al., 2011) and 1518 cm–1
(monodentate nitrate) (Zhang et al., 2013b), respectively. Band intensity improved gradually with time. Compared to Mn/SAPO-34, the amount of nitrate species is much higher on the surface of the catalysts with Ce modification, indicating
4000 3500 3000 2000 1500 1000
Kub
elka
-Mun
k
Wavenumbers(cm-1)
O-H
1407
1595162618471904
30 min
20 min
10 min
5 min
0 min
SO2 30 min
Ar purge 30 min
17421699 1644
1540 15091460
1425 13751339
(A)
4000 3500 3000 2000 1500 1000
Kub
elka
-Mun
k
Wavenumbers(cm-1)
15301725
17421699 1644
1540 1509
14601425
1375
1339
14561483
15951626
167018471904
30 min
20 min
10 min
5 min
0 min
SO2 30 min
Ar purge 30 min
O-H
(B)
Fig. 1. In situ FT-IR spectra of (A) Mn/SAPO-34, (B) Mn/CeAPSO-34, (C) Mn-Ce/SAPO-34, (D) Mn-Ce/CeAPSO-34 exposed to NO + O2 at 180°C for 30 min and then purged with Ar for 30 min and finally SO2 was introduced. Experiment conditions: 0.08% NO, 5.0% O2, 0.01% SO2 and a balanced of Ar, total flow rate 100 mL min–1.
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 658
4000 3500 3000 2000 1500 1000
14251475
15901644
(C)
Kub
elka
-Mun
k
Wavenumbers(cm-1)
30 min
20 min
10 min
5 min
0 min
SO2 30 min
Ar purge 30 min
O-H
18471904
1725
17421339
1375
1530
14561483
15951626
16701407
Fig. 1. (continued).
that Ce modification would be beneficial to increase the nitrate species adsorbed on the catalyst surface. Then purged with Ar for 30 min, the initial peaks about nitrate species on all of the catalysts were vanished, indicating that nitrate species weakly adsorbed on catalysts surface. And finally SO2 was introduced, the new bands appeared at 1742, 1699, 1644, 1540, 1509, 1460, 1425, 1375 and 1339 cm–1 on Mn/SAPO-34. Similarly, these new bands were also detected on Mn/CeAPSO-34. The bands at 1742, 1699, 1540, 1425 and 1375 cm–1 associated with surface sulfate species (Jin et al., 2014), 1644 cm–1 ascribed to HSO4
– (Wei
et al., 2016), 1509 and 1460 cm–1 corresponded to SO32–
species (Yang et al., 1998; Watson et al., 2003; Pan et al., 2013), and 1339 cm–1 attributed to SO4
2– (Yang et al., 2013). For Mn-Ce/SAPO-34, the new bands at 1540 and 1460 cm–1 shifted to 1590 (surface sulfate species) and 1475 cm–1 (SO3
2–
species), respectively. While there are only three new bands at 1425 and 1375 cm–1 (surface sulfate species) and 1339 cm–1 (SO4
2–) were observed on Mn-Ce/CeAPSO-34. It was noted that SO2 would be weakly adsorbed on the surface of Mn-Ce/CeAPSO-34, indicating that cerium exist in the framework and the surface of catalysts have a significant
4000 3500 3000 2000 1500 1000
(D)
Kub
elka
-Mun
k
Wavenumbers(cm-1)
O-H SO2 30 min
Ar purge 30 min
30 min
20 min
10 min
5 min
0 min
15181743
16971904 1847
16261595
14251375
1339
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 659
inhibiting influence on the formation of sulfate species. The effect of adsorbed SO2 on NO adsorption over all of
the catalysts was investigated and the results are shown in Fig. 2. The catalysts were first exposed to SO2 at 180°C for 30 min and then purged with Ar for 30 min, finally NO + O2 was introduced. After exposing Mn/SAPO-34 to SO2, the bands corresponded to the surface O-H stretching (3800–3500 cm–1), surface sulfate species (1742, 1699, 1540, 1425 and 1375 cm–1), SO3
2– species (1509 and 1460 cm–1), HSO4–
(1644 cm–1) and SO42– (1339 cm–1) were observed. Similarly,
these new bands were also detected on Mn/CeAPSO-34 and Mn-Ce/SAPO-34. And for Mn-Ce/CeAPSO-34, the bands at 1590, 1475, 1425, 1375, 1339 cm–1 were found. It was noted that the amount of sulfate species was much lower on Mn-Ce/CeAPSO-34, indicating that cerium exist in the framework and the surface of catalyst would be inhibit the sulfate species adsorbed on catalyst surface. Then purged with Ar for 30 min, the initial peaks about sulfate species on the catalysts remained almost unchanged, indicating that the deposition of sulfate species were stable,
4000 3500 3000 2000 1500 1000
30 min
20 min
10 min
5 min
0 min
Ar purge 30 min
Kub
elka
-Mun
k
Wavenumbers(cm-1)
O-H
1595162618471904
16441699
1742
15401509
14601425 1375
NO+O2 30 min
(A)
1339
4000 3500 3000 2000 1500 1000
1595
1626
18471904
16441699
17421540
15091460
14251375
1339
Ar purge 30 min
30 min
20 min
10 min
5 min
0 min
NO+O2 30 min
Kub
elka
-Mun
k
Wavenumbers(cm-1)
O-H
(B)
Fig. 2. In situ FT-IR spectra of (A) Mn/SAPO-34, (B) Mn/CeAPSO-34, (C) Mn-Ce/SAPO-34, (D) Mn-Ce/CeAPSO-34 exposed to SO2 at 180°C for 30 min and then purged with Ar for 30 min and finally NO + O2 was introduced. Experiment conditions: 0.08% NO, 5.0% O2, 0.01% SO2 and a balanced of Ar, total flow rate 100 mL min–1.
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 660
4000 3500 3000 2000 1500 1000
O-H 1595
1626
18471904
17421699 1644
15401509
146014251375
133930 min
20 min
10 min
5 min
0 min
Ar purge 30 min
NO+O2 30 min
Kub
elka
-Mun
k
Wavenumbers(cm-1)
(C)
4000 3500 3000 2000 1500 1000
1456
O-H 1595
1626
18471904 1725
1590 14751425
1375133930 min
20 min
10 min
5 min
0 min
Ar purge 30 min
Kub
elka
-Mun
k
Wavenumbers(cm-1)
(D)
NO+O2 30 min
Fig. 2. (continued).
which maybe one of the reasons for the deactivation by SO2 was irreversible. After NO + O2 was introduced, the new bands appeared at 1904, 1847, 1626, 1595 cm–1 on all of the catalysts, which attributed to the adsorbed nitrate species. It was noted that the new peaks at 1725 cm–1
(N2O4) and 1456 cm–1 (nitrite compounds) were observed on Mn-Ce/CeAPSO-34. It is know that NO and SO2 tend to be adsorbed on the same active sites on the surface of catalysts. From these results, the competitive adsorption between NO and SO2 presented on all of the catalysts. Compared to other catalysts, the adsorption ability of SO2
was much lower on Mn-Ce/CeAPSO-34. Meanwhile, more
nitrate species adsorbed on the surface, indicating that NO adsorption over Mn-Ce/CeAPSO-34 was less affected by SO2 adsorbed. The results implied that cerium presented in the framework and the surface of catalyst could inhibit the sulfate species formed and increase the nitrate species adsorbed on catalyst surface.
The effect of adsorbed NH3 on SO2 over all of the catalysts was investigated and the results are shown in Fig. 3. The catalysts were first exposed to NH3 at 180°C for 30 min and then purged with Ar for 30 min, finally SO2 + O2 was introduced. After injecting NH3, several bands could be attributed to the surface O-H stretching (3800–3500 cm–1),
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 661
NH4+ species formed on Brønsted acid sites(1690, 1664,
1652, 1623, 1478, 1456 and 1402 cm–1) (Jin et al., 1986; Jiang et al., 2010; Liu et al., 2010), coordinated NH3 on Lewis acid sites (1278, 1248, 1120, 1077 and 1040 cm–1 ) (Sun et al., 2009; Jiang et al., 2014; Li et al., 2016) and -NH2 species (1588, 1558 and 1538 cm–1) (Sun et al., 2009; Qi et al., 2004b; Ettireddy et al., 2012) were observed over all of the catalysts (Ma et al., 2014; Ding et al., 2015; Zhu
et al., 2015). Compared with Mn/SAPO-34, the band at 3331 cm–1 was detected in the NH stretching region on the catalysts with Ce modification (Sun et al., 2009). It is noted that the amount of NH3 species is much higher on the catalysts with Ce modification. The results suggest that Ce modification would be beneficial to the improved NH3 adsorption on catalyst surface. Their intensities improved with exposure time. Then purged with Ar for 30 min, the
4000 3500 3000 2000 1500 1000
O-H
(A)
Kub
elka
-Mun
k
Wavenumbers(cm-1)
1664
15881478
14021278 1040
SO2+O
2 30 min
Ar purge 30 min
30 min
20 min
10 min
5 min
0 min
1540
164416991742
1509
14251460
13751339
4000 3500 3000 2000 1500 1000
3331
O-H
(B)
Kub
elka
-Mun
k
Wavenumbers(cm-1)
1478
1558
1248112010771040
SO2+O
2 30 min
Ar purge 30 min
30 min
20 min
10 min
5 min
0 min
17421699 1644
1540 1509
14601425 1375
1339
14021623
1664
Fig. 3. In situ FT-IR spectra of (A) Mn/SAPO-34, (B) Mn/CeAPSO-34, (C) Mn-Ce/SAPO-34, (D) Mn-Ce/CeAPSO-34 exposed to NH3 at 180°C for 30 min and then purged with Ar for 30 min and finally SO2 + O2 was introduced. Experiment conditions: 0.08% NO, 5.0% O2, 0.01% SO2 and a balanced of Ar, total flow rate 100 mL min–1.
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 662
4000 3500 3000 2000 1500 1000
3331
O-H
(C)
Kub
elka
-Mun
k
Wavenumbers(cm-1)
SO2+O
2 30 min
Ar purge 30 min
30 min
20 min
10 min
5 min
0 min
16521690
15581538162314561402
1248
1120
1540
164416991742
1509
14251460
13751339
4000 3500 3000 2000 1500 1000
1375 1339
15581588 14021623
16641478 1248 1120
1077 1040
30 min
20 min
10 min
5 min
0 min
Ar purge 30 min
SO2+O
2 30 min
Kub
elka
-Mun
k
Wavenumbers(cm-1)
3331
O-H
(D)
Fig. 3. (continued).
intensity of the initial peaks was declined. After SO2 + O2 was introduced, the new bands appeared at 1742, 1699, 1644, 1540, 1509, 1460, 1425, 1375 and 1339 cm–1 on Mn/SAPO-34, Mn/CeAPSO-34 and Mn-Ce/SAPO-34, which attributed to the adsorbed sulfate species, indicating the same sulfate species were formed. While there are only two new bands at 1375 cm–1 (surface sulfate species) and 1339 cm–1 (SO4
2–) were observed on Mn-Ce/CeAPSO-34, indicating that less the amount of sulfate species adsorbed and SO2 would be weakly adsorbed or the deposition rate of sulfate is slower
compared with other catalysts. The effect of adsorbed NO + NH3 + O2 on SO2 adsorption
on all of the catalysts was investigated and the results are shown in Fig. 4. The catalysts were first exposed to NO + NH3 + O2 at 180°C for 30 min and then purged with Ar for 30 min, finally SO2 was introduced. After injecting NO + NH3 + O2, the new bands could be assigned to nitrosyl NO- (1904 and 1847 cm–1), N2O4 (1754 cm–1), bidentate nitrate (1670 cm–1), the gaseous or weakly adsorbed NO2 (1626 cm–1), bridging nitrate (1595 cm-1), monodentate nitrate
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 663
(1483 cm–1), nitrite compounds (1456 cm–1), NH4+ species
formed on Brønsted acid sites (1402 cm–1) and coordinated NH3 on Lewis acid sites (1120, 1077 and 1040 cm–1) were observed on all of the catalysts. For Mn-Ce/CeAPSO-34, another new bands at 1530 cm–1 (monodentate nitrate) and 1248 cm–1 (coordinated NH3 on Lewis acid sites) were detected. Then purged with Ar for 30 min, the bands at 1904, 1847, 1120, 1077 and 1040 cm–1 were vanished. After SO2 was introduced, the new bands attributed to the adsorbed
sulfate species appeared at 1742, 1699, 1644, 1540, 1509, 1460, 1375 and 1339 cm–1 on Mn/SAPO-34. Similarly, these new bands were also detected on Mn/CeAPSO-34 and Mn-Ce/SAPO-34. While there are only two new bands at 1375 cm–1 surface sulfate species) and 1339 cm–1 (SO4
2–) were observed on Mn-Ce/CeAPSO-34. The results implied that SO2 would be weakly adsorbed on the surface of Mn-Ce/CeAPSO-34 after the catalyst in flowing NO + NH3 + O2 then purged with Ar.
4000 3500 3000 2000 1500 1000
Kub
elka
-Mun
k
Wavenumbers(cm-1)
O-H
SO2 30 min
30 min
20 min
10 min
5 min
0 min
Ar purge 30 min
174216991644
154015091460 1375
1339
1754 104010771120
140214561483
15951626
1670
18471904
(A)
4000 3500 3000 2000 1500 1000
Kub
elka
-Mun
k
Wavenumbers(cm-1)
O-H(B)
SO2 30 min
30 min
20 min
10 min
5 min
0 min
Ar purge 30 min
15091540 14601375
13391644
175410401077
1120140214561483
15951626
1670
18471904
Fig. 4. In situ FT-IR spectra of (A) Mn/SAPO-34, (B) Mn/CeAPSO-34, (C) Mn-Ce/SAPO-34, (D) Mn-Ce/CeAPSO-34 exposed to NO + NH3 + O2 at 180°C for 30 min and then purged with Ar for 30 min and finally SO2 was introduced. Experiment conditions: 0.08% NO, 5.0% O2, 0.01% SO2 and a balanced of Ar, total flow rate 100 mL min–1.
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 664
4000 3500 3000 2000 1500 1000
O-H
107711201402
1456148315951626
167018471904
SO2 30 min
Ar purge 30 min
30 min
20 min
10 min
5 min
Kub
elka
-Mun
k
Wavenumbers(cm-1)
0 min
(C)
17421699 1644
1540 15091460
1754 1040
4000 3500 3000 2000 1500 1000
13751339
O-H
1754 1248
15301456
140215951626
167018471904
30 min
20 min
10 min
5 min
0 min
SO2 30 min
Ar purge 30 min
Kub
elka
-Mun
k
Wavenumbers(cm-1)
(D)
11201077 1040
Fig. 4. (continued).
The formation of surface species on all of the catalysts under an atmosphere of NO NH3, O2 and SO2 mixture was also investigated and the results are shown in Fig. 5. After all the reaction gases were supplied, the bands could be assigned to the surface O-H stretching (3800–3500 cm–1), NH stretching (3331 cm–1), nitrosyl NO- (1904 and 1847 cm–1), weakly adsorbed sulfate species (1742 and 1540 cm–1), bidentate nitrate (1670 cm–1), the gaseous or weakly adsorbed NO2 (1626 cm–1), bridging nitrate (1595 cm–1), nitrite compounds (1456 cm–1), NH4
+ species formed on Brønsted acid sites (1402 cm–1) and coordinated NH3 on
Lewis acid sites (1120, 1077 and 1040 cm–1) were observed on Mn/SAPO-34. Band intensity improved gradually with time. It was noted that several nitrate species were first detected after injection of all the reaction gases for about 5 min, indicating that the rate of the NOx adsorption was much faster than the process of ammonia adsorption. Compared with Mn/SAPO-34, the amount of nitrate species was higher that N2O4 (1754, 1725 cm–1) and monodentate nitrate (1483 cm–1) were detected. Meanwhile, the amount of NH3 species was almost the same on Mn/CeAPSO-34, Mn-Ce/SAPO-34 and Mn-Ce/CeAPSO-34. While the sulfate
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 665
species was not found on the catalysts with Ce modification. It is known that the NH3-SCR reaction occurs following
two pathways: L-H mechanism (between NO2 and NH4+)
and E-R mechanism (between gas phase NO and coordinated NH3). In this work, the mechanism of NH3-SCR of NOx with SO2 on the catalysts has been discussed at 180°C. After all the reaction gases participated in the SCR reaction, NH4
+ species formed on Brønsted acid sites, coordinated NH3 on Lewis acid sites, nitrosyl NO- species and the gaseous or
weakly adsorbed NO2 were appeared on all of the catalysts. Hence, the reaction both takes place via L-H mechanism and E-R mechanism. The reaction could take place as follows: NH3(g) → NH3 (a) (2) NH3 (g) + H+ → NH4
+ (a) (3) O2 (g) → 2O (a) (4)
4000 3500 3000 2000 1500 1000
3331 1742
60 min
30 min
20 min
10 min
5 min
0 min
Kub
elka
-Mun
k
Wavenumbers(cm-1)
190410401077
11201402
154015951626
14561670
O-H
1847
(A)
4000 3500 3000 2000 1500 1000
3331O-H
0 min
5 min
10 min
20 min
30 min
60 min
Kub
elka
-Mun
k
Wavenumbers(cm-1)
104010771120
19041847
1595
14021456
1483
(B)
1725
17541670
1626
Fig. 5. In situ FT-IR spectra of (A) Mn/SAPO-34, (B) Mn/CeAPSO-34, (C) Mn-Ce/SAPO-34, (D) Mn-Ce/CeAPSO-34 exposed to NO + NH3 + O2 + SO2 at 180°C for 60 min. Experiment conditions: 0.08% NO, 5.0% O2, 0.01% SO2 and a balanced of Ar, total flow rate 100 mL min–1.
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 666
4000 3500 3000 2000 1500 1000
3331
1725O-H
175460 min
30 min
20 min
10 min
5 min
0 min
Kub
elka
-Mun
k
Wavenumbers(cm-1)
1904 1847
1670
16261595
10401077
1120
(C)1402
14561483
4000 3500 3000 2000 1500 1000
3331
1725
1754
Kub
elka
-Mun
k
Wavenumbers(cm-1)
19041847
1670
16261595 10401077
1120140214561483
0 min
5 min
10 min
20 min
30 min
60 minO-H
(D)
Fig. 5. (continued).
NH3 (a) + O (a) → OH (a) + NH2(a) (5) NH3 (a) + O2– → OH (a) + NH2 (a) (6) NO (g) + e → NO-(a) (7) NO-(a) + O2 (g) → NO2(a)/NO2
–/NO3– (8)
2NO2 (a) → N2O4 (a) (9) NH2 (a) + NO2
– → NH2NO2 (a) → … → H2O + N2 (g) +
O (a) (10) NH2 (a) + NO3
– → NH2NO3 (a) → … → H2O + N2 (g) + 2O (a) (11) 2NH2(a) + N2O4 (a) → 2NH2NO2(a) → …→ H2O + N2(g) + O(a) (12) NH4
+ (a) + N2O4 (a) → NH4N2O4 (a) → …→ H2O + N2 (g) + O (a) (13)
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 667
NH4+ (a) + NO2
– → NH4NO2 (a) → …→ H2O + N2 (g) (14) NH4
+ (a) + NO3– → NH4NO3 (a) → …→ H2O + N2 (g) +
O (a) (15)
In our previous study (Fan et al., 2017), Mn-Ce/CeAPSO-34 catalyst show outstanding SO2 tolerance. It is known that SO2 deactivated the catalysts by the deposition of ammonium sulfates or forming metal sulfites/sulfates lead to irreversible loss of active sites. The in situ FT-IR spectrum show that more nitrate species and NH3 species formed on catalyst surface with Ce modification. And in the presence of SO2, less the amount of sulfate species adsorbed on Mn-Ce/CeAPSO-34, indicating the amount of the deposition of ammonium sulfates or forming metal sulfites/sulfates was much lower. So NO conversion is still at higher level. DFT Study
The model of Mn/CeAPSO-34, Mn-Ce/SAPO-34 and Mn-Ce/CeAPSO-34 were established to research the synergistic effect present between the cerium in the framework and the surface. The Ce cation in the framework was labeled as Ce1 and on the surface neighbored by Ce site existed in the framework was labeled as Ce2. The adsorption energy of NO and NH3 molecule adsorbed on the surface of the catalysts were analyzed and the results shown in Table 1, and the optimized structures of NO and
NH3 adsorption over the catalysts was shown in Fig. 6. It was noted that the Ead(NO) and Ead(NH3) of Ce site supported on the surface are greater than Ce site existed in the framework, respectively. Meanwhile, the cerium incorporated in the framework and supported on the surface of the catalysts simultaneously, the Ead(NO) and Ead(NH3) of Ce sites are improved. Moreover, the Ead(NO) and Ead(NH3) of Ce site supported on the surface neighbored by Ce site existed in the framework are greater than other Ce sites. We know that the positive value of Ead reveals a strong interaction between adsorption surface and gas. Therefore, these results implied that Ce site supported on the surface neighbored by Ce site existed in the framework are more capable of reacting with NO and NH3, indicating a synergistic effect existing between the cerium in the framework and the surface. CONCLUSIONS
The synergistic effects of cerium existing in the framework and the surface of Mn-/SAPO-34 for low temperature NH3-SCR was investigated by in situ FT-IR and DFT calculations. The in situ FT-IR spectrum revealed that the strong synergistic effect would be beneficial to promote the adsorbtion of more nitrate species and NH3 species adsorbed on the surface of Mn-Ce/CeAPSO-34, and inhibit the deposition of sulfate species, which in the presence of SO2. Meanwhile, the theoretical results of DFT
Table 1. Adsorption energies of NO and NH3 on catalysts.
Sample Ead(NO) (eV) Ead(NH3) (eV)
Ce1 Ce2 Ce1 Ce2 Mn/CeAPSO-34 0.43 -- 0.67 -- Mn-Ce/SAPO-34 -- 0.52 -- 0.79 Mn-Ce/CeAPSO-34 0.61 0.75 0.94 1.08
Fig. 6. Optimized structures of NO and NH3 adsorptions on Mn/CeAPSO-34 (a, e), Mn-Ce/SAPO-34 (b, f) and Mn-Ce/CeAPSO-34 (c, d, g, h). The red balls are oxygen, purple balls are manganese, white balls are cerium, yellow balls are silicon, pink balls are aluminum, light pink balls are phosphorus.
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 668
calculations illumnate that the cerium incorporated in the framework and supported on the surface of the catalysts simultaneously were more capable of reacting with NO and NH3, enhancing the catalyst activity of low temperature NH3-SCR. ACKNOWLEDGMENT
The research was financially supported by the National Natural Science Foundation of China (NSFC-51478191) and Science and Technology Project of Guangdong Province (2014A020216003). REFERENCES Andreoli, S., Deorsola, F.A., Galletti, C. and Pirone, R.
(2015). Nanostructured MnOx catalysts for low-temperature NOx SCR. Chem. Eng. J. 278: 174–182.
Bosch, H. and Jamssen, F. (1988). Formation and control of nitrogen oxide. Catal. Today 2: 369–379.
Busca, G., Lietti, L., Ramis, G. and Berti, F. (1998). Chemical and mechanistic aspects of the selective catalytic reduction of NOx by ammonia over oxide catalysts: A review. Appl. Catal. B 18: 1–36.
Cao, F., Xiang, J., Su, S., Wang, P.Y., Sun, L.S., Hu, S. and Lei, S.Y. (2014). The activity and characterization of MnOx-CeO2-ZrO2/γ-Al2O3 catalysts for low temperature selective catalytic reduction of NO with NH3. Chem. Eng. J. 243: 347–354.
Chang, H.Z., Chen, X.Y., Li, J.H., Ma, L., Wang, C.Z., Liu, C.X., Schwank, J.W. and Hao, J.M. (2013). Improvement of activity and SO2 tolerance of Sn-modified MnOx-CeO2 catalysts for NH3-SCR at low temperatures. Environ. Sci. Technol. 47: 5294–5301.
Ding, S.P., Liu, F.D., Shi, X.Y., Liu, K., Lian, Z.H., Xie, L.J. and He, H. (2015). Significant promotion effect of Mo additive on a novel Ce-Zr mixed oxide catalyst for the selective catalytic reduction of NOx with NH3. ACS Appl. Mater. Interfaces 7: 9497–9506.
Du, X.S., Wang, X.M., Chen, Y.R., Gao, X. and Zhang, L. (2016). Supported metal sulfates on Ce-TiOx as catalysts for NH3-SCR of NO: High resistance to SO2 and potassium. J. Ind. Eng. Chem. 36: 271–278.
Ettireddy, P.R., Ettireddy, N. and Boningari, T. (2012). Investigation of the selective catalytic reduction of nitric oxide with ammonia over Mn/TiO2 catalysts through transient isotopic labeling and in situ FT-IR studies. J. Catal. 292: 53–63.
Fan, Y.M., Ling, W., Huang, B.C., Dong, L.F., Yu, C.L. and Xi, H.X. (2017). The synergistic effects of cerium presence in the framework and the surface resistance to SO2 and H2O in NH3-SCR. J. Ind. Eng. Chem. 56: 108–119.
Fang, C., Zhang, D.S., Cai, S.X., Zhang, L., Huang, L., Li, H.R., Maitarad, P., Shi, L.Y., Gao, R.H. and Zhang, J.P. (2013). Low-temperature selective catalytic reduction of NO with NH3 over nanoflaky MnOx on carbon nanotubes in situ prepared via a chemical bath deposition route. Nanoscale 5: 9199–9207.
Forzatti, P. and Lietti, L. (1996). Recent advances in De-NOxing catalysis for stationary applications. Heterogen. Chem. Rev. 3: 33–51.
Fu, M.F., Li, C.T., Lu, P., Qu, L., Zhang, M.Y., Zhou, Y., Yu, M.G. and Fang, Y. (2014). A review on selective catalytic reduction of NOx by supported catalysts at 100-300°C-catalysts, mechanism, kinetics. Catal. Sci. Technol. 4: 14–25.
Guo, R.T., Zhou, Y., Pan, W.G., Hong, J.N., Zhen, W.L., Jin, Q., Ding, C.G. and Guo, S.Y. (2013). Effect of preparation methods on the performance of CeO2/Al2O3 catalysts for selective catalytic reduction of NO with NH3. J. Ind. Eng. Chem. 19: 2022–2025.
Guo, R.T., Zhen, W.L., Pan, W.G., Zhou, Y., Hong, J.N., Xu, H.J., Jin, Q., Ding, C.G. and Guo, S.Y. (2014). Effect of Cu doping on the SCR activity of CeO2 catalyst prepared by citric acid method. J. Ind. Eng. Chem. 20: 1577–1580.
Jiang, B.Q., Liu, Y. and Wu, Z.B. (2009). Low-temperature selective catalytic reduction of NO on MnOx/TiO2 prepared by different methods. J. Hazard. Mater. 162: 1249–1254.
Jiang, B.Q., Wu, Z.B. and Liu, Y. (2010). DRIFT study of the SO2 effect on low-temperature SCR Reaction over Fe-Mn/TiO2. J. Phys. Chem. C 114: 4961–4965.
Jiang, B.Q., Deng, B.Y., Zhang, Z.Q., Wu, Z.L., Tang, X.J., Yao, S.L. and Lu, H. (2014). Effect of Zr addition on the low-temperature SCR activity and SO2 tolerance of Fe-Mn/Ti catalysts. J. Phys. Chem. C 118: 14866–14875.
Jiao, J.Z., Li, S.H. and Huang, B.C. (2015). Preparation of manganese oxides supported on graphene catalysts and their activity in low-temperature NH3-SCR. Acta Phys. Chim. Sin. 31: 1383–1390.
Jin, R.B., Liu, Y., Wu, Z.B., Wang, H.B. and Gu, T.T. (2010a). Relationship between SO2 poisoning effects and reaction temperature for selective catalytic reduction of NO over Mn-Ce/TiO2 catalyst. Catal. Today 153: 84–89.
Jin, R.B., Liu, Y., Wu, Z.B., Wang, H. and Gu, T. (2010b). Relationship between SO2 poisoning effects and reaction temperature for selective catalytic reduction of NO over Mn-Ce/TiO2 catalyst. Catal. Today 153: 84.
Jin, R.B., Liu, Y., Wang, Y., Cen, W.L., Wu, Z.B., Wang, H.Q, and Weng, X.L. (2014). The role of cerium in the improved SO2 tolerance for NO reduction with NH3 over Mn-Ce/TiO2 catalyst at low temperature. Appl. Catal. B 148–149: 582–588.
Jin, R., Liu, Y. and Wu, Z. (2010c). Low-temperature selective catalytic reduction of NO with NH3 over Mn-Ce oxides supported on TiO2 and Al2O3: A comparative study. Chemosphere 78: 1160–1166.
Jin, T., Yamaguchi, T. and Tanabe, K. (1986). Mechanism of acidity generation on sulfur-promoted metal oxides. J. Phys. Chem. 90: 4794–4796.
Li, Y., Li, Y.P., Wan, Y., Zhan, S.H., Guan, Q.X. and Tian, Y. (2016). Structure-performance relationships of MnOx nanocatalyst for the low-temperature SCR removal of NOx under ammonia. RSC Adv. 6: 54926–54937.
Liu, F. and He, H. (2010). Selective catalytic reduction of
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 669
NO with NH3 over manganese substituted iron titanate catalyst: Reaction mechanism and H2O/SO2 inhibition mechanism study. Catal. Today 53: 70–76.
Lou, X.R., Liu, P.F., Li, J., Li, Z. and He, K. (2014). Effects of calcination temperature on Mn species and catalytic activities of Mn/ZSM-5 catalyst for selective catalytic reduction of NO with ammonia. Appl. Surf. Sci. 307: 382–387.
Ma, L., Cheng, Y. and Cavataio, G. (2014). In situ DRIFTS and temperature-programmed technology study on NH3-SCR of NOx over Cu-SSZ-13 and Cu-SAPO-34 catalysts. Appl. Catal. B 156–157: 428–437.
Meng, D.M., Zhan, W.C., Guo, Y., Guo, Y.L., Wang, L. and Lu, G.Z. (2015). A highly effective catalyst of Sm-MnOx for the NH3-SCR of NOx at low temperature: Promotional role of Sm and its catalytic performance. ACS Catal. 5: 5973–5983.
Niu, C., Shi, X.Y., Liu, K., You, Y., Wang, S.X. and He, H. (2016). A novel one-pot synthesized CuCe-SAPO-34 catalyst with high NH3-SCR activity and H2O resistance. Catal. Commun. 81: 20–23.
Nova, I., Ciardelli, C., Tronconi, E., Chatterjee, D. and Bandl-Konrad, B. (2006). NH3-NO/NO2 chemistry over V-based catalysts and its role in the mechanism of the fast SCR reaction. Catal. Today 114: 3–12.
Pan, S.C., Luo, H.C., Li, L.S., Wei, Z.L. and Huang, B.C. (2013). H2O and SO2 deactivation mechanism of MnOx/MWCNTs for low-temperature SCR of NOx with NH3. J. Mol. Catal. A: Chem. 377: 154–161.
Pan, W.G., Hong, J.N., Guo, R.T., Zhen, W.L., Ding, H.L., Jin, Q., Ding, C.G. and Guo, S.Y. (2014). Effect of support on the performance of Mn-Cu oxides for low temperature selective catalytic reduction of NO with NH3. J. Ind. Eng. Chem. 20: 2224–2227.
Peng, Y., Li, J.H., Si, W.Z., Li, X., Shi, W.B., Luo, J.M., Fu, J., Crittenden, J. and Hao, J.M. (2015). Ceria promotion on the potassium resistance of MnOx/TiO2 SCR catalysts: An experimental and DFT study. Chem. Eng. J. 269: 44–50.
Qi, G.S., Yang, R.T. and Chang, R. (2003). Low-temperature SCR of NO with NH3 over USY-supported manganese oxide-based catalysts. Catal. Lett. 87: 67–71.
Qi, G.S. and Yang, R.T. (2004a). Characterization and FTIR Studies of MnOx-CeO2 Catalyst for low-temperature Selective Catalytic Reduction of NO with NH3. J. Phys. Chem. B 108: 15738–15747.
Qi, G., Yang, R.T. and Chang, R. (2004b). MnOx-CeO2 mixed oxides prepared by co-precipitation for selective catalytic reduction of NO with NH3 at low temperatures. Appl. Catal. B 51: 93–106.
Qiu, L., Pang, D. and Zhang, C. (2015). In situ IR studies of Co and Ce doped Mn/TiO2 catalyst for low-temperature selective catalytic reduction of NO with NH3. Appl. Surf. Sci. 357: 189–196.
Qu, Z.P., Miao, L., Wang, H. and Fu, Q. (2015). Highly dispersed Fe2O3 on carbon nanotubes for low-temperature selective catalytic reduction of NO with NH3. Chem. Commun. 51: 956.
Shen, B.X., Liu, T., Zhao, N., Yang, X.Y. and Deng, L.D.
(2010). Iron-doped Mn-Ce/TiO2 catalyst for low temperature selective catalytic reduction of NO with NH3. J. Environ. Sci. 22: 1447–1454.
Shu, Y., Aikebaier, T., Quan, X., Chen, S. and Yu, H.T. (2014). Selective catalytic reaction of NOx with NH3 over Ce-Fe/TiO2-loaded wire-mesh honeycomb: Resistance to SO2 poisoning. Appl. Catal. B 150–151: 630–635.
Sun, D.K., Liu, Q.Y., Liu, Z.Y., Gui, G.Q. and Huang, Z.G. (2009). An in situ DRIFTS study on SCR of NO with NH3 over V2O5/AC surface. Catal. Lett. 132: 122–126.
Thirupathi, B. and Smirniotis, P.G. (2011). Co-doping a metal (Cr, Fe, Co, Ni, Cu, Zn, Ce, and Zr) on Mn/TiO2 catalyst and its effect on the selective reduction of NO with NH3 at low-temperatures. Appl. Catal. B 110: 195–206.
Wang, J., Yan, Z. and Liu, L. (2014). In situ DRIFTS investigation on the SCR of NO with NH3 over V2O5 catalyst supported by activated semi-coke. Appl. Surf. Sci. 313: 660–669.
Wang, L.S., Huang, B.C., Su, Y.X., Zhou, G.Y., Wang, K.L., Luo, H.C. and Ye, D.Q. (2012). Manganese oxides supported on multi-walled carbon nanotubes for selective catalytic reduction of NO with NH3: Catalytic activity and characterization. Chem. Eng. J. 19: 232–241.
Wang, S.X., Guo, R.T., Pan, W.G., Li, M.Y., Sun, P., Liu, S.M., Liu, S.W., Sun, X. and Liu, J. (2017). The deactivation mechanism of Pb on the Ce/TiO2 catalyst for the selective catalystic of NOx with NH3: TPD and DRIFT studies. Phys. Chem. Chen. Phys. 19: 5333–5342.
Watson, J.M. and Ozkan, U.S. (2003). Spectroscopic characterization of surface species in deactivation of sol-gel Gd-Pd catalysts in NO reduction with CH4 in the presence of SO2. J. Catal. 217: 1–11.
Wei, L., Cui, S.P., Guo, H.X., Ma, X.Y. and Zhang, L.J. (2016). DRIFT and DFT study of cerium addition on SO2 of Manganese-based Catalysts for low temperature SCR. J. Mol. Catal. A: Chem. 421: 102–108.
Wu, Z.B., Jiang, B.Q., Liu, Y., Jin, R.B., Wang, H.Q. and Jin, R.B. (2007). DRIFT study of manganese/titania-based catalysts for low-temperature selective catalystic reduction of NO with NH3. Environ. Sci. Technol. 41: 5812–5817.
Wu, Z.B., Jin, R.B., Wang, H.Q. and Liu, Y. (2009). Effect of ceria doping on SO2 resistance of Mn/TiO2 for selective catalytic reduction of NO with NH3 at low temperature. Catal. Commun. 10: 935–939.
Wu, Z., Tang, N. and Xiao, L. (2010). MnOx/TiO2 composite nanoxides synthesized by deposition-precipitation method as a superior catalyst for NO oxidation. J. Colloid Interface Sci. 352: 143–148.
Xu, L., Li, X. and Crocker, M. (2013). A study of the mechanism of low-temperature SCR of NO with NH3 on MnOx/CeO2. J. Mol. Catal. A: Chem. 378: 82–90.
Xue, J.J., Wang, X.Q., Qi, G.S., Wang, J., Shen, M.Q. and Li, W. (2013). Characterization of copper species over Cu/SAPO-34 in selective catalytic reduction of NOx with ammonia: Relationships between active Cu sites and de-NOx performance at low temperature. J. Catal. 297: 56–64.
Fan et al., Aerosol and Air Quality Research, 18: 655–670, 2018 670
Yang, B., Zheng, D.H., Shen, Y.S., Qiu, Y.S., Li, B., Zeng, Y.W., Shen, S.B. and Zhu, S.M. (2015). Influencing factors on low-temperature deNOx performance of Mn-La-Ce-Ni-Ox/PPS catalytic filters applied for cement kiln. J. Ind. Eng. Chem. 24: 148–152.
Yang, R.T., Li, W.B. and Chen, N. (1998). Reversible chemisorption of nitric oxide in the presence of oxygen on titania and titania modified with surface sulfate. Appl. Catal. A 169: 215–225.
Yang, S.J., Guo, Y.F., Chang, H.Z., Ma, L., Peng, Y., Qu, Z., Yan, N.Q., Wang, C.Z. and Li, J.H. (2013). Novel effect of SO2 on the SCR reaction over CeO2: Mechanism and significance. Appl. Catal. B 136–137: 19–28.
Yang, Y.X., Ma, J.W., Yu, C.L., Sun, M.T., Huang, B.C. and Wu, Y.M. (2016). Low-temperature NH3-SCR activity of manganese oxides supported on different SAPO molecular sieves catalysts. Acta Sci. Circumst. 36: 3400–3408.
Zhang, D., Zhang, L. and Shi, L. (2013a). In situ supported MnOx-CeOx on carbon nanotubes for the low-temperature selective catalytic reduction of NO with NH3. Nanoscale 5: 1127–1136.
Zhang, L., Wang, D., Liu, Y., Kamasamudram, K., Li, J.H. and Epling, W. (2014). SO2 poisoning impact on the NH3-SCR reaction over a commercial Cu-SAPO-34 SCR catalyst. Appl. Catal. B 156–157: 371–377.
Zhang, L., Li, L.L., Cao, Y., Yao, X.J., Ge, C.Y., Gao, F.,
Deng, Y., Tang, C.J. and Dong, L. (2015). Getting insight into the influence of SO2 on TiO2/CeO2 for the selective catalytic reduction of NO by NH3. Appl. Catal. B 165: 589–598.
Zhang, L., Qu, H.X., Du, T.Y., Ma, W.H. and Zhong, Q. (2016). H2O and SO2 tolerance, activity and reaction mechanism of sulfated Ni-Ce-La composite oxide nanocrystals in NH3-SCR. Chem. Eng. J. 296: 122–131.
Zhang, R.D., Luo, N., Yang, W., Liu, N. and Chen, B.H. (2013b). Low-temperature selective catalytic reduction of NO with NH3 using perovskite-type oxides as the novel catalysts. J. Mol. Catal. A: Chem. 371: 86–93.
Zhou, G.Y., Zhong, B.C., Wang, W.H., Guan, X.J., Huang, B.C., Ye, D.Q. and Wu, H.J. (2011). In situ DRIFTS study of NO reduction by NH3 over Fe-Ce-Mn/ZSM-5 catalysts. Catal. Today 175:157–163.
Zhu, L., Zhang, L., Qu, H.X. and Zhong, Q. (2015). A study on chemisorbed oxygen and reaction process of Fe-CuOx/ZSM-5 via ultrasonic impregnation method for low-temperature NH3-SCR. J. Mol. Catal. A: Chem. 409: 207–215.
Received for review, May 9, 2017 Revised, July 31, 2017
Accepted, August 1, 2017