Cu-SAPO-18 for NH3-SCR Reaction: The Effect of Different Aging


Jan 18, 2019 - Cu-SAPO-18 for NH3-SCR Reaction: The Effect of Different Aging Temperatures on Cu2+Active Sites and Catalytic Performances. Jingwen Ma ...
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Cu-SAPO-18 for NH-SCR reaction: The effect of the different aging temperatures on Cu active sites and the catalytic performances 2+

Jingwen Ma, Yongheng Li, Jian Liu, Zhen Zhao, Chunming Xu, Yuechang Wei, Weiyu Song, Yuanqing Sun, and Xiao Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b05439 • Publication Date (Web): 18 Jan 2019 Downloaded from http://pubs.acs.org on January 19, 2019

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Cu-SAPO-18 for NH3-SCR reaction: The effect of the different aging temperatures on Cu2+ active sites and the catalytic performances Jingwen Ma, Yongheng Li, Jian Liu*, Zhen Zhao, Chunming Xu, Yuechang Wei, Weiyu Song, Yuanqing Sun, Xiao Zhang State Key Laboratory of Heavy Oil and Beijing Key Lab of Oil & Gas Pollution Control, China University of Petroleum, Beijing 102249, P. R. China; *Corresponding Author:*Tel: (+86)10-89732778; Email: [email protected] (J. L.)

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ABSTRACT: Cu-based silicoaluminophosphate zeolite with AEI structure (Cu-SAPO-18) was directly synthesized through hydrothermal crystallization. The fresh and aged catalysts were applied for the selective catalytic reduction of NO using NH3. XRD, XPS, H2-TPR, EPR, BET, SEM, NH3-TPD, NMR, as well as in-situ DRIFTS are performed to investigate the samples. The results show that different aging temperatures remarkably affect the dispersion of the active sites and catalytic performances. Cu-T-800 exhibits the best NH3-SCR performance, which is attributed to that high-temperature aging decreases the inactive Cu oxides, meanwhile increases the isolated Cu2+. However, under severe aging temperature of 900 oC, Cu-T-900 almost has low SCR activity due to the damage of the zeolite framework. The kinetics result indicates that the pore diffusion limitations have a big impact on the NH3-SCR activity and the aging treatment could decrease the pore diffusion limitations of Cu-F-500.

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1. INTRODUCTION Nitrogen oxides (NOx), emitted from vehicle engines and industrial boilers, have serious harm to ecosystems and human health.1-2 Among several technologies applied on NOx elimination, NH3-selective catalytic reduction (NH3-SCR) technology is an effective mean for the catalytic removal of NOx.3-5 Recently, Cu-based zeolites such as CHA-typed Cu-SSZ-13 and Cu-SAPO-34, with smallpore structure, have drawn a great deal of attention for the elimination of NOx pollution due to their good stability and outstanding SCR activity.6-9 Cu-AEI zeolites such as Cu-SSZ-39 and CuSAPO-18 are also two kinds of efficient SCR catalysts for exhaust after-treatment.10-11 As silicoaluminophosphate (SAPO) zeolites, SAPO-18 has more rigid double 6-membered ring (D6R) arrangement, larger cages and smaller extent of unit cells than SAPO-34.12 Compared to the extensive study for methanol-to-olefins (MTO) reaction, research about SAPO-18 for NH3SCR has received less attention. 13-14 Martínez-Franco et al. reported a one-pot preparation of Cu-SAPO-18 zeolite through employing copper-tetraethylenepentamine complex as both Cu source and template, directly introducing the copper species into the AEI cages.15 However, reagent N,N-dimethyl-3,5dimethylpiperidinium was also concomitantly necessary, which limited the further development and application. Indeed, inorganic Cu salts can be introduced into the gel of the zeolite support prior to hydrothermal crystallization. The as-prepared zeolite and Cu precursor can thoroughly mix together. During the calcination process for removing the occluded organic species for asprepared zeolite, it can be speculated that copper oxides species will predominantly generate due to the decomposing of Cu precursors. Furthermore, it has also been reported that under hightemperature condition the solid-state ion exchange reaction can proceed between copper oxides

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and hydrogen typed SAPO zeolite through the following pathway: CuO + H-SAPO → Cu/SAPO + H2O. It is possible for the reaction that CuO reacts with the proton to produce Cu2+, [Cu(OH)]+ or Cu+ at ion exchange sites of zeolite.16-19 The isolated Cu2+ ions incorporated in AEI zeolite framework are very important for NH3-SCR, while copper oxides facilitate unselective NH3 oxidation reaction.10,

15, 20

However, it is few reports on the effect of thermal treatment

temperatures on copper active sites of Cu-based zeolite catalysts. Thus it is very significant to investigate Cu-SAPO-18 with highly NH3-SCR catalytic activity by means of high-temperature aging on the fresh Cu/SAPO-18 zeolite. And it is meaningful to study the relationship between different states of Cu species and SCR performance for the directly synthetic Cu/SAPO-18 catalyst via different aging temperatures. In this study, the influence of high-temperature treatment on the one-pot prepared Cu/SAPO18 zeolite for NH3-SCR reaction is investigated. The purpose of this study is to use facile method to incorporate copper into the AEI cage, as well as to investigate the impact of aging condition on the catalytic active sites and NH3-SCR performance.

2. EXPERIMENTAL SECTION 2.1 Preparation of Cu-SAPO-18. The fresh Cu/SAPO-18 was prepared hydrothermally using aluminum hydroxide (Al(OH)3) as Al source, 85% o-phosphoric acid as P source, Ludox AS-40 as Si source, and copper sulfate (CuSO4) as Cu source. After homogeneous mixing of Al and P sources, a certain amount of CuSO4 was directly added into the gel, then the template agent and Si source were added in turn into the above gel. The molar ration of Al2O3: P2O5: SiO2: SDA: H2O is 1.0:0.9:0.6:2.0:50, and the final Cu loading on the SAPO-18 support was about 2.36, which was measured via Inductively Coupled Plasma (ICP). The mixture of N,N-

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diisopropylethylamine (DIPEA) and TEA (triethylamine) agents were applied as structure directing agent (SDA), and the molar composition of DIPEA: (DIPEA+TEA) is 0.5. The homogeneous gel was transferred into a stainless autoclave and kept 96 h at 160oC. After crystallization process the precipitate was filtered and cleaned with deionized water for 3 times. The product was dried at 110 oC overnight. The fresh sample (labeled as Cu-F-500) was obtained by calcinating the product at 500 oC for 6 h in air. Then Cu-F-500 was divided and further calcined at 600, 700, 800 and 900 oC for 8 h, respectively. The thermally treated samples were labeled as Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900, respectively. 2.2. Characterization. X-ray diffraction (XRD) profiles were obtained on a Bruker D8 Advance. Micrometrics TriStar II 3020 analyzer was used to obtain the N2 adsorption-desorption isotherm, before which the samples were degassed at 300 oC for 2h. The morphology images were obtained by using a Zeiss field-emission scanning electron microscope (SEM) equipment. Thermo Fisher instrument was applied to acquire the X-ray photoelectron spectra (XPS). Bruker EMX-plus model spectrometer was applied to acquire the electron paramagnetic resonance (EPR) spectra. Bruker DMX-500 MHz instrument was used to acquire

27Al

solid state NMR spectra.

HUASI (Hunan, China) physical-chemical adsorption instrument was used to analyze the Hydrogen temperature programmed reduction (H2-TPR). Nicolet iS50 FTIR spectrometer was used to obtain the In-situ DRIFTS. 2.3. Activity Tests. A fixed bed quartz micro-reactor was used to evaluate the NH3-SCR. All the samples were sieved to 60-80 mesh for measurement. The reactant gas was composed of 500 ppm NO, 500 ppm NH3, 5% O2, balance N2 and the total flow rate was 500 mL/min. The gas hourly space velocity (GHSV) was 100 000 h−1. The concentration of NO was measured on a

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SIGNAL 4000 VM NOx analyzer after the reactant gas was stably flowing through the reactor. The NO conversion was calculated by the following equation.

NO conversion (%) =

[NO ]inlet ― [NO ]outlet [NO ]inlet

× 100

NH3-SCR kinetic measurements of the samples were measured under GHSV = 800000 h−1. Under this condition, the intracrystalline diffusion effect could be eliminated. NH3-SCR rate (RNO/(gcat·s)) can be calculated through the following equation: RNO =

XNO × FNO mcata × 22.4 × 60

The apparent activation energy (Ea) could be obtained according to the following equation.

ln R NO  lnA 

Ea RT

3. RESULTS AND DISCUSSIONS Figure 1a shows the NO conversion for all the samples. It can be found that the conversion of NO increases with the increasing of the temperature in the low-temperature range, while decreases in the high-temperature range. The deNOx temperature window for fresh Cu-F-500 is narrow, NO conversion reaches to 80% at 250 oC and decreases rapidly when the temperature excess 350 oC. Many previous researches have proved that low-temperature SCR performance is primarily dominated by isolated Cu2+ for Cu-based zeolites, while the degraded high-temperature SCR performance is mainly due to the unselective NH3 oxidation.6,

17, 21

It indicates that Cu

species on the one-pot synthesized Cu-F-500 sample are lack for catalyzing NO reduction.

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Interestingly, for those aged samples except Cu-T-900, the both low-temperature and hightemperature SCR performance are improved. For instance, NO conversion for Cu-T-600 catalyst is more than 90% at 250 oC and still maintains 80% at 400 oC. When the temperature rises to 700 oC,

NO conversion can be improved to 98% at 225 oC. Though the improvement of the low-

temperature NO conversion is no longer obvious for Cu-T-800 catalyst compared with Cu-T-700 catalyst, its high-temperature performance is still improved, and NO conversion can still maintain excess 80% when the temperature excess 450 oC. The amount of total Cu species on each catalyst is equal, thus it can be speculated that there are less active Cu sites and more insensitive Cu species on fresh Cu-F-500 sample than that of the aged samples. The results suggest the transformation among the different Cu species may occur under the aging treatment for fresh Cu-F-500 catalyst. Figure 1b shows the profiles of N2O concentration in the product versus temperature for the samples. It can be noticed that concentration of N2O is low over all the samples except Cu-T-900, indicating the good N2 selectivity. It should be noted that when the aging temperature achieves at 900 oC, NO conversion and N2 selectivity show serious deteriorations.

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Figure 1. NO conversion (a) and N2O concentration (b) curves of Cu-F-500, Cu-T-600, Cu-T700, Cu-T-800 and Cu-T-900 samples.

XRD is used to investigate the crystallinities and phase compositions of the samples, and the results are shown in Figure 2. The diffraction peaks for all, except Cu-T-900 sample are uniform and in accordance with the peaks of the AEI structure (PDF# 45-0118).22 It indicates that the direct introduction of Cu precursor into the initial gel hardly induces changes to the structure of SAPO-18 zeolite, whether in hydrothermal crystallization or the calcined processes. Unlike the samples preserving original crystalline structure under anabatic aging condition till 800 oC, CuT-900 sample transfers to a dense phase of SiO2, indicating the collapse of SAPO-18 framework. It can be inferred that Cu precursor is inclined to form as CuOx species after the hydrothermal crystallization and calcination processes. However, no peaks of copper oxides (Cu2O and CuO) can be observed in the fresh Cu-F-500 sample or in the aged samples, indicating that CuOx are highly dispersed or the size of the particles is too small to be detected. SEM images (Figure S1a) show that the crystalline grains for Cu-F-500 are cubic and the crystal sizes distribute in 2-4 μm. After aging treatment, the structures have not changed, indicating the high thermal stability of Cu-SAPO-18 catalysts (Figure S1b-d). However for Cu-T-900 (Figure S1e), it can be clearly seen that abundant pores form inside SAPO-18 crystalline grains, indicating that SAPO-18 zeolitic framework are gravely damaged, which is consistent with XRD results. BET results (Figure S2 and Table S1) also indicate the collapse of microporous structures of Cu-T-900.

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Cu-T-900 Cu-T-800

Intensity (a.u.)

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Cu-T-700 Cu-T-600 Cu-F-500 5

10

15

20

25

30

2 Theta (degree)

35

40

45

Figure 2. XRD patterns of Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples.

XPS is used to detect the copper state on the surface of the samples. Figure 3 exhibits the XPS spectra of Cu 2p. The main peak could be decomposed into two peaks, 933.3 and 935.5 eV. The peak at binding energy=935.5 eV can be attributed to isolated Cu2+, and the peak at 933.3 eV is attributed to CuO species.23-25 The two peaks at located at 943.2 and 963.2 eV are corresponded to the satellite peaks of corresponding Cu2+. As shown in Table 1 which is obtained from XPS results, with the aging temperature increasing, the percentage of Cu2+ rises and reaches to the maximum at 800 oC. The intensity of CuO peak for Cu-T-900 is much higher than the other catalysts, suggesting that CuO species are transferred to the surface of the sample owing to the collapse of the structure.

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Figure 3. Cu 2p XPS spectra for Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples. Table 1. Integral Areas and percentage of different Cu species on Cu-SAPO-18 samples Cu2+

Sample Integral area

CuO

Percentage (%)

Integral area

Percentage (%)

Cu-F-500

1311.20

37.1

2223.96

62.9

Cu-T-600

2266.43

47.5

2500.10

52.5

Cu-T-700

2171.23

48.3

2319.53

51.7

Cu-T-800

1916.71

48.5

2035.70

51.5

Cu-T-900

2192.28

38.2

3552.43

61.8

On account of no EPR signals of CuO and Cu+, EPR spectra can be performed to investigate the hyperfine structure of isolated Cu2+.26-27 With the aging temperature increases, the intensity of EPR signal increases, which indicates that the content of isolated Cu2+ on Cu-T-800 is largest. For Cu-T-900, the intensity of the Cu2+ decreases, indicating the decrease of isolated Cu2+ (Figure 4). The coordination environment of Cu2+ is often identified by utilizing g and A values.

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The spectra are almost identical for Cu-F-500 and those aged samples under 900 oC, indicating that isolated Cu2+ ions are stable under the aging treatment.28 However, after aging at 900 oC, new kinds of Cu species appear (new g and A values), which may be closely related to the collapse of the zeolitic framework.25, 29-30

Figure 4. EPR spectra of Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples.

H2-TPR is applied to characterize the reducibility of different copper species. As shown in Figure 5, an intensely narrow peak at 270 oC appears in Cu-F-500, which is ascribed to the reduction of CuO to Cu0 under hydrogen.21, 23 It suggests that the majority of Cu species are CuO on Cu-F-500 sample. After aging treatment till 800 oC, this reduction peak broadens and can be decomposed into three reduction peaks (α, β and γ), meanwhile a new reduction peak ξ appears at high temperature at ~500 oC for these aged samples. Peak α can be referred to the reduction from less stable Cu2+ to Cu+; peak β is attributed to the reduction from CuO to Cu0; peak γ corresponds to the reduction of more stable Cu2+ to Cu+; peak ξ is attributed to the reduction of Cu+ ions to Cu0.31-32 It can be found that with the increasing of the reductive content of isolated Cu2+, the reductive content of CuO accordingly reduces with the increasing of aging temperature.

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It indicates the partial transformation of CuO to isolated Cu2+. For Cu-T-900 sample, only one broad peak centered at 450 oC is obtained. In consideration of the characteristic reduction temperature, it cannot be curtly attributed to Cu oxides or Cu2+. XRD results demonstrate the collapse of SAPO-18 framework for Cu-T-900. One can tentatively allot the peak to the reduction of the named CuxAlyOz species, which are probably generated through Cu ions and AlO4 species.33-34

Figure 5. H2-TPR curves of Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples.

The acidity shows a great effect on the activity for NH3-SCR. NH3-TPD results are displayed in Figure 6. The asymmetry peaks for each sample can be deconvoluted into three peaks centered at around 200 oC (A), 300 oC (B) and 400 oC (C). Peak A is corresponding to the weakly adsorbed ammonia including physical adsorbed ammonia and weak Lewis acid sites absorbed ammonium. Peak B is attributed to desorption of ammonia on weak Brønsted acid sites and newly formed Lewis acid sites. Peak C is corresponding to the desorption of ammonia on strong acid sites.32, 35 With the aging temperature increases, it can be found that the intensity of peak B increases yet peak C decreases, indicating segmental Brønsted acid sites transform to Lewis acid

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sites. This also demonstrates more isolated Cu2+ on these aged samples, in which CuO species can react with the zeolite support and generate Cu2+ undergo the thermal treatment. The intensity of NH3 desorption decreases sharply when the temperature reaches to 900 oC, which indicates that SAPO-18 zeolite framework and the coordination environment of Cu2+ are gravely damaged.

Cu-T-900

Cu-T-800

Intensity (a.u.)

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Cu-T-700

Cu-T-600

Cu-F-500 A

100

200

B

300

C

400

Temperature (o C)

500

600

Figure 6. NH3-TPD curves of Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples.

27Al

Solid-state NMR is used to obtain more informations about the interactions between Cu2+

and AEI framework in high-temperature condition. As shown in Figure 7, for Cu-F-500, features

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at 45 ppm can be corresponding to tetrahedral aluminum atoms (AlIV) in the framework.36 Peak at -10 ppm can be ascribed to octahedral Al atoms (AlVI), which are comprised of an additional coordination of two water molecules to Al atoms. The weak peak at 16 ppm suggests the formation of a low amount of pentacoordinated Al atoms (AlV), which is comprised of an additional coordination of one water molecule to Al atoms.37 For the aged samples except for Cu-T-900, all spectra are similar, indicating that after thermal treatment the structure is not changed. The peak of AlIV exhibits a slight shift, which may be caused by the perturbations from extra framework Cu2+. While for Cu-T-900, the peaks for AlV and AlVI are disappeared and the peak for AlIV has a large shift than the other samples, which indicates that a large change has taken place on the structure of SAPO-18.

45 IV Al 16 Al V

Cu-F-500

-11 VI Al

Cu-T-600 Cu-T-700 Cu-T-800 Cu-T-900 80

60

40

20

0

-20

Chemical shift (ppm)

-40

Figure 7. 27Al MAS NMR spectra of Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples.

DRIFTS experiments are carried out to study the intermediate ammonia species, aiming at the ammonia adsorption properties and acids sites for these catalysts. All the catalysts are kept under

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the flowing NH3/N2 at 200 oC for at least 60 minutes in order to ensure the ammonia adsorption saturation. The obtained spectra are shown in Figure 8. For Cu-F-500 and the aged samples except Cu-T-900, all the NH3 adsorption spectra are similar but a little different. The negative peaks at 3620 cm-1 and 3593 cm-1 should be ascribed to the occupation of NH3 with the terminal and structural O-H stretching bands of the catalyst (P-OH and Si-OH-Al). The bands at 3278 and 1458 cm-1 could be attributed to ammonium ions, while the bands at 3336, 3186 and 1617 cm-1 could be corresponding to coordinated ammonia.38-39 It can be found that with the aging temperature rises, the intensity assigned to coordinated NH3 on Cu species become stronger, while the peak for NH4+ on the Brønsted acid sites become weaker inversely, suggesting more active Cu2+ exist on the SAPO-18 zeolite support. It can be speculate that during the thermal treatment, CuO species can react with the zeolitic hydroxyl groups and generate isolated Cu2+.

Figure 8. In-situ DRIFTS of the samples after saturated adsorption in the flowing gas of NH3/N2 at 200 oC.

NH3-SCR kinetic tests are performed at a high GHSV and the NO conversion is displayed in

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Figure 9a. Figure 9b shows the corresponding Arrhenius plots and Ea results. The Ea values are close for the samples, indicating that the samples have similar rate controlling mechanism. However, the samples exhibit different Ea values, yet the nature of isolated Cu2+ ions is likely the same (Figure 4). According to the previous studies, it can be realized by introducing pore diffusion limitations.40-42 Among all of the samples, Cu-F-500 exhibits the lowest Ea value, which suggests the largest pore diffusion limitations.41 This may be due to that the size of CuO nanoparticles could occupy AEI cage and block pore openings, resulting in more pore diffusion limitations for Cu-F-500 sample.42 After aging treatment, Ea values of Cu-T-600 and Cu-T-700 increase to 54.2 and 62.8 KJ/mol, respectively This may be attributed to that the inactive CuO species are transferred to Cu2+ after aging treatment, thus reducing the pore diffusion limitations for Cu-T-600 and Cu-T-700 samples. However, Ea value for Cu-T-800 is lower than that of CuT-700, this may be due to that with the further increase of the temperature, Cu2+ will migrates from the surface into the inner pores, thus cause the pore diffusion limitations.18

60

b -6.0

Cu-F-500 Cu-T-600 Cu-T-700 Cu-T-800

ln (RateNO)[mol NO/mol Cu/s]

a NO Conversion (%)

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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-6.5

Ea=54.2KJ/mol Ea=62.8 KJ/mol

-7.0

40

-7.5

20

Cu-F-500 Cu-T-600 Cu-T-700 Cu-T-800

Ea=57.5 KJ/mol

Ea=50.3KJ/mol

-8.0

0 200

300

400

o Temperature ( C)

500

-8.5

1.95

2.00

2.05

2.10

2.15

1000/T (K -1)

2.20

2.25

2.30

Figure 9. NO conversion curves (a) and corresponding Arrhenius plots (b) of Cu-F-500, CuT-600, Cu-T-700 and Cu-T-800. 4. CONCLUSIONS

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1. Cu-SAPO-18 is directly synthesized through hydrothermal crystallization. NO conversion for fresh Cu-F-500 reaches to 80% at 250 oC and decreases dramatically when the temperature excess 350 oC. After thermal treatment, the aged Cu/SAPO-18 samples show a continually improved SCR activity. Cu-T-800 presents the best performance, with a wide range (200-450 oC) for high NO conversion (>80%). 2. After aging treatment, more isolated Cu2+ are formed through proton substitution of CuO species, confirmed by XPS, EPR, H2-TPR and NH3-TPD, thus the aged samples exhibit higher activities. However, harsh aging at 900 °C causes collapse of the zeolite structure thus deteriorating SCR performance. 3. The kinetic tests show that the pore diffusion limitations have a big impact on the activity for NH3-SCR reaction. Aging treatment could decrease the pore diffusion limitations of the CuF-500. Supporting Information The Supporting Information is available on the ACS Publications website. Characterization of SEM (Figure S1) and BET results (Figure S2 and Table S1) ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (21673290, U1662103), Beijing Natural Science Foundation (2182060).

REFERENCES (1) Yao, X.; Chen, L.; Cao, J.; Yang, F.; Tan, W.; Dong, L., Morphology and Crystal-Plane Effects of CeO2 on TiO2/CeO2 Catalysts during NH3-SCR Reaction. Ind. Eng. Chem. Res. 2018, 57, 12407-12419.

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(2) Peng, Y.; Li, J.; Si, W.; Luo, J.; Wang, Y.; Fu, J.; Li, X.; Crittenden, J.; Hao, J., Deactivation and regeneration of a commercial SCR catalyst: Comparison with alkali metals and arsenic. Appl. Catal., B 2015, 168-169, 195-202. (3) Smirniotis, P. G.; Peña, D. A.; Uphade, B. S., Low-Temperature Selective Catalytic Reduction (SCR) of NO with NH3 by Using Mn, Cr, and Cu Oxides Supported on Hombikat TiO2. Angew. Chem. Int. Ed. 2001, 40, 2479-2482. (4) Gao, F.; Zheng, Y.; Kukkadapu, R. K.; Wang, Y.; Walter, E. D.; Schwenzer, B.; Szanyi, J.; Peden, C. H. F., Iron Loading Effects in Fe/SSZ-13 NH3-SCR Catalysts: Nature of the Fe Ions and Structure–Function Relationships. ACS Catal. 2016, 6, 2939-2954. (5) Chen, Y.; Li, C.; Chen, J.; Tang, X., Self-Prevention of Well-Defined-Facet Fe2O3/MoO3 against Deposition of Ammonium Bisulfate in Low-Temperature NH3-SCR. Environ. Sci. Technol. 2018, 52, 11796-11802. (6) Xue, J.; Wang, X.; Qi, G.; Wang, J.; Shen, M.; Li, W., 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. 2013, 297, 56-64. (7) Kwak, J. H.; Tonkyn, R. G.; Kim, D. H.; Szanyi, J.; Peden, C. H. F., Excellent activity and selectivity of Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3. J. Catal. 2010, 275, 187-190. (8) Xin, Y.; Li, Q.; Zhang, Z., Zeolitic Materials for DeNOx Selective Catalytic Reduction. ChemCatChem 2018, 10. (9) Niu, C.; Shi, X.; Liu, F.; Liu, K.; Xie, L.; You, Y.; He, H., High hydrothermal stability of Cu–SAPO-34 catalysts for the NH3-SCR of NOx. Chem. Eng. J. 2016, 294, 254-263. (10) Ye, Q.; Wang, L.; Yang, R. T., Activity, propene poisoning resistance and hydrothermal stability of copper exchanged chabazite-like zeolite catalysts for SCR of NO with ammonia in comparison to Cu/ZSM-5. Appl. Catal. A 2012, 427-428, 24-34. (11) Moliner, M.; Franch, C.; Palomares, E.; Grill, M.; Corma, A., Cu-SSZ-39, an active and hydrothermally stable catalyst for the selective catalytic reduction of NOx. Chem. Commun. 2012, 48, 8264-6. (12) Abdollahi, S.; Ghavipour, M.; Nazari, M.; Behbahani, R. M.; Moradi, G. R., Effects of static and stirring aging on physiochemical properties of SAPO-18 and its performance in MTO process. J. Nat. Gas Sci. Eng. 2015, 22, 245-251.

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(13) Martinez-Franco, R.; Li, Z.; Martinez-Triguero, J.; Moliner, M.; Corma, A., Improving the catalytic performance of SAPO-18 for the methanol-to-olefins (MTO) reaction by controlling the Si distribution and crystal size. Catal. Sci. Technol. 2016, 6, 2796-2806. (14) Wragg, D. S.; Akporiaye, D.; Fjellvåg, H., Direct observation of catalyst behaviour under real working conditions with X-ray diffraction: Comparing SAPO-18 and SAPO-34 methanol to olefin catalysts. J. Catal. 2011, 279, 397-402. (15) Martínez-Franco, R.; Moliner, M.; Corma, A., Direct synthesis design of Cu-SAPO-18, a very efficient catalyst for the SCR of NOx. J. Catal. 2014, 319, 36-43. (16) Wang, L.; Gaudet, J. R.; Li, W.; Weng, D., Migration of Cu species in Cu/SAPO-34 during hydrothermal aging. J. Catal. 2013, 306, 68-77. (17) Fan, S.; Xue, J.; Yu, T.; Fan, D.; Hao, T.; Shen, M.; Li, W., The effect of synthesis methods on Cu species and active sites over Cu/SAPO-34 for NH3-SCR reaction. Catal. Sci. Technol. 2013, 3, 2357. (18) Vennestrøm, P. N. R.; Katerinopoulou, A.; Tiruvalam, R. R.; Kustov, A.; Moses, P. G.; Concepcion, P.; Corma, A., Migration of Cu Ions in SAPO-34 and Its Impact on Selective Catalytic Reduction of NOx with NH3. ACS Catal. 2013, 3, 2158–2161. (19) Gao, F.; Walter, E. D.; Washton, N. M.; Szanyi, J.; Peden, C. H. F., Synthesis and evaluation of Cu/SAPO-34 catalysts for NH3-SCR 2: Solid-state ion exchange and one-pot synthesis. Appl. Catal. B 2015, 162, 501-514. (20) Li, Y.; Deng, J.; Song, W.; Liu, J.; Zhao, Z.; Gao, M.; Wei, Y.; Zhao, L., Nature of Cu Species in Cu–SAPO-18 Catalyst for NH3–SCR: Combination of Experiments and DFT Calculations. J. Phys. Chem. C 2016, 120, 14669-14680. (21) Xie, L.; Liu, F.; Ren, L.; Shi, X.; Xiao, F. S.; He, H., Excellent performance of one-pot synthesized Cu-SSZ-13 catalyst for the selective catalytic reduction of NOx with NH3. Environ. Sci. Technol. 2014, 48, 566-572. (22) Chen, J.; Thomas, J. M.; Wright, P. A., Silicoaluminophosphate number eighteen (SAPO18): a new microporous solid acid catalyst. Catal. Lett. 1994, 28, 241-248. (23) Pereda-Ayo, B.; De La Torre, U.; Illán-Gómez, M. J.; Bueno-López, A.; González-Velasco, J. R., Role of the different copper species on the activity of Cu/zeolite catalysts for SCR of NOx with NH3. Appl. Catal., B 2014, 147, 420-428.

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(24) Peng, C.; Liang, J.; Peng, H.; Yan, R.; Liu, W.; Wang, Z.; Wu, P.; Wang, X., Design and Synthesis of Cu/ZSM-5 Catalyst via a Facile One-Pot Dual-Template Strategy with Controllable Cu Content for Removal of NOx. Ind. Eng. Chem. Res. 2018, 57, 14967-14976. (25) Tang, J.; Xu, M.; Yu, T.; Ma, H.; Shen, M.; Wang, J., Catalytic deactivation mechanism research over Cu/SAPO-34 catalysts for NH3-SCR (II): The impact of copper loading. Chem. Eng. Sci. 2017, 168, 414-422. (26) Wang, J.; Peng, Z.; Qiao, H.; Yu, H.; Hu, Y.; Chang, L.; Bao, W., Cerium-Stabilized CuSSZ-13 Catalyst for the Catalytic Removal of NOx by NH3. Ind. Eng. Chem. Res. 2016, 55, 1174-1182. (27) Xu, M.; Wang, J.; Yu, T.; Wang, J.; Shen, M., New insight into Cu/SAPO-34 preparation procedure: Impact of NH4-SAPO-34 on the structure and Cu distribution in Cu-SAPO-34 NH3SCR catalysts. Appl. Catal., B 2018, 220, 161-170. (28) Fan, D.; Wang, J.; Yu, T.; Wang, J.; Hu, X.; Shen, M., Catalytic deactivation mechanism research over Cu/SAPO-34 catalysts for NH 3 -SCR (I): The impact of 950 °C hydrothermal aging time. Chem. Eng. Sci. 2018, 176, 285-293. (29) Lai, L.; Zhang, L.; Hu, C., Galvanic-like cells produced by negative charge nonuniformity of lattice oxygen on d-TiCuAl-SiO2 nanospheres for enhancement of Fenton-catalytic efficiency. Environ. Sci. Nano 2016, 3. (30) Yamaguchi, S.; Suzuki, A.; Togawa, M.; Nishibori, M.; Yahiro, H., Selective Oxidation of Thioanisole with Hydrogen Peroxide using Copper Complexes Encapsulated in Zeolite: Formation of a Thermally Stable and Reactive Copper Hydroperoxo Species. ACS Catal. 2018, 8, 2645-2650. (31) Zhao, Z.; Yu, R.; Zhao, R.; Shi, C.; Gies, H.; Xiao, F.-S.; De Vos, D.; Yokoi, T.; Bao, X.; Kolb, U.; Feyen, M.; McGuire, R.; Maurer, S.; Moini, A.; Müller, U.; Zhang, W., Cu-exchanged Al-rich SSZ-13 zeolite from organotemplate-free synthesis as NH3-SCR catalyst: Effects of Na+ ions on the activity and hydrothermal stability. Appl. Catal., B 2017, 217, 421-428. (32) Liu, X.; Wu, X.; Weng, D.; Si, Z.; Ran, R., Evolution of copper species on Cu/SAPO-34 SCR catalysts upon hydrothermal aging. Catal. Today 2017, 281, 596-604. (33) Senna, M.; Billik, P.; Yermakov, A. Y.; Škrátek, M.; Majerová, M.; Čaplovičová, M.; Mičušík, M.; Čaplovič, L.; Bujdoš, M.; Nosko, M., Synthesis and magnetic properties of CuAlO2 from high-energy ball-milled Cu2O–Al2O3 mixture. J. Alloy. Compd. 2016.

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(34) Yan, Q.; Nie, Y.; Yang, R.; Cui, Y.; O’Hare, D.; Wang, Q., Highly dispersed CuyAlOx mixed oxides as superior low-temperature alkali metal and SO2 resistant NH3 -SCR catalysts. Appl. Catal. A 2017, 538. (35) Yu, T.; Fan, D.; Hao, T.; Wang, J.; Shen, M.; Li, W., The effect of various templates on the NH3-SCR activities over Cu/SAPO-34 catalysts. Chem. Eng. J 2014, 243, 159-168. (36) Kwak, J. H.; Tran, D.; Burton, S. D.; Szanyi, J.; Lee, J. H.; Peden, C. H. F., Effects of hydrothermal aging on NH3-SCR reaction over Cu/zeolites. J. Catal. 2012, 287, 203-209. (37) Buchholz, A.; Wang, W.; Xu, M.; Arnold, A.; Hunger, M., Thermal stability and dehydroxylation of Brønsted acid sites in silicoaluminophosphates H-SAPO-11, H-SAPO-18, HSAPO-31, and H-SAPO-34 investigated by multi-nuclear solid-state NMR spectroscopy. Micropor. Mesopor. Mat.s 2002, 56, 267-278. (38) Liu, J.; Shi, X.; Shan, Y.; Yan, Z.; Shan, W.; Yu, Y.; He, H., Hydrothermal Stability of CeO2–WO3–ZrO2 Mixed Oxides for Selective Catalytic Reduction of NOx by NH3. Environ. Sci. Technol. 2018, 52, 11769-11777. (39) Lian, Z.; Shan, W.; Zhang, Y.; Wang, M.; He, H., Morphology-Dependent Catalytic Performance of NbOx/CeO2 Catalysts for Selective Catalytic Reduction of NOx with NH3. Ind. Eng. Chem. Res. 2018, 57, 12736-12741. (40) Gao, F.; Walter, E. D.; Washton, N. M.; Szanyi, J.; Peden, C. H. F., Synthesis and Evaluation of Cu-SAPO-34 Catalysts for Ammonia Selective Catalytic Reduction. 1. Aqueous Solution Ion Exchange. ACS Catal. 2013, 3, 2083-2093. (41) Gao, F.; Walter, E. D.; Karp, E. M.; Luo, J.; Tonkyn, R. G.; Kwak, J. H.; Szanyi, J.; Peden, C. H. F., Structure–activity relationships in NH3-SCR over Cu-SSZ-13 as probed by reaction kinetics and EPR studies. J. Catal. 2013, 300, 20-29. (42) Zhang, T.; Qiu, F.; Chang, H.; Li, X.; Li, J., Identification of active sites and reaction mechanism on low-temperature SCR activity over Cu-SSZ-13 catalysts prepared by different methods. Catal. Sci. Technol. 2016, 6. 6294-6304.

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Figure 1. NO conversion (a) and N2O concentration (b) curves of Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples. 140x72mm (300 x 300 DPI)

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Figure 2. XRD patterns of Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples. 85x65mm (300 x 300 DPI)

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Figure 3. Cu 2p XPS spectra for Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples. 85x65mm (300 x 300 DPI)

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Figure 4. EPR spectra of Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples. 85x65mm (300 x 300 DPI)

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Figure 5. H2-TPR curves of Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples. 85x65mm (300 x 300 DPI)

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Figure 6. NH3-TPD curves of Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples. 85x110mm (300 x 300 DPI)

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Figure 7. 27Al MAS NMR spectra of Cu-F-500, Cu-T-600, Cu-T-700, Cu-T-800 and Cu-T-900 samples. 85x65mm (300 x 300 DPI)

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Figure 8. In-situ DRIFTS of the samples after saturated adsorption in the flowing gas of NH3/N2 at 200 oC.

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Figure 9. NO conversion curves (a) and corresponding Arrhenius plots (b) of of Cu-F-500, Cu-T-600, Cu-T700 and Cu-T-800. 84x37mm (300 x 300 DPI)

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