Synergistic Promotion Effect between NOx and Chlorobenzene

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Synergistic Promotion Effect between NOx and Chlorobenzene Removal on MnOx-CeO2 Catalyst Lina Gan, Wenbo Shi, Kezhi Li, Jianjun Chen, Yue Peng, and Junhua Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b10636 • Publication Date (Web): 21 Aug 2018 Downloaded from http://pubs.acs.org on August 22, 2018

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ACS Applied Materials & Interfaces

Synergistic Promotion Effect between NOx and Chlorobenzene Removal on MnOx-CeO2 Catalyst Lina Gana, Wenbo Shib, Kezhi Lia, Jianjun Chena, Yue Penga*, Junhua Lia* a

National Engineering Laboratory for Multi Flue Gas Pollution Control Technology

and Equipment, State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, 100084, China b

Department of Chemical and Environmental Engineering, Yale University, New

Haven, CT 06520, USA * Corresponding authors: E-mail address: [email protected], [email protected] Tel.: +86 10 62771093, fax: +86 10 62771093

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ABSTRACT Developing new technologies for the simultaneous removal of NOx and dioxins from metallurgical facility and waste incinerator emissions remains challenging. Here we present a new synergistic improvement effect of NOx and chlorobenzene (CB) on the MnOx-CeO2 catalyst. CB promoted both the NOx conversion and N2 selectivity below 300 °C during the NOx reduction process, in which the MnOx-CeO2 catalyst caused the undesired side reactions due to the over-oxidation of NH3. Meanwhile, NOx and NH3 promoted the CB oxidation activity above 100 °C in the presence of O2. Based on the DRIFTs and kinetic studies, the promotion was due to the separation of the MnOx-CeO2 catalyst into different temperature windows: NOx reduction at 100-200 °C and CB oxidation at 200-300 °C. The side reactions mainly occurred above 200 °C, which is suppressed by the coverage and activation of CB on catalyst surface. Key words: NOx, chlorobenzene, NH3-SCR, synergistic promotion, MnOx-CeO2.

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1. INTRODUCTION NOx and dioxins are emitted from metallurgical sintering facility, coking furnace and waste incinerator etc. NOx contributes to photochemical smog, particulate matters and ozone depletion. Dioxins are highly toxic persistent organic pollutants to the environment and biology. 1-3 The development of novel technologies to control their emission from the stationary sources is still a challenge. Selective catalytic reduction of NOx (SCR) with NH3 is a widely applied method to control NOx emission of coal-fired power plant and is being used as a potential technology in steel and waste boilers.4 Current commercial catalyst is V2O5 supported on TiO2 with excellent balance of surface acidity and reducibility. Catalytic combustion is performed to oxidized dioxins to less harmful products at relatively low temperatures.5 The catalysts are usually noble metals or transitional metals supported on TiO2 or Al2O3 with good reducibility and great surface oxygen vacancies. The similar properties of them ignited us to develop new catalysts for the NOx and dioxin removal together in the flue gas. The rationally designed dual-function catalysts might enable a coupled NOx reduction with NH3 and dioxins oxidation with O2.5, 6 The development relies on a thorough understanding of the possible interactions among NOx, NH3 and dioxins at catalysts surface and interface. Previous works revealed the facilitative effects of NOx and dioxins abatement on V2O5/TiO2 catalyst: (1) chlorobenzene (CB, as a mimic molecule of dioxins) is first oxidized by a V5+Ox species; (2) NO is oxidized to NO2 by Oad; (3) in situ-generated NO2 facilitates the reoxidation of the reduced V4+Ox species, closing the CB oxidation loop.7-10 Moreover, 3



dioxins inhibited NOx reduction, because the SCR reaction temperature window is overlapped with the CB oxidation (300-400 °C).11-14 Therefore, it is necessary to develop new catalysts working at distinct temperatures in terms of SCR reaction and CB oxidation. As one of promising low temperature SCR catalysts,15-19 the MnOx-CeO2 catalyst might trigger undesired side reactions: slow SCR process, nonselective catalytic reduction (NSCR) and NH3 catalytic oxidation (C-O) at elevated temperatures.20-23 Moreover, the mechanism of CB oxidation on Mn-based catalyst includes adsorption of the aromatic compounds, nucleophilic substitution of Cl- ions, and electrophilic substitution to break the aromatic ring.24-27 Due to the difficulty and complexity of the oxidation process, CB oxidation usually needs to be conducted in the temperature window, where SCR side reactions occur on the MnOx-CeO2. Taking advantage of the competition between CB oxidation and NH3 (NO) oxidation, the overall performance of the reaction might be enhanced by conducting those reactions simultaneously and determined the active components of each reaction. In this work, we investigate the NOx reduction and CB oxidation on the MnOx-CeO2 catalyst. The SCR performance on the MnOx-CeO2 catalyst was promoted by CB in 200-300 °C. The oxidation activity of CB was also promoted in the presence of NO and NH3. Since the mechanism by which NO promotes CB catalytic oxidation could be explained by previously proposed mechanisms, we focus on the impacts of CB on the SCR and side reactions to probe this co-optimization phenomenon. 4


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2. EXPERIMENTAL 2.1 Catalyst preparation The MnOx-CeO2 catalyst with a mole ratio of Mn/(Mn+Ce)=0.4 was prepared by coprecipitation. Mn(NO3)2 and Ce(NO3)3, an ammonia solution were used as catalyst precursors and precipitator with the concentration of 0.5 mol/L, 0.75mol/L and 12.5 wt.%, respectively. The mixed solution was stirred for 2 h at room temperature. The obtained paste from the coprecipitation was centrifuged and washed with deionized water several times to remove residual ammonia solution, and then, the solid was dried at 110 °C for 10 h and calcined at 650 °C for 6 h in air. Finally, the sample was sieved through 40-60 meshes prior to the catalytic activity test. 2.2 Catalytic performance The catalytic performance of NOx and CB removal was evaluated in a fixed-bed quartz reactor (internal diameter 6mm). The catalyst (200 mg) was tested in a mixture of 500 ppm NO, 50 ppm CB, 500 ppm NH3, 10 vol.% O2, 5 vol.% H2O (when used) and N2 as the balance gas. The total flow rate was 200 mL/min, equivalent to a gas hourly space velocity (GHSV) of 60,000 mL/(g·h) (STP). The concentrations of all gas-phase components were monitored in real time by an FTIR spectrometer (Gasmet DX-4000). The NOx conversion, N2 selectivity, CB conversion and CO2 selectivity were calculated with the following equations: =

= 1 − '( =

× 100%

" #$% $ %

)* )* )*

(1) & × 100%

× 100%

(2) (3)

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' =

) "

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× 100%

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(4),

where NOx refers to the sum of NO and NO2. 2.3 Catalyst characterization Temperature programmed desorption of NH3 (NH3-TPD) and NH3+CB (NH3+CB-TPD) were conducted in the same quartz reactor that was used as the catalyst performance test reactor. The catalyst (100 mg) catalyst was pretreated with 200 mL/min of N2 at 350 °C for 1 h and then cooled to 50 °C. Then, the catalyst was exposed of 500 ppm NH3 or 500 ppm NH3+50 ppm CB for 1 h to achieve adsorption saturation. The gas was switched back to N2 for 1 h to purge the physically adsorbed species, and then the temperature was programmed to increase at a rate of 10 °C/min. During the temperature ramp up, the concentration of the desorbed products (NH3, N2O, NO, NO2 and CB) were measured by on-line FTIR (Gasmet DX-4000). DRIFTs experiments were conducted with a Nicolet NEXUS 6700 spectrometer equipped with a Harrick IR cell and an MCT/A detector under a mixture of 500 ppm NH3 and 50 ppm CB with a total flow rate of 100 mL/min balanced by N2. Prior to each DRIFTs test, the sample was pretreated at 350 °C for 1 h under a N2 flow of 100 mL/min. 3. RESULTS AND DISCUSSION 3.1 Performance of NO reduction and CB oxidation The influence of CB on NOx conversion and N2 selectivity of the MnOx-CeO2 catalyst was studied. As shown in Figure 1(a), the NOx conversion and N2 selectivity were substantially enhanced in the presence of CB at high temperatures (200-300 °C) despite a minor decrease in the NOx conversion in the range of 50-200 °C. The results 6


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suggest that CB broadened the optimal SCR temperature window of the MnOx-CeO2, resolving the low NOx conversion and poor N2 selectivity issues effectively at high temperatures. The influence of NO+NH3 on CB oxidation activity was investigated, as displayed in Figure 1(b). In both scenarios, nearly 100% CO2 yielding was demonstrated by the complete mineralization of CB with MnOx-CeO2, which is an indicator of MnOx-CeO2 activity in the CB oxidation. When NO and NH3 was added, the CB conversion increased. This result is in agreement with previous studies: the in situ-generated NO2 facilitates the catalytic oxidation cycle.7, 8 To study the influence of H2O, similar performance tests were conducted in wet condition (Figure S1). The addition of H2O caused slight decreased in NOx conversion and CB conversion. These results revealed a unique phenomenon of the reactions (SCR and CB oxidation) and their co-optimization on the MnOx-CeO2 catalyst. SO2 still exhibited irreversible poisoning effect on the catalyst activity by the formation of sulfite and sulfate species. Therefore, this catalyst may be suitable for the coexistence of SCR and CB without SO2, such as MSWIs. 3.2 Influence of CB on NO oxidation, NSCR, and C-O oxidation Figure 2(a) shows the NO2 concentration during SCR process with/without CB. The generated NO2 was less than 10 ppm below 200 °C without CB, whereas a noticeable amount of NO2 (13-246 ppm) was formed in the range of 200-300 °C. In the presence of CB, however, NO2 concentration remained low (1-17 ppm) throughout the entire temperature range. Since NO2 is formed by NO oxidation in the presence of CB, the stable, low NO2 concentration implies NO oxidation was 7



suppressed by CB. To confirm this, the effect of CB on NO oxidation was further studied (Figure 2(b)). The results of NO to NO2 oxidation was significantly inhibited by CB at high temperatures: the ratio of NO2/NOx dropped from 70% to 3% at 250 °C. Theoretically, when NO2/NO ratios were larger than 1, the NO2-SCR reaction determined the overall SCR process. Since NO2-SCR is a slow SCR pathway,28 high NO2/NO ratios limit the high NOx reduction activity. CB inhibits the over NO to NO2 oxidation at high temperatures on the MnOx-CeO2, decreasing the percentage of slow SCR reaction. N2O is another undesired byproduct, and it mainly originates from the NSCR reaction between NH3 and NO and C-O oxidation between NH3 and O2.21, 22, 29, 30 CB significantly suppressed the formation of N2O during NOx reduction (Figure 2 (c)) and directed the majority of NH3 to participate in the standard SCR reaction instead of the NSCR reaction, enhancing the N2 selectivity. In addition to using the N2O formation to probe the occurring of NSCR, the influence of CB on the oxidation of NH3 was investigated (Figure 2(d)). NH3 tended to be more readily oxidized at higher temperature, the oxidation process was suppressed by CB at both tested temperatures. CB inhibited the oxidation of NO, the NSCR between NH3 and NO, and the C-O oxidation, leading to higher and faster NOx conversion with excellent N2 selectivity. 3.3 Interplay of NH3 and CB adsorption on MnOx-CeO2 To evaluate the adsorption capacity of NH3 and CB on the MnOx-CeO2 catalysts, temperature programmed desorption methods (NH3-TPD and NH3+CB-TPD) were carried out and shown in Figure 3. The desorbed products were calculated and listed 8


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in Table 1. The total acidity was the sum of NH3+2N2O+NO, which (164.64 µmol/g) was much more than the amount of absorbed CB (3.93 µmol/g). Although the presence of CB had little effect on the total acidity, the composition of the desorbed species changed. Specifically, compared with the results of NH3-TPD, the desorbed NH3 for NH3+CB-TPD increased, whereas N2O and NO decreased. The total amount of N-species reflects the NH3 adsorption capacity, because N2O and NO are the products of the oxidation of adsorbed NH3. Therefore, CB reduces the oxidation extent of NH3 on the surface of the MnOx-CeO2 catalyst, which is consistent with the previous discussion that CB suppresses the C-O oxidation. To investigate the interaction details between CB and NH3 when they are both present, in situ DRIFTs spectra of NH3 adsorption, CB adsorption, and NH3+CB coadsorption were performed at 150 °C. The spectra of the MnOx-CeO2 catalyst after treated with 500 ppm NH3 for 60 min are shown in SI Figure S2(a). The bands at 1178 and 1600 cm-1 were assigned to the symmetric and asymmetric deformation, respectively, of coordinated NH3 on the Lewis acid sites.16 The band 1430 cm-1 was assigned to the asymmetric deformation of NH4+ formed by the adsorption of NH3 on the Brønsted acid sites. The band 1270 cm-1 was assigned to the oxidation of adsorbed NH3.21, 31 Hence, NH3 will adsorb on both types of acid sites when introduced by itself to the catalyst, and partial oxidation will be observed. For the absorbed CB, bands at 1605, 1575, 1550, 1430 and 1210 cm-1 can be observed (Figure S2(b)). The band at 1605 cm-1 was attributed to the vibration of aromatic ring adsorbed parallel to the surface.24 The bands at 1430 cm-1 and 1550 cm-1 were assigned to the symmetric and 9



asymmetric stretching vibrations of COO- on the catalyst surface. The bands at 1210 cm-1 and 1575 cm-1 are related to the C-O and C=C stretching vibrations, respectively, of the adsorbed phenolate species.25 The results demonstrate that CB can be chemically adsorbed on the MnOx-CeO2 catalyst, and the absorption peak intensities are much lower than those of NH3, which is consistent with TPD results. The in situ DRIFTs spectra of NH3+CB coadsorption after pre-adsorption of NH3 for 60 min on MnOx-CeO2 are shown in Figure 4(a). The intensity of the band at 1430 cm-1 gradually increased in the presence of CB. It was difficult to distinguish this band because of the overlap of the NH4+ and COO- species. By subtracting the full spectra before and after CB adsorption (Figure 4(c)), the band at 1550 cm-1 emerged, indicating both of these bands could be assigned to the COO- species. In addition, the intensity of other bands attributed to the adsorbed NH3 on Lewis sites exhibited no significant change. The results suggest that CB can be adsorbed on the surface after pre-adsorption of NH3 and do not reduce the quantity of adsorbed NH3. The CB+NH3 coadsorption after pre-adsorption of CB for 60 min was also studied, as shown in Figure 4(b). After the introduction of NH3, the intensities of the bands at 1595, 1550, 1428, 1210 and 1178 cm-1 increased with increasing the time. Surprisingly, the intensities of the bands at 1210 and 1550 cm-1 related to CB adsorption also increased. In comparison with Figure 4(a), the C-O vibration band (1210 cm-1, representative of adsorbed CB) was notably stronger with the pre-adsorption of NH3 after 30 min CB and NH3 purging. The results suggest that NH3 could promote the adsorption of CB and contribute to its oxidative removal. 10


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Furthermore, the band at 1270 cm-1, assigned to the oxidation of adsorbed NH3, was much weaker than those of adsorbed NH3 in the absence of CB (Figure S2(a)). To clarify the effects of CB on NH3 adsorption, the integrated peak of the oxidation products of adsorbed NH3 (S1270) and Lewis acids (S1178) were calculated and are displayed in Figure 4(d). The S1270/ S1178 ratio dropped with increasing exposure time (from 0.207 to 0.088), indicating that adsorbed CB weakens the oxidation ability of the catalyst. The inhibition of the C-O oxidation and the preservation of intact NH3 might account for the promotion at high temperature. 3.4 Decoding the reaction kinetics To elucidate the relationship between SCR reaction and CB oxidation, kinetic experiments were conducted on the MnOx-CeO2 catalyst regarding to different temperatures and densities. The rates constants of NH3 conversion (δNH3), NSCR reaction (./012 ) and C-O reaction (δC-O) decreased at 250 and 300 °C respectively, whereas, the rate constants of δSCR was essentially unaffected in the presence of CB. The rate constants of SCR reaction through E-R mechanism (.012(32) ), L-H mechanism (.012(45) ), ./012 and δC-O were calculated and displayed in Figure 5. The specific models and calculation methods are shown in SI. In both cases with/without CB, SCR reaction is mainly dominated by the E-R pathway with a minor contribution from the L-H pathway. For example, .012(32) (264-611 mmol/(g·min)) was much higher than .012(45) (5-96 µmol/(g·min)) in the absence of CB. When CB was introduced into the flue gas, both ./012 and δC-O declined significantly especially above 200 °C. This direct evidence proved that CB notably suppresses 11



NSCR and C-O reactions at high temperatures. The effects of CB concentration on the NOx conversion and N2O formation were also studied (Figure S5). With increasing the CB concentration, the NOx conversion rates dropped slightly, but the N2O formation rates dropped substantially at 250 and 300 °C. Note that the competition between the SCR reaction and side reactions (NSCR and C-O) from NH3 oxidation determines the SCR N2 selectivity at high temperatures. The observed rapid decline of ./012 with increasing CB concentration inherently improved N2 selectivity, which is the main reason for the overall promotional effect of CB on the SCR performance. 3.5 Mechanistic insights on the synergistic effect The overall mechanism of NO reduction is proposed (Figure 6). NH3 was dehydrated to NH2 radicals and subsequent pathways altered by CB on the dual-function MnOx-CeO2 surface. In the absence of CB, (1) NH2 was further oxidized to NH/N and then reacted with NO, leading to the NO reduction to N2; (2) NH/N was reacted with O2 to form NO, decreasing NOx conversion; (3) a substantial amount of NO was oxidized to NO2, shifting the reaction pathway toward undesired slow SCR.20, 32, 33 When CB was added, the undesired oxidation processes (2) and (3) above were inhibited, promoting the participation of the adsorbed NH2 and NO process (1). 4. CONCLUSION We observed a synergistic effect of the SCR of NOx and the oxidation of CB on the MnOx-CeO2 catalyst; CB not only could be consumed with NOx but also 12


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overcame the drawbacks of the MnOx-CeO2 catalyst for SCR of NOx at high temperatures. Specifically, (1) CB improved the N2 selectivity of the SCR reaction because of the inhibition of NSCR and C-O oxidation; (2) CB widened the active temperature window because of the suppression of NO over-oxidation at higher temperatures; (3) CB had minor effects on NH3 adsorption, which guarantees the standard SCR route is the dominant pathway. ASSOCIATED CONTENT Supporting Information. Brief statement in nonsentence format listing the contents of the material supplied as Supporting Information. ACKNOWLEDGEMENTS We gratefully acknowledge National Natural Science Foundation of China (21777081) and China Postdoctoral Science Foundation (2017M620798).

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Temperatures. Environ. Sci. Technol. 2013, 47 (10), 5294-5301. 16. Qi, G.; Yang, R. T.; Chang, R. MnOx-CeO2 Mixed Oxides Prepared by Co-Precipitation for Selective Catalytic Reduction of NO with NH3 at Low Temperatures. Appl. Catal., B 2004, 51 (2), 93-106. 17. Yang, P.; Li, J.; Zuo, S. Promoting Oxidative Activity and Stability of CeO2 Addition on the MnOx Modified Kaolin-Based Catalysts for Catalytic Combustion of Benzene. Chem. Eng. Sci. 2017, 162, 218-226. 18. Hu, H.; Zha, K.; Li, H.; Shi, L.; Zhang, D. In Situ DRIFTs Investigation of the Reaction Mechanism over MnOx-MOy/Ce0.75Zr0.25O2 (M=Fe, Co, Ni, Cu) for the Selective Catalytic Reduction of NOx with NH3. Appl. Surf. Sci. 2016, 387, 921-928. 19. Zha, K.; Cai, S.; Hu, H.; Li, H.; Yan, T.; Shi, L.; Zhang, D. In Situ DRIFTs Investigation of Promotional Effects of Tungsten on MnOx-CeO2/Meso-TiO2 Catalysts for NOx Reduction. J. Phys. Chem. C 2017, 121 (45), 25243-25254. 20. Yang, S.; Xiong, S.; Liao, Y.; Xiao, X.; Qi, F.; Peng, Y.; Fu, Y.; Shan, W.; Li, J. Mechanism of N2O Formation during the Low-Temperature Selective Catalytic Reduction of NO with NH3 over Mn-Fe Spinel. Environ. Sci. Technol. 2014, 48 (17), 10354-10362. 21. Yang, S.; Qi, F.; Xiong, S.; Dang, H.; Liao, Y.; Wong, P. K.; Li, J. MnOx Supported on Fe-Ti Spinel: A Novel Mn Based Low Temperature SCR Catalyst with a High N2 Selectivity. Appl. Catal., B 2016, 181, 570-580. 22. Xiong, S. C.; Liao, Y.; Xiao, X.; Dang, H.; Yang, S. J. Novel Effect of H2O on the Low Temperature Selective Catalytic Reduction of NO with NH3 over MnOx-CeO2: Mechanism and Kinetic Study. J. Phys. Chem. C 2015, 119 (8), 4180-4187. 23. Yang, S.; Liao, Y.; Xiong, S.; Qi, F.; Dang, H.; Xiao, X.; Li, J. N2 Selectivity of NO Reduction by NH3 over MnOx-CeO2: Mechanism and Key Factors. J. Phys. Chem. C 2014, 118 (37), 21500-21508. 24. Lichtenberger, J.; Amiridis, M. D. Catalytic Oxidation of Chlorinated Benzenes over V2O5/TiO2 Catalysts. J. Catal. 2004, 223 (2), 296-308. 25. Wang, J.; Wang, X.; Liu, X. L.; Zhu, T. Y.; Guo, Y. Y.; Qi, H. Catalytic Oxidation of Chlorinated Benzenes over V2O5/TiO2 Catalysts: The Effects of Chlorine Substituents. Catal. Today 2015, 241, 92-99. 26. Sun, P.; Wang, W.; Dai, X.; Weng, X.; Wu, Z. Mechanism Study on Catalytic Oxidation of Chlorobenzene over MnxCe1-xO2/H-ZSM5 Catalysts under Dry and Humid Conditions. Appl. Catal., B 2016, 198, 389-397. 27. Abecassis-Wolfovich, M.; Landau, M. V.; Brenner, A.; Herskowitz, M. Low-Temperature Combustion of 2,4,6-Trichlorophenol in Catalytic Wet Oxidation with Nanocasted Mn-Ce-Oxide Catalyst. J. Catal. 2007, 247 (2), 201-213. 28. Iwasaki, M.; Shinjoh, H. A Comparative Study of "Standard", "Fast" and "NO2" SCR Reactions over Fe/Zeolite Catalyst. Appl. Catal., A 2010, 390 (1-2), 71-77. 29. Ettireddy, P. R.; Ettireddy, N.; Boningari, T.; Pardemann, R.; Smirniotis, P. G. 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. 2012, 292, 53-63. 30. Xiao, X.; Xiong, S.; Shi, Y.; Shan, W.; Yang, S. Effect of H2O and SO2 on the Selective Catalytic Reduction of NO with NH3 over Ce/TiO2 Catalyst: Mechanism and Kinetic Study. J. Phys. Chem. C 2016, 120 (2), 1066-1076. 31. Kijlstra, W. S.; Brands, D. S.; Poels, E. K.; Bliek, A. Mechanism of the Selective Catalytic Reduction of NO by NH3 over MnOx/Al2O3 .1. Adsorption and Desorption of the Single Reaction Components. J. 15



Catal. 1997, 171 (1), 208-218. 32. Tang, X.; Li, J.; Sun, L.; Hao, J. Origination of N2O from NO Reduction by NH3 over β-MnO2 and α-Mn2O3. Appl. Catal., B 2010, 99 (1), 156-162. 33. Busca, G.; Lietti, L.; Ramis, G.; Berti, F. Chemical and Mechanistic Aspects of the Selective Catalytic Reduction of NOx by Ammonia over Oxide Catalysts: A Review. Appl. Catal., B 1998, 18 (1), 1-36.

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Table and figure captions Table 1. Quantitative analysis of NH3-TPD and NH3+CB-TPD profiles. Figure 1. The interaction effect of CB and SCR performance on (a) NOx conversion and N2 selectivity of the MnOx-CeO2 catalyst, and the (b) effect of NO+NH3 on CB conversion and CO2 selectivity. Reaction conditions: NO 500 ppm (when used), CB 50 ppm (when used), NH3 500 ppm (when used), O2 10 vol.%, N2 as balance gas, GHSV 60,000 mL/(g·h). Figure 2. (a) and (c) NO2 and N2O concentrations in the SCR reaction with/without CB, (b) and (d) the effect of CB on NO and NH3 oxidation on the MnOx-CeO2 catalyst. Reaction conditions: NO 500 ppm, CB 50 ppm, NH3 500 ppm (when used), O2 10 vol.%, N2 as balance gas, GHSV 60,000 mL/(g·h). Figure 3. (a) NH3-TPD and (b) CB+NH3-TPD profiles of the MnOx-CeO2 catalyst in the temperature range of 50-600 °C. Figure 4. In situ DRIFTs spectra of the MnOx-CeO2 catalyst exposed to (a) and (c) NH3, (b) and (d) CB for 60 min followed by exposure to CB + NH3 for various times at 150 °C. Figure 5. SCR reaction rate constants of the MnOx-CeO2 catalyst through the E-R mechanism (.012(32) ) and L-H mechanism (.012(45) ), the NSCR reaction rate constant (./012 ) and the C-O reaction rate (δC-O) (a) without CB and (b) with CB. Figure 6. Synergetic mechanism of the removal of NO and chlorobenzene.

17



Page 18 of 25

Table 1. Quantitative analysis of NH3-TPD and NH3+CB-TPD profiles.

NH3-TPD NH3+CB-TPD

Total acidity (µmol/g) 170.5 164.6

NH3 (µmol/g) 96.2 107.1

N2 O (µmol/g) 28.6 23.5

18


NO (µmol/g) 17.1 10.5

CB (µmol/g) -3.9

(a)

80

80

80

60

60

40

40 without CB with CB

20

20

0 100

150

200

250

(b)

100 without NO+NH3 with NO+NH3

80

60

60

40

40

20

20

0

0 50

CB conversion (%)

100

N2 selectivity (%)

100

100

NOx 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


0 50

300

CO2 selectivity (%)

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100

Temperature (℃ )

150

200

250

300

Temperature ( )

Figure 1. The interaction effect of CB and SCR performance on (a) NOx conversion and N2 selectivity of the MnOx-CeO2 catalyst, and the (b) effect of NO+NH3 on CB conversion and CO2 selectivity. Reaction conditions: NO 500 ppm (when used), CB 50 ppm (when used), NH3 500 ppm (when used), O2 10 vol.%, N2 as balance gas, GHSV 60,000 mL/(g·h).

19



600

(a)

(b) 150℃

without CB with CB

200

Concentrations (ppm)

NO2 concentration (ppm)

250

150

100

50

0 50

100

150

200

250

300

NO2 NO

250℃

400

200

0

300

NO+O2 NO+O2+CB NO+O2 NO+O2+CB

Temperature (℃)

(c)

500

(d)

NO N2O N2 NH3

150℃

250 without CB with CB

200


N2O concentration (ppm)

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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150 100 50

400 250℃ 300 200 100 0

0 50

100

150

200

250

NH3+O2 NH3+O2+CB NH3+O2 NH3+O2+CB

300

Temperature (℃)

Figure 2. (a) and (c) NO2 and N2O concentrations in the SCR reaction with/without CB, (b) and (d) the effect of CB on NO and NH3 oxidation on the MnOx-CeO2 catalyst. Reaction conditions: NO 500 ppm, CB 50 ppm, NH3 500 ppm (when used), O2 10 vol.%, N2 as balance gas, GHSV 60,000 mL/(g·h).

20


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(a)

25

NH3 (without CB) NH3 (with CB) CB

80 60 40 20


100


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


(b) NO (without CB) N2O (without CB) NO (with CB) N2O (with CB)

20 15 10 5 0

0 100

200

300

400

500

600

100

Temperature ( )

200

300

400

500

600

Temperature ( )

Figure 3. (a) NH3-TPD and (b) CB+NH3-TPD profiles of the MnOx-CeO2 catalyst in the temperature range of 50-600 °C.

21


(c)

(d)

1430

1270 0.02

NH3 60min (NH3+CB 30min) - (NH3 60min)

1550

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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1178


I1270/I1178 0.088

0.151

0.207 2000

1800

1600

1400

1200

1000

1300

-1

Wavenumber (cm

1250

1200

1150

1100

1050

-1

Wavenumber (cm

)

)

Figure 4. In situ DRIFTs spectra of the MnOx-CeO2 catalyst exposed to (a) and (c) NH3, (b) and (d) CB for 60 min followed by exposure to CB + NH3 for various times at 150 °C.

22


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Figure 5. SCR reaction rate constants of the MnOx-CeO2 catalyst through the E-R mechanism (.012(32) ) and L-H mechanism (.012(45) ), the NSCR reaction rate constant (./012) and the C-O reaction rate (δC-O) (a) without CB and (b) with CB.

23



MnOx-CeO2

NO

NO2

SCR reaction

Side reaction

CB NH3(g)

NH3(ad)

NO N2+H2O

NH2

NSCR C-O NO N2O+H2O NO+H2O

NH/N

MnOx-CeO2 Figure 6. Synergetic mechanism of the removal of NO and chlorobenzene.

24


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Graphical Abstract

25


Synergistic Promotion Effect between NOx and Chlorobenzene

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