Effect of sulfate species on the performance of Ce-Fe-Ox catalysts in the selective catalytic reduction of NO by NH3
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摘要: 采用四种不同的方法制备了一系列含
$ {\rm{SO}}^{2-}_{4} $ 改性Ce-Fe-Ox催化剂，并研究其NH3选择性催化还原NOx的催化活性。结果表明，水热法制备的Ce-Fe-Ox（Fe-HT）可提高其催化性能。其优异的SCR性能与硫酸的加入有关，$ {\rm{SO}}^{2-}_{4} $ 的加入会导致CeO2晶体的弱化，提高其催化活性。Fe和Ce协同作用可提高催化剂的氧化还原能力，进而提高化学吸附氧的含量、Ce3+/(Ce4+ + Ce3+)和Fe3+/(Fe3+ + Fe2+)的比例，从而提高催化性能。过量的硫酸盐会导致Fe3+和Ce3+的下降，降低催化性能。Abstract: A series of Ce-Fe-Ox catalysts containing sulfate species was prepared by four different methods including sol-gel (Fe-SG), hydrothermal (Fe-HT), co-precipitation (Fe-10) and solid state grinding synthesis (Fe-SSGS) methods. The Ce-Fe-Ox catalysts were used in the selective catalytic reduction (SCR) of NOx by NH3 and the effect of sulfate species on the catalytic performance was investigated. The results indicate that the Fe-HT catalyst prepared by the hydrothermal method exhibits excellent performance in the NH3-SCR of NO, with a NO conversion of nearly 100% even at 250 °C. The Fe-HT catalyst contains proper amount of sulfate, which can decrease the CeO2 crystallinity and enhance the catalytic performance in the NH3-SCR of NO. The Fe-HT catalyst has a high content of surface Ce3+ and Fe3+ and there is a synergy between the Fe and Ce species, which can improve the redox capacity and greatly increase the quantity of chemisorbed oxygen. In contrast, excessive amount of sulfate species in Fe-SSGS and Fe-SG may reduce the synergy between Fe and Ce and then impair the catalytic performance of Ce-Fe-Ox in NH3-SCR.-
Key words:
- selective catalytic reduction /
- sulfates /
- surface acidity /
- chemisorption oxygen
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图 1 Fe-SSGS、Fe-10、Fe-HT和Fe-SG催化剂的脱硝性能
Figure 1 NOx conversion for NH3-SCR over the Fe-SSGS, Fe-10, Fe-HT and Fe-SG catalysts with different feed flow rates : (a) 100 mL/min; (b) 200 mL/min; (c) 300 mL/min
reaction conditions: 0.2 mL catalyst; inlet gas = 0.05% NO, 0.05% NH3, 5% O2, N2 as balance
图 2 Fe-SSGS、Fe-10、Fe-HT和Fe-SG催化剂（a）N2选择性，（b） 催化NO氧化成NO2的性能
Figure 2 (a) N2 selectivity and (b) performance test diagram of NO oxidation to NO2 over the Fe-SSGS, Fe-10, Fe-HT and Fe-SG catalysts. Reaction conditions: 0.2 mL catalyst; inlet gas = 0.05% NO, 0.05% NH3, 5% O2, N2 as balance; total flow rate = 200 mL/min
图 3 Fe-SSGS、Fe-10、Fe-HT和Fe-SG催化剂的X射线衍射谱图
Figure 3 XRD patterns of the Fe-SSGS, Fe-10, Fe-HT and Fe-SG catalysts
图 4 Fe-SSGS、Fe-10、Fe-HT和Fe-SG催化剂的Raman光谱谱图
Figure 4 Raman spectra of the Fe-SSGS, Fe-10, Fe-HT and Fe-SG catalysts
图 5 Fe-SSGS、Fe-10、Fe-HT和Fe-SG催化剂的热重谱图
Figure 5 TGA curves of the Fe-SSGS, Fe-10, Fe-HT and Fe-SG catalysts
图 6 Fe-SSGS、Fe-10、Fe-HT和Fe-SG催化剂N2吸附-解吸等温曲线
Figure 6 N2 adsorption/desorption isotherms of Fe-SSGS, Fe-10, Fe-HT and Fe-SG catalysts
图 7 Fe-SSGS、Fe-10、Fe-HT和Fe-SG催化剂的NH3-TPD谱图
Figure 7 NH3-TPD profiles of the Fe-SSGS, Fe-10, Fe-HT and Fe-SG catalysts
图 8 Fe-SSGS、Fe-10、Fe-HT和Fe-SG催化剂的H2-TPR谱图
Figure 8 H2-TPR profiles of the Fe-SSGS, Fe-10, Fe-HT and Fe-SG catalysts
图 9 Fe-SSGS、Fe-10、Fe-HT和Fe-SG催化剂的XPS谱图：（a） Ce 3d, （b） O 1s, （c） Fe 2p, （d） S 2p
Figure 9 Ce 3d (a), O 1s (b), Fe 2p (c) and S 2p (d) XPS spectra of the Fe-SSGS, Fe-10, Fe-HT and Fe-SG catalysts
图 10 Fe-SSGS、Fe-10、Fe-HT和Fe-SG催化剂的FT-IR谱图
Figure 10 FT-IR spectra of the Fe-SSGS, Fe-10, Fe-HT and Fe-SG catalysts
图 11 Fe-HT 催化剂在215和300 ℃下的抗硫性能测试
Figure 11 Effect of SO2 on the conversion of NOx for NH3-SCR over the Fe-HT catalyst at 215 and 300 °Creaction conditions: 0.2 mL catalyst; inlet gas = 0.05% NO, 0.05% NH3, 0.005% SO2, 5% O2, N2 as balance; total flow rate = 200 mL/min
表 1 Fe-SSGS、Fe-10、Fe-HT和Fe-SG催化剂的比表面积和总孔体积
Table 1 Specific surface area and total pore volume of Fe-SSGS, Fe-10, Fe-HT and Fe-SG samples
Sample SBET/
(m2·g−1)Total pore volume/
(cm3·g−1)Average pore
diameter/nmFe-SSGS 33 0.20 12.3 Fe-10 50 0.40 15.9 Fe-HT 47 0.37 15.6 Fe-SG 13 0.08 12.0 
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表 2 XPS结合能和表面原子比
Table 2 Binding energies and surface atomic ratios derived from XPS
Sample Surface atomic concentration/atomic% Ce3+/
(Ce4+ + Ce3+)Oα/
(Oα + Oβ)Fe3+/
(Fe3+ + Fe2+)Fe-SSGS 19.3 41.8 48.7 Fe-10 29.2 45.2 84.7 Fe-HT 34.1 51.6 79.2 Fe-SG 24.6 45.3 18.2
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