Chinese Journal of Catalysis ›› 2021, Vol. 42 ›› Issue (5): 795-807.DOI: 10.1016/S1872-2067(20)63694-4
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Dongyue Zhaoa, Yuexi Yanga, Zhongnan Gaoa, Mengxin Yina, Ye Tiana, Jing Zhangb, Zheng Jiangc, Xiaobo Yud, Xingang Lia,*()
Received:
2020-04-26
Accepted:
2020-04-26
Online:
2021-05-18
Published:
2021-01-29
Contact:
Xingang Li
About author:
* E-mail: xingang_li@tju.edu.cnSupported by:
Dongyue Zhao, Yuexi Yang, Zhongnan Gao, Mengxin Yin, Ye Tian, Jing Zhang, Zheng Jiang, Xiaobo Yu, Xingang Li. Promoting NOx reduction via in situ activation of perovskite supported Pd catalysts under alternating lean-burn/fuel-rich operating atmospheres[J]. Chinese Journal of Catalysis, 2021, 42(5): 795-807.
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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(20)63694-4
Fig. 1. XRD patterns of the fresh La0.7Sr0.3MnO3 (1), fresh sol-gel-prepared La0.7Sr0.3MnO3-supported Pd (2), and fresh wet-impregnation-prepared La0.7Sr0.3MnO3-supported Pd (3) catalysts.
Catalyst | Pd content a (wt%) | Specific surface area (m2 g-1) | NOx storage efficiency b(%) | NOx reducing efficiency b (%) | NOx removal percentage b (%) | N2O selectivity c (%) |
---|---|---|---|---|---|---|
LSM d | — | 14.3 | 59.0 | 58.3 | 34.4 | 2.7 |
Pd-LSM-SG e | 2.1 | 14.9 | 98.9 | 91.1 | 90.1 | 2.6 |
Pd-LSM-IM f | 2.1 | 13.4 | 97.2 | 74.0 | 72.0 | 5.0 |
Table 1 Physicochemical properties and De-NOx activities of the catalysts at 350 °C.
Catalyst | Pd content a (wt%) | Specific surface area (m2 g-1) | NOx storage efficiency b(%) | NOx reducing efficiency b (%) | NOx removal percentage b (%) | N2O selectivity c (%) |
---|---|---|---|---|---|---|
LSM d | — | 14.3 | 59.0 | 58.3 | 34.4 | 2.7 |
Pd-LSM-SG e | 2.1 | 14.9 | 98.9 | 91.1 | 90.1 | 2.6 |
Pd-LSM-IM f | 2.1 | 13.4 | 97.2 | 74.0 | 72.0 | 5.0 |
Fig. 2. Normalized Pd K-edge X-ray absorption near-edge structure spectra (a) and radial distribution function profiles (b) of the Pd-foil (1), PdO (2), fresh sol-gel-prepared La0.7Sr0.3MnO3-supported Pd (3), and fresh wet-impregnation-prepared La0.7Sr0.3MnO3-supported Pd (4) catalysts.
Fig. 3. Pd 3d (a) and Mn 2p (b) XPS profiles of the fresh sol-gel-prepared La0.7Sr0.3MnO3-supported Pd (1) and fresh wet-impregnation-prepared La0.7Sr0.3MnO3-supported Pd (2) catalysts.
Catalyst | XANES | XPS | |||||
---|---|---|---|---|---|---|---|
Pd0 (%) | Pd2+ (%) | Pd0 (%) | Pd2+ (%) | Mn3+ (%) | Mn4+ (%) | ||
Fresh Pd-LSM-SG | 100 | 0 | 100 | 0 | 57.4 | 42.6 | |
Fresh Pd-LSM-IM | 100 | 0 | 100 | 0 | 66.5 | 33.5 | |
Activated Pd-LSM-SG | 53.0 | 47.0 | 43.6 | 56.4 | 58.0 | 42.0 | |
Activated Pd-LSM-IM | 6.0 | 94.0 | 0 | 100 | 67.1 | 32.9 |
Table 2 Chemical states of the Pd and Mn species in the fresh and activated catalysts determined from the XANES and XPS results.
Catalyst | XANES | XPS | |||||
---|---|---|---|---|---|---|---|
Pd0 (%) | Pd2+ (%) | Pd0 (%) | Pd2+ (%) | Mn3+ (%) | Mn4+ (%) | ||
Fresh Pd-LSM-SG | 100 | 0 | 100 | 0 | 57.4 | 42.6 | |
Fresh Pd-LSM-IM | 100 | 0 | 100 | 0 | 66.5 | 33.5 | |
Activated Pd-LSM-SG | 53.0 | 47.0 | 43.6 | 56.4 | 58.0 | 42.0 | |
Activated Pd-LSM-IM | 6.0 | 94.0 | 0 | 100 | 67.1 | 32.9 |
Fig. 4. H2-TPR profiles (a) and magnified area marked with a dashed square (b) in (a). (1) PdO; (2) fresh pure La0.7Sr0.3MnO3; (3) fresh sol-gel-prepared La0.7Sr0.3MnO3-supported Pd; (4) fresh wet-impregnation-prepared La0.7Sr0.3MnO3-supported Pd catalysts.
Fig. 5. (a) De-NOx activity of La0.7Sr0.3MnO3 (LSM) (1), sol-gel-prepared La0.7Sr0.3MnO3-supported Pd (Pd-LSM-SG) (2), and wet-impregnation-prepared La0.7Sr0.3MnO3-supported Pd (Pd-LSM-IM) (3) at 200-450 °C. (b) Time evolution of the De-NOx activity of LSM (1), Pd-LSM-SG (2), Pd-LSM-IM (3), and pretreated Pd-LSM-SG (4) at 350 °C. Reaction conditions: lean-burn phase: 50 s, 400 ppm NO/5% O2/N2; fuel-rich phase: 10 s, 1000 ppm C3H6/N2; space velocity: 120 000 mL g-1 h-1.
Fig. 6. (a) XRD patterns of the fresh sol-gel-prepared Pd-LSM-SG (1), activated Pd-LSM-SG (2), fresh Pd-LSM-IM (3), and activated Pd-LSM-IM (4); Normalized Pd K-edge X-ray absorption near-edge structure spectra (b) and radial distribution functions (c) of Pd foil (1), PdO (2), activated Pd-LSM-SG (3), activated Pd-LSM-IM (4), and sample (3) oxidized under lean-burn atmosphere at 350 oC for 8 min (5).
Fig. 7. Pd 3d XPS profiles of fresh Pd/BaO/Al2O3 (1), activated Pd/BaO/Al2O3 (2), Pd/BaO/Al2O3 reduced in 1000 ppm C3H6/N2 at 350 °C for 3 min (3), and sample (3) after five NOx storage and reduction cycles (4).
Fig. 8. (a) C3H6 oxidation profiles of the fresh Pd-LSM-SG (1), activated Pd-LSM-SG (2), fresh Pd-LSM-IM (3), activated Pd-LSM-IM catalysts (4), and fresh pure La0.7Sr0.3MnO3 (5). (b) De-NOx reaction at 200 °C over the fresh Pd-LSM-SG (1), activated Pd-LSM-SG (2), fresh Pd-LSM-IM (3), and activated Pd-LSM-IM (4) catalysts.
Catalyst | R(mol g-1 s-1 × 10-8) | Exposed Pd atoms a(mol g-1 s-1 × 10-5) | Pd dispersion (%) | Pd TOF(s-1 × 10-3) | Pd2+ TOF b (s-1 × 10-3) | Pd0 TOF b (s-1 × 10-3) |
---|---|---|---|---|---|---|
Fresh Pd-LSM-SG | 3.0 | 2.3 | 12.1 | 1.3 | 1.3 | — |
Activated Pd-LSM-SG | 12.6 | 2.3 | 11.9 | 5.3 | 1.3 | 10.6 |
Fresh Pd-LSM-IM | 6.4 | 5.9 | 30.1 | 1.1 | 1.1 | — |
Activated Pd-LSM-IM | 7.3 | 5.8 | 29.4 | 1.3 | 1.3 | — |
Table 3 Surface Pd contents and kinetic results at 200 °C.
Catalyst | R(mol g-1 s-1 × 10-8) | Exposed Pd atoms a(mol g-1 s-1 × 10-5) | Pd dispersion (%) | Pd TOF(s-1 × 10-3) | Pd2+ TOF b (s-1 × 10-3) | Pd0 TOF b (s-1 × 10-3) |
---|---|---|---|---|---|---|
Fresh Pd-LSM-SG | 3.0 | 2.3 | 12.1 | 1.3 | 1.3 | — |
Activated Pd-LSM-SG | 12.6 | 2.3 | 11.9 | 5.3 | 1.3 | 10.6 |
Fresh Pd-LSM-IM | 6.4 | 5.9 | 30.1 | 1.1 | 1.1 | — |
Activated Pd-LSM-IM | 7.3 | 5.8 | 29.4 | 1.3 | 1.3 | — |
Fig. 9. De-NOx activity over the conventional and perovskite-based catalysts at 350 °C in the absence of H2O and CO2 (1) and in the presence of 5% H2O (2), 5% CO2 (3), and 5% H2O and 5% CO2 (4).
Fig. 10. De-NOx activity of the sol-gel-prepared La0.7Sr0.3MnO3-supported Pd (black lines) and wet-impregnation-prepared La0.7Sr0.3MnO3-supported Pd (red lines) in the absence (solid lines) and presence (dashed lines) of H2O and CO2 as function of the O2 concentration at 350 °C.
Fig. 11. De-NOx activities of the conventional Pd/BaO/Al2O3 (Pd/Ba/Al) and Pt/BaO/Al2O3 (Pt/Ba/Al) and perovskite-based catalysts at 350 °C in the absence of H2O, CO2 and SO2 (1), in the presence of 125 ppm SO2 (2), and 5% H2O, 5% CO2 and 125 ppm SO2 (3).
Fig. 12. Product selectivity of the fresh Pd-LSM-SG (a) and activated Pd-LSM-SG (b) catalysts at 350 °C: N2 (■), N2O (▼), NO (▲), NO2 (?), and C3H6 (●). Feeding gas: 1000 ppm C3H6, 5 vol% H2O, 5 vol% CO2 balanced with N2; space velocity: 120000 mL g-1 h-1.
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