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摘要: 采用液相离子交换法制备了不同Ce含量的CeUSY分子筛，并通过Mitchell等体积浸渍法对其进行Ni污染，运用ICP-AES、XRD和N2吸附等温线等方法对其织构性质进行表征，并利用微反应活性评价装置考察了其抗镍性能。结果表明，不同Ce含量改性的USY样品其抗镍效果存在差异，CeUSY分子筛的抗镍效果与Ce含量的关系呈现火山型变化。结合Ni污染前后CeUSY分子筛的H2-TPR和Py-FTIR表征结果探讨了Ce物种的抗镍机制，证实了Ce物种形态的变化是不同Ce含量的CeUSY分子筛具有不同抗镍效果的重要成因，其中，SOD笼中的Ce（OH）2+在高温条件下可与Ni（OH）+相互作用，脱去一分子H2O形成Ce3+-O-Ni2+的稳定结构，阻碍了Ni物种与骨架铝的结合导致CeUSY分子筛中B酸中心的破坏，同时有效抑制了易还原NiO物种的生成。而Ce含量过高使得SOD笼内的Ce物种变成二聚以及三聚物，与Ni（OH）+作用减弱，使其抗镍性能减弱。Abstract: The CeUSY zeolites loaded with Ce were prepared by liquid phase ion exchange method, and the Ni contamination was conducted by Mitchell impregnation method. The texture properties were characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD) and N2 adsorption. Moreover, the nickel tolerance was evaluated by the MAT evaluation device. The results show that CeUSY zeolites with different Ce contents possess a nickel tolerance performance varying in a volcano type with the increase of Ce content. Through the H2-TPR and Py-FTIR characterization of CeUSY zeolite before and after Ni contamination, it is evident that the change in Ce species morphology is one of the reasons affecting nickel tolerances. It is thought that the interaction between Ce(OH)2+ and Ni(OH)+ in the SOD cages of the CeUSY zeolite results in a loss of H2O molecule to form a stable Ce3+-O-Ni2+ structure at high temperature, which hinders the combination of Ni species with the framework aluminum to prevent the destruction of the Brønsted acid sites in CeUSY zeolite and effectively inhibits the formation of reducible NiO species. However, with the increase of the content of Ce3+, the part of the introduced Ce would happen to self-assemble in the zeolites as multinuclear hydroxylated species which interacts weakly with Ni2+ species compared to mononuclear species and then reduces the nickel tolerance.
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Key words:
- rare earth /
- location /
- morphology /
- USY /
- nickel tolerance
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图 1 不同Ce含量的CeUSY分子筛经Ni污染前(a)和污染后(b)的XRD谱图
Figure 1 XRD patterns of CeUSY zeolites with different Ce contents before(a)/after(b) Ni contamination
a: USY; b: CeUSY-1; c: CeUSY-2; d: CeUSY-3
图 2 不同Ce含量USY分子筛经Ni污染后的SEM照片及EDS谱图
Figure 2 SEM (a) and EDS (b) spectra of CeUSY zeolites with different Ce contents after Ni contamination
(a): Ni/USY; (b): Ni/CeUSY-1; (c): Ni/CeUSY-2; (d): Ni/CeUSY-3 red and blue points denote the Ni and Ce element in EDS maps, respectively
图 3 不同Ce含量的CeUSY分子筛经Ni污染前(a)和污染后(b)的H2-TPR谱图
Figure 3 H2-TPR spectra of CeUSY zeolites with different Ce contents before (a)/after (b) Ni contamination
a: USY; b: CeUSY-1; c: CeUSY-2; d: CeUSY-3
图 4 Ni/CeUSY分子筛中Ce物种与Ni物种的作用机理
Figure 4 Interaction mechanism of Ce species and Ni species in Ni/CeUSY zeolites
图 5 不同Ce含量的CeUSY分子筛经Ni污染前后的微反应活性指数
Figure 5 MAT index of CeUSY zeolites with different Ce contents before and after Ni contamination
表 1 不同Ce含量的CeUSY分子筛经Ni污染前后的物理性质
Table 1 Physical properties of CeUSY zeolites with different Ce contents before/after Ni contamination
Sample USY Ni/USY CeUSY-1 Ni/CeUSY-1 CeUSY-2 Ni/CeUSY-2 CeUSY-3 Ni/CeUSY-3 n(SiO2)/n(Al2O3) 7.1 6.9 7.5 7.3 7.9 7.8 7.4 7.2 Ni content w/% - 0.29 - 0.28 - 0.30 - 0.29 Ce2O3 content w/% - - 3.16 3.16 5.68 5.68 6.14 6.14 
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表 2 不同Ce含量的CeUSY分子筛经Ni污染前后的孔结构性质
Table 2 Pore structural properties of CeUSY zeolites with different Ce contents before/after Ni contamination
Sample USY Ni/USY CeUSY-1 Ni/CeUSY-1 CeUSY-2 Ni/CeUSY-2 CeUSY-3 Ni/CeUSY-3 ABET/(m2·g-1) 608 590 571 580 596 574 582 588 Amic/(m2·g-1) 545 518 515 494 528 511 521 515 vtotal/(cm3·g-1) 0.375 0.374 0.363 0.385 0.381 0.369 0.374 0.376 vmic/(cm3·g-1) 0.286 0.272 0.268 0.258 0.275 0.268 0.273 0.271 ABET: surface area determined by the BET method; Amic: surface area determined by t-plot method; vtotal: total pore volume;
vmic: micropore pore volume determined by the HK method
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表 3 以吡啶为探针分子测定不同Ce含量的CeUSY分子筛经Ni污染前后的酸性质
Table 3 Acidic properties of CeUSY zeolites with different Ce contents before/after Ni contamination with pyridine as probe molecules
Sample USY Ni/USY CeUSY-1 Ni/CeUSY-1 CeUSY-2 Ni/CeUSY-2 CeUSY-3 Ni/CeUSY-3 TB/(μmol·g-1) 170 133 135 109 136 120 128 118 TL/(μmol·g-1) 60 93 84 75 72 75 58 68 SB/(μmol·g-1) 166 129 115 95 115 104 98 82 SL/(μmol·g-1) 42 43 31 25 28 35 22 30 WB/(μmol·g-1) 4 4 20 14 21 16 30 36 WL/(μmol·g-1) 39 50 53 50 44 40 36 38 TB: total Brønsted acid sites; TL: total Lewis acid sites; SB: strong Brønsted acid sites; SL: strong Lewis acid sites; WB: weak Brønsted acid sites; WL: weak Lewis acid sites
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