Effect of the additives PVP and MTS on structural properties and synthesis mechanism of Beta zeolite
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摘要: 分别以铝酸钠和硅溶胶为铝源和硅源，四乙基氢氧化铵为模板剂，在水热条件下，考察了添加剂（聚乙烯吡咯烷酮（PVP）和甲基三乙氧基硅烷（MTS））对合成Beta分子筛结构与性能的影响，并通过XRD、TEM、BET、ICP、29Si-NMR和NH3-TPD等方法对合成样品进行了结构表征和作用机理讨论，同时以催化裂化异丙苯为模型反应评价其催化性能。结果表明，与传统Beta分子筛相比，加入PVP后所得样品具有更高结晶度和较高的硅铝物质的量比（25.68）以及较大的比表面积（772 m2/g）；而加入MTS后尽管具有较大比表面积（657 m2/g）和较高硅铝物质的量比（25.76），但是结晶度却相对降低，且粒径减小（160-320 nm）。两种添加剂作用下所得样品均具有更多酸量，在催化裂化异丙苯的反应中表现出较高的催化活性。Abstract: Beta zeolites were successfully synthesized via hydrothermal method using sodium aluminate as aluminium source, silica sol (Ludox) as silicon source and TEAOH as template, respectively. The effects of different additives polyvinyl pyrrolidone (PVP) and Methyltriethoxysilane (MTS) on their structural properties and synthesis mechanism were investigated in detail by various characterizations, such as XRD, TEM, BET, ICP, 29Si-NMR and NH3-TPD method. Also, their catalytic performances were evaluated through catalytic cracking of cumene. The results showed that the beta zeolite obtained in the PVP-added system presented a better crystallinity, higher Si/Al molar ratio (25.68), and larger surface area (772 m2/g). Comparably, the MTS-effected samples revealed a larger surface area (657 m2/g), higher Si/Al molar ratio (25.76), but lower crystallinity and smaller particle sizes (around 160-320 nm). Moreover, both of them exhibited a good catalytic activity for cumene cracking due to the existences of abundant and strong acid content.
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Key words:
- PVP /
- MTS /
- Beta zeolite /
- catalytic cracking /
- structural characterization /
- hydrothermal synthesis
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图 1 不同添加剂合成Beta分子筛的XRD谱图
Figure 1 XRD patterns of Beta zeolite with different additives
a: traditional; b: (MTS/Al2O3) 2.3; c: (PVP (K15)/Al2O3) 4.54×10-2; d: (PVP (K15)/Al2O3) 1.36×10-1; e: (PVP (K15)/Al2O3) 2.72×10-1; f: (PVP (K30)/Al2O3) 7.81×10-3; g: (PVP (K30)/Al2O3) 2.34×10-2; h: (PVP (K30)/Al2O3) 4.68×10-2; i: (PVP (K90)/Al2O3) 3.50×10-4; j: (PVP (K90)/Al2O3) 1.05×10-3
图 2 不同添加剂晶化动力学曲线
Figure 2 Crystallization kinetics curves of different additives
a: traditional; b: MTS; c: PVP (K30)/Al2O3 (2.34×10-2)
图 3 不同添加剂合成Beta分子筛的TEM照片
Figure 3 TEM micrographs of traditional ((a), (b)), MTS ((c), (d)), PVP (K30)/Al2O3 (2.34×10-2) ((e), (f))
图 4 不同PVP添加量的Beta分子筛N2等温吸附-脱附曲线及孔径分布
Figure 4 N2 adsorption/desorption isotherms (a) and their corresponding pore size distributions (right panel)(b) with different additives
a: traditional; b: MTS; c: PVP (K30)/Al2O3(7.81×10-3); d: PVP (K30)/Al2O3 (2.34×10-2)
图 5 不同添加剂29Si-NMR核磁共振谱图
Figure 5 29Si-NMR spectra of samples with different additives
a: traditional; b: MTS; c: PVP (K30)/Al2O3(2.34×10-2)
图 6 不同PVP添加量的NH3-TPD谱图
Figure 6 NH3-TPD profiles of samples with different additives
a: traditional; b: MTS; c: PVP (K30)/Al2O3(7.81×10-3); d: PVP (K30)/Al2O3 (2.34×10-2); e: PVP (K30)/Al2O3(4.68×10-2)
图 7 不同添加剂Beta分子筛催化裂化异丙苯性能
Figure 7 Catalytic performance to cumene cracking of the samples with different additives
a: traditional; b: traditional after ion exchange; c: MTS; d: PVP (K30)/Al2O3 (7.81×10-3); e: PVP (K30)/Al2O3 (2.34×10-2); f: PVP (K30)/Al2O3 (4.68×10-2)
表 1 样品的织构参数
Table 1 Textural parameters of the samples
Sample ABET /(m2·g-1) Amicro/(m2·g-1) vmicro/(cm3·g-1) vpore/(cm3·g-1) Traditional 577 390 0.22 0.59 MTS 657 394 0.26 0.67 PVP (K30)/Al2O3(7.81×10-3) 772 578 0.30 0.57 PVP (K30)/Al2O3(2.34×10-2) 755 589 0.29 0.52 
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表 2 NMR及ICP测定的样品元素含量
Table 2 Elemental content measured by ICP and NMR
Sample NMR ICP/(mg·L-1) Si/Al
(molar ratio)Q4:Q3:Q2 Si/Al Na Al Si Beta (traditional) 0.22:1:5.89 19.75 0.27 1.73 38.52 21.47 Beta (traditional) (after ion exchanged) 0.15 1.46 39.82 26.37 Beta (MTS) 0.08:1:5.67 23.28 0.27 2.05 54.80 25.76 Beta (K30 2.34×10-2) 0.36:1:8.57 23.09 0.24 1.66 44.21 25.68
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表 3 不同PVP添加量的样品酸量
Table 3 Acid amount of Samples with different additives
Catalyst Acid amount /(μmol·g-1) weak-
acidmedium-
acidstrong-
acidTraditional 6.9 143.3 230.9 MTS 6.0 280.4 648.6 PVP (K30)/Al2O3(7.81×10-3) 3.9 162.0 577.0 PVP (K30)/Al2O3 (2.34×10-2) 4.0 220.0 395.0 PVP (K30)/Al2O3(4.68×10-2) 5.7 205.8 342.8
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