Hierarchical SAPO-11 prepared using SBA-15 as the silicon source and its application in n-dodecane hydroisomerization
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摘要: 以脱除模板剂后的SBA-15为硅源和间接模板剂，在水热条件下制备多级孔SAPO-11分子筛，并通过XRD、SEM、红外光谱、氮气物理吸附-脱附等表征手段对样品的晶相、形貌、酸性和织构性质进行表征。结果表明，以焙烧后的SBA-15为硅源合成出纯相的SAPO-11分子筛，且SBA-15已完全转化。合成的SAPO-11样品呈空心的近方柱体形貌，由宽度为100 nm左右的细条聚集而成，晶粒粒径为1-3 μm。与白炭黑、硅溶胶合成的常规SAPO-11分子筛对比发现，添加SBA-15可在SAPO-11中引入介孔孔道，孔径为5-10 nm，且样品以中强度的Brønsted酸为主，弱Brønsted酸相对较少。以正十二烷为探针分子，考察Pt/SAPO-11催化剂的临氢异构化反应性能。结果表明，多级孔Pt/SAPO-11催化剂具有优良的异构化反应性能。催化剂的高活性和选择性与SAPO-11分子筛的酸性质和孔道结构密切相关，中强度的Brønsted酸量的增加有助于活性提高，同时介孔孔道有利于产物扩散，异构产物的选择性明显提高。Abstract: SBA-15 with the removal of template agent, which served as both the silicon source and indirect template agent, was used to hydrothermally synthesize hierarchical SAPO-11 molecular sieve. The crystal structure, morphology, acidity and texture of the samples were characterized by XRD, SEM, FT-IR and N2 physical adsorption. The results showed that the pure SAPO-11 can be obtained by using calcined SBA-15 as the silicon source. At the same time, SBA-15 was completely transformed in the synthesis system. The obtained SAPO-11 sample showed a hollow near-column shape with particle size of about 1-3 μm, which was composed of bar-shape structure with a width of about 100 nm. Compared with conventional SAPO-11 synthesized by adopting white carbon black or colloidal silica as the silicon source, the addition of SBA-15 successfully introduced mesoporous channels with pore size of 5-10 nm into SAPO-11 molecular sieve. Moreover, the proportion of moderate and strong Brønsted acid was larger than that of weak Brønsted acid. Finally, the catalytic behaviors of Pt/SAPO-11 bifunctional catalysts were investigated in the hydroisomerization of n-dodecane. The results indicated that the hierarchical catalyst synthesized with SBA-15 was much more active and selective. The excellent isomerization performance was closely related to the acidity and pore structure of the hierarchical SAPO-11 molecular sieve. The increase of moderate and strong Brønsted acidity contributed to the improvement of activity. Meanwhile, the mesopores were conducive to the significant increase of selectivity via accelerating diffusion of the isomerization products.
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Key words:
- SAPO-11 /
- SBA-15 /
- hierarchical /
- Brønsted acid /
- hydroisomerization
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图 1 SAPO-11分子筛的XRD谱图
Figure 1 Wide angle XRD patterns of the SAPO-11 samples
(a): as-synthesized SAPO-11; (b): calcined SAPO-11
图 2 SAPO-11-S和SBA-15的小角XRD谱图
Figure 2 Low-angle XRD patterns of the SAPO-11-S and SBA-15 samples
图 3 SAPO-11分子筛样品的N2吸附-脱附等温线和孔径分布
Figure 3 N2 adsorption-desorption isotherms and pore size distributions of the SAPO-11 samples
(a): N2 adsorption-desorption isotherms; (b): pore size distributions
图 4 SAPO-11分子筛的SEM照片
Figure 4 SEM images of the SAPO-11 samples
(a), (b): SAPO-11-S; (c), (d): SAPO-11-C; (e), (f): SAPO-11-F
图 5 不同晶化时间的SAPO-11-S的SEM照片
Figure 5 SEM images of the SAPO-11-S with different crystallization time
(a): SBA-15; (b): 0.5h; (c): 1h; (d): 6h
图 6 SAPO-11分子筛样品的FT-IR和Py-FTIR谱图
Figure 6 FT-IR (a) and Py-FTIR (b) graphs of the SAPO-11 samples
图 7 Pt/SAPO-11催化剂在正十二烷临氢异构化性能变化
Figure 7 Variation of hydroisomerization performance of n-C12 over the Pt/ SAPO-11 catalysts
(a): conversion of n-C12; (b): selectivity of i-C12; (c): yield of i-C12; (d): mono-branched i-C12/multi-branched i-C12
表 1 SAPO-11分子筛样品的织构参数
Table 1 Textural parameters of the SAPO-11 samples
Sample ABET/(m2·g-1) Amicro/(m2·g-1) vtotal/(cm3·g-1) vmeso/(cm3·g-1) vmeso/vtotal /% SAPO-11-S 214 176 0.13 0.06 46 SAPO-11-C 261 220 0.13 0.04 31 SAPO-11-F 247 222 0.14 0.05 36 
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表 2 SAPO-11分子筛的Brønsted酸量和Lewis酸量
Table 2 Amount of Brønsted and Lewis acid sites in the SAPO-11 samples determined by Py-FTIR
Sample SiO2/Al2O3 Acidity /(μmol·g-1) 150℃ 300℃ B acid L acid B acid L acid SAPO-11-S 0.27 29 46 28 15 SAPO-11-C 0.24 37 43 19 19 SAPO-11-F 0.24 45 46 26 19
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